2.5.5
ApplicationContext
LoadTimeWeaver
Resource
interfaceResource
implementationsResourceLoader
ResourceLoaderAware
interfaceResources
as dependenciesResource
pathsBeanWrapper
, and PropertyEditors
Advice
types<tx:advice/>
settings@Transactional
@Transactional
with AspectJSessionFactory
setup in a Spring
containerHibernateTemplate
JpaDialect
DispatcherServlet
@Controller
@RequestMapping
@RequestParam
@ModelAttribute
@SessionAttributes
WebDataBinder
initializationform
taginput
tagcheckbox
tagcheckboxes
tagradiobutton
tagradiobuttons
tagpassword
tagselect
tagoption
tagoptions
tagtextarea
taghidden
tagerrors
tagDispatcherPortlet
ViewRendererServlet
@Controller
@RequestMapping
@RequestParam
@ModelAttribute
@SessionAttributes
WebDataBinder
initializationMBeanInfoAssembler
InterfaceAutodetectCapableMBeanInfoAssembler
interfaceMethodNameBasedMBeanInfoAssembler
ObjectName
s for your beansutil
schemajee
schema<jee:jndi-lookup/>
(simple)<jee:jndi-lookup/>
(with single JNDI environment setting)<jee:jndi-lookup/>
(with multiple JNDI environment settings)<jee:jndi-lookup/>
(complex)<jee:local-slsb/>
(simple)<jee:local-slsb/>
(complex)<jee:remote-slsb/>
lang
schemajms
schematx
(transaction) schemaaop
schemacontext
schematool
schemabeans
schemaspring-beans-2.0.dtd
checkbox
tagcheckboxes
tagerrors
tagform
taghidden
taginput
taglabel
tagoption
tagoptions
tagpassword
tagradiobutton
tagradiobuttons
tagselect
tagtextarea
tagDeveloping software applications is hard enough even with good tools and technologies. Implementing applications using platforms which promise everything but turn out to be heavy-weight, hard to control and not very efficient during the development cycle makes it even harder. Spring provides a light-weight solution for building enterprise-ready applications, while still supporting the possibility of using declarative transaction management, remote access to your logic using RMI or web services, and various options for persisting your data to a database. Spring provides a full-featured MVC framework, and transparent ways of integrating AOP into your software.
Spring could potentially be a one-stop-shop for all your enterprise applications; however, Spring is modular, allowing you to use just those parts of it that you need, without having to bring in the rest. You can use the IoC container, with Struts on top, but you could also choose to use just the Hibernate integration code or the JDBC abstraction layer. Spring has been (and continues to be) designed to be non-intrusive, meaning dependencies on the framework itself are generally none (or absolutely minimal, depending on the area of use).
This document provides a reference guide to Spring's features. Since this document is still to be considered very much work-in-progress, if you have any requests or comments, please post them on the user mailing list or on the support forums at http://forum.springframework.org/.
Before we go on, a few words of gratitude are due to Christian Bauer (of the Hibernate team), who prepared and adapted the DocBook-XSL software in order to be able to create Hibernate's reference guide, thus also allowing us to create this one. Also thanks to Russell Healy for doing an extensive and valuable review of some of the material.
Java applications (a loose term which runs the gamut from constrained applets to full-fledged n-tier server-side enterprise applications) typically are composed of a number of objects that collaborate with one another to form the application proper. The objects in an application can thus be said to have dependencies between themselves.
The Java language and platform provides a wealth of functionality for architecting and building applications, ranging all the way from the very basic building blocks of primitive types and classes (and the means to define new classes), to rich full-featured application servers and web frameworks. One area that is decidedly conspicuous by its absence is any means of taking the basic building blocks and composing them into a coherent whole; this area has typically been left to the purvey of the architects and developers tasked with building an application (or applications). Now to be fair, there are a number of design patterns devoted to the business of composing the various classes and object instances that makeup an all-singing, all-dancing application. Design patterns such as Factory, Abstract Factory, Builder, Decorator, and Service Locator (to name but a few) have widespread recognition and acceptance within the software development industry (presumably that is why these patterns have been formalized as patterns in the first place). This is all very well, but these patterns are just that: best practices given a name, typically together with a description of what the pattern does, where the pattern is typically best applied, the problems that the application of the pattern addresses, and so forth. Notice that the last paragraph used the phrase “... a description of what the pattern does...”; pattern books and wikis are typically listings of such formalized best practice that you can certainly take away, mull over, and then implement yourself in your application.
The IoC component of the Spring Framework addresses the enterprise concern of taking the classes, objects, and services that are to compose an application, by providing a formalized means of composing these various disparate components into a fully working application ready for use. The Spring Framework takes best practices that have been proven over the years in numerous applications and formalized as design patterns, and actually codifies these patterns as first class objects that you as an architect and developer can take away and integrate into your own application(s). This is a Very Good Thing Indeed as attested to by the numerous organizations and institutions that have used the Spring Framework to engineer robust, maintainable applications.
The Spring Framework contains a lot of features, which are well-organized in six modules shown in the diagram below. This chapter discusses each of the modules in turn.
Overview of the Spring Framework
The Core package is
the most fundamental part of the framework and provides the IoC and
Dependency Injection features. The basic concept here is the
BeanFactory
, which provides a sophisticated
implementation of the factory pattern which removes the need for
programmatic singletons and allows you to decouple the configuration and
specification of dependencies from your actual program logic.
The Context package build on the solid base provided by the Core package: it provides a way to access objects in a framework-style manner in a fashion somewhat reminiscent of a JNDI-registry. The context package inherits its features from the beans package and adds support for internationalization (I18N) (using for example resource bundles), event-propagation, resource-loading, and the transparent creation of contexts by, for example, a servlet container.
The DAO package provides a JDBC-abstraction layer that removes the need to do tedious JDBC coding and parsing of database-vendor specific error codes. Also, the JDBC package provides a way to do programmatic as well as declarative transaction management, not only for classes implementing special interfaces, but for all your POJOs (plain old Java objects).
The ORM package provides integration layers for popular object-relational mapping APIs, including JPA, JDO, Hibernate, and iBatis. Using the ORM package you can use all those O/R-mappers in combination with all the other features Spring offers, such as the simple declarative transaction management feature mentioned previously.
Spring's AOP package provides an AOP Alliance-compliant aspect-oriented programming implementation allowing you to define, for example, method-interceptors and pointcuts to cleanly decouple code implementing functionality that should logically speaking be separated. Using source-level metadata functionality you can also incorporate all kinds of behavioral information into your code, in a manner similar to that of .NET attributes.
Spring's Web package provides basic web-oriented integration features, such as multipart file-upload functionality, the initialization of the IoC container using servlet listeners and a web-oriented application context. When using Spring together with WebWork or Struts, this is the package to integrate with.
Spring's MVC package provides a Model-View-Controller (MVC) implementation for web-applications. Spring's MVC framework is not just any old implementation; it provides a clean separation between domain model code and web forms, and allows you to use all the other features of the Spring Framework.
With the building blocks described above you can use Spring in all sorts of scenarios, from applets up to fully-fledged enterprise applications using Spring's transaction management functionality and web framework integration.
Typical full-fledged Spring web application
By using Spring's declarative transaction management
features the web application is fully transactional, just as it
would be when using container managed transactions as provided by
Enterprise JavaBeans. All your custom business logic can be implemented
using simple POJOs, managed by Spring's IoC container. Additional services
include support for sending email, and validation that is independent of
the web layer enabling you to choose where to execute validation rules.
Spring's ORM support is integrated with JPA, Hibernate, JDO and iBatis;
for example, when using Hibernate, you can continue to use your existing
mapping files and standard Hibernate
SessionFactory
configuration. Form
controllers seamlessly integrate the web-layer with the domain model,
removing the need for ActionForms
or other classes
that transform HTTP parameters to values for your domain model.
Spring middle-tier using a third-party web framework
Sometimes the current circumstances do not allow you to completely
switch to a different framework. The Spring Framework does
not force you to use everything within it; it is not
an all-or-nothing solution. Existing front-ends built
using WebWork, Struts, Tapestry, or other UI frameworks can be integrated
perfectly well with a Spring-based middle-tier, allowing you to use the
transaction features that Spring offers. The only thing you need to do is
wire up your business logic using an
ApplicationContext
and integrate your web layer
using a WebApplicationContext
.
Remoting usage scenario
When you need to access existing code via web services, you can use
Spring's Hessian-
, Burlap-
,
Rmi-
or JaxRpcProxyFactory
classes. Enabling remote access to existing applications suddenly is not
that hard anymore.
EJBs - Wrapping existing POJOs
The Spring Framework also provides an access- and abstraction- layer for Enterprise JavaBeans, enabling you to reuse your existing POJOs and wrap them in Stateless Session Beans, for use in scalable, failsafe web applications that might need declarative security.
If you have been using the Spring Framework for some time, you will be aware that Spring has undergone two major revisions: Spring 2.0, released in October 2006, and Spring 2.5, released in November 2007.
This chapter is a guide to the new and improved features of Spring 2.0 and 2.5. It is intended to provide a high-level summary so that seasoned Spring architects and developers can become immediately familiar with the new Spring 2.x functionality. For more in-depth information on the features, please refer to the corresponding sections hyperlinked from within this chapter.
One of the areas that contains a considerable number of 2.0 and 2.5 improvements is Spring's IoC container.
Previous versions of Spring had IoC container level support for exactly two distinct bean scopes (singleton and prototype). Spring 2.0 improves on this by not only providing a number of additional scopes depending on the environment in which Spring is being deployed (for example, request and session scoped beans in a web environment), but also by providing integration points so that Spring users can create their own scopes.
It should be noted that although the underlying (and internal) implementation for singleton- and prototype-scoped beans has been changed, this change is totally transparent to the end user... no existing configuration needs to change, and no existing configuration will break.
Both the new and the original scopes are detailed in the section entitled Section 3.4, “Bean scopes”.
Spring XML configuration is now even easier, thanks to the advent of the new XML configuration syntax based on XML Schema. If you want to take advantage of the new tags that Spring provides (and the Spring team certainly suggest that you do because they make configuration less verbose and easier to read), then do read the section entitled Appendix A, XML Schema-based configuration.
On a related note, there is a new, updated DTD for Spring 2.0 that
you may wish to reference if you cannot take advantage of the XML
Schema-based configuration. The DOCTYPE declaration is included below
for your convenience, but the interested reader should definitely read
the 'spring-beans-2.0.dtd'
DTD included in the
'dist/resources'
directory of the
Spring 2.5 distribution.
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd">
Not only is XML configuration easier to write, it is now also extensible.
What 'extensible' means in this context is that you, as an application developer, or (more likely) as a third party framework or product vendor, can write custom tags that other developers can then plug into their own Spring configuration files. This allows you to have your own domain specific language (the term is used loosely here) of sorts be reflected in the specific configuration of your own components.
Implementing custom Spring tags may not be of interest to every single application developer or enterprise architect using Spring in their own projects. We expect third-party vendors to be highly interested in developing custom configuration tags for use in Spring configuration files.
The extensible configuration mechanism is documented in Appendix B, Extensible XML authoring.
Spring 2.0 introduced support for various annotations for
configuration purposes, such as @Transactional
,
@Required
and @PersistenceContext
/@PersistenceUnit
.
Spring 2.5 introduces support for a complete set of configuration
annotations: @Autowired
in combination
with support for the JSR-250 annotations @Resource
,
@PostConstruct
and @PreDestroy
.
Annotation-driven bean configuration is discussed in Section 3.11, “Annotation-based configuration”. Check out annotation support for Spring MVC as well: Section 2.5.3, “Annotation-based controllers”
Spring 2.5 introduces support component scanning: autodetecting
annotated components in the classpath. Typically, such component classes
will be annotated with stereotypes such as @Component
,
@Repository
, @Service
,
@Controller
. Depending on the application
context configuration, such component classes will be autodetected and
turned into Spring bean definitions, not requiring explicit configuration
for each such bean.
Annotation-driven bean configuration is discussed in Section 3.12.1, “@Component
and further stereotype
annotations”.
Spring 2.0 has a much improved AOP offering. The Spring AOP framework itself is markedly easier to configure in XML, and significantly less verbose as a result; and Spring 2.0 integrates with the AspectJ pointcut language and @AspectJ aspect declaration style. The chapter entitled Chapter 6, Aspect Oriented Programming with Spring is dedicated to describing this new support.
Spring 2.0 introduces new schema support for defining aspects
backed by regular Java objects. This support takes advantage of the
AspectJ pointcut language and offers fully typed advice (i.e. no more
casting and Object[]
argument manipulation). Details
of this support can be found in the section entitled Section 6.3, “Schema-based AOP support”.
Spring 2.0 also supports aspects defined using the @AspectJ annotations. These aspects can be shared between AspectJ and Spring AOP, and require (honestly!) only some simple configuration. Said support for @AspectJ aspects is discussed in Section 6.2, “@AspectJ support”.
Spring 2.5 introduces support for the bean(...)
pointcut element, matching specific named beans according to Spring-defined
bean names. See Section 6.2.3.1, “Supported Pointcut Designators” for details.
Spring 2.5 introduces explicit support AspectJ load-time weaving,
as alternative to the proxy-based AOP framework. The new
context:load-time-weaver
configuration element
automatically activates AspectJ aspects as defined in AspectJ's
META-INF/aop.xml
descriptor, applying them to the
current application context through registering a transformer with the
underlying ClassLoader. Note that this only works in environments with
class transformation support. Check out Section 6.8.4, “Load-time weaving with AspectJ in the Spring Framework”
for the capabilities and limitations.
The way that transactions are configured in Spring 2.0 has been changed significantly. The previous 1.2.x style of configuration continues to be valid (and supported), but the new style is markedly less verbose and is the recommended style. Spring 2.0 also ships with an AspectJ aspects library that you can use to make pretty much any object transactional - even objects not created by the Spring IoC container.
Spring 2.5 supports convenient annotation-driven transaction
management in combination with load-time weaving, through the use of
context:load-time-weaver
in combination with
tx:annotation-driven mode="aspectj"
.
The chapter entitled Chapter 9, Transaction management contains all of the details.
Spring 2.5 explicitly supports IBM's WebSphere Application Server,
in particular with respect to WebSphere's transaction manager.
Transaction suspension is now fully supported through the use of
WebSphere's new UOWManager
API, which
is available on WAS 6.0.2.19+ and 6.0.1.9+.
So if you run a Spring-based application on the WebSphere
Application Server, we highly recommend to use Spring 2.5's
WebSphereUowTransactionManager
as your
PlatformTransactionManager
of choice.
This is also IBM's official recommendation.
For automatic detection of the underlying JTA-based transaction
platform, consider the use of Spring 2.5's new
tx:jta-transaction-manager
configuration element.
This will autodetect BEA WebLogic and IBM WebSphere, registering the
appropriate PlatformTransactionManager
.
Spring 2.0 ships with a JPA abstraction layer that is similar in intent to Spring's JDBC abstraction layer in terms of scope and general usage patterns.
If you are interested in using a JPA-implementation as the backbone of your persistence layer, the section entitled Section 12.6, “JPA” is dedicated to detailing Spring's support and value-add in this area.
Spring 2.5 upgrades its OpenJPA support to OpenJPA 1.0, with support for advanced features such as savepoints.
Prior to Spring 2.0, Spring's JMS offering was limited to sending
messages and the synchronous receiving of messages.
This functionality (encapsulated in the
JmsTemplate
class) is great, but it doesn't
address the requirement for the asynchronous
receiving of messages.
Spring 2.0 now ships with full support for the reception of messages in an asynchronous fashion, as detailed in the section entitled Section 19.4.2, “Asynchronous Reception - Message-Driven POJOs”.
As of Spring 2.5, the JCA style of setting up asynchronous
message listeners is supported as well, through the
GenericMessageEndpointManager
facility.
This is an alternative to the standard JMS listener facility, allowing
closer integration with message brokers such as ActiveMQ and JORAM.
See Section 19.5, “Support for JCA Message Endpoints”.
Spring 2.5 also introduces an XML namespace for simplifying JMS configuration, offering concise configuration of a large numbers of listeners. This namespace supports both the standard JMS listener facility as well as the JCA setup style, with minimal changes in the configuration. See Section 19.6, “JMS Namespace Support”.
There are some small (but nevertheless notable) new classes in the
Spring Framework's JDBC support library. The first, NamedParameterJdbcTemplate
,
provides support for programming JDBC statements using named parameters
(as opposed to programming JDBC statements using only classic
placeholder ('?'
) arguments.
Another of the new classes, the SimpleJdbcTemplate
,
is aimed at making using the JdbcTemplate
even
easier to use when you are developing against Java 5+ (Tiger).
Spring 2.5 significantly extends the functionality of
SimpleJdbcTemplate
and introduces
SimpleJdbcCall
and SimpleJdbcInsert
operation objects.
The web tier support has been substantially improved and expanded in Spring 2.0, with annotation-based controllers introduced in Spring 2.5.
For a lot of projects, sticking to established conventions and
having reasonable defaults is just what the projects need... this theme
of convention-over-configuration now has explicit support in Spring MVC.
What this means is that if you establish a set of naming conventions for
your Controllers
and views, you can
substantially cut down on the amount of XML
configuration that is required to setup handler mappings, view
resolvers, ModelAndView
instances, etc. This is a
great boon with regards to rapid prototyping, and can also lend a degree
of (always good-to-have) consistency across a codebase.
Spring MVC's convention-over-configuration support is detailed in the section entitled Section 13.10, “Convention over configuration”
Spring 2.0 ships with a Portlet framework that is conceptually similar to the Spring MVC framework. Detailed coverage of the Spring Portlet framework can be found in the section entitled Chapter 16, Portlet MVC Framework.
Spring 2.5 introduces an annotation-based programming model for MVC
controllers, using annotations such as @RequestMapping
,
@RequestParam
, @ModelAttribute
,
etc. This annotation support is available for both Servlet MVC and Portlet
MVC. Controllers implemented in this style do not have to extend specific
base classes or implement specific interfaces. Furthermore, they do not
usually have direct dependencies on Servlet or Portlet API's, although
they can easily get access to Servlet or Portlet facilities if desired.
For further details, see Section 13.11, “Annotation-based controller configuration”.
A rich JSP tag library for Spring MVC was the JIRA issue that garnered the most votes from Spring users (by a wide margin).
Spring 2.0 ships with a full featured JSP tag library that makes the job of authoring JSP pages much easier when using Spring MVC; the Spring team is confident it will satisfy all of those developers who voted for the issue on JIRA. The new tag library is itself covered in the section entitled Section 14.2.4, “Using Spring's form tag library”, and a quick reference to all of the new tags can be found in the appendix entitled Appendix E, spring-form.tld.
Spring 2.5 ships support for Tiles 2, the next generation of the popular Tiles templating framework. This supersedes Spring's former support for Tiles 1, as included in Struts 1.x. See Section 14.3, “Tiles” for details.
Spring 2.5 supports JSF 1.2, providing a JSF 1.2 variant of Spring's
DelegatingVariableResolver
in the form of the new
SpringBeanFacesELResolver
.
This final section outlines all of the other new and improved Spring 2.0/2.5 features and functionality.
Spring 2.0 introduced support for beans written in languages other than Java, with the currently supported dynamic languages being JRuby, Groovy and BeanShell. This dynamic language support is comprehensively detailed in the section entitled Chapter 24, Dynamic language support.
Spring 2.5 refines the dynamic languages support with autowiring and support for the recently released JRuby 1.0.
Spring 2.5 introduces the Spring TestContext Framework which provides annotation-driven unit and integration testing support that is agnostic of the actual testing framework in use. The same techniques and annotation-based configuration used in, for example, a JUnit 3.8 environment can also be applied to tests written with JUnit 4.4, TestNG, etc.
In addition to providing generic and extensible testing infrastructure, the Spring TestContext Framework provides out-of-the-box support for Spring-specific integration testing functionality such as context management and caching, dependency injection of test fixtures, and transactional test management with default rollback semantics.
To discover how this new testing support can assist you with writing unit and integration tests, consult Section 8.3.7, “Spring TestContext Framework” of the revised testing chapter.
The Spring Framework 2.0 has support for
Notifications
; it is also possible to exercise
declarative control over the registration behavior of MBeans with an
MBeanServer
.
Furthermore, Spring 2.5 provides a
context:mbean-export
configuration element for convenient registration of annotated bean classes,
detecting Spring's @ManagedResource
annotation.
Spring 2.5 supports the deployment of a Spring application context as JCA resource adapter, packaged as a JCA RAR file. This allows headless application modules to be deployed into J2EE servers, getting access to all the server's infrastructure e.g. for executing scheduled tasks, listening for incoming messages, etc.
Spring 2.0 offers an abstraction around the scheduling of tasks.
For the interested developer, the section entitled Section 23.4, “The Spring TaskExecutor
abstraction” contains all of the
details.
The TaskExecutor
abstraction is used
throughout the framework itself as well, e.g. for the asynchronous JMS support.
In Spring 2.5, it is also used in the JCA environment support.
Find below pointers to documentation describing some of the new Java 5 support in Spring 2.0 and 2.5.
This final section details issues that may arise during any migration from Spring 1.2/2.0 to Spring 2.5.
Upgrading to Spring 2.5 from a Spring 2.0.x application should simply be a matter of dropping the Spring 2.5 jar into the appropriate location in your application's directory structure. We highly recommend upgrading to Spring 2.5 from any Spring 2.0 application that runs on JDK 1.4.2 or higher, in particular when running on Java 5 or higher, leveraging the significant configuration conveniences and performance improvements that Spring 2.5 has to offer.
Whether an upgrade from Spring 1.2.x will be as seamless depends on how much of the Spring APIs you are using in your code. Spring 2.0 removed pretty much all of the classes and methods previously marked as deprecated in the Spring 1.2.x codebase, so if you have been using such classes and methods, you will of course have to use alternative classes and methods (some of which are summarized below).
With regards to configuration, Spring 1.2.x style XML configuration is 100%, satisfaction-guaranteed compatible with the Spring 2.5 library. Of course if you are still using the Spring 1.2.x DTD, then you won't be able to take advantage of some of the new Spring 2.0 functionality (such as scopes and easier AOP and transaction configuration), but nothing will blow up.
The suggested migration strategy is to drop in the Spring 2.5 jar(s) to benefit from the improved code present in the release (bug fixes, optimizations, etc.). You can then, on an incremental basis, choose to start using the new Spring 2.5 features and configuration. For example, you could choose to start configuring just your aspects in the new Spring 2 style; it is perfectly valid to have 90% of your configuration using the old-school Spring 1.2.x configuration (which references the 1.2.x DTD), and have the other 10% using the new Spring 2 configuration (which references the 2.0/2.5 DTD or XSD). Bear in mind that you are not forced to upgrade your XML configuration should you choose to drop in the Spring 2.5 libraries.
For a comprehensive list of changes, consult the
'changelog.txt'
file that is located in the top
level directory of the Spring Framework distribution.
As of Spring 2.5, support for JDK 1.3 has been removed, following Sun's official deprecation of JDK 1.3 in late 2006. If you haven't done so already, upgrade to JDK 1.4.2 or higher.
If you need to stick with an application server that only supports JDK 1.3, such as WebSphere 4.0 or 5.0, we recommend using the Spring Framework version 2.0.7/2.0.8 which still supports JDK 1.3.
As of Spring 2.5, Spring Web MVC is no longer part of the
'spring.jar'
file. Spring MVC
can be found in 'spring-webmvc.jar'
and 'spring-webmvc-portlet.jar'
in the lib/modules
directory of the distribution.
Furthermore, the Struts 1.x support has been factored out into
'spring-webmvc-struts.jar'
.
Note: The commonly used Spring's DispatcherServlet
is part of Spring's Web MVC framework. As a consequence,
you need to add 'spring-webmvc.jar'
(or 'spring-webmvc-portlet/struts.jar'
)
to a 'spring.jar'
scenario,
even if you are just using DispatcherServlet
for remoting purposes (e.g. exporting Hessian or HTTP invoker services).
Spring 2.0's 'spring-jmx.jar'
and 'spring-remoting.jar'
have been
merged into Spring 2.5's 'spring-context.jar'
(for the JMX and non-HTTP remoting support) and partly into
'spring-web.jar'
(for the HTTP remoting support).
Spring 2.0's 'spring-support.jar'
has been renamed to 'spring-context-support.jar'
,
expressing the actual support relationship more closely.
'spring-portlet.jar'
has been
renamed to 'spring-webmvc-portlet.jar'
,
since it is technically a submodule of Spring's Web MVC framework.
Analogously, 'spring-struts.jar'
has been renamed to 'spring-webmvc-struts.jar'
.
Spring 2.0's 'spring-jdo.jar'
,
'spring-jpa.jar'
,
'spring-hibernate3.jar'
,
'spring-toplink.jar'
and 'spring-ibatis.jar'
have been combined into Spring 2.5's coarse-granular
'spring-orm.jar'
.
Spring 2.5's 'spring-test.jar'
supersedes the previous 'spring-mock.jar'
,
indicating the stronger focus on the test context framework.
Note that 'spring-test.jar'
contains everything 'spring-mock.jar'
contained in previous Spring versions; hence it can be used as a
straightforward replacement for unit and integration testing purposes.
Spring 2.5's 'spring-tx.jar'
supersedes the previous 'spring-dao.jar'
and 'spring-jca.jar'
files,
indicating the stronger focus on the transaction framework.
Spring 2.5 ships its framework jars as OSGi-compliant bundles out of the box. This facilitates use of Spring in OSGi environments, not requiring custom packaging anymore.
Spring 2.0 ships with XSDs that describe Spring's XML metadata format in a much richer fashion than the DTD that shipped with previous versions. The old DTD is still fully supported, but if possible you are encouraged to reference the XSD files at the top of your bean definition files.
One thing that has changed in a (somewhat) breaking fashion is
the way that bean scopes are defined. If you are using the Spring 1.2
DTD you can continue to use the 'singleton'
attribute. You can however choose to reference the new Spring 2.0
DTD which does not permit the use of the
'singleton'
attribute, but rather uses the
'scope'
attribute to define the bean lifecycle
scope.
A number of classes and methods that previously were marked as
@deprecated
have been removed from the Spring 2.0
codebase. The Spring team decided that the 2.0 release marked a fresh
start of sorts, and that any deprecated 'cruft' was better excised now
instead of continuing to haunt the codebase for the foreseeable
future.
As mentioned previously, for a comprehensive list of changes,
consult the 'changelog.txt'
file that is located
in the top level directory of the Spring Framework distribution.
The following classes/interfaces have been removed as of Spring 2.0:
ResultReader
: Use the
RowMapper
interface instead.
BeanFactoryBootstrap
: Consider using
a BeanFactoryLocator
or a custom
bootstrap class instead.
As of Spring 2.0, support for Apache OJB was totally removed from the main Spring source tree. The Apache OJB integration library is still available, but can be found in it's new home in the Spring Modules project.
Please note that support for iBATIS SQL Maps 1.3 has been removed. If you haven't done so already, upgrade to iBATIS SQL Maps 2.3.
As of Spring 2.5, support for Hibernate 2.1 and Hibernate 3.0 has been removed. If you haven't done so already, upgrade to Hibernate 3.1 or higher.
If you need to stick with Hibernate 2.1 or 3.0 for the time being, we recommend to keep using the Spring Framework version 2.0.7/2.0.8 which still supports those versions of Hibernate.
As of Spring 2.5, support for JDO 1.0 has been removed. If you haven't done so already, upgrade to JDO 2.0 or higher.
If you need to stick with JDO 1.0 for the time being, we recommend to keep using the Spring Framework version 2.0.7/2.0.8 which still supports that version of JDO.
Since Spring 2.0, the view name that is determined by the
UrlFilenameViewController
now takes into
account the nested path of the request. This is a breaking change
from the original contract of the
UrlFilenameViewController
, and means that if
you are upgrading from Spring 1.x to Spring 2.x and you are using this
class you might have to change your Spring Web
MVC configuration slightly. Refer to the class level Javadocs of the
UrlFilenameViewController
to see examples of
the new contract for view name determination.
A number of the sample applications have also been updated to
showcase the new and improved features of Spring 2.0. So do take the time
to investigate them. The aforementioned sample applications can be found
in the 'samples'
directory of the
full Spring distribution
('spring-with-dependencies.[zip|tar.gz]'
).
Spring 2.5 features revised versions of the PetClinic and PetPortal sample applications, reengineered from the ground up for leveraging Spring 2.5's annotation configuration features. It also uses Java 5 autoboxing, generics, varargs and the enhanced for loop. A Java 5 or 6 SDK is now required to build and run the sample. Check out PetClinic and PetPortal to get an impression of what Spring 2.5 has to offer!
The Spring reference documentation has also substantially been updated to reflect all of the above features new in Spring 2.0 and 2.5. While every effort has been made to ensure that there are no errors in this documentation, some errors may nevertheless have crept in. If you do spot any typos or even more serious errors, and you can spare a few cycles during lunch, please do bring the error to the attention of the Spring team by raising an issue.
Special thanks to Arthur Loder for his tireless proofreading of the Spring Framework reference documentation and JavaDocs.
This initial part of the reference documentation covers all of those technologies that are absolutely integral to the Spring Framework.
Foremost amongst these is the Spring Framework's Inversion of Control (IoC) container. A thorough treatment of the Spring Framework's IoC container is closely followed by comprehensive coverage of Spring's Aspect-Oriented Programming (AOP) technologies. The Spring Framework has its own AOP framework, which is conceptually easy to understand, and which successfully addresses the 80% sweet spot of AOP requirements in Java enterprise programming.
Coverage of Spring's integration with AspectJ (currently the richest - in terms of features - and certainly most mature AOP implementation in the Java enterprise space) is also provided.
Finally, the adoption of the test-driven-development (TDD) approach to software development is certainly advocated by the Spring team, and so coverage of Spring's support for integration testing is covered (alongside best practices for unit testing). The Spring team have found that the correct use of IoC certainly does make both unit and integration testing easier (in that the presence of setter methods and appropriate constructors on classes makes them easier to wire together on a test without having to set up service locator registries and suchlike)... the chapter dedicated solely to testing will hopefully convince you of this as well.
This chapter covers the Spring Framework's implementation of the Inversion of Control (IoC) [1] principle.
The org.springframework.beans
and
org.springframework.context
packages provide the basis
for the Spring Framework's IoC container. The BeanFactory
interface provides an advanced configuration mechanism capable of managing
objects of any nature. The ApplicationContext
interface builds on top of the BeanFactory
(it is a sub-interface) and adds other functionality such as easier
integration with Spring's AOP features, message resource handling (for use
in internationalization), event propagation, and application-layer
specific contexts such as the
WebApplicationContext
for use in web
applications.
In short, the BeanFactory
provides
the configuration framework and basic functionality, while the
ApplicationContext
adds more
enterprise-centric functionality to it. The
ApplicationContext
is a complete superset
of the BeanFactory
, and any description of
BeanFactory
capabilities and behavior is to
be considered to apply to the
ApplicationContext
as well.
This chapter is divided into two parts, with the first part covering the basic principles
that apply to both the BeanFactory
and
ApplicationContext
, and with the second part covering those features
that apply only to the ApplicationContext
interface.
In Spring, those objects that form the backbone of your application and that are managed by the Spring IoC container are referred to as beans. A bean is simply an object that is instantiated, assembled and otherwise managed by a Spring IoC container; other than that, there is nothing special about a bean (it is in all other respects one of probably many objects in your application). These beans, and the dependencies between them, are reflected in the configuration metadata used by a container.
The
org.springframework.beans.factory.BeanFactory
is the actual representation of the Spring IoC
container that is responsible for containing and
otherwise managing the aforementioned beans.
The BeanFactory
interface is the
central IoC container interface in Spring. Its responsibilities include
instantiating or sourcing application objects, configuring such objects,
and assembling the dependencies between these objects.
There are a number of implementations of the
BeanFactory
interface that come supplied
straight out-of-the-box with Spring. The most commonly used
BeanFactory
implementation is the
XmlBeanFactory
class. This implementation allows
you to express the objects that compose your application, and the
doubtless rich interdependencies between such objects, in terms of XML.
The XmlBeanFactory
takes this XML
configuration metadata and uses it to create a
fully configured system or application.
The Spring IoC container
As can be seen in the above image, the Spring IoC container consumes some form of configuration metadata; this configuration metadata is nothing more than how you (as an application developer) inform the Spring container as to how to “instantiate, configure, and assemble [the objects in your application]”. This configuration metadata is typically supplied in a simple and intuitive XML format. When using XML-based configuration metadata, you write bean definitions for those beans that you want the Spring IoC container to manage, and then let the container do it's stuff.
![]() | Note |
---|---|
XML-based metadata is by far the most commonly used form of configuration metadata. It is not however the only form of configuration metadata that is allowed. The Spring IoC container itself is totally decoupled from the format in which this configuration metadata is actually written. The XML-based configuration metadata format really is simple though, and so the majority of this chapter will use the XML format to convey key concepts and features of the Spring IoC container. You can find details of another form of metadata that the Spring container can consume in the section entitled Section 3.11, “Annotation-based configuration” |
In the vast majority of application scenarios, explicit user code
is not required to instantiate one or more instances of a Spring IoC
container. For example, in a web application scenario, a simple eight
(or so) lines of boilerplate J2EE web descriptor XML in the
web.xml
file of the application will typically
suffice (see Section 3.8.5, “Convenient ApplicationContext
instantiation for web applications”).
Spring configuration consists of at least one bean definition that
the container must manage, but typically there will be more than one bean
definition. When using XML-based configuration metadata, these beans are
configured as <bean/>
elements inside a top-level
<beans/>
element.
These bean definitions correspond to the actual objects that make up
your application. Typically you will have bean definitions for your
service layer objects, your data access objects (DAOs), presentation
objects such as Struts Action
instances,
infrastructure objects such as Hibernate
SessionFactories
, JMS
Queues
, and so forth. Typically one does
not configure fine-grained domain objects in the container, because it is
usually the responsibility of DAOs and business logic to create/load
domain objects.
Find below an example of the basic structure of XML-based configuration metadata.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"> <bean id="..." class="..."> <!-- collaborators and configuration for this bean go here --> </bean> <bean id="..." class="..."> <!-- collaborators and configuration for this bean go here --> </bean> <!-- more bean definitions go here --> </beans>
Instantiating a Spring IoC container is straightforward.
ApplicationContext context = new ClassPathXmlApplicationContext(
new String[] {"services.xml", "daos.xml"});
// an ApplicationContext
is also a BeanFactory
(via inheritance)
BeanFactory factory = context;
It can often be useful to split up container definitions into
multiple XML files. One way to then load an application context which
is configured from all these XML fragments is to use the application
context constructor which takes multiple
Resource
locations. With a bean
factory, a bean definition reader can be used multiple times to read
definitions from each file in turn.
Generally, the Spring team prefers the above approach, since it
keeps container configuration files unaware of the fact that they are
being combined with others. An alternate approach is to use one or
more occurrences of the <import/>
element to
load bean definitions from another file (or files). Let's look at a
sample:
<beans> <import resource="services.xml"/> <import resource="resources/messageSource.xml"/> <import resource="/resources/themeSource.xml"/> <bean id="bean1" class="..."/> <bean id="bean2" class="..."/> </beans>
In this example, external bean definitions are being loaded from
3 files, services.xml
,
messageSource.xml
, and
themeSource.xml
. All location paths are considered
relative to the definition file doing the importing, so
services.xml
in this case must be in the same
directory or classpath location as the file doing the importing, while
messageSource.xml
and
themeSource.xml
must be in a
resources
location below the location of the
importing file. As you can see, a leading slash is actually ignored,
but given that these are considered relative paths, it is probably
better form not to use the slash at all. The contents of the files
being imported must be valid XML bean definition files according to
the Spring Schema or DTD, including the top level
<beans/>
element.
![]() | Note |
---|---|
It is possible to reference files in parent directories using a relative "../" path. However, this is not recommended because it creates a dependency on a file that is outside the current application. This is in particular not recommended for "classpath:" URLs (e.g. "classpath:../services.xml") where the runtime resolution process will pick the "nearest" classpath root and then look into its parent directory. This is fragile since classpath configuration changes may lead to a different directory being picked. Note that you can always use fully qualified resource locations instead of relative paths: e.g. "file:C:/config/services.xml" or "classpath:/config/services.xml". However, be aware that you are coupling your application's configuration to specific absolute locations then. It is generally preferable to keep an indirection for such absolute locations, e.g. through "${...}" placeholders that are resolved against JVM system properties at runtime. |
A Spring IoC container manages one or more
beans. These beans are created using the
configuration metadata that has been supplied to the container
(typically in the form of XML <bean/>
definitions).
Within the container itself, these bean definitions are
represented as BeanDefinition
objects,
which contain (among other information) the following metadata:
a package-qualified class name: typically this is the actual implementation class of the bean being defined.
bean behavioral configuration elements, which state how the bean should behave in the container (scope, lifecycle callbacks, and so forth).
references to other beans which are needed for the bean to do its work; these references are also called collaborators or dependencies.
other configuration settings to set in the newly created object. An example would be the number of connections to use in a bean that manages a connection pool, or the size limit of the pool.
The concepts listed above directly translate to a set of properties that each bean definition consists of. Some of these properties are listed below, along with a link to further documentation about each of them.
Table 3.1. The bean definition
Feature | Explained in... |
---|---|
class | |
name | |
scope | |
constructor arguments | |
properties | |
autowiring mode | |
dependency checking mode | |
lazy-initialization mode | |
initialization method | |
destruction method |
Besides bean definitions which contain information on how to
create a specific bean, certain
BeanFactory
implementations also permit
the registration of existing objects that have been created outside the
factory (by user code). The
DefaultListableBeanFactory
class supports this
through the registerSingleton(..)
method.
(Typical applications solely work with beans defined through metadata
bean definitions though.)
Every bean has one or more id
s (also called
identifiers, or names; these terms refer to the same thing). These
id
s must be unique within the container the bean is
hosted in. A bean will almost always have only one id, but if a bean
has more than one id, the extra ones can essentially be considered
aliases.
When using XML-based configuration metadata, you use the
'id'
or 'name'
attributes to
specify the bean identifier(s). The 'id'
attribute
allows you to specify exactly one id, and as it is a real XML element
ID attribute, the XML parser is able to do some extra validation when
other elements reference the id; as such, it is the preferred way to
specify a bean id. However, the XML specification does limit the
characters which are legal in XML IDs. This is usually not a
constraint, but if you have a need to use one of these special XML
characters, or want to introduce other aliases to the bean, you may
also or instead specify one or more bean id
s,
separated by a comma (,
), semicolon
(;
), or whitespace in the 'name'
attribute.
Please note that you are not required to supply a name for a bean. If no name is supplied explicitly, the container will generate a unique name for that bean. The motivations for not supplying a name for a bean will be discussed later (one use case is inner beans).
In a bean definition itself, you may supply more than one name
for the bean, by using a combination of up to one name specified via
the id
attribute, and any number of other names
via the name
attribute. All these names can be
considered equivalent aliases to the same bean, and are useful for
some situations, such as allowing each component used in an
application to refer to a common dependency using a bean name that
is specific to that component itself.
Having to specify all aliases when the bean is actually
defined is not always adequate however. It is sometimes desirable to
introduce an alias for a bean which is defined elsewhere. In
XML-based configuration metadata this may be accomplished via the
use of the <alias/>
element.
<alias name="fromName" alias="toName"/>
In this case, a bean in the same container which is named
'fromName'
, may also after the use of this alias
definition, be referred to as 'toName'
.
As a concrete example, consider the case where component A defines a DataSource bean called componentA-dataSource, in its XML fragment. Component B would however like to refer to the DataSource as componentB-dataSource in its XML fragment. And the main application, MyApp, defines its own XML fragment and assembles the final application context from all three fragments, and would like to refer to the DataSource as myApp-dataSource. This scenario can be easily handled by adding to the MyApp XML fragment the following standalone aliases:
<alias name="componentA-dataSource" alias="componentB-dataSource"/> <alias name="componentA-dataSource" alias="myApp-dataSource" />
Now each component and the main application can refer to the dataSource via a name that is unique and guaranteed not to clash with any other definition (effectively there is a namespace), yet they refer to the same bean.
A bean definition essentially is a recipe for creating one or more objects. The container looks at the recipe for a named bean when asked, and uses the configuration metadata encapsulated by that bean definition to create (or acquire) an actual object.
If you are using XML-based configuration metadata, you can
specify the type (or class) of object that is to be instantiated using
the 'class'
attribute of the
<bean/>
element. This
'class'
attribute (which internally eventually
boils down to being a Class
property on a
BeanDefinition
instance) is normally
mandatory (see Section 3.2.3.2.3, “Instantiation using an instance factory method” and Section 3.6, “Bean definition inheritance” for the two exceptions) and
is used for one of two purposes. The class property specifies the
class of the bean to be constructed in the common case where the
container itself directly creates the bean by calling its constructor
reflectively (somewhat equivalent to Java code using the
'new' operator). In the less common case where
the container invokes a static
,
factory method on a class to create the bean, the
class property specifies the actual class containing the
static
factory method that is to be invoked to
create the object (the type of the object returned from the invocation
of the static
factory method may be the same class
or another class entirely, it doesn't matter).
When creating a bean using the constructor approach, all normal classes are usable by and compatible with Spring. That is, the class being created does not need to implement any specific interfaces or be coded in a specific fashion. Just specifying the bean class should be enough. However, depending on what type of IoC you are going to use for that specific bean, you may need a default (empty) constructor.
Additionally, the Spring IoC container isn't limited to just managing true JavaBeans, it is also able to manage virtually any class you want it to manage. Most people using Spring prefer to have actual JavaBeans (having just a default (no-argument) constructor and appropriate setters and getters modeled after the properties) in the container, but it is also possible to have more exotic non-bean-style classes in your container. If, for example, you need to use a legacy connection pool that absolutely does not adhere to the JavaBean specification, Spring can manage it as well.
When using XML-based configuration metadata you can specify your bean class like so:
<bean id="exampleBean" class="examples.ExampleBean"/> <bean name="anotherExample" class="examples.ExampleBeanTwo"/>
The mechanism for supplying arguments to the constructor (if required), or setting properties of the object instance after it has been constructed, is described shortly.
When defining a bean which is to be created using a static
factory method, along with the class
attribute
which specifies the class containing the static
factory method, another attribute named
factory-method
is needed to specify the name of
the factory method itself. Spring expects to be able to call this
method (with an optional list of arguments as described later) and
get back a live object, which from that point on is treated as if it
had been created normally via a constructor. One use for such a bean
definition is to call static
factories in legacy
code.
The following example shows a bean definition which specifies
that the bean is to be created by calling a factory-method. Note
that the definition does not specify the type (class) of the
returned object, only the class containing the factory method. In
this example, the createInstance()
method
must be a static method.
<bean id="exampleBean" class="examples.ExampleBean2" factory-method="createInstance"/>
The mechanism for supplying (optional) arguments to the factory method, or setting properties of the object instance after it has been returned from the factory, will be described shortly.
In a fashion similar to instantiation via a static factory
method, instantiation using an instance factory method is
where a non-static method of an existing bean from the container is
invoked to create a new bean. To use this mechanism, the
'class'
attribute must be left empty, and the
'factory-bean'
attribute must specify the name of
a bean in the current (or parent/ancestor) container that contains
the instance method that is to be invoked to create the object. The
name of the factory method itself must be set using the
'factory-method'
attribute.
<!-- the factory bean, which contains a method called createInstance()
-->
<bean id="serviceLocator" class="com.foo.DefaultServiceLocator">
<!-- inject any dependencies required by this locator bean -->
</bean>
<!-- the bean to be created via the factory bean -->
<bean id="exampleBean"
factory-bean="serviceLocator"
factory-method="createInstance"/>
Although the mechanisms for setting bean properties are still to be discussed, one implication of this approach is that the factory bean itself can be managed and configured via DI.
![]() | Note |
---|---|
When the Spring documentation makes mention of a 'factory
bean', this will be a reference to a bean that is configured in the
Spring container that will create objects via an instance
or static
factory method. When the documentation mentions a
|
A BeanFactory
is essentially
nothing more than the interface for an advanced factory capable of
maintaining a registry of different beans and their dependencies. The
BeanFactory
enables you to read bean
definitions and access them using the bean factory. When using just the
BeanFactory
you would create one and read
in some bean definitions in the XML format as follows:
Resource res = new FileSystemResource("beans.xml"); BeanFactory factory = new XmlBeanFactory(res);
Basically that is all there is to it. Using
getBean(String)
you can retrieve instances of
your beans; the client-side view of the
BeanFactory
is simple. The
BeanFactory
interface has just a few
other methods, but ideally your application code should never use
them... indeed, your application code should have no calls to the
getBean(String)
method at all, and thus no
dependency on Spring APIs at all.
Your typical enterprise application is not made up of a single object (or bean in the Spring parlance). Even the simplest of applications will no doubt have at least a handful of objects that work together to present what the end-user sees as a coherent application. This next section explains how you go from defining a number of bean definitions that stand-alone, each to themselves, to a fully realized application where objects work (or collaborate) together to achieve some goal (usually an application that does what the end-user wants).
The basic principle behind Dependency Injection (DI) is that objects define their dependencies (that is to say the other objects they work with) only through constructor arguments, arguments to a factory method, or properties which are set on the object instance after it has been constructed or returned from a factory method. Then, it is the job of the container to actually inject those dependencies when it creates the bean. This is fundamentally the inverse, hence the name Inversion of Control (IoC), of the bean itself being in control of instantiating or locating its dependencies on its own using direct construction of classes, or something like the Service Locator pattern.
It becomes evident upon usage that code gets much cleaner when the DI principle is applied, and reaching a higher grade of decoupling is much easier when objects do not look up their dependencies, but are provided with them (and additionally do not even know where the dependencies are located and of what concrete class they are). DI exists in two major variants, namely Constructor Injection and Setter Injection.
Constructor-based DI is effected by
invoking a constructor with a number of arguments, each representing a
dependency. Additionally, calling a static
factory
method with specific arguments to construct the bean, can be
considered almost equivalent, and the rest of this text will consider
arguments to a constructor and arguments to a
static
factory method similarly. Find below an
example of a class that could only be dependency injected using
constructor injection. Notice that there is nothing
special about this class.
public class SimpleMovieLister { // theSimpleMovieLister
has a dependency on aMovieFinder
private MovieFinder movieFinder; // a constructor so that the Spring container can 'inject' aMovieFinder
public SimpleMovieLister(MovieFinder movieFinder) { this.movieFinder = movieFinder; } // business logic that actually 'uses' the injectedMovieFinder
is omitted... }
Constructor argument resolution matching occurs using the argument's type. If there is no potential for ambiguity in the constructor arguments of a bean definition, then the order in which the constructor arguments are defined in a bean definition is the order in which those arguments will be supplied to the appropriate constructor when it is being instantiated. Consider the following class:
package x.y;
public class Foo {
public Foo(Bar bar, Baz baz) {
// ...
}
}
There is no potential for ambiguity here (assuming of course
that Bar
and Baz
classes are not related in an inheritance hierarchy). Thus the
following configuration will work just fine, and you do not need to
specify the constructor argument indexes and / or types
explicitly.
<beans> <bean name="foo" class="x.y.Foo"> <constructor-arg> <bean class="x.y.Bar"/> </constructor-arg> <constructor-arg> <bean class="x.y.Baz"/> </constructor-arg> </bean> </beans>
When another bean is referenced, the type is known, and
matching can occur (as was the case with the preceding example).
When a simple type is used, such as
<value>true<value>
, Spring cannot
determine the type of the value, and so cannot match by type without
help. Consider the following class:
package examples; public class ExampleBean { // No. of years to the calculate the Ultimate Answer private int years; // The Answer to Life, the Universe, and Everything private String ultimateAnswer; public ExampleBean(int years, String ultimateAnswer) { this.years = years; this.ultimateAnswer = ultimateAnswer; } }
The above scenario can use type
matching with simple types by explicitly specifying the type of
the constructor argument using the 'type'
attribute. For example:
<bean id="exampleBean" class="examples.ExampleBean"> <constructor-arg type="int" value="7500000"/> <constructor-arg type="java.lang.String" value="42"/> </bean>
Constructor arguments can have their index specified
explicitly by use of the index
attribute. For
example:
<bean id="exampleBean" class="examples.ExampleBean"> <constructor-arg index="0" value="7500000"/> <constructor-arg index="1" value="42"/> </bean>
As well as solving the ambiguity problem of multiple simple values, specifying an index also solves the problem of ambiguity where a constructor may have two arguments of the same type. Note that the index is 0 based.
Setter-based DI is realized by calling
setter methods on your beans after invoking a no-argument constructor
or no-argument static
factory method to instantiate
your bean.
Find below an example of a class that can only be dependency injected using pure setter injection. Note that there is nothing special about this class... it is plain old Java.
public class SimpleMovieLister { // theSimpleMovieLister
has a dependency on theMovieFinder
private MovieFinder movieFinder; // a setter method so that the Spring container can 'inject' aMovieFinder
public void setMovieFinder(MovieFinder movieFinder) { this.movieFinder = movieFinder; } // business logic that actually 'uses' the injectedMovieFinder
is omitted... }
The BeanFactory
supports both of
these variants for injecting dependencies into beans it manages. (It in
fact also supports injecting setter-based dependencies after some
dependencies have already been supplied via the constructor approach.)
The configuration for the dependencies comes in the form of a
BeanDefinition
, which is used together
with PropertyEditor
instances to know how
to convert properties from one format to another. However, most users of
Spring will not be dealing with these classes directly (that is
programmatically), but rather with an XML definition file which will be
converted internally into instances of these classes, and used to load
an entire Spring IoC container instance.
Bean dependency resolution generally happens as follows:
The BeanFactory
is created and
initialized with a configuration which describes all the beans.
(Most Spring users use a BeanFactory
or ApplicationContext
implementation
that supports XML format configuration files.)
Each bean has dependencies expressed in the form of properties, constructor arguments, or arguments to the static-factory method when that is used instead of a normal constructor. These dependencies will be provided to the bean, when the bean is actually created.
Each property or constructor argument is either an actual definition of the value to set, or a reference to another bean in the container.
Each property or constructor argument which is a value must be able
to be converted from whatever format it was specified in, to the
actual type of that property or constructor argument. By default
Spring can convert a value supplied in string format to all built-in
types, such as int
, long
,
String
, boolean
, etc.
The Spring container validates the configuration of each bean as
the container is created, including the validation that properties which
are bean references are actually referring to valid beans. However, the
bean properties themselves are not set until the bean is
actually created. For those beans that are singleton-scoped
and set to be pre-instantiated (such as singleton beans in an
ApplicationContext
), creation happens at
the time that the container is created, but otherwise this is only when
the bean is requested. When a bean actually has to be created, this will
potentially cause a graph of other beans to be created, as its
dependencies and its dependencies' dependencies (and so on) are created
and assigned.
You can generally trust Spring to do the right thing. It will
detect misconfiguration issues, such as references to non-existent beans
and circular dependencies, at container load-time. It will actually set
properties and resolve dependencies as late as possible, which is when
the bean is actually created. This means that a Spring container which
has loaded correctly can later generate an exception when you request a
bean if there is a problem creating that bean or one of its
dependencies. This could happen if the bean throws an exception as a
result of a missing or invalid property, for example. This potentially
delayed visibility of some configuration issues is why
ApplicationContext
implementations by
default pre-instantiate singleton beans. At the cost of some upfront
time and memory to create these beans before they are actually needed,
you find out about configuration issues when the
ApplicationContext
is created, not later.
If you wish, you can still override this default behavior and set any of
these singleton beans to lazy-initialize (that is not be
pre-instantiated).
If no circular dependencies are involved (see sidebar for a discussion of circular dependencies), when one or more collaborating beans are being injected into a dependent bean, each collaborating bean is totally configured prior to being passed (via one of the DI flavors) to the dependent bean. This means that if bean A has a dependency on bean B, the Spring IoC container will totally configure bean B prior to invoking the setter method on bean A; you can read 'totally configure' to mean that the bean will be instantiated (if not a pre-instantiated singleton), all of its dependencies will be set, and the relevant lifecycle methods (such as a configured init method or the IntializingBean callback method) will all be invoked.
First, an example of using XML-based configuration metadata for setter-based DI. Find below a small part of a Spring XML configuration file specifying some bean definitions.
<bean id="exampleBean" class="examples.ExampleBean">
<!-- setter injection using the nested <ref/>
element -->
<property name="beanOne"><ref bean="anotherExampleBean"/></property>
<!-- setter injection using the neater 'ref' attribute -->
<property name="beanTwo" ref="yetAnotherBean"/>
<property name="integerProperty" value="1"/>
</bean>
<bean id="anotherExampleBean" class="examples.AnotherBean"/>
<bean id="yetAnotherBean" class="examples.YetAnotherBean"/>
public class ExampleBean { private AnotherBean beanOne; private YetAnotherBean beanTwo; private int i; public void setBeanOne(AnotherBean beanOne) { this.beanOne = beanOne; } public void setBeanTwo(YetAnotherBean beanTwo) { this.beanTwo = beanTwo; } public void setIntegerProperty(int i) { this.i = i; } }
As you can see, setters have been declared to match against the properties specified in the XML file. Find below an example of using constructor-based DI.
<bean id="exampleBean" class="examples.ExampleBean">
<!-- constructor injection using the nested <ref/>
element -->
<constructor-arg>
<ref bean="anotherExampleBean"/>
</constructor-arg>
<!-- constructor injection using the neater 'ref' attribute -->
<constructor-arg ref="yetAnotherBean"/>
<constructor-arg type="int" value="1"/>
</bean>
<bean id="anotherExampleBean" class="examples.AnotherBean"/>
<bean id="yetAnotherBean" class="examples.YetAnotherBean"/>
public class ExampleBean { private AnotherBean beanOne; private YetAnotherBean beanTwo; private int i; public ExampleBean( AnotherBean anotherBean, YetAnotherBean yetAnotherBean, int i) { this.beanOne = anotherBean; this.beanTwo = yetAnotherBean; this.i = i; } }
As you can see, the constructor arguments specified in the bean
definition will be used to pass in as arguments to the constructor of
the ExampleBean
.
Now consider a variant of this where instead of using a
constructor, Spring is told to call a static
factory method to return an instance of the object:
<bean id="exampleBean" class="examples.ExampleBean" factory-method="createInstance"> <constructor-arg ref="anotherExampleBean"/> <constructor-arg ref="yetAnotherBean"/> <constructor-arg value="1"/> </bean> <bean id="anotherExampleBean" class="examples.AnotherBean"/> <bean id="yetAnotherBean" class="examples.YetAnotherBean"/>
public class ExampleBean { // a private constructor private ExampleBean(...) { ... } // a static factory method; the arguments to this method can be // considered the dependencies of the bean that is returned, // regardless of how those arguments are actually used. public static ExampleBean createInstance ( AnotherBean anotherBean, YetAnotherBean yetAnotherBean, int i) { ExampleBean eb = new ExampleBean (...); // some other operations... return eb; } }
Note that arguments to the static
factory
method are supplied via <constructor-arg/>
elements, exactly the same as if a constructor had actually been used.
Also, it is important to realize that the type of the class being
returned by the factory method does not have to be of the same type as
the class which contains the static
factory method,
although in this example it is. An instance (non-static) factory
method would be used in an essentially identical fashion (aside from
the use of the factory-bean
attribute instead of
the class
attribute), so details will not be
discussed here.
As mentioned in the previous section, bean properties and
constructor arguments can be defined as either references to other
managed beans (collaborators), or values defined inline. Spring's
XML-based configuration metadata supports a number of sub-element types
within its <property/>
and
<constructor-arg/>
elements for just this
purpose.
The <value/>
element specifies a
property or constructor argument as a human-readable string
representation. As mentioned
previously, JavaBeans PropertyEditors
are
used to convert these string values from a
String
to the actual type of the property or
argument.
<bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
<!-- results in a setDriverClassName(String)
call -->
<property name="driverClassName">
<value>com.mysql.jdbc.Driver</value>
</property>
<property name="url">
<value>jdbc:mysql://localhost:3306/mydb</value>
</property>
<property name="username">
<value>root</value>
</property>
<property name="password">
<value>masterkaoli</value>
</property>
</bean>
The <property/>
and
<constructor-arg/>
elements also support the
use of the 'value'
attribute, which can lead to
much more succinct configuration. When using the
'value'
attribute, the above bean definition reads
like so:
<bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
<!-- results in a setDriverClassName(String)
call -->
<property name="driverClassName" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mydb"/>
<property name="username" value="root"/>
<property name="password" value="masterkaoli"/>
</bean>
The Spring team generally prefer the attribute style over the
use of nested <value/>
elements. If you are
reading this reference manual straight through from top to bottom
(wow!) then we are getting slightly ahead of ourselves here, but you
can also configure a java.util.Properties
instance like so:
<bean id="mappings" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<!-- typed as a java.util.Properties
-->
<property name="properties">
<value>
jdbc.driver.className=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mydb
</value>
</property>
</bean>
Can you see what is happening? The Spring container is
converting the text inside the <value/>
element into a java.util.Properties
instance
using the JavaBeans PropertyEditor
mechanism. This is a nice shortcut, and is one of a few places where
the Spring team do favor the use of the nested
<value/>
element over the
'value'
attribute style.
The idref
element is simply an error-proof
way to pass the id of another bean in the
container (to a <constructor-arg/>
or
<property/>
element).
<bean id="theTargetBean" class="..."/> <bean id="theClientBean" class="..."> <property name="targetName"> <idref bean="theTargetBean" /> </property> </bean>
The above bean definition snippet is exactly equivalent (at runtime) to the following snippet:
<bean id="theTargetBean" class="..." /> <bean id="client" class="..."> <property name="targetName" value="theTargetBean" /> </bean>
The main reason the first form is preferable to the second is
that using the idref
tag allows the container to
validate at deployment time that the
referenced, named bean actually exists. In the second variation, no
validation is performed on the value that is passed to the
'targetName'
property of the
'client'
bean. Any typo will only be discovered
(with most likely fatal results) when the
'client'
bean is actually instantiated. If the
'client'
bean is a prototype bean, this typo (and
the resulting exception) may only be discovered long after the
container is actually deployed.
Additionally, if the bean being referred to is in the same XML
unit, and the bean name is the bean id, the
'local'
attribute may be used, which allows the
XML parser itself to validate the bean id even earlier, at XML
document parse time.
<property name="targetName">
<!-- a bean with an id of 'theTargetBean
' must exist; otherwise an XML exception will be thrown -->
<idref local="theTargetBean"/>
</property>
By way of an example, one common place (at least in pre-Spring
2.0 configuration) where the <idref/> element brings value is
in the configuration of AOP
interceptors in a ProxyFactoryBean
bean definition. If you use <idref/> elements when specifying
the interceptor names, there is no chance of inadvertently
misspelling an interceptor id.
The ref
element is the final element allowed
inside a <constructor-arg/>
or
<property/>
definition element. It is used to
set the value of the specified property to be a reference to another
bean managed by the container (a collaborator). As mentioned in a
previous section, the referred-to bean is considered to be a
dependency of the bean who's property is being set, and will be
initialized on demand as needed (if it is a singleton bean it may have
already been initialized by the container) before the property is set.
All references are ultimately just a reference to another object, but
there are 3 variations on how the id/name of the other object may be
specified, which determines how scoping and validation is
handled.
Specifying the target bean by using the bean
attribute of the <ref/>
tag is the most
general form, and will allow creating a reference to any bean in the
same container (whether or not in the same XML file), or parent
container. The value of the 'bean'
attribute may be
the same as either the 'id'
attribute of the target
bean, or one of the values in the 'name'
attribute
of the target bean.
<ref bean="someBean"/>
Specifying the target bean by using the local
attribute leverages the ability of the XML parser to validate XML id
references within the same file. The value of the
local
attribute must be the same as the
id
attribute of the target bean. The XML parser
will issue an error if no matching element is found in the same file.
As such, using the local variant is the best choice (in order to know
about errors as early as possible) if the target bean is in the same
XML file.
<ref local="someBean"/>
Specifying the target bean by using the
'parent'
attribute allows a reference to be created
to a bean which is in a parent container of the current container. The
value of the 'parent'
attribute may be the same as
either the 'id'
attribute of the target bean, or
one of the values in the 'name'
attribute of the
target bean, and the target bean must be in a parent container to the
current one. The main use of this bean reference variant is when you
have a hierarchy of containers and you want to wrap an existing bean
in a parent container with some sort of proxy which will have the same
name as the parent bean.
<!-- in the parent context --> <bean id="accountService" class="com.foo.SimpleAccountService"> <!-- insert dependencies as required as here --> </bean>
<!-- in the child (descendant) context -->
<bean id="accountService" <-- notice that the name of this bean is the same as the name of the 'parent'
bean
class="org.springframework.aop.framework.ProxyFactoryBean">
<property name="target">
<ref parent="accountService"/> <-- notice how we refer to the parent bean
</property>
<!-- insert other configuration and dependencies as required as here -->
</bean>
A <bean/>
element inside the
<property/>
or
<constructor-arg/>
elements is used to define
a so-called inner bean. An inner bean
definition does not need to have any id or name defined, and it is
best not to even specify any id or name value because the id or name
value simply will be ignored by the container.
<bean id="outer" class="..."> <!-- instead of using a reference to a target bean, simply define the target bean inline --> <property name="target"> <bean class="com.example.Person"> <!-- this is the inner bean --> <property name="name" value="Fiona Apple"/> <property name="age" value="25"/> </bean> </property> </bean>
Note that in the specific case of inner beans, the
'scope'
flag and any 'id'
or
'name'
attribute are effectively ignored. Inner
beans are always anonymous and they are
always scoped as prototypes. Please
also note that it is not possible to inject inner
beans into collaborating beans other than the enclosing bean.
The <list/>
,
<set/>
, <map/>
, and
<props/>
elements allow properties and
arguments of the Java Collection
type
List
,
Set
,
Map
, and
Properties
, respectively, to be defined
and set.
<bean id="moreComplexObject" class="example.ComplexObject"> <!-- results in a setAdminEmails(java.util.Properties
) call --> <property name="adminEmails"> <props> <prop key="administrator">administrator@example.org</prop> <prop key="support">support@example.org</prop> <prop key="development">development@example.org</prop> </props> </property> <!-- results in a setSomeList(java.util.List
) call --> <property name="someList"> <list> <value>a list element followed by a reference</value> <ref bean="myDataSource" /> </list> </property> <!-- results in a setSomeMap(java.util.Map
) call --> <property name="someMap"> <map> <entry> <key> <value>an entry</value> </key> <value>just some string</value> </entry> <entry> <key> <value>a ref</value> </key> <ref bean="myDataSource" /> </entry> </map> </property> <!-- results in a setSomeSet(java.util.Set) call --> <property name="someSet"> <set> <value>just some string</value> <ref bean="myDataSource" /> </set> </property> </bean>
Note that the value of a map key or value, or a set value, can also again be any of the following elements:
bean | ref | idref | list | set | map | props | value | null
As of Spring 2.0, the container also supports the
merging of collections. This allows an
application developer to define a parent-style
<list/>
, <map/>
,
<set/>
or <props/>
element, and have child-style <list/>
,
<map/>
, <set/>
or
<props/>
elements inherit and override
values from the parent collection; that is to say the child
collection's values will be the result obtained from the merging of
the elements of the parent and child collections, with the child's
collection elements overriding values specified in the parent
collection.
Please note that this section on merging makes use of the parent-child bean mechanism. This concept has not yet been introduced, so readers unfamiliar with the concept of parent and child bean definitions may wish to read the relevant section before continuing.
Find below an example of the collection merging feature:
<beans>
<bean id="parent" abstract="true" class="example.ComplexObject">
<property name="adminEmails">
<props>
<prop key="administrator">administrator@example.com</prop>
<prop key="support">support@example.com</prop>
</props>
</property>
</bean>
<bean id="child" parent="parent">
<property name="adminEmails">
<!-- the merge is specified on the *child* collection definition -->
<props merge="true">
<prop key="sales">sales@example.com</prop>
<prop key="support">support@example.co.uk</prop>
</props>
</property>
</bean>
<beans>
Notice the use of the merge=true
attribute
on the <props/>
element of the
adminEmails
property of the
child
bean definition. When the
child
bean is actually resolved and instantiated
by the container, the resulting instance will have an
adminEmails
Properties
collection that contains the result of the merging of the child's
adminEmails
collection with the parent's
adminEmails
collection.
administrator=administrator@example.com sales=sales@example.com support=support@example.co.uk
Notice how the child Properties
collection's value set will have inherited all the property elements
from the parent <props/>
. Notice also how
the child's value for the support
value overrides
the value in the parent collection.
This merging behavior applies similarly to the
<list/>
, <map/>
,
and <set/>
collection types. In the
specific case of the <list/>
element, the
semantics associated with the List
collection
type, that is the notion of an ordered
collection
of values, is maintained; the parent's values will precede all of
the child list's values. In the case of the
Map
,
Set
, and
Properties
collection types, there is
no notion of ordering and hence no ordering semantics are in effect
for the collection types that underlie the associated
Map
,
Set
and
Properties
implementation types used
internally by the container.
Finally, some minor notes about the merging support are in
order; you cannot merge different collection types (e.g. a
Map
and a
List
), and if you do attempt to do so
an appropriate Exception
will be thrown; and
in case it is not immediately obvious, the
'merge'
attribute must be specified on the lower
level, inherited, child definition; specifying the
'merge'
attribute on a parent collection
definition is redundant and will not result in the desired merging;
and (lastly), please note that this merging feature is only
available in Spring 2.0 (and later versions).
If you are using Java 5 or Java 6, you will be aware that it
is possible to have strongly typed collections (using generic
types). That is, it is possible to declare a
Collection
type such that it can only
contain String
elements (for example). If you
are using Spring to dependency inject a strongly-typed
Collection
into a bean, you can take
advantage of Spring's type-conversion support such that the elements
of your strongly-typed Collection
instances will be converted to the appropriate type prior to being
added to the Collection
.
public class Foo { private Map<String, Float> accounts; public void setAccounts(Map<String, Float> accounts) { this.accounts = accounts; } }
<beans> <bean id="foo" class="x.y.Foo"> <property name="accounts"> <map> <entry key="one" value="9.99"/> <entry key="two" value="2.75"/> <entry key="six" value="3.99"/> </map> </property> </bean> </beans>
When the 'accounts'
property of the
'foo'
bean is being prepared for injection, the
generics information about the element type of the strongly-typed
Map<String, Float>
is actually
available via reflection, and so Spring's type conversion
infrastructure will actually recognize the various value elements as
being of type Float
and so the string values
'9.99', '2.75'
, and '3.99'
will be converted into an actual Float
type.
The <null/>
element is used to handle
null
values. Spring treats empty arguments for
properties and the like as empty Strings
. The
following XML-based configuration metadata snippet results in the
email property being set to the empty String
value ("")
<bean class="ExampleBean"> <property name="email"><value/></property> </bean>
This is equivalent to the following Java code:
exampleBean.setEmail("")
. The special
<null>
element may be used to indicate a
null
value. For example:
<bean class="ExampleBean"> <property name="email"><null/></property> </bean>
The above configuration is equivalent to the following Java
code: exampleBean.setEmail(null)
.
The configuration metadata shown so far is a tad verbose. That
is why there are several options available for you to limit the amount
of XML you have to write to configure your components. The first is a
shortcut to define values and references to other beans as part of a
<property/>
definition. The second is
slightly different format of specifying properties altogether.
The <property/>
,
<constructor-arg/>
, and
<entry/>
elements all support a
'value'
attribute which may be used instead of
embedding a full <value/>
element.
Therefore, the following:
<property name="myProperty"> <value>hello</value> </property>
<constructor-arg> <value>hello</value> </constructor-arg>
<entry key="myKey"> <value>hello</value> </entry>
are equivalent to:
<property name="myProperty" value="hello"/>
<constructor-arg value="hello"/>
<entry key="myKey" value="hello"/>
The <property/>
and
<constructor-arg/>
elements support a
similar shortcut 'ref'
attribute which may be
used instead of a full nested <ref/>
element. Therefore, the following:
<property name="myProperty"> <ref bean="myBean"> </property>
<constructor-arg> <ref bean="myBean"> </constructor-arg>
... are equivalent to:
<property name="myProperty" ref="myBean"/>
<constructor-arg ref="myBean"/>
Note however that the shortcut form is equivalent to a
<ref bean="xxx">
element; there is no
shortcut for <ref local="xxx"
>. To enforce
a strict local reference, you must use the long form.
Finally, the entry element allows a shortcut form to specify
the key and/or value of the map, in the form of the
'key'
/ 'key-ref'
and
'value'
/ 'value-ref'
attributes. Therefore, the following:
<entry> <key> <ref bean="myKeyBean" /> </key> <ref bean="myValueBean" /> </entry>
is equivalent to:
<entry key-ref="myKeyBean" value-ref="myValueBean"/>
Again, the shortcut form is equivalent to a <ref
bean="xxx">
element; there is no shortcut for
<ref local="xxx"
>.
The second option you have to limit the amount of XML you have
to write to configure your components is to use the special
"p-namespace". Spring 2.0 and later features support for extensible
configuration formats using
namespaces. Those namespaces are all based on an XML Schema
definition. In fact, the beans
configuration
format that you've been reading about is defined in an XML Schema
document.
One special namespace is not defined in an XSD file, and only
exists in the core of Spring itself. The so-called p-namespace
doesn't need a schema definition and is an alternative way of
configuring your properties differently than the way you have seen
so far. Instead of using nested <property/>
elements, using the p-namespace you can use attributes as part of
the bean
element that describe your property
values. The values of the attributes will be taken as the values for
your properties.
The following two XML snippets boil down to the same thing in the end: the first is using the standard XML format whereas the second example is using the p-namespace.
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"> <bean name="classic" class="com.example.ExampleBean"> <property name="email" value="foo@bar.com/> </bean> <bean name="p-namespace" class="com.example.ExampleBean" p:email="foo@bar.com"/> </beans>
As you can see, we are including an attribute in the p-namespace called email in the bean definition - this is telling Spring that it should include a property declaration. As previously mentioned, the p-namespace doesn't have a schema definition, so the name of the attribute can be set to whatever name your property has.
This next example includes two more bean definitions that both have a reference to another bean:
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"> <bean name="john-classic" class="com.example.Person"> <property name="name" value="John Doe"/> <property name="spouse" ref="jane"/> </bean> <bean name="john-modern" class="com.example.Person" p:name="John Doe" p:spouse-ref="jane"/> <bean name="jane" class="com.example.Person"> <property name="name" value="Jane Doe"/> </bean> </beans>
As you can see, this example doesn't only include a property
value using the p-namespace, but also uses a special format to
declare property references. Whereas the first bean definition uses
<property name="spouse" ref="jane"/>
to
create a reference from bean john
to bean
jane
, the second bean definition uses
p:spouse-ref="jane"
as an attribute to do the
exact same thing. In this case 'spouse
' is the
property name whereas the '-ref
' part indicates
that this is not a straight value but rather a reference to another
bean.
![]() | Note |
---|---|
Please note that the p-namespace is not quite as flexible as
the standard XML format - for example particular, the 'special'
format used to declare property references will clash with
properties that end in ' |
Compound or nested property names are perfectly legal when
setting bean properties, as long as all components of the path except
the final property name are not null
. Consider the
following bean definition...
<bean id="foo" class="foo.Bar"> <property name="fred.bob.sammy" value="123" /> </bean>
The foo
bean has a fred
property which has a bob
property, which has a
sammy
property, and that final
sammy
property is being set to the value
123
. In order for this to work, the
fred
property of foo
, and the
bob
property of fred
must not be
null
be non-null after the bean is constructed, or
a NullPointerException
will be
thrown.
For most situations, the fact that a bean is a dependency of
another is expressed by the fact that one bean is set as a property of
another. This is typically accomplished with the <ref/>
element in XML-based configuration metadata. For the relatively
infrequent situations where dependencies between beans are less direct
(for example, when a static initializer in a class needs to be
triggered, such as database driver registration), the
'depends-on'
attribute may be used to explicitly
force one or more beans to be initialized before the bean using this
element is initialized. Find below an example of using the
'depends-on'
attribute to express a dependency on a
single bean.
<bean id="beanOne" class="ExampleBean" depends-on="manager"/> <bean id="manager" class="ManagerBean" />
If you need to express a dependency on multiple beans, you can
supply a list of bean names as the value of the
'depends-on'
attribute, with commas, whitespace and
semicolons all valid delimiters, like so:
<bean id="beanOne" class="ExampleBean" depends-on="manager,accountDao"> <property name="manager" ref="manager" /> </bean> <bean id="manager" class="ManagerBean" /> <bean id="accountDao" class="x.y.jdbc.JdbcAccountDao" />
![]() | Note |
---|---|
The ' |
The default behavior for
ApplicationContext
implementations is to
eagerly pre-instantiate all singleton
beans at
startup. Pre-instantiation means that an
ApplicationContext
will eagerly create
and configure all of its singleton beans as part
of its initialization process. Generally this is a good
thing, because it means that any errors in the configuration
or in the surrounding environment will be discovered immediately (as
opposed to possibly hours or even days down the line).
However, there are times when this behavior is
not what is wanted. If you do not want a singleton
bean to be pre-instantiated when using an
ApplicationContext
, you can selectively
control this by marking a bean definition as lazy-initialized. A
lazily-initialized bean indicates to the IoC container whether or not a
bean instance should be created at startup or when it is first
requested.
When configuring beans via XML, this lazy loading is controlled by
the 'lazy-init'
attribute on the
<bean/>
element; for example:
<bean id="lazy" class="com.foo.ExpensiveToCreateBean" lazy-init="true"/>
<bean name="not.lazy" class="com.foo.AnotherBean"/>
When the above configuration is consumed by an
ApplicationContext
, the bean named
'lazy'
will not be eagerly
pre-instantiated when the
ApplicationContext
is starting up,
whereas the 'not.lazy'
bean will be eagerly
pre-instantiated.
One thing to understand about lazy-initialization is that even
though a bean definition may be marked up as being lazy-initialized, if
the lazy-initialized bean is the dependency of a singleton bean that is
not lazy-initialized, when the
ApplicationContext
is eagerly
pre-instantiating the singleton, it will have to satisfy all of the
singletons dependencies, one of which will be the lazy-initialized bean!
So don't be confused if the IoC container creates one of the beans that
you have explicitly configured as lazy-initialized at startup; all that
means is that the lazy-initialized bean is being injected into a
non-lazy-initialized singleton bean elsewhere.
It is also possible to control lazy-initialization at the
container level by using the 'default-lazy-init'
attribute on the <beans/>
element; for
example:
<beans default-lazy-init="true">
<!-- no beans will be pre-instantiated... -->
</beans>
The Spring container is able to autowire
relationships between collaborating beans. This means that it is
possible to automatically let Spring resolve collaborators (other beans)
for your bean by inspecting the contents of the
BeanFactory
. The autowiring functionality
has five modes. Autowiring is specified per bean
and can thus be enabled for some beans, while other beans will not be
autowired. Using autowiring, it is possible to reduce or eliminate the
need to specify properties or constructor arguments, thus saving a
significant amount of typing. [2] When using XML-based configuration metadata, the autowire
mode for a bean definition is specified by using the
autowire
attribute of the
<bean/>
element. The following values are
allowed:
Table 3.2. Autowiring modes
Mode | Explanation |
---|---|
no | No autowiring at all. Bean references must be
defined via a |
byName | Autowiring by property name. This option will
inspect the container and look for a bean named exactly the same
as the property which needs to be autowired. For example, if you
have a bean definition which is set to autowire by name, and it
contains a master property (that is, it has
a setMaster(..) method), Spring will look
for a bean definition named |
byType | Allows a property to be autowired if there is
exactly one bean of the property type in the container. If there
is more than one, a fatal exception is thrown, and this
indicates that you may not use byType
autowiring for that bean. If there are no matching beans,
nothing happens; the property is not set. If this is not
desirable, setting the
|
constructor | This is analogous to byType, but applies to constructor arguments. If there isn't exactly one bean of the constructor argument type in the container, a fatal error is raised. |
autodetect | Chooses constructor or byType through introspection of the bean class. If a default constructor is found, the byType mode will be applied. |
Note that explicit dependencies in property
and
constructor-arg
settings
always
override autowiring. Please also
note that it is not currently possible to autowire so-called
simple properties such as primitives,
Strings
, and Classes
(and
arrays of such simple properties). (This is by-design and should be
considered a feature.) When using either the
byType or constructor
autowiring mode, it is possible to wire arrays and typed-collections. In
such cases all autowire candidates within the
container that match the expected type will be provided to satisfy the
dependency. Strongly-typed Maps can even be autowired if the expected
key type is String
. An autowired Map's values
will consist of all bean instances that match the expected type, and the
Map's keys will contain the corresponding bean names.
Autowire behavior can be combined with dependency checking, which will be performed after all autowiring has been completed.
It is important to understand the various advantages and disadvantages of autowiring. Some advantages of autowiring include:
Autowiring can significantly reduce the volume of configuration required. However, mechanisms such as the use of a bean template (discussed elsewhere in this chapter) are also valuable in this regard.
Autowiring can cause configuration to keep itself up to date as your objects evolve. For example, if you need to add an additional dependency to a class, that dependency can be satisfied automatically without the need to modify configuration. Thus there may be a strong case for autowiring during development, without ruling out the option of switching to explicit wiring when the code base becomes more stable.
Some disadvantages of autowiring:
Autowiring is more magical than explicit wiring. Although, as noted in the above table, Spring is careful to avoid guessing in case of ambiguity which might have unexpected results, the relationships between your Spring-managed objects are no longer documented explicitly.
Wiring information may not be available to tools that may generate documentation from a Spring container.
Another issue to consider when autowiring by type is that multiple
bean definitions within the container may match the type specified by
the setter method or constructor argument to be autowired. For arrays,
collections, or Maps, this is not necessarily a problem. However for
dependencies that expect a single value, this ambiguity will not be
arbitrarily resolved. Instead, if no unique bean definition is
available, an Exception will be thrown. You do have several options when
confronted with this scenario. First, you may abandon autowiring in
favor of explicit wiring. Second, you may designate that certain bean
definitions are never to be considered as candidates by setting their
'autowire-candidate'
attributes to
'false'
as described in the next section. Third, you
may designate a single bean definition as the
primary candidate by setting the
'primary'
attribute of its
<bean/>
element to 'true'
.
Finally, if you are using at least Java 5, you may be interested in
exploring the more fine-grained control available with annotation-based
configuration as described in the section entitled Section 3.11, “Annotation-based configuration”.
When deciding whether to use autowiring, there is no wrong or right answer in all cases. A degree of consistency across a project is best though; for example, if autowiring is not used in general, it might be confusing to developers to use it just to wire one or two bean definitions.
You can also (on a per-bean basis) totally exclude a bean from
being an autowire candidate. When configuring beans using Spring's XML
format, the 'autowire-candidate'
attribute of the
<bean/>
element can be set to
'false'
; this has the effect of making the
container totally exclude that specific bean definition from being
available to the autowiring infrastructure.
Another option is to limit autowire candidates based on
pattern-matching against bean names. The top-level
<beans/>
element accepts one or more patterns
within its 'default-autowire-candidates'
attribute.
For example, to limit autowire candidate status to any bean whose name
ends with 'Repository', provide a value of
'*Repository'. To provide multiple patterns, define them in a
comma-separated list. Note that an explicit value of
'true'
or 'false'
for a bean
definition's 'autowire-candidate'
attribute always
takes precedence, and for such beans, the pattern matching rules will
not apply.
These techniques can be useful when you have one or more beans that you absolutely never ever want to have injected into other beans via autowiring. It does not mean that an excluded bean cannot itself be configured using autowiring... it can, it is rather that it itself will not be considered as a candidate for autowiring other beans.
The Spring IoC container also has the ability to check for the existence of unresolved dependencies of a bean deployed into the container. These are JavaBeans properties of the bean, which do not have actual values set for them in the bean definition, or alternately provided automatically by the autowiring feature.
This feature is sometimes useful when you want to ensure that all
properties (or all properties of a certain type) are set on a bean. Of
course, in many cases a bean class will have default values for many
properties, or some properties do not apply to all usage scenarios, so
this feature is of limited use. Dependency checking can also be enabled
and disabled per bean, just as with the autowiring functionality. The
default is to not check dependencies. Dependency
checking can be handled in several different modes. When using XML-based
configuration metadata, this is specified via the
'dependency-check'
attribute in a bean definition,
which may have the following values.
Table 3.3. Dependency checking modes
Mode | Explanation |
---|---|
none | No dependency checking. Properties of the bean which have no value specified for them are simply not set. |
simple | Dependency checking is performed for primitive types and collections (everything except collaborators). |
object | Dependency checking is performed for collaborators only. |
all | Dependency checking is done for collaborators, primitive types and collections. |
If you are using Java 5 and thus have access to source-level
annotations, you may find the section entitled Section 25.3.1, “@Required
” to be of interest.
For most application scenarios, the majority of the beans in the container will be singletons. When a singleton bean needs to collaborate with another singleton bean, or a non-singleton bean needs to collaborate with another non-singleton bean, the typical and common approach of handling this dependency by defining one bean to be a property of the other is quite adequate. There is a problem when the bean lifecycles are different. Consider a singleton bean A which needs to use a non-singleton (prototype) bean B, perhaps on each method invocation on A. The container will only create the singleton bean A once, and thus only get the opportunity to set the properties once. There is no opportunity for the container to provide bean A with a new instance of bean B every time one is needed.
One solution to this issue is to forego some inversion of control.
Bean A can be made
aware of the container by implementing the
BeanFactoryAware
interface, and use programmatic means to ask the
container via a getBean("B")
call for (a
typically new) bean B instance every time it needs it. Find below an
admittedly somewhat contrived example of this approach:
// a class that uses a stateful Command-style class to perform some processing package fiona.apple; // lots of Spring-API imports import org.springframework.beans.BeansException; import org.springframework.beans.factory.BeanFactory; import org.springframework.beans.factory.BeanFactoryAware; public class CommandManager implements BeanFactoryAware { private BeanFactory beanFactory; public Object process(Map commandState) { // grab a new instance of the appropriateCommand
Command command = createCommand(); // set the state on the (hopefully brand new)Command
instance command.setState(commandState); return command.execute(); } // theCommand
returned here could be an implementation that executes asynchronously, or whatever protected Command createCommand() { return (Command) this.beanFactory.getBean("command"); // notice the Spring API dependency } public void setBeanFactory(BeanFactory beanFactory) throws BeansException { this.beanFactory = beanFactory; } }
The above example is generally not a desirable solution since the business code is then aware of and coupled to the Spring Framework. Method Injection, a somewhat advanced feature of the Spring IoC container, allows this use case to be handled in a clean fashion.
Lookup method injection refers to the ability of the container to override methods on container managed beans, to return the result of looking up another named bean in the container. The lookup will typically be of a prototype bean as in the scenario described above. The Spring Framework implements this method injection by dynamically generating a subclass overriding the method, using bytecode generation via the CGLIB library.
So if you look at the code from previous code snippet (the
CommandManager
class), the Spring container is
going to dynamically override the implementation of the
createCommand()
method. Your
CommandManager
class is not going to have any
Spring dependencies, as can be seen in this reworked example
below:
package fiona.apple; // no more Spring imports! public abstract class CommandManager { public Object process(Object commandState) { // grab a new instance of the appropriateCommand
interface Command command = createCommand(); // set the state on the (hopefully brand new)Command
instance command.setState(commandState); return command.execute(); } // okay... but where is the implementation of this method? protected abstract Command createCommand(); }
In the client class containing the method to be injected (the
CommandManager
in this case), the method that
is to be 'injected' must have a signature of the following
form:
<public|protected> [abstract] <return-type> theMethodName(no-arguments);
If the method is abstract
, the
dynamically-generated subclass will implement the method. Otherwise,
the dynamically-generated subclass will override the concrete method
defined in the original class. Let's look at an example:
<!-- a stateful bean deployed as a prototype (non-singleton) --> <bean id="command" class="fiona.apple.AsyncCommand" scope="prototype"> <!-- inject dependencies here as required --> </bean> <!--commandProcessor
usesstatefulCommandHelper
--> <bean id="commandManager" class="fiona.apple.CommandManager"> <lookup-method name="createCommand" bean="command"/> </bean>
The bean identified as commandManager will
call its own method createCommand()
whenever
it needs a new instance of the command bean. It
is important to note that the person deploying the beans must be
careful to deploy the command
bean as a prototype
(if that is actually what is needed). If it is deployed as a singleton, the same
instance of the command
bean will be returned each
time!
Please be aware that in order for this dynamic subclassing to
work, you will need to have the CGLIB jar(s) on your classpath.
Additionally, the class that the Spring container is going to subclass
cannot be final
, and the method that is being
overridden cannot be final
either. Also, testing a
class that has an abstract
method can be somewhat
odd in that you will have to subclass the class yourself and supply a
stub implementation of the abstract
method.
Finally, objects that have been the target of method injection cannot
be serialized.
![]() | Tip |
---|---|
The interested reader may also find the
|
A less commonly useful form of method injection than Lookup Method Injection is the ability to replace arbitrary methods in a managed bean with another method implementation. Users may safely skip the rest of this section (which describes this somewhat advanced feature), until this functionality is actually needed.
When using XML-based configuration metadata, the
replaced-method
element may be used to replace an
existing method implementation with another, for a deployed bean.
Consider the following class, with a method computeValue, which we
want to override:
public class MyValueCalculator { public String computeValue(String input) { // some real code... } // some other methods... }
A class implementing the
org.springframework.beans.factory.support.MethodReplacer
interface provides the new method definition.
/** meant to be used to override the existingcomputeValue(String)
implementation inMyValueCalculator
*/ public class ReplacementComputeValue implements MethodReplacer { public Object reimplement(Object o, Method m, Object[] args) throws Throwable { // get the input value, work with it, and return a computed result String input = (String) args[0]; ... return ...; } }
The bean definition to deploy the original class and specify the method override would look like this:
<bean id="myValueCalculator class="x.y.z.MyValueCalculator">
<!-- arbitrary method replacement -->
<replaced-method name="computeValue" replacer="replacementComputeValue">
<arg-type>String</arg-type>
</replaced-method>
</bean>
<bean id="replacementComputeValue" class="a.b.c.ReplacementComputeValue"/>
One or more contained <arg-type/>
elements within the <replaced-method/>
element may be used to indicate the method signature of the method
being overridden. Note that the signature for the arguments is
actually only needed in the case that the method is actually
overloaded and there are multiple variants within the class. For
convenience, the type string for an argument may be a substring of the
fully qualified type name. For example, all the following would match
java.lang.String
.
java.lang.String String Str
Since the number of arguments is often enough to distinguish between each possible choice, this shortcut can save a lot of typing, by allowing you to type just the shortest string that will match an argument type.
When you create a bean definition what you are actually creating is a recipe for creating actual instances of the class defined by that bean definition. The idea that a bean definition is a recipe is important, because it means that, just like a class, you can potentially have many object instances created from a single recipe.
You can control not only the various dependencies and configuration
values that are to be plugged into an object that is created from a
particular bean definition, but also the scope of
the objects created from a particular bean definition. This approach is
very powerful and gives you the flexibility to choose
the scope of the objects you create through configuration instead of
having to 'bake in' the scope of an object at the Java class level. Beans
can be defined to be deployed in one of a number of scopes: out of the
box, the Spring Framework supports exactly five scopes (of which three are
available only if you are using a web-aware
ApplicationContext
).
The scopes supported out of the box are listed below:
Table 3.4. Bean scopes
Scope | Description |
---|---|
Scopes a single bean definition to a single object instance per Spring IoC container. | |
Scopes a single bean definition to any number of object instances. | |
Scopes a single bean definition to the lifecycle of a
single HTTP request; that is each and every HTTP request will
have its own instance of a bean created off the back of a single
bean definition. Only valid in the context of a web-aware Spring
| |
Scopes a single bean definition to the lifecycle of a HTTP
| |
Scopes a single bean definition to the lifecycle of a
global HTTP |
When a bean is a singleton, only one shared
instance of the bean will be managed, and all requests for beans with an
id or id
s matching that bean definition will result
in that one specific bean instance being returned by the Spring
container.
To put it another way, when you define a bean definition and it is scoped as a singleton, then the Spring IoC container will create exactly one instance of the object defined by that bean definition. This single instance will be stored in a cache of such singleton beans, and all subsequent requests and references for that named bean will result in the cached object being returned.
Please be aware that Spring's concept of a singleton bean is quite
different from the Singleton pattern as defined in the seminal Gang of
Four (GoF) patterns book. The GoF Singleton hard codes the scope of an
object such that one and only one instance of a
particular class will ever be created per
ClassLoader
. The scope of the Spring
singleton is best described as per container and per
bean. This means that if you define one bean for a particular
class in a single Spring container, then the Spring container will
create one and only one instance of the class
defined by that bean definition. The singleton scope is the
default scope in Spring. To define a bean as a singleton in
XML, you would write configuration like so:
<bean id="accountService" class="com.foo.DefaultAccountService"/> <!-- the following is equivalent, though redundant (singleton scope is the default); usingspring-beans-2.0.dtd
--> <bean id="accountService" class="com.foo.DefaultAccountService" scope="singleton"/> <!-- the following is equivalent and preserved for backward compatibility inspring-beans.dtd
--> <bean id="accountService" class="com.foo.DefaultAccountService" singleton="true"/>
The non-singleton, prototype scope of bean deployment results in
the creation of a new bean instance every time a
request for that specific bean is made (that is, it is injected into
another bean or it is requested via a programmatic
getBean()
method call on the container). As a rule of
thumb, you should use the prototype scope for all beans that are
stateful, while the singleton scope should be used for stateless
beans.
The following diagram illustrates the Spring prototype scope. Please note that a DAO would not typically be configured as a prototype, since a typical DAO would not hold any conversational state; it was just easier for this author to reuse the core of the singleton diagram.
To define a bean as a prototype in XML, you would write configuration like so:
<!-- usingspring-beans-2.0.dtd
--> <bean id="accountService" class="com.foo.DefaultAccountService" scope="prototype"/> <!-- the following is equivalent and preserved for backward compatibility inspring-beans.dtd
--> <bean id="accountService" class="com.foo.DefaultAccountService" singleton="false"/>
There is one quite important thing to be aware of when deploying a bean in the prototype scope, in that the lifecycle of the bean changes slightly. Spring does not manage the complete lifecycle of a prototype bean: the container instantiates, configures, decorates and otherwise assembles a prototype object, hands it to the client and then has no further knowledge of that prototype instance. This means that while initialization lifecycle callback methods will be called on all objects regardless of scope, in the case of prototypes, any configured destruction lifecycle callbacks will not be called. It is the responsibility of the client code to clean up prototype scoped objects and release any expensive resources that the prototype bean(s) are holding onto. (One possible way to get the Spring container to release resources used by prototype-scoped beans is through the use of a custom bean post-processor which would hold a reference to the beans that need to be cleaned up.)
In some respects, you can think of the Spring containers role when
talking about a prototype-scoped bean as somewhat of a replacement for
the Java 'new'
operator. All lifecycle aspects past
that point have to be handled by the client. (The lifecycle of a bean in
the Spring container is further described in the section entitled Section 3.5.1, “Lifecycle callbacks”.)
When using singleton-scoped beans that have dependencies on beans that are scoped as prototypes, please be aware that dependencies are resolved at instantiation time. This means that if you dependency inject a prototype-scoped bean into a singleton-scoped bean, a brand new prototype bean will be instantiated and then dependency injected into the singleton bean... but that is all. That exact same prototype instance will be the sole instance that is ever supplied to the singleton-scoped bean, which is fine if that is what you want.
However, sometimes what you actually want is for the singleton-scoped bean to be able to acquire a brand new instance of the prototype-scoped bean again and again and again at runtime. In that case it is no use just dependency injecting a prototype-scoped bean into your singleton bean, because as explained above, that only happens once when the Spring container is instantiating the singleton bean and resolving and injecting its dependencies. If you are in the scenario where you need to get a brand new instance of a (prototype) bean again and again and again at runtime, you are referred to the section entitled Section 3.3.7, “Method Injection”
![]() | Backwards compatibility note: specifying the lifecycle scope in XML |
---|---|
If you are referencing the To be totally clear about this, this means that if you use the
" |
The other scopes, namely request
,
session
, and global session
are
for use only in web-based applications (and can be used irrespective of
which particular web application framework you are using, if indeed
any). In the interest of keeping related concepts together in one place
in the reference documentation, these scopes are described here.
![]() | Note |
---|---|
The scopes that are described in the following paragraphs are
only available if you are using a web-aware
Spring |
In order to support the scoping of beans at the
request
, session
, and
global session
levels (web-scoped beans), some
minor initial configuration is required before you can set about
defining your bean definitions. Please note that this extra setup is
not required if you just want to use the
'standard' scopes (namely singleton and prototype).
Now as things stand, there are a couple of ways to effect this initial setup depending on your particular Servlet environment...
If you are accessing scoped beans within Spring Web MVC, i.e.
within a request that is processed by the Spring
DispatcherServlet
, or
DispatcherPortlet
, then no special setup is
necessary: DispatcherServlet
and
DispatcherPortlet
already expose all relevant
state.
When using a Servlet 2.4+ web container, with requests processed
outside of Spring's DispatcherServlet (e.g. when using JSF or Struts),
you need to add the following
javax.servlet.ServletRequestListener
to
the declarations in your web application's
'web.xml'
file.
<web-app> ... <listener> <listener-class>org.springframework.web.context.request.RequestContextListener</listener-class> </listener> ... </web-app>
If you are using an older web container (Servlet 2.3), you will
need to use the provided
javax.servlet.Filter
implementation.
Find below a snippet of XML configuration that has to be included in
the 'web.xml'
file of your web application if you
want to have access to web-scoped beans in requests outside of
Spring's DispatcherServlet on a Servlet 2.3 container. (The filter
mapping depends on the surrounding web application configuration and
so you will have to change it as appropriate.)
<web-app> .. <filter> <filter-name>requestContextFilter</filter-name> <filter-class>org.springframework.web.filter.RequestContextFilter</filter-class> </filter> <filter-mapping> <filter-name>requestContextFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> ... </web-app>
That's it. DispatcherServlet
,
RequestContextListener
and
RequestContextFilter
all do exactly the same
thing, namely bind the HTTP request object to the
Thread
that is servicing that request. This
makes beans that are request- and session-scoped available further
down the call chain.
Consider the following bean definition:
<bean id="loginAction" class="com.foo.LoginAction" scope="request"/>
With the above bean definition in place, the Spring container
will create a brand new instance of the
LoginAction
bean using the
'loginAction'
bean definition for each and every
HTTP request. That is, the 'loginAction'
bean will
be effectively scoped at the HTTP request level. You can change or
dirty the internal state of the instance that is created as much as
you want, safe in the knowledge that other requests that are also
using instances created off the back of the same
'loginAction'
bean definition will not be seeing
these changes in state since they are particular to an individual
request. When the request is finished processing, the bean that is
scoped to the request will be discarded.
Consider the following bean definition:
<bean id="userPreferences" class="com.foo.UserPreferences" scope="session"/>
With the above bean definition in place, the Spring container
will create a brand new instance of the
UserPreferences
bean using the
'userPreferences'
bean definition for the lifetime
of a single HTTP Session
. In other
words, the 'userPreferences'
bean will be
effectively scoped at the HTTP Session
level. Just like request-scoped
beans, you can
change the internal state of the instance that is created as much as
you want, safe in the knowledge that other HTTP
Session
instances that are also using
instances created off the back of the same
'userPreferences'
bean definition will not be
seeing these changes in state since they are particular to an
individual HTTP Session
. When the HTTP
Session
is eventually discarded, the
bean that is scoped to that particular HTTP
Session
will also be discarded.
Consider the following bean definition:
<bean id="userPreferences" class="com.foo.UserPreferences" scope="globalSession"/>
The global session
scope is similar to the
standard HTTP Session
scope (described immediately
above), and really only makes sense in the context of
portlet-based web applications. The portlet specification defines the
notion of a global Session
that is
shared amongst all of the various portlets that make up a single
portlet web application. Beans defined at the global
session
scope are scoped (or bound) to the lifetime of the
global portlet Session
.
Please note that if you are writing a standard Servlet-based web
application and you define one or more beans as having global
session
scope, the standard HTTP
Session
scope will be used, and no
error will be raised.
Being able to define a bean scoped to a HTTP request or
Session
(or indeed a custom scope of your
own devising) is all very well, but one of the main value-adds of the
Spring IoC container is that it manages not only the instantiation of
your objects (beans), but also the wiring up of collaborators (or
dependencies). If you want to inject a (for example) HTTP request
scoped bean into another bean, you will need to inject an AOP proxy in
place of the scoped bean. That is, you need to inject a proxy object
that exposes the same public interface as the scoped object, but that
is smart enough to be able to retrieve the real, target object from
the relevant scope (for example a HTTP request) and delegate method
calls onto the real object.
![]() | Note |
---|---|
You do not need to use the
|
Let's look at the configuration that is required to effect this; the configuration is not hugely complex (it takes just one line), but it is important to understand the “why” as well as the “how” behind it.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <!-- a HTTPSession
-scoped bean exposed as a proxy --> <bean id="userPreferences" class="com.foo.UserPreferences" scope="session"> <!-- this next element effects the proxying of the surrounding bean --> <aop:scoped-proxy/> </bean> <!-- a singleton-scoped bean injected with a proxy to the above bean --> <bean id="userService" class="com.foo.SimpleUserService"> <!-- a reference to the proxied'userPreferences'
bean --> <property name="userPreferences" ref="userPreferences"/> </bean> </beans>
To create such a proxy, you need only to insert a child
<aop:scoped-proxy/>
element into a scoped
bean definition (you may also need the CGLIB library on your classpath
so that the container can effect class-based proxying; you will also
need to be using Appendix A, XML Schema-based configuration). So, just why do you
need this <aop:scoped-proxy/>
element in the
definition of beans scoped at the request
,
session
, globalSession
and
'insert your custom scope here' level? The reason
is best explained by picking apart the following bean definition
(please note that the following 'userPreferences'
bean definition as it stands is
incomplete):
<bean id="userPreferences" class="com.foo.UserPreferences" scope="session"/> <bean id="userManager" class="com.foo.UserManager"> <property name="userPreferences" ref="userPreferences"/> </bean>
From the above configuration it is evident that the singleton
bean 'userManager'
is being injected with a
reference to the HTTP Session
-scoped
bean 'userPreferences'
. The salient point here is
that the 'userManager'
bean is a singleton... it
will be instantiated exactly once per container,
and its dependencies (in this case only one, the
'userPreferences'
bean) will also only be injected
(once!). This means that the 'userManager'
will
(conceptually) only ever operate on the exact same
'userPreferences'
object, that is the one that it
was originally injected with. This is not what
you want when you inject a HTTP
Session
-scoped bean as a dependency
into a collaborating object (typically). Rather, what we
do want is a single
'userManager'
object, and then, for the lifetime of
a HTTP Session
, we want to see and use
a 'userPreferences'
object that is specific to said
HTTP Session
.
Rather what you need then is to inject some sort of object that
exposes the exact same public interface as the
UserPreferences
class (ideally an object that
is a UserPreferences
instance) and that is smart enough to be able to go off and fetch the
real
UserPreferences
object from whatever underlying
scoping mechanism we have chosen (HTTP request,
Session
, etc.). We can then safely
inject this proxy object into the 'userManager'
bean, which will be blissfully unaware that the
UserPreferences
reference that it is holding
onto is a proxy. In the case of this example, when a
UserManager
instance invokes a method
on the dependency-injected UserPreferences
object, it is really invoking a method on the proxy... the proxy will
then go off and fetch the real UserPreferences
object from (in this case) the HTTP
Session
, and delegate the method
invocation onto the retrieved real
UserPreferences
object.
That is why you need the following, correct and complete,
configuration when injecting request-
,
session-
, and
globalSession-scoped
beans into collaborating
objects:
<bean id="userPreferences" class="com.foo.UserPreferences" scope="session">
<aop:scoped-proxy/>
</bean>
<bean id="userManager" class="com.foo.UserManager">
<property name="userPreferences" ref="userPreferences"/>
</bean>
By default, when the Spring container is creating a proxy for
a bean that is marked up with the <aop:scoped-proxy/>
element, a CGLIB-based class proxy will be created.
This means that you need to have the CGLIB library on the classpath
of your application.
Note: CGLIB proxies will only intercept public method calls! Do not call non-public methods on such a proxy; they will not be delegated to the scoped target object.
You can choose to have the Spring container create 'standard'
JDK interface-based proxies for such scoped beans by specifying
'false
' for the value of the
'proxy-target-class
' attribute of the
<aop:scoped-proxy/>
element. Using JDK
interface-based proxies does mean that you don't need any additional
libraries on your application's classpath to effect such proxying,
but it does mean that the class of the scoped bean must implement at
least one interface, and all of the
collaborators into which the scoped bean is injected must be
referencing the bean via one of its interfaces.
<!--DefaultUserPreferences
implements theUserPreferences
interface --> <bean id="userPreferences" class="com.foo.DefaultUserPreferences" scope="session"> <aop:scoped-proxy proxy-target-class="false"/> </bean> <bean id="userManager" class="com.foo.UserManager"> <property name="userPreferences" ref="userPreferences"/> </bean>
The section entitled Section 6.6, “Proxying mechanisms” may also be of some interest with regard to understanding the nuances of choosing whether class-based or interface-based proxying is right for you.
As of Spring 2.0, the bean scoping mechanism in Spring is
extensible. This means that you are not limited to just the bean scopes
that Spring provides out of the box; you can define your own scopes, or
even redefine the existing scopes (although that last one would probably
be considered bad practice - please note that you
cannot override the built-in
singleton
and prototype
scopes).
Scopes are defined by the
org.springframework.beans.factory.config.Scope
interface. This is the interface that you will need to implement in
order to integrate your own custom scope(s) into the Spring container,
and is described in detail below. You may wish to look at the
Scope
implementations that are supplied
with the Spring Framework itself for an idea of how to go about
implementing your own. The Scope
Javadoc explains the main class to implement when you need
your own scope in more detail too.
The Scope
interface has four methods dealing
with getting objects from the scope, removing them from the scope and
allowing them to be 'destroyed' if needed.
The first method should return the object from the underlying scope. The session scope implementation for example will return the session-scoped bean (and if it does not exist, return a new instance of the bean, after having bound it to the session for future reference).
Object get(String name, ObjectFactory objectFactory)
The second method should remove the object from the underlying scope. The session scope implementation for example, removes the session-scoped bean from the underlying session. The object should be returned (you are allowed to return null if the object with the specified name wasn't found)
Object remove(String name)
The third method is used to register callbacks the scope should execute when it is destroyed or when the specified object in the scope is destroyed. Please refer to the Javadoc or a Spring scope implementation for more information on destruction callbacks.
void registerDestructionCallback(String name, Runnable destructionCallback)
The last method deals with obtaining the conversation identifier for the underlying scope. This identifier is different for each scope. For a session for example, this can be the session identifier.
String getConversationId()
After you have written and tested one or more custom
Scope
implementations, you then need to
make the Spring container aware of your new scope(s). The central
method to register a new Scope
with the
Spring container is declared on the
ConfigurableBeanFactory
interface
(implemented by most of the concrete
BeanFactory
implementations that ship
with Spring); this central method is displayed below:
void registerScope(String scopeName, Scope scope);
The first argument to the
registerScope(..)
method is the unique name
associated with a scope; examples of such names in the Spring
container itself are 'singleton'
and
'prototype'
. The second argument to the
registerScope(..)
method is an actual
instance of the custom Scope
implementation that you wish to register and use.
Let's assume that you have written your own custom
Scope
implementation, and you have
registered it like so:
// note: the ThreadScope
class does not ship with the Spring Framework
Scope customScope = new ThreadScope();
beanFactory.registerScope("thread", customScope);
You can then create bean definitions that adhere to the scoping
rules of your custom Scope
like
so:
<bean id="..." class="..." scope="thread"/>
If you have your own custom Scope
implementation(s), you are not just limited to only programmatic
registration of the custom scope(s). You can also do the
Scope
registration declaratively, using
the CustomScopeConfigurer
class.
The declarative registration of custom
Scope
implementations using the
CustomScopeConfigurer
class is shown
below:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <bean class="org.springframework.beans.factory.config.CustomScopeConfigurer"> <property name="scopes"> <map> <entry key="thread"> <bean class="com.foo.ThreadScope"/> </entry> </map> </property> </bean> <bean id="bar" class="x.y.Bar" scope="thread"> <property name="name" value="Rick"/> <aop:scoped-proxy/> </bean> <bean id="foo" class="x.y.Foo"> <property name="bar" ref="bar"/> </bean> </beans>
The Spring Framework provides several callback interfaces to change
the behavior of your bean in the container; they include
InitializingBean
and
DisposableBean
. Implementing these
interfaces will result in the container calling
afterPropertiesSet()
for the former and
destroy()
for the latter to allow the bean to
perform certain actions upon initialization and destruction.
Internally, the Spring Framework uses
BeanPostProcessor
implementations to
process any callback interfaces it can find and call the appropriate
methods. If you need custom features or other lifecycle behavior Spring
doesn't offer out-of-the-box, you can implement a
BeanPostProcessor
yourself. More
information about this can be found in the section entitled Section 3.7, “Container extension points”.
All the different lifecycle callback interfaces are described below. In one of the appendices, you can find diagrams that show how Spring manages beans, how those lifecycle features change the nature of your beans, and how they are managed.
Implementing the
org.springframework.beans.factory.InitializingBean
interface allows a bean to perform initialization work after all
necessary properties on the bean have been set by the container. The
InitializingBean
interface specifies
exactly one method:
void afterPropertiesSet() throws Exception;
Generally, the use of the
InitializingBean
interface can be
avoided and is actually discouraged since it unnecessarily couples the
code to Spring. As an alternative, bean definitions provide support
for a generic initialization method to be specified. In the case of
XML-based configuration metadata, this is done using the
'init-method'
attribute. For example, the following
definition:
<bean id="exampleInitBean" class="examples.ExampleBean" init-method="init"/>
public class ExampleBean {
public void init() {
// do some initialization work
}
}
...is exactly the same as...
<bean id="exampleInitBean" class="examples.AnotherExampleBean"/>
public class AnotherExampleBean implements InitializingBean {
public void afterPropertiesSet() {
// do some initialization work
}
}
... but does not couple the code to Spring.
Implementing the
org.springframework.beans.factory.DisposableBean
interface allows a bean to get a callback when the container
containing it is destroyed. The
DisposableBean
interface specifies a
single method:
void destroy() throws Exception;
Generally, the use of the
DisposableBean
callback interface can be
avoided and is actually discouraged since it unnecessarily couples the
code to Spring. As an alternative, bean definitions provide support
for a generic destroy method to be specified. When using XML-based
configuration metadata this is done via the
'destroy-method'
attribute on the
<bean/>
. For example, the following
definition:
<bean id="exampleInitBean" class="examples.ExampleBean" destroy-method="cleanup"/>
public class ExampleBean {
public void cleanup() {
// do some destruction work (like releasing pooled connections)
}
}
...is exactly the same as...
<bean id="exampleInitBean" class="examples.AnotherExampleBean"/>
public class AnotherExampleBean implements DisposableBean {
public void destroy() {
// do some destruction work (like releasing pooled connections)
}
}
... but does not couple the code to Spring.
When writing initialization and destroy method callbacks that do
not use the Spring-specific
InitializingBean
and
DisposableBean
callback interfaces, one
typically finds oneself writing methods with names such as
init()
, initialize()
,
dispose()
, etc. The names of such lifecycle
callback methods are (hopefully!) standardized across a project so
that all developers on a team use the same method names and thus
ensure some level of consistency.
The Spring container can be configured to
'look'
for named initialization and destroy
callback method names on every bean. This means
that you, as an application developer, can simply write your
application classes, use a convention of having an initialization
callback called init()
, and then (without having to
configure each and every bean with, in the case of XML-based
configuration, an 'init-method="init"'
attribute)
be safe in the knowledge that the Spring IoC container
will call that method when the bean is being
created (and in accordance with the standard lifecycle callback
contract described previously).
Let's look at an example to make the use of this feature
completely clear. For the sake of the example, let us say that one of
the coding conventions on a project is that all initialization
callback methods are to be named init()
and that
destroy callback methods are to be called
destroy()
. This leads to classes like so...
public class DefaultBlogService implements BlogService {
private BlogDao blogDao;
public void setBlogDao(BlogDao blogDao) {
this.blogDao = blogDao;
}
// this is (unsurprisingly) the initialization callback method
public void init() {
if (this.blogDao == null) {
throw new IllegalStateException("The [blogDao] property must be set.");
}
}
}
<beans default-init-method="init">
<bean id="blogService" class="com.foo.DefaultBlogService">
<property name="blogDao" ref="blogDao" />
</bean>
</beans>
Notice the use of the 'default-init-method'
attribute on the top-level <beans/>
element.
The presence of this attribute means that the Spring IoC container
will recognize a method called 'init'
on beans as
being the initialization method callback, and when a bean is being
created and assembled, if the bean's class has such a method, it will
be invoked at the appropriate time.
Destroy method callbacks are configured similarly (in XML that
is) using the 'default-destroy-method'
attribute on
the top-level <beans/>
element.
The use of this feature can save you the (small) housekeeping chore of specifying an initialization and destroy method callback on each and every bean, and it is great for enforcing a consistent naming convention for initialization and destroy method callbacks, as consistency is something that should always be aimed for.
Consider the case where you have some existing beans where the
underlying classes already have initialization callback methods that
are named at variance with the convention. You can
always override the default by specifying (in XML
that is) the method name using the 'init-method'
and 'destroy-method'
attributes on the
<bean/>
element itself.
Finally, please be aware that the Spring container guarantees that a configured initialization callback is called immediately after a bean has been supplied with all of its dependencies. This means that the initialization callback will be called on the raw bean reference, which means that any AOP interceptors or suchlike that will ultimately be applied to the bean will not yet be in place. A target bean is fully created first, then an AOP proxy (for example) with its interceptor chain is applied. Note that, if the target bean and the proxy are defined separately, your code can even interact with the raw target bean, bypassing the proxy. Hence, it would be very inconsistent to apply the interceptors to the init method, since that would couple the lifecycle of the target bean with its proxy/interceptors and leave strange semantics when talking to the raw target bean directly.
As of Spring 2.5, there are three options for controlling bean
lifecycle behavior: the InitializingBean
and DisposableBean
callback interfaces; custom init()
and
destroy()
methods; and the @PostConstruct
and @PreDestroy
annotations.
When combining different lifecycle mechanisms - for example, in a class hierarchy in which various lifecycle mechanisms are in use - developers should be aware of the order in which these mechanisms are applied. The following is the ordering for initialization methods:
Methods annotated with
@PostConstruct
afterPropertiesSet()
as defined by the
InitializingBean
callback
interface
A custom configured init()
method
Destroy methods are called in the same order:
Methods annotated with
@PreDestroy
destroy()
as defined by the
DisposableBean
callback
interface
A custom configured destroy()
method
![]() | Note |
---|---|
If multiple lifecycle mechanisms are configured for a given
bean, and each mechanism is configured with a different method name,
then each configured method will be executed in the order listed
above; however, if the same method name is configured - for example,
|
![]() | Note |
---|---|
This next section does not apply to web applications (in case
the title of this section did not make that abundantly clear).
Spring's web-based |
If you are using Spring's IoC container in a non-web application environment, for example in a rich client desktop environment, and you want the container to shutdown gracefully and call the relevant destroy callbacks on your singleton beans, you will need to register a shutdown hook with the JVM. This is quite easy to do (see below), and will ensure that your Spring IoC container shuts down gracefully and that all resources held by your singletons are released. Of course it is still up to you to both configure the destroy callbacks for your singletons and implement such destroy callbacks correctly.
So to register a shutdown hook that enables the graceful
shutdown of the relevant Spring IoC container, you simply need to call
the registerShutdownHook()
method that is
declared on the AbstractApplicationContext
class. To wit...
import org.springframework.context.support.AbstractApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public final class Boot { public static void main(final String[] args) throws Exception { AbstractApplicationContext ctx = new ClassPathXmlApplicationContext(new String []{"beans.xml"}); // add a shutdown hook for the above context... ctx.registerShutdownHook(); // app runs here... // main method exits, hook is called prior to the app shutting down... } }
A class which implements the
org.springframework.beans.factory.BeanFactoryAware
interface is provided with a reference to the
BeanFactory
that created it, when it is
created by that BeanFactory
.
public interface BeanFactoryAware { void setBeanFactory(BeanFactory beanFactory) throws BeansException; }
This allows beans to manipulate the
BeanFactory
that created them
programmatically, through the
BeanFactory
interface, or by casting
the reference to a known subclass of this which exposes additional
functionality. Primarily this would consist of programmatic retrieval
of other beans. While there are cases when this capability is useful,
it should generally be avoided, since it couples the code to Spring
and does not follow the Inversion of Control style, where
collaborators are provided to beans as properties.
An alternative option that is equivalent in effect to the
BeanFactoryAware
-based approach is to
use the
org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean
.
(It should be noted that this approach still does not reduce the
coupling to Spring, but it does not violate the central principle of
IoC as much as the
BeanFactoryAware
-based
approach.)
The ObjectFactoryCreatingFactoryBean
is a
FactoryBean
implementation that returns a reference to an object (factory) that
can in turn be used to effect a bean lookup. The
ObjectFactoryCreatingFactoryBean
class does
itself implement the BeanFactoryAware
interface; what client beans are actually injected with is an instance
of the ObjectFactory
interface. This is
a Spring-specific interface (and hence there is still no total
decoupling from Spring), but clients can then use the
ObjectFactory
's
getObject()
method to effect the bean lookup
(under the hood the ObjectFactory
implementation instance that is returned simply delegates down to a
BeanFactory
to actually lookup a bean
by name). All that you need to do is supply the
ObjectFactoryCreatingFactoryBean
with the name
of the bean that is to be looked up. Let's look at an example:
package x.y; public class NewsFeed { private String news; public void setNews(String news) { this.news = news; } public String getNews() { return this.toString() + ": '" + news + "'"; } }
package x.y; import org.springframework.beans.factory.ObjectFactory; public class NewsFeedManager { private ObjectFactory factory; public void setFactory(ObjectFactory factory) { this.factory = factory; } public void printNews() { // here is where the lookup is performed; note that there is no // need to hard code the name of the bean that is being looked up... NewsFeed news = (NewsFeed) factory.getObject(); System.out.println(news.getNews()); } }
Find below the XML configuration to wire together the above
classes using the
ObjectFactoryCreatingFactoryBean
approach.
<beans> <bean id="newsFeedManager" class="x.y.NewsFeedManager"> <property name="factory"> <bean class="org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean"> <property name="targetBeanName"> <idref local="newsFeed" /> </property> </bean> </property> </bean> <bean id="newsFeed" class="x.y.NewsFeed" scope="prototype"> <property name="news" value="... that's fit to print!" /> </bean> </beans>
And here is a small driver program to test the fact that new
(prototype) instances of the newsFeed
bean are
actually being returned for each call to the injected
ObjectFactory
inside the
NewsFeedManager
's
printNews()
method.
import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import x.y.NewsFeedManager; public class Main { public static void main(String[] args) throws Exception { ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml"); NewsFeedManager manager = (NewsFeedManager) ctx.getBean("newsFeedManager"); manager.printNews(); manager.printNews(); } }
The output from running the above program will look like so (results will of course vary on your machine).
x.y.NewsFeed@1292d26: '... that's fit to print!' x.y.NewsFeed@5329c5: '... that's fit to print!'
As of Spring 2.5, you can rely upon autowiring of the
BeanFactory
as yet another alternative
to implementing the BeanFactoryAware
interface. The "traditional" constructor
and
byType
autowiring modes (as described in the
section entitled Section 3.3.5, “Autowiring collaborators”) are now
capable of providing a dependency of type
BeanFactory
for either a constructor
argument or setter method parameter respectively. For more flexibility
(including the ability to autowire fields and multiple parameter
methods), consider using the new annotation-based autowiring features.
In that case, the BeanFactory
will be
autowired into a field, constructor argument, or method parameter that
is expecting the BeanFactory
type as
long as the field, constructor, or method in question carries the
@Autowired
annotation. For more
information, see the section entitled Section 3.11.2, “@Autowired
”.
If a bean implements the
org.springframework.beans.factory.BeanNameAware
interface and is deployed in a
BeanFactory
, the
BeanFactory
will call the bean through
this interface to inform the bean of the name it
was deployed under. The callback will be invoked after population of
normal bean properties but before an initialization callback like
InitializingBean
's
afterPropertiesSet or a custom
init-method.
A bean definition potentially contains a large amount of configuration information, including container specific information (for example initialization method, static factory method name, and so forth) and constructor arguments and property values. A child bean definition is a bean definition that inherits configuration data from a parent definition. It is then able to override some values, or add others, as needed. Using parent and child bean definitions can potentially save a lot of typing. Effectively, this is a form of templating.
When working with a BeanFactory
programmatically, child bean definitions are represented by the
ChildBeanDefinition
class. Most users will never
work with them on this level, instead configuring bean definitions
declaratively in something like the XmlBeanFactory
.
When using XML-based configuration metadata a child bean definition is
indicated simply by using the 'parent'
attribute,
specifying the parent bean as the value of this attribute.
<bean id="inheritedTestBean" abstract="true" class="org.springframework.beans.TestBean"> <property name="name" value="parent"/> <property name="age" value="1"/> </bean> <bean id="inheritsWithDifferentClass" class="org.springframework.beans.DerivedTestBean" parent="inheritedTestBean" init-method="initialize"> <property name="name" value="override"/> <!-- the age property value of 1 will be inherited from parent --> </bean>
A child bean definition will use the bean class from the parent definition if none is specified, but can also override it. In the latter case, the child bean class must be compatible with the parent, that is it must accept the parent's property values.
A child bean definition will inherit constructor argument values,
property values and method overrides from the parent, with the option to
add new values. If any init-method, destroy-method and/or
static
factory method settings are specified, they will
override the corresponding parent settings.
The remaining settings will always be taken from the child definition: depends on, autowire mode, dependency check, singleton, scope, lazy init.
Note that in the example above, we have explicitly marked the parent
bean definition as abstract by using the abstract
attribute. In the case that the parent definition does not specify a
class, and so explicitly marking the parent bean definition as
abstract
is required:
<bean id="inheritedTestBeanWithoutClass" abstract="true">
<property name="name" value="parent"/>
<property name="age" value="1"/>
</bean>
<bean id="inheritsWithClass" class="org.springframework.beans.DerivedTestBean"
parent="inheritedTestBeanWithoutClass" init-method="initialize">
<property name="name" value="override"/>
<!-- age will inherit the value of 1
from the parent bean definition-->
</bean>
The parent bean cannot get instantiated on its own since it is
incomplete, and it is also explicitly marked as
abstract
. When a definition is defined to be
abstract
like this, it is usable only as a pure
template bean definition that will serve as a parent definition for child
definitions. Trying to use such an abstract
parent bean
on its own (by referring to it as a ref property of another bean, or doing
an explicit getBean()
call with the parent bean
id), will result in an error. Similarly, the container's internal
preInstantiateSingletons()
method will completely
ignore bean definitions which are defined as abstract.
![]() | Note |
---|---|
|
The IoC component of the Spring Framework has been designed for
extension. There is typically no need for an application developer to
subclass any of the various BeanFactory
or
ApplicationContext
implementation classes.
The Spring IoC container can be infinitely extended by plugging in
implementations of special integration interfaces. The next few sections
are devoted to detailing all of these various integration
interfaces.
The first extension point that we will look at is the
BeanPostProcessor
interface. This
interface defines a number of callback methods
that you as an application developer can implement in order to provide
your own (or override the containers default) instantiation logic,
dependency-resolution logic, and so forth. If you want to do some custom
logic after the Spring container has finished instantiating, configuring
and otherwise initializing a bean, you can plug in one or more
BeanPostProcessor
implementations.
You can configure multiple BeanPostProcessors
if you wish. You can control the order in which these
BeanPostProcessors
execute by setting the
'order'
property (you can only set this property if
the BeanPostProcessor
implements the
Ordered
interface; if you write your own
BeanPostProcessor
you should consider
implementing the Ordered
interface too);
consult the Javadoc for the
BeanPostProcessor
and
Ordered
interfaces for more
details.
![]() | Note |
---|---|
If you want to change the actual bean definition (that is the
recipe that defines the bean), then you rather need to use a
Also, |
The
org.springframework.beans.factory.config.BeanPostProcessor
interface consists of exactly two callback methods. When such a class is
registered as a post-processor with the container (see below for how
this registration is effected), for each bean instance that is created
by the container, the post-processor will get a callback from the
container both before any container initialization
methods (such as afterPropertiesSet and any
declared init method) are called, and also afterwards. The
post-processor is free to do what it wishes with the bean instance,
including ignoring the callback completely. A bean post-processor will
typically check for callback interfaces, or do something such as wrap a
bean with a proxy; some of the Spring AOP infrastructure classes are
implemented as bean post-processors and they do this proxy-wrapping
logic.
It is important to know that a
BeanFactory
treats bean post-processors
slightly differently than an
ApplicationContext
. An
ApplicationContext
will
automatically detect any beans which are defined in
the configuration metadata which is supplied to it that implement the
BeanPostProcessor
interface, and register
them as post-processors, to be then called appropriately by the
container on bean creation. Nothing else needs to be done other than
deploying the post-processors in a similar fashion to any other bean. On
the other hand, when using a BeanFactory
implementation, bean post-processors explicitly have to be registered,
with code like this:
ConfigurableBeanFactory factory = new XmlBeanFactory(...);
// now register any needed BeanPostProcessor
instances
MyBeanPostProcessor postProcessor = new MyBeanPostProcessor();
factory.addBeanPostProcessor(postProcessor);
// now start using the factory
This explicit registration step is not convenient, and this is one
of the reasons why the various
ApplicationContext
implementations are
preferred above plain BeanFactory
implementations in the vast majority of Spring-backed applications,
especially when using BeanPostProcessors
.
![]() | BeanPostProcessors and AOP
auto-proxying |
---|---|
Classes that implement the
For any such bean, you should see an info log message: “Bean 'foo' is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)”. |
Find below some examples of how to write, register, and use
BeanPostProcessors
in the context of an
ApplicationContext
.
This first example is hardly compelling, but serves to
illustrate basic usage. All we are going to do is code a custom
BeanPostProcessor
implementation that
simply invokes the toString()
method of each
bean as it is created by the container and prints the resulting string
to the system console. Yes, it is not hugely useful, but serves to get
the basic concepts across before we move into the second example which
is actually useful.
Find below the custom
BeanPostProcessor
implementation class
definition:
package scripting; import org.springframework.beans.factory.config.BeanPostProcessor; import org.springframework.beans.BeansException; public class InstantiationTracingBeanPostProcessor implements BeanPostProcessor { // simply return the instantiated bean as-is public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { return bean; // we could potentially return any object reference here... } public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { System.out.println("Bean '" + beanName + "' created : " + bean.toString()); return bean; } }
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:lang="http://www.springframework.org/schema/lang"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang-2.5.xsd">
<lang:groovy id="messenger"
script-source="classpath:org/springframework/scripting/groovy/Messenger.groovy">
<lang:property name="message" value="Fiona Apple Is Just So Dreamy."/>
</lang:groovy>
<!--
when the above bean ('messenger') is instantiated, this custom
BeanPostProcessor
implementation will output the fact to the system console
-->
<bean class="scripting.InstantiationTracingBeanPostProcessor"/>
</beans>
Notice how the
InstantiationTracingBeanPostProcessor
is simply
defined; it doesn't even have a name, and because it is a bean it can
be dependency injected just like any other bean. (The above
configuration also just so happens to define a bean that is backed by
a Groovy script. The Spring 2.0 dynamic language support is detailed
in the chapter entitled Chapter 24, Dynamic language support.)
Find below a small driver script to exercise the above code and configuration;
import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import org.springframework.scripting.Messenger; public final class Boot { public static void main(final String[] args) throws Exception { ApplicationContext ctx = new ClassPathXmlApplicationContext("scripting/beans.xml"); Messenger messenger = (Messenger) ctx.getBean("messenger"); System.out.println(messenger); } }
The output of executing the above program will be (something like) this:
Bean 'messenger' created : org.springframework.scripting.groovy.GroovyMessenger@272961 org.springframework.scripting.groovy.GroovyMessenger@272961
Using callback interfaces or annotations in conjunction with a
custom BeanPostProcessor
implementation
is a common means of extending the Spring IoC container. This next
example is a bit of a cop-out, in that you are directed to the section
entitled Section 25.3.1, “@Required
” which
demonstrates the usage of a custom
BeanPostProcessor
implementation that
ships with the Spring distribution which ensures that JavaBean
properties on beans that are marked with an (arbitrary) annotation are
actually (configured to be) dependency-injected with a value.
The next extension point that we will look at is the
org.springframework.beans.factory.config.BeanFactoryPostProcessor
.
The semantics of this interface are similar to the
BeanPostProcessor
, with one major
difference: BeanFactoryPostProcessors
operate on the bean
configuration metadata; that is, the Spring IoC container will allow
BeanFactoryPostProcessors
to read the configuration
metadata and potentially change it before the
container has actually instantiated any other beans.
You can configure multiple
BeanFactoryPostProcessors
if you wish. You can
control the order in which these
BeanFactoryPostProcessors
execute by setting the
'order'
property (you can only set this property if
the BeanFactoryPostProcessor
implements
the Ordered
interface; if you write your
own BeanFactoryPostProcessor
you should
consider implementing the Ordered
interface too); consult the Javadoc for the
BeanFactoryPostProcessor
and
Ordered
interfaces for more
details.
![]() | Note |
---|---|
If you want to change the actual bean
instances (the objects that are created from the
configuration metadata), then you rather need to use a
Also, |
A bean factory post-processor is executed manually (in the case of
a BeanFactory
) or automatically (in the
case of an ApplicationContext
) to apply
changes of some sort to the configuration metadata that defines a
container. Spring includes a number of pre-existing bean factory
post-processors, such as PropertyOverrideConfigurer
and PropertyPlaceholderConfigurer
, both described
below. A custom BeanFactoryPostProcessor
can also be used to register custom property editors, for example.
In a BeanFactory
, the process of
applying a BeanFactoryPostProcessor
is
manual, and will be similar to this:
XmlBeanFactory factory = new XmlBeanFactory(new FileSystemResource("beans.xml"));
// bring in some property values from a Properties
file
PropertyPlaceholderConfigurer cfg = new PropertyPlaceholderConfigurer();
cfg.setLocation(new FileSystemResource("jdbc.properties"));
// now actually do the replacement
cfg.postProcessBeanFactory(factory);
This explicit registration step is not convenient, and this is one
of the reasons why the various
ApplicationContext
implementations are
preferred above plain BeanFactory
implementations in the vast majority of Spring-backed applications,
especially when using
BeanFactoryPostProcessors
.
An ApplicationContext
will detect
any beans which are deployed into it which implement the
BeanFactoryPostProcessor
interface, and
automatically use them as bean factory post-processors, at the
appropriate time. Nothing else needs to be done other than deploying
these post-processor in a similar fashion to any other bean.
![]() | Note |
---|---|
Just as in the case of |
The PropertyPlaceholderConfigurer
is used to externalize property values from a
BeanFactory
definition, into another
separate file in the standard Java Properties
format. This is useful to allow the person deploying an application to
customize environment-specific properties (for example database URLs,
usernames and passwords), without the complexity or risk of modifying
the main XML definition file or files for the container.
Consider the following XML-based configuration metadata
fragment, where a DataSource
with
placeholder values is defined. We will configure some properties from
an external Properties
file, and at runtime, we
will apply a PropertyPlaceholderConfigurer
to
the metadata which will replace some properties of the
DataSource:
<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="locations"> <value>classpath:com/foo/jdbc.properties</value> </property> </bean> <bean id="dataSource" destroy-method="close" class="org.apache.commons.dbcp.BasicDataSource"> <property name="driverClassName" value="${jdbc.driverClassName}"/> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </bean>
The actual values come from another file in the standard Java
Properties
format:
jdbc.driverClassName=org.hsqldb.jdbcDriver jdbc.url=jdbc:hsqldb:hsql://production:9002 jdbc.username=sa jdbc.password=root
With the context
namespace introduced in
Spring 2.5, it is possible to configure property placeholders with a
dedicated configuration element. Multiple locations may be provided as a
comma-separated list for the location
attribute.
<context:property-placeholder location="classpath:com/foo/jdbc.properties"/>
The PropertyPlaceholderConfigurer
doesn't
only look for properties in the Properties
file
you specify, but also checks against the Java
System
properties if it cannot find a property
you are trying to use. This behavior can be customized by setting the
systemPropertiesMode
property of the configurer. It
has three values, one to tell the configurer to always override, one
to let it never override and one to let it
override only if the property cannot be found in the properties file
specified. Please consult the Javadoc for the
PropertyPlaceholderConfigurer
for more
information.
![]() | Class name substitution |
---|---|
The <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="locations"> <value>classpath:com/foo/strategy.properties</value> </property> <property name="properties"> <value>custom.strategy.class=com.foo.DefaultStrategy</value> </property> </bean> <bean id="serviceStrategy" class="${custom.strategy.class}"/> If the class is unable to be resolved at runtime to a valid
class, resolution of the bean will fail once it is about to be
created (which is during the
|
The PropertyOverrideConfigurer
, another
bean factory post-processor, is similar to the
PropertyPlaceholderConfigurer
, but in
contrast to the latter, the original definitions can have default
values or no values at all for bean properties. If an overriding
Properties
file does not have an entry for a
certain bean property, the default context definition is used.
Note that the bean factory definition is
not aware of being overridden, so it is not
immediately obvious when looking at the XML definition file that the
override configurer is being used. In case that there are multiple
PropertyOverrideConfigurer
instances that
define different values for the same bean property, the last one will
win (due to the overriding mechanism).
Properties file configuration lines are expected to be in the format:
beanName.property=value
An example properties file might look like this:
dataSource.driverClassName=com.mysql.jdbc.Driver dataSource.url=jdbc:mysql:mydb
This example file would be usable against a container definition which contains a bean called dataSource, which has driver and url properties.
Note that compound property names are also supported, as long as every component of the path except the final property being overridden is already non-null (presumably initialized by the constructors). In this example...
foo.fred.bob.sammy=123
... the sammy
property of the
bob
property of the fred
property of the foo
bean is being set to the scalar
value 123
.
With the context
namespace introduced in
Spring 2.5, it is possible to configure property overriding with a
dedicated configuration element:
<context:property-override location="classpath:override.properties"/>
The
org.springframework.beans.factory.FactoryBean
interface is to be implemented by objects that are themselves
factories.
The FactoryBean
interface is a
point of pluggability into the Spring IoC containers instantiation
logic. If you have some complex initialization code that is better
expressed in Java as opposed to a (potentially) verbose amount of XML,
you can create your own FactoryBean
,
write the complex initialization inside that class, and then plug your
custom FactoryBean
into the
container.
The FactoryBean
interface provides
three methods:
Object getObject()
: has to return an
instance of the object this factory creates. The instance can
possibly be shared (depending on whether this factory returns
singletons or prototypes).
boolean isSingleton()
: has to return
true
if this
FactoryBean
returns singletons,
false
otherwise
Class getObjectType()
: has to return
either the object type returned by the
getObject()
method or
null
if the type isn't known in advance
The FactoryBean
concept and
interface is used in a number of places within the Spring Framework; at
the time of writing there are over 50 implementations of the
FactoryBean
interface that ship with
Spring itself.
Finally, there is sometimes a need to ask a container for an
actual FactoryBean
instance itself, not
the bean it produces. This may be achieved by prepending the bean id
with '&'
(sans quotes) when calling the
getBean
method of the
BeanFactory
(including
ApplicationContext
). So for a given
FactoryBean
with an id of
myBean
, invoking getBean("myBean")
on the container will return the product of the
FactoryBean
, but invoking
getBean("&myBean")
will return the
FactoryBean
instance itself.
While the beans
package provides basic
functionality for managing and manipulating beans, including in a
programmatic way, the context
package adds the ApplicationContext
interface, which enhances BeanFactory
functionality in a more framework-oriented style.
Many users will use ApplicationContext
in a
completely declarative fashion, not even having to create it manually, but
instead relying on support classes such as
ContextLoader
to automatically instantiate an
ApplicationContext
as part of the normal
startup process of a J2EE web-app. (Of course, it is still possible to
create an ApplicationContext
programmatically.)
The basis for the context package is the
ApplicationContext
interface, located in
the org.springframework.context
package. Deriving from
the BeanFactory
interface, it provides all
the functionality of BeanFactory
. To allow
working in a more framework-oriented fashion, using layering and
hierarchical contexts, the context package also provides the following
functionality:
MessageSource
, providing access
to messages in i18n-style.
Access to resources, such as URLs and files.
Event propagation to beans implementing the
ApplicationListener
interface.
Loading of multiple (hierarchical) contexts, allowing each to be focused on one particular layer, for example the web layer of an application.
Short version: use an
ApplicationContext
unless you have a
really good reason for not doing so. For those of you that are looking
for slightly more depth as to the 'but why' of the above recommendation,
keep reading.
As the ApplicationContext
includes
all functionality of the BeanFactory
, it
is generally recommended that it be used in preference to the
BeanFactory
, except for a few limited
situations such as in an Applet
, where memory
consumption might be critical and a few extra kilobytes might make a
difference. However, for most 'typical' enterprise applications and
systems, the ApplicationContext
is what
you will want to use. Versions of Spring 2.0 and above make
heavy use of the BeanPostProcessor
extension point (to effect proxying and suchlike), and if you are
using just a plain BeanFactory
then a
fair amount of support such as transactions and AOP will not take effect
(at least not without some extra steps on your part), which could be
confusing because nothing will actually be wrong with the
configuration.
Find below a feature matrix that lists what features are provided
by the BeanFactory
and
ApplicationContext
interfaces (and
attendant implementations). (The following sections describe
functionality that ApplicationContext
adds to the basic BeanFactory
capabilities in a lot more depth than the said feature matrix.)
Table 3.5. Feature Matrix
Feature | BeanFactory | ApplicationContext |
---|---|---|
Bean instantiation/wiring | Yes | Yes |
Automatic
| No | Yes |
Automatic
| No | Yes |
Convenient
| No | Yes |
| No | Yes |
The ApplicationContext
interface
extends an interface called
MessageSource
, and therefore provides
messaging (i18n or internationalization) functionality. Together with
the HierarchicalMessageSource
, capable of
resolving hierarchical messages, these are the basic interfaces Spring
provides to do message resolution. Let's quickly review the methods
defined there:
String getMessage(String code, Object[] args,
String default, Locale loc)
: the basic method used to
retrieve a message from the
MessageSource
. When no message is
found for the specified locale, the default message is used. Any
arguments passed in are used as replacement values, using the
MessageFormat
functionality provided
by the standard library.
String getMessage(String code, Object[] args,
Locale loc)
: essentially the same as the previous
method, but with one difference: no default message can be
specified; if the message cannot be found, a
NoSuchMessageException
is thrown.
String getMessage(MessageSourceResolvable
resolvable, Locale locale)
: all properties used in the
methods above are also wrapped in a class named
MessageSourceResolvable
, which you
can use via this method.
When an ApplicationContext
gets
loaded, it automatically searches for a
MessageSource
bean defined in the
context. The bean has to have the name
'messageSource'
. If such a bean is found, all calls
to the methods described above will be delegated to the message source
that was found. If no message source was found, the
ApplicationContext
attempts to see if it
has a parent containing a bean with the same name. If so, it uses that
bean as the MessageSource
. If it can't
find any source for messages, an empty
StaticMessageSource
will be instantiated in order
to be able to accept calls to the methods defined above.
Spring currently provides two
MessageSource
implementations. These are
the ResourceBundleMessageSource
and the
StaticMessageSource
. Both implement
HierarchicalMessageSource
in order to do
nested messaging. The StaticMessageSource
is
hardly ever used but provides programmatic ways to add messages to the
source. The ResourceBundleMessageSource
is more
interesting and is the one we will provide an example for:
<beans> <bean id="messageSource" class="org.springframework.context.support.ResourceBundleMessageSource"> <property name="basenames"> <list> <value>format</value> <value>exceptions</value> <value>windows</value> </list> </property> </bean> </beans>
This assumes you have three resource bundles defined on your
classpath called format
,
exceptions
and windows
. Using the
JDK standard way of resolving messages through ResourceBundles, any
request to resolve a message will be handled. For the purposes of the
example, lets assume the contents of two of the above resource bundle
files are...
# in 'format.properties'
message=Alligators rock!
# in 'exceptions.properties'
argument.required=The '{0}' argument is required.
Some (admittedly trivial) driver code to exercise the
MessageSource
functionality can be found below.
Remember that all ApplicationContext
implementations are also MessageSource
implementations and so can be cast to the
MessageSource
interface.
public static void main(String[] args) { MessageSource resources = new ClassPathXmlApplicationContext("beans.xml"); String message = resources.getMessage("message", null, "Default", null); System.out.println(message); }
The resulting output from the above program will be...
Alligators rock!
So to summarize, the MessageSource
is
defined in a file called 'beans.xml'
(this file
exists at the root of your classpath). The
'messageSource'
bean definition refers to a number of
resource bundles via it's basenames
property; the
three files that are passed in the list to the
basenames
property exist as files at the root of your
classpath (and are called format.properties
,
exceptions.properties
, and
windows.properties
respectively).
Lets look at another example, and this time we will look at passing arguments to the message lookup; these arguments will be converted into strings and inserted into placeholders in the lookup message. This is perhaps best explained with an example:
<beans> <!-- thisMessageSource
is being used in a web application --> <bean id="messageSource" class="org.springframework.context.support.ResourceBundleMessageSource"> <property name="baseName" value="WEB-INF/test-messages"/> </bean> <!-- let's inject the aboveMessageSource
into this POJO --> <bean id="example" class="com.foo.Example"> <property name="messages" ref="messageSource"/> </bean> </beans>
public class Example { private MessageSource messages; public void setMessages(MessageSource messages) { this.messages = messages; } public void execute() { String message = this.messages.getMessage("argument.required", new Object [] {"userDao"}, "Required", null); System.out.println(message); } }
The resulting output from the invocation of the
execute()
method will be...
The 'userDao' argument is required.
With regard to internationalization (i18n), Spring's various
MessageResource
implementations follow the same
locale resolution and fallback rules as the standard JDK
ResourceBundle
. In short, and continuing with the
example 'messageSource'
defined previously, if you
want to resolve messages against the British (en-GB) locale, you would
create files called format_en_GB.properties
,
exceptions_en_GB.properties
, and
windows_en_GB.properties
respectively.
Locale resolution is typically going to be managed by the surrounding environment of the application. For the purpose of this example though, we'll just manually specify the locale that we want to resolve our (British) messages against.
# in 'exceptions_en_GB.properties'
argument.required=Ebagum lad, the '{0}' argument is required, I say, required.
public static void main(final String[] args) { MessageSource resources = new ClassPathXmlApplicationContext("beans.xml"); String message = resources.getMessage("argument.required", new Object [] {"userDao"}, "Required", Locale.UK); System.out.println(message); }
The resulting output from the running of the above program will be...
Ebagum lad, the 'userDao' argument is required, I say, required.
The MessageSourceAware
interface can also
be used to acquire a reference to any
MessageSource
that has been defined. Any bean
that is defined in an ApplicationContext
that
implements the MessageSourceAware
interface will
be injected with the application context's
MessageSource
when it (the bean) is being created
and configured.
Event handling in the
ApplicationContext
is provided through
the ApplicationEvent
class and
ApplicationListener
interface. If a bean
which implements the ApplicationListener
interface is deployed into the context, every time an
ApplicationEvent
gets published to the
ApplicationContext
, that bean will be
notified. Essentially, this is the standard
Observer design pattern. Spring provides the
following standard events:
Table 3.6. Built-in Events
Event | Explanation |
---|---|
ContextRefreshedEvent | Published when the
ApplicationContext is initialized
or refreshed, e.g. using the refresh()
method on the
ConfigurableApplicationContext
interface. "Initialized" here means that all beans are loaded,
post-processor beans are detected and activated, singletons are
pre-instantiated, and the
ApplicationContext object is
ready for use. A refresh may be triggered multiple times,
as long as the context hasn't been closed - provided that
the chosen ApplicationContext
actually supports such "hot" refreshes (which e.g.
XmlWebApplicationContext does but
GenericApplicationContext doesn't). |
ContextStartedEvent | Published when the
ApplicationContext is started,
using the start() method on the
ConfigurableApplicationContext
interface. "Started" here means that all
Lifecycle beans will receive
an explicit start signal. This will typically be used for
restarting after an explicit stop, but may also be used
for starting components that haven't been configured for
autostart (e.g. haven't started on initialization already). |
ContextStoppedEvent | Published when the
ApplicationContext is stopped,
using the stop() method on the
ConfigurableApplicationContext
interface. "Stopped" here means that all
Lifecycle beans will receive
an explicit stop signal. A stopped context may be restarted
through a start() call. |
ContextClosedEvent | Published when the
ApplicationContext is closed,
using the close() method on the
ConfigurableApplicationContext
interface. "Closed" here means that all singleton beans
are destroyed. A closed context has reached its end of life;
it cannot be refreshed or restarted. |
RequestHandledEvent | A web-specific event telling all beans that an
HTTP request has been serviced (this will be published
after the request has been finished).
Note that this event is only applicable for web applications
using Spring's
DispatcherServlet . |
Implementing custom events can be done as well. Simply call the
publishEvent()
method on the
ApplicationContext
, specifying a
parameter which is an instance of your custom event class implementing
ApplicationEvent
. Event listeners receive events
synchronously. This means the publishEvent()
method blocks until all listeners have finished processing the event (it
is possible to supply an alternate event publishing strategy via a
ApplicationEventMulticaster
implementation). Furthermore, when a listener receives an event it
operates inside the transaction context of the publisher, if a
transaction context is available.
Let's look at an example. First, the
ApplicationContext
:
<bean id="emailer" class="example.EmailBean"> <property name="blackList"> <list> <value>black@list.org</value> <value>white@list.org</value> <value>john@doe.org</value> </list> </property> </bean> <bean id="blackListListener" class="example.BlackListNotifier"> <property name="notificationAddress" value="spam@list.org"/> </bean>
Now, let's look at the actual classes:
public class EmailBean implements ApplicationContextAware {
private List blackList;
private ApplicationContext ctx;
public void setBlackList(List blackList) {
this.blackList = blackList;
}
public void setApplicationContext(ApplicationContext ctx) {
this.ctx = ctx;
}
public void sendEmail(String address, String text) {
if (blackList.contains(address)) {
BlackListEvent event = new BlackListEvent(address, text);
ctx.publishEvent(event);
return;
}
// send email...
}
}
public class BlackListNotifier implements ApplicationListener {
private String notificationAddress;
public void setNotificationAddress(String notificationAddress) {
this.notificationAddress = notificationAddress;
}
public void onApplicationEvent(ApplicationEvent event) {
if (event instanceof BlackListEvent) {
// notify appropriate person...
}
}
}
Of course, this particular example could probably be implemented in better ways (perhaps by using AOP features), but it should be sufficient to illustrate the basic event mechanism.
For optimal usage and understanding of application contexts, users
should generally familiarize themselves with Spring's
Resource
abstraction, as described in the
chapter entitled Chapter 4, Resources.
An application context is a
ResourceLoader
, able to be used to load
Resource
s. A
Resource
is essentially a
java.net.URL
on steroids (in fact, it just wraps and
uses a URL where appropriate), which can be used to obtain low-level
resources from almost any location in a transparent fashion, including
from the classpath, a filesystem location, anywhere describable with a
standard URL, and some other variations. If the resource location string
is a simple path without any special prefixes, where those resources
come from is specific and appropriate to the actual application context
type.
A bean deployed into the application context may implement the
special callback interface,
ResourceLoaderAware
, to be automatically
called back at initialization time with the application context itself
passed in as the ResourceLoader
. A bean
may also expose properties of type
Resource
, to be used to access static
resources, and expect that they will be injected into it like any other
properties. The person deploying the bean may specify those
Resource
properties as simple String
paths, and rely on a special JavaBean
PropertyEditor
that is automatically
registered by the context, to convert those text strings to actual
Resource
objects.
The location path or paths supplied to an
ApplicationContext
constructor are
actually resource strings, and in simple form are treated appropriately
to the specific context implementation (
ClassPathXmlApplicationContext
treats a simple
location path as a classpath location), but may also be used with
special prefixes to force loading of definitions from the classpath or a
URL, regardless of the actual context type.
As opposed to the BeanFactory
,
which will often be created programmatically,
ApplicationContext
instances can be
created declaratively using for example a
ContextLoader
. Of course you can also create
ApplicationContext
instances
programmatically using one of the
ApplicationContext
implementations.
First, let's examine the ContextLoader
mechanism
and its implementations.
The ContextLoader
mechanism comes in two
flavors: the ContextLoaderListener
and the
ContextLoaderServlet
. They both have the same
functionality but differ in that the listener version cannot be reliably
used in Servlet 2.3 containers. Since the Servlet 2.4 specification,
servlet context listeners are required to execute immediately after the
servlet context for the web application has been created and is
available to service the first request (and also when the servlet
context is about to be shut down): as such a servlet context listener is
an ideal place to initialize the Spring
ApplicationContext
. It is up to you as to
which one you use, but all things being equal you should probably prefer
ContextLoaderListener
; for more information on
compatibility, have a look at the Javadoc for the
ContextLoaderServlet
.
You can register an
ApplicationContext
using the
ContextLoaderListener
as follows:
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/daoContext.xml /WEB-INF/applicationContext.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<!-- or use the ContextLoaderServlet
instead of the above listener
<servlet>
<servlet-name>context</servlet-name>
<servlet-class>org.springframework.web.context.ContextLoaderServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
-->
The listener inspects the
'contextConfigLocation'
parameter. If the parameter
does not exist, the listener will use
/WEB-INF/applicationContext.xml
as a default. When it
does exist, it will separate the String using
predefined delimiters (comma, semicolon and whitespace) and use the
values as locations where application contexts will be searched for.
Ant-style path patterns are supported as well: e.g.
/WEB-INF/*Context.xml
(for all files whose name ends
with "Context.xml", residing in the "WEB-INF" directory) or
/WEB-INF/**/*Context.xml
(for all such files in any
subdirectory of "WEB-INF").
The ContextLoaderServlet
can be used
instead of the ContextLoaderListener
. The servlet
will use the 'contextConfigLocation'
parameter just
as the listener does.
The majority of the code inside an application is best written in a
DI style, where that code is served out of a Spring IoC container, has its
own dependencies supplied by the container when it is created, and is
completely unaware of the container. However, for the small glue layers of
code that are sometimes needed to tie other code together, there is
sometimes a need for singleton (or quasi-singleton) style access to a
Spring IoC container. For example, third party code may try to construct
new objects directly (Class.forName()
style), without
the ability to force it to get these objects out of a Spring IoC
container. If the object constructed by the third party code is just a
small stub or proxy, which then uses a singleton style access to a Spring
IoC container to get a real object to delegate to, then inversion of
control has still been achieved for the majority of the code (the object
coming out of the container); thus most code is still unaware of the
container or how it is accessed, and remains decoupled from other code,
with all ensuing benefits. EJBs may also use this stub/proxy approach to
delegate to a plain Java implementation object, coming out of a Spring IoC
container. While the Spring IoC container itself ideally does not have to
be a singleton, it may be unrealistic in terms of memory usage or
initialization times (when using beans in the Spring IoC container such as
a Hibernate SessionFactory
) for each bean
to use its own, non-singleton Spring IoC container.
As another example, in complex J2EE applications with multiple
layers (various JAR files, EJBs, and WAR files packaged as an EAR), with
each layer having its own Spring IoC container definition (effectively
forming a hierarchy), the preferred approach when there is only one
web-app (WAR) in the top hierarchy is to simply create one composite
Spring IoC container from the multiple XML definition files from each
layer. All of the various Spring IoC container implementations may be
constructed from multiple definition files in this fashion. However, if
there are multiple sibling web-applications at the root of the hierarchy,
it is problematic to create a Spring IoC container for each
web-application which consists of mostly identical bean definitions from
lower layers, as there may be issues due to increased memory usage, issues
with creating multiple copies of beans which take a long time to
initialize (for example a Hibernate
SessionFactory
), and possible issues due to
side-effects. As an alternative, classes such as ContextSingletonBeanFactoryLocator
or SingletonBeanFactoryLocator
may be used to demand-load multiple hierarchical (that is one container is
the parent of another) Spring IoC container instances in a singleton
fashion, which may then be used as the parents of the web-application
Spring IoC container instances. The result is that bean definitions for
lower layers are loaded only as needed, and loaded only once.
You can see a detailed example of the usage of these classes by
viewing the Javadoc for the SingletonBeanFactoryLocator
and ContextSingletonBeanFactoryLocator
classes. As mentioned in the chapter on EJBs,
the Spring convenience base classes for EJBs normally use a non-singleton
BeanFactoryLocator
implementation, which is
easily replaced by the use of
SingletonBeanFactoryLocator
and
ContextSingletonBeanFactoryLocator
.
Since Spring 2.5, it is possible to deploy a Spring ApplicationContext as a RAR file, encapsulating the context and all of its required bean classes and library JARs in a J2EE RAR deployment unit. This is the equivalent of bootstrapping a standalone ApplicationContext, just hosted in J2EE environment, being able to access the J2EE server's facilities. RAR deployment is intended as a more 'natural' alternative to the not uncommon scenario of deploying a headless WAR file - i.e. a WAR file without any HTTP entry points, just used for bootstrapping a Spring ApplicationContext in a J2EE environment.
RAR deployment is ideal for application contexts that do not need any
HTTP entry points but rather just consist of message endpoints and scheduled
jobs etc. Beans in such a context may use application server resources such
as the JTA transaction manager and JNDI-bound JDBC DataSources and JMS
ConnectionFactory instances, and may also register with the platform's
JMX server - all through Spring's standard transaction management and
JNDI and JMX support facilities. Application components may also interact
with the application's server JCA WorkManager through Spring's
TaskExecutor
abstraction.
Check out the JavaDoc of the SpringContextResourceAdapter class for the configuration details involved in RAR deployment.
For simple deployment needs, all you need to do is the following:
Package all application classes into a RAR file (which is just a standard
JAR file with a different file extension), add all required library jars
into the root of the RAR archive, add a "META-INF/ra.xml" deployment descriptor
(as shown in SpringContextResourceAdapter
's JavaDoc)
as well as the corresponding Spring XML bean definition file(s)
(typically "META-INF/applicationContext.xml"), and drop the resulting RAR
file into your application server's deployment directory!
NOTE: Such RAR deployment units are usually self-contained; they do not expose components to the 'outside' world, not even to other modules of the same application. Interaction with a RAR-based ApplicationContext usually happens through JMS destinations that it shares with other modules. A RAR-based ApplicationContext may also - for example - schedule some jobs, reacting to new files in the file system (or the like). If it actually needs to allow for synchronous access from the outside, it could for example export RMI endpoints, which of course may be used by other application modules on the same machine as well.
As mentioned in the section entitled Section 3.7.1.2, “Example: The
RequiredAnnotationBeanPostProcessor
”, using a
BeanPostProcessor
in conjunction with
annotations is a common means of extending the Spring IoC container. For
example, Spring 2.0 introduced the possibility of enforcing required
properties with the @Required annotation. As of
Spring 2.5, it is now possible to follow that same general approach to
drive Spring's dependency injection. Essentially, the
@Autowired
annotation provides the same
capabilities as described in Section 3.3.5, “Autowiring collaborators” but
with more fine-grained control and wider applicability. Spring 2.5 also
adds support for JSR-250 annotations such as
@Resource
,
@PostConstruct
, and
@PreDestroy
. Of course, these options are
only available if you are using at least Java 5 (Tiger) and thus have
access to source level annotations. Use of these annotations also requires
that certain BeanPostProcessors
be
registered within the Spring container. As always, these can be registered
as individual bean definitions, but they can also be implicitly registered
by including the following tag in an XML-based Spring configuration
(notice the inclusion of the 'context
'
namespace):
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd"> <context:annotation-config/> </beans>
(The implicitly registered post-processors include AutowiredAnnotationBeanPostProcessor
,
CommonAnnotationBeanPostProcessor
,
PersistenceAnnotationBeanPostProcessor
,
as well as the aforementioned RequiredAnnotationBeanPostProcessor
.)
The @Required
annotation applies
to bean property setter methods, as in the following example:
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Required
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
// ...
}
This annotation simply indicates that the affected bean property must
be populated at configuration time: either through an explicit property value
in a bean definition or through autowiring. The container will throw an exception
if the affected bean property has not been populated; this allows for eager and
explicit failure, avoiding NullPointerException
s or the
like later on. Note that it is still recommended to put assertions into the
bean class itself (for example into an init method) in order to enforce those
required references and values even when using the class outside of a container.
As expected, the @Autowired
annotation may be applied to "traditional" setter methods:
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Autowired
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
// ...
}
The annotation may also be applied to methods with arbitrary names and/or multiple arguments:
public class MovieRecommender {
private MovieCatalog movieCatalog;
private CustomerPreferenceDao customerPreferenceDao;
@Autowired
public void prepare(MovieCatalog movieCatalog, CustomerPreferenceDao customerPreferenceDao) {
this.movieCatalog = movieCatalog;
this.customerPreferenceDao = customerPreferenceDao;
}
// ...
}
The @Autowired
annotation may even
be applied on constructors and fields:
public class MovieRecommender {
@Autowired
private MovieCatalog movieCatalog;
private CustomerPreferenceDao customerPreferenceDao;
@Autowired
public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
this.customerPreferenceDao = customerPreferenceDao;
}
// ...
}
It is also possible to provide all beans of a
particular type from the
ApplicationContext
by adding the
annotation to a field or method that expects an array of that
type:
public class MovieRecommender {
@Autowired
private MovieCatalog[] movieCatalogs;
// ...
}
The same applies for typed collections:
public class MovieRecommender {
private Set<MovieCatalog> movieCatalogs;
@Autowired
public void setMovieCatalogs(Set<MovieCatalog> movieCatalogs) {
this.movieCatalogs = movieCatalogs;
}
// ...
}
Even typed Maps may be autowired as long as the expected key type
is String
. The Map values will contain all beans
of the expected type, and the keys will contain the corresponding bean
names:
public class MovieRecommender {
private Map<String, MovieCatalog> movieCatalogs;
@Autowired
public void setMovieCatalogs(Map<String, MovieCatalog> movieCatalogs) {
this.movieCatalogs = movieCatalogs;
}
// ...
}
By default, the autowiring will fail whenever zero candidate beans are available; the default behavior is to treat annotated methods, constructors, and fields as indicating required dependencies. This behavior can be changed as demonstrated below.
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Autowired(required=false)
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
// ...
}
![]() | Note |
---|---|
Only one annotated constructor per-class may be marked as required, but multiple non-required constructors can be annotated. In that case, each will be considered among the candidates and Spring will use the greediest constructor whose dependencies can be satisfied. Prefer the use of |
@Autowired
may also be used for
well-known "resolvable dependencies": the BeanFactory
interface, the ApplicationContext
interface,
the ResourceLoader
interface,
the ApplicationEventPublisher
interface
and the MessageSource
interface.
These interfaces (and their extended interfaces such as
ConfigurableApplicationContext
or
ResourcePatternResolver
) will be
automatically resolved, with no special setup necessary.
public class MovieRecommender {
@Autowired
private ApplicationContext context;
public MovieRecommender() {
}
// ...
}
Since autowiring by type may lead to multiple candidates, it is
often necessary to have more control over the selection process. One way
to accomplish this is with Spring's
@Qualifier
annotation. This allows for
associating qualifier values with specific arguments, narrowing the
set of type matches so that a specific bean is chosen for each argument.
In the simplest case, this can be a plain descriptive value:
public class MovieRecommender { @Autowired @Qualifier("main") private MovieCatalog movieCatalog; // ... }
The @Qualifier
annotation can also
be specified on individual constructor arguments or method
parameters:
public class MovieRecommender { private MovieCatalog movieCatalog; private CustomerPreferenceDao customerPreferenceDao; @Autowired public void prepare(@Qualifier("main") MovieCatalog movieCatalog, CustomerPreferenceDao customerPreferenceDao) { this.movieCatalog = movieCatalog; this.customerPreferenceDao = customerPreferenceDao; } // ... }
The corresponding bean definitions would look like as follows. The bean with qualifier value "main" would be wired with the constructor argument that has been qualified with the same value.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd"> <context:annotation-config/> <bean class="example.SimpleMovieCatalog"> <qualifier value="main"/> <!-- inject any dependencies required by this bean --> </bean> <bean class="example.SimpleMovieCatalog"> <qualifier value="action"/> <!-- inject any dependencies required by this bean --> </bean> <bean id="movieRecommender" class="example.MovieRecommender"/> </beans>
For a fallback match, the bean name is considered as a default qualifier
value. This means that the bean may be defined with an id "main" instead of
the nested qualifier element, leading to the same matching result. However,
note that while this can be used to refer to specific beans by name,
@Autowired
is fundamentally about type-driven
injection with optional semantic qualifiers. This means that qualifier values,
even when using the bean name fallback, always have narrowing semantics within
the set of type matches; they do not semantically express a reference to a
unique bean id. Good qualifier values would be "main" or "EMEA" or "persistent",
expressing characteristics of a specific component - independent from the bean
id (which may be auto-generated in case of an anonymous bean definition like
the one above).
Qualifiers also apply to typed collections (as discussed above):
e.g. to Set<MovieCatalog>
. In such a case,
all matching beans according to the declared qualifiers are going to
be injected as a collection. This implies that qualifiers do not have
to be unique; they rather simply constitute filtering criteria.
For example, there could be multiple MovieCatalog
beans defined with the same qualifier value "action"; all of which
would be injected into a Set<MovieCatalog>
annotated with @Qualifier("action")
.
![]() | Tip |
---|---|
If you intend to express annotation-driven injection by name,
do not primarily use As a specific consequence of this semantic difference,
beans which are themselves defined as a collection or map type
cannot be injected via Note: In contrast to
|
You may create your own custom qualifier annotations as well.
Simply define an annotation and provide the
@Qualifier
annotation within your
definition:
@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface Genre {
String value();
}
Then you can provide the custom qualifier on autowired fields and parameters:
public class MovieRecommender { @Autowired @Genre("Action") private MovieCatalog actionCatalog; private MovieCatalog comedyCatalog; @Autowired public void setComedyCatalog(@Genre("Comedy") MovieCatalog comedyCatalog) { this.comedyCatalog = comedyCatalog; } // ... }
The next step is to provide the information on the candidate bean
definitions. You can add <qualifier/>
tags as
sub-elements of the <bean/>
tag and then
specify the 'type'
and 'value'
to
match your custom qualifier annotations. The type will be matched
against the fully-qualified class name of the annotation, or as a
convenience when there is no risk of conflicting names, you may use the
'short' class name. Both are demonstrated in the following
example.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd"> <context:annotation-config/> <bean class="example.SimpleMovieCatalog"> <qualifier type="Genre" value="Action"/> <!-- inject any dependencies required by this bean --> </bean> <bean class="example.SimpleMovieCatalog"> <qualifier type="example.Genre" value="Comedy"/> <!-- inject any dependencies required by this bean --> </bean> <bean id="movieRecommender" class="example.MovieRecommender"/> </beans>
In the next section, entitled Section 3.12, “Classpath scanning for managed components”, you will see an annotation-based alternative to providing the qualifier metadata in XML. Specifically, see: Section 3.12.6, “Providing qualifier metadata with annotations”.
In some cases, it may be sufficient to use an annotation without a value. This may be useful when the annotation serves a more generic purpose and could be applied across several different types of dependencies. For example, you may provide an offline catalog that would be searched when no Internet connection is available. First define the simple annotation:
@Target({ElementType.FIELD, ElementType.PARAMETER}) @Retention(RetentionPolicy.RUNTIME) @Qualifier public @interface Offline { }
Then add the annotation to the field or property to be autowired:
public class MovieRecommender { @Autowired @Offline private MovieCatalog offlineCatalog; // ... }
Now the bean definition only needs a qualifier
'type'
:
<bean class="example.SimpleMovieCatalog"> <qualifier type="Offline"/> <!-- inject any dependencies required by this bean --> </bean>
It is also possible to define custom qualifier annotations that
accept named attributes in addition to or instead of the simple
'value'
attribute. If multiple attribute values are
then specified on a field or parameter to be autowired, a bean
definition must match all such attribute values to
be considered an autowire candidate. As an example, consider the
following annotation definition:
@Target({ElementType.FIELD, ElementType.PARAMETER}) @Retention(RetentionPolicy.RUNTIME) @Qualifier public @interface MovieQualifier { String genre(); Format format(); }
In this case Format
is an enum:
public enum Format { VHS, DVD, BLURAY }
The fields to be autowired are annotated with the custom qualifier
and include values for both attributes: 'genre'
and
'format'
.
public class MovieRecommender {
@Autowired
@MovieQualifier(format=Format.VHS, genre="Action")
private MovieCatalog actionVhsCatalog;
@Autowired
@MovieQualifier(format=Format.VHS, genre="Comedy")
private MovieCatalog comedyVhsCatalog;
@Autowired
@MovieQualifier(format=Format.DVD, genre="Action")
private MovieCatalog actionDvdCatalog;
@Autowired
@MovieQualifier(format=Format.BLURAY, genre="Comedy")
private MovieCatalog comedyBluRayCatalog;
// ...
}
Finally, the bean definitions should contain matching qualifier
values. This example also demonstrates that bean
meta attributes may be used instead of the
<qualifier/>
sub-elements. If available, the
<qualifier/>
and its attributes would take
precedence, but the autowiring mechanism will fallback on the values
provided within the <meta/>
tags if no such
qualifier is present (see the last 2 bean definitions below).
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd"> <context:annotation-config/> <bean class="example.SimpleMovieCatalog"> <qualifier type="MovieQualifier"> <attribute key="format" value="VHS"/> <attribute key="genre" value="Action"/> </qualifier> <!-- inject any dependencies required by this bean --> </bean> <bean class="example.SimpleMovieCatalog"> <qualifier type="MovieQualifier"> <attribute key="format" value="VHS"/> <attribute key="genre" value="Comedy"/> </qualifier> <!-- inject any dependencies required by this bean --> </bean> <bean class="example.SimpleMovieCatalog"> <meta key="format" value="DVD"/> <meta key="genre" value="Action"/> <!-- inject any dependencies required by this bean --> </bean> <bean class="example.SimpleMovieCatalog"> <meta key="format" value="BLURAY"/> <meta key="genre" value="Comedy"/> <!-- inject any dependencies required by this bean --> </bean> </beans>
The CustomAutowireConfigurer
is a BeanFactoryPostProcessor
that
enables further customization of the autowiring process. Specifically,
it allows you to register your own custom qualifier annotation types
even if they are not themselves annotated with Spring's
@Qualifier
annotation.
<bean id="customAutowireConfigurer" class="org.springframework.beans.factory.annotation.CustomAutowireConfigurer"> <property name="customQualifierTypes"> <set> <value>example.CustomQualifier</value> </set> </property> </bean>
Note that the particular implementation of
AutowireCandidateResolver
that will be
activated for the application context depends upon the Java version. If
running on less than Java 5, the qualifier annotations are not
supported, and therefore autowire candidates are solely determined by
the 'autowire-candidate'
value of each bean
definition as well as any
'default-autowire-candidates'
pattern(s) available on
the <beans/>
element. If running on Java 5 or
greater, the presence of @Qualifier
annotations or any custom annotations registered with the
CustomAutowireConfigurer
will also play a
role.
Regardless of the Java version, the determination of a "primary"
candidate (when multiple beans qualify as autowire candidates) is the
same: if exactly one bean definition among the candidates has a
'primary'
attribute set to 'true'
,
it will be selected.
Spring also supports injection using the JSR-250
@Resource
annotation on fields or
bean property setter methods. This is a common pattern found in
Java EE 5 and Java 6 (e.g. in JSF 1.2 managed beans or JAX-WS 2.0
endpoints), which Spring supports for Spring-managed objects as well.
@Resource
takes a 'name' attribute,
and by default Spring will interpret that value as the bean name to be
injected. In other words, it follows by-name
semantics as demonstrated in this example:
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Resource(name="myMovieFinder")
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
}
If no name is specified explicitly, then the default name will be derived from the name of the field or setter method: In case of a field, it will simply be equivalent to the field name; in case of a setter method, it will be equivalent to the bean property name. So the following example is going to have the bean with name "movieFinder" injected into its setter method:
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Resource
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
}
![]() | Note |
---|---|
The name provided with the annotation will be resolved as a bean
name by the |
Similar to @Autowired
,
@Resource
may fall back to standard bean type
matches (i.e. find a primary type match instead of a specific named bean)
as well as resolve well-known "resolvable dependencies":
the BeanFactory
interface,
the ApplicationContext
interface,
the ResourceLoader
interface,
the ApplicationEventPublisher
interface
and the MessageSource
interface.
Note that this only applies to @Resource
usage with no explicit name specified!
So the following example will have its customerPreferenceDao
field looking for a bean with name "customerPreferenceDao" first, then falling
back to a primary type match for the type CustomerPreferenceDao
.
The "context" field will simply be injected based on the known resolvable dependency
type ApplicationContext
.
public class MovieRecommender {
@Resource
private CustomerPreferenceDao customerPreferenceDao;
@Resource
private ApplicationContext context;
public MovieRecommender() {
}
// ...
}
The CommonAnnotationBeanPostProcessor
not
only recognizes the @Resource
annotation
but also the JSR-250 lifecycle annotations.
Introduced in Spring 2.5, the support for these annotations offers yet
another alternative to those described in the sections on initialization
callbacks and destruction
callbacks. Provided that the
CommonAnnotationBeanPostProcessor
is registered
within the Spring ApplicationContext
, a
method carrying one of these annotations will be invoked at the same
point in the lifecycle as the corresponding Spring lifecycle interface's
method or explicitly declared callback method. In the example below, the
cache will be pre-populated upon initialization and cleared upon
destruction.
public class CachingMovieLister { @PostConstruct public void populateMovieCache() { // populates the movie cache upon initialization... } @PreDestroy public void clearMovieCache() { // clears the movie cache upon destruction... } }
![]() | Note |
---|---|
For details regarding the effects of combining various lifecycle mechanisms, see Section 3.5.1.4, “Combining lifecycle mechanisms”. |
Thus far most of the examples within this chapter have used XML for
specifying the configuration metadata that produces each
BeanDefinition
within the Spring container.
The previous section (Section 3.11, “Annotation-based configuration”)
demonstrated the possibility of providing a considerable amount of the
configuration metadata using source-level annotations. Even in those
examples however, the "base" bean definitions were explicitly defined in
the XML file while the annotations were driving the dependency injection
only. The current section introduces an option for implicitly detecting the
candidate components by scanning the classpath and
matching against filters.
Beginning with Spring 2.0, the
@Repository
annotation was introduced as
a marker for any class that fulfills the role or
stereotype of a repository (a.k.a. Data Access
Object or DAO). Among the possibilities for leveraging such a marker is
the automatic translation of exceptions as described in Section 12.6.4, “Exception Translation”.
Spring 2.5 introduces further stereotype annotations:
@Component
,
@Service
and
@Controller
.
@Component
serves as a generic stereotype
for any Spring-managed component; whereas,
@Repository
,
@Service
, and
@Controller
serve as specializations of
@Component
for more specific use cases
(e.g., in the persistence, service, and presentation layers,
respectively). What this means is that you can annotate your component
classes with @Component
, but by
annotating them with @Repository
,
@Service
, or
@Controller
instead, your classes are
more properly suited for processing by tools or associating with aspects.
For example, these stereotype annotations make ideal targets for
pointcuts. Of course, it is also possible that
@Repository
,
@Service
, and
@Controller
may carry additional
semantics in future releases of the Spring Framework. Thus, if you are
making a decision between using @Component
or @Service
for your service layer,
@Service
is clearly the better choice.
Similarly, as stated above, @Repository
is already supported as a marker for automatic exception translation in
your persistence layer.
Spring provides the capability of automatically detecting
'stereotyped' classes and registering corresponding
BeanDefinition
s with the
ApplicationContext
. For example, the
following two classes are eligible for such autodetection:
@Service public class SimpleMovieLister { private MovieFinder movieFinder; @Autowired public SimpleMovieLister(MovieFinder movieFinder) { this.movieFinder = movieFinder; } }
@Repository
public class JpaMovieFinder implements MovieFinder {
// implementation elided for clarity
}
To autodetect these classes and register the corresponding beans requires the inclusion of the following element in XML where 'basePackage' would be a common parent package for the two classes (or alternatively a comma-separated list could be specified that included the parent package of each class).
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd"> <context:component-scan base-package="org.example"/> </beans>
![]() | Note |
---|---|
Note that the scanning of classpath packages requires the presence of corresponding directory entries in the classpath. When building jars with Ant, make sure to not activate the files-only switch of the jar task! |
Furthermore, the
AutowiredAnnotationBeanPostProcessor
and
CommonAnnotationBeanPostProcessor
are
both included implicitly when using the component-scan element. That
means that the two components are autodetected and
wired together - all without any bean configuration metadata provided in
XML.
![]() | Note |
---|---|
The registration of those post-processors can be disabled by including the annotation-config attribute with a value of 'false'. |
By default, classes annotated with
@Component
,
@Repository
,
@Service
, or
@Controller
(or classes annotated with a
custom annotation that itself is annotated with
@Component
) are the only detected
candidate components. However it is simple to modify and extend this
behavior by applying custom filters. These can be added as either
include-filter or
exclude-filter sub-elements of the
'component-scan
' element. Each filter element requires
the 'type
' and 'expression
'
attributes. Five filtering options exist as described below.
Table 3.7. Filter Types
Filter Type | Example Expression | Description |
---|---|---|
annotation | org.example.SomeAnnotation | An annotation to be present at the type level in target components. |
assignable | org.example.SomeClass | A class (or interface) that the target components are assignable to (extend/implement). |
aspectj | org.example..*Service+ | An AspectJ type expression to be matched by the target components. |
regex | org\.example\.Default.* | A regex expression to be matched by the target components' class names. |
custom | org.example.MyCustomTypeFilter | A custom implementation of the org.springframework.core.type.TypeFilter interface. |
Find below an example of the XML configuration for ignoring all
@Repository
annotations and using "stub"
repositories instead.
<beans ...> <context:component-scan base-package="org.example"> <context:include-filter type="regex" expression=".*Stub.*Repository"/> <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Repository"/> </context:component-scan> </beans>
![]() | Note |
---|---|
It is also possible to disable the default filters by providing
use-default-filters="false" as an attribute of
the <component-scan/> element. This will in effect disable
automatic detection of classes annotated with
|
When a component is autodetected as part of the scanning process,
its bean name will be generated by the
BeanNameGenerator
strategy known to that
scanner. By default, any Spring 'stereotype' annotation
(@Component
,
@Repository
,
@Service
, and
@Controller
) that contains a
name
value will thereby provide that name to the
corresponding bean definition. If such an annotation contains no
name
value or for any other detected component (such as
those discovered due to custom filters), the default bean name generator
will return the uncapitalized non-qualified class name. For example, if
the following two components were detected, the names would be
'myMovieLister' and 'movieFinderImpl':
@Service("myMovieLister")
public class SimpleMovieLister {
// ...
}
@Repository
public class MovieFinderImpl implements MovieFinder {
// ...
}
![]() | Note |
---|---|
If you don't want to rely on the default bean-naming strategy,
you may provide a custom bean-naming strategy. First, implement the
|
<beans ...> <context:component-scan base-package="org.example" name-generator="org.example.MyNameGenerator" /> </beans>
As a general rule, consider specifying the name with the annotation whenever other components may be making explicit references to it. On the other hand, the auto-generated names are adequate whenever the container is responsible for wiring.
As with Spring-managed components in general, the default and by
far most common scope is 'singleton'. However, there are times when
other scopes are needed. Therefore Spring 2.5 introduces a new
@Scope
annotation as well. Simply provide
the name of the scope within the annotation, such as:
@Scope("prototype")
@Repository
public class MovieFinderImpl implements MovieFinder {
// ...
}
![]() | Note |
---|---|
If you would like to provide a custom strategy for scope
resolution rather than relying on the annotation-based approach,
implement the |
<beans ...> <context:component-scan base-package="org.example" scope-resolver="org.example.MyScopeResolver" /> </beans>
When using certain non-singleton scopes, it may be necessary to generate proxies for the scoped objects. The reasoning is described in detail within the section entitled Section 3.4.4.5, “Scoped beans as dependencies”. For this purpose, a scoped-proxy attribute is available on the 'component-scan' element. The three possible values are: 'no', 'interfaces', and 'targetClass'. For example, the following configuration will result in standard JDK dynamic proxies:
<beans ...> <context:component-scan base-package="org.example" scoped-proxy="interfaces" /> </beans>
The @Qualifier
annotation was
introduced in the section above entitled
Section 3.11.3, “Fine-tuning annotation-based autowiring with qualifiers”. The
examples in that section demonstrated use of the
@Qualifier
annotation as well
as custom qualifier annotations to provide fine-grained control
when resolving autowire candidates. Since those examples were
based on XML bean definitions, the qualifier metadata was provided
on the candidate bean definitions using the 'qualifier
'
or 'meta
' sub-elements of the 'bean
'
element in the XML. When relying upon classpath scanning for
autodetection of components, then the qualifier metadata may
be provided with type-level annotations on the candidate class.
The following three examples demonstrate this technique.
@Component @Qualifier("Action") public class ActionMovieCatalog implements MovieCatalog { // ... }
@Component @Genre("Action") public class ActionMovieCatalog implements MovieCatalog { // ... }
@Component @Offline public class CachingMovieCatalog implements MovieCatalog { // ... }
![]() | Note |
---|---|
As with most of the annotation-based alternatives, keep in mind that the annotation metadata is bound to the class definition itself, while the use of XML allows for multiple beans of the same type to provide variations in their qualifier metadata since that metadata is provided per-instance rather than per-class. |
The context
namespace introduced in Spring 2.5
provides a load-time-weaver
element.
<beans ...> <context:load-time-weaver/> </beans>
Adding this element to an XML-based Spring configuration file
activates a Spring LoadTimeWeaver
for the
ApplicationContext
. Any bean within that
ApplicationContext
may implement
LoadTimeWeaverAware
thereby receiving a
reference to the load-time weaver instance. This is particularly useful in
combination with Spring's JPA support where
load-time weaving may be necessary for JPA class transformation. Consult
the LocalContainerEntityManagerFactoryBean
Javadoc
for more detail. For more on AspectJ load-time weaving, see Section 6.8.4, “Load-time weaving with AspectJ in the Spring Framework”.
[1] See the section entitled Background
[2] See the section entitled Section 3.3.1, “Injecting dependencies”
Java's standard java.net.URL
class and
standard handlers for various URL prefixes unfortunately are not quite
adequate enough for all access to low-level resources. For example,
there is no standardized URL
implementation
that may be used to access a resource that needs to be obtained from
the classpath, or relative to a
ServletContext
. While it is possible
to register new handlers for specialized URL
prefixes (similar to existing handlers for prefixes such as
http:
), this is generally quite complicated, and the
URL
interface still lacks some desirable
functionality, such as a method to check for the existence of the
resource being pointed to.
Spring's Resource
interface is meant
to be a more capable interface for abstracting access to low-level
resources.
public interface Resource extends InputStreamSource { boolean exists(); boolean isOpen(); URL getURL() throws IOException; File getFile() throws IOException; Resource createRelative(String relativePath) throws IOException; String getFilename(); String getDescription(); }
public interface InputStreamSource { InputStream getInputStream() throws IOException; }
Some of the most important methods from the
Resource
interface are:
getInputStream()
: locates and opens the
resource, returning an InputStream
for reading
from the resource. It is expected that each invocation returns a
fresh InputStream
. It is the responsibility of
the caller to close the stream.
exists()
: returns a
boolean
indicating whether this resource actually
exists in physical form.
isOpen()
: returns a
boolean
indicating whether this resource represents
a handle with an open stream. If true
, the
InputStream
cannot be read multiple times, and
must be read once only and then closed to avoid resource leaks. Will
be false
for all usual resource implementations,
with the exception of
InputStreamResource
.
getDescription()
: returns a description
for this resource, to be used for error output when working with the
resource. This is often the fully qualified file name or the actual
URL of the resource.
Other methods allow you to obtain an actual
URL
or File
object
representing the resource (if the underlying implementation is compatible,
and supports that functionality).
The Resource
abstraction is used
extensively in Spring itself, as an argument type in many method
signatures when a resource is needed. Other methods in some Spring APIs
(such as the constructors to various
ApplicationContext
implementations), take a
String
which in unadorned or simple form is used to
create a Resource
appropriate to that
context implementation, or via special prefixes on the
String
path, allow the caller to specify that a
specific Resource
implementation must be
created and used.
While the Resource
interface is used
a lot with Spring and by Spring, it's actually very useful to use as a
general utility class by itself in your own code, for access to resources,
even when your code doesn't know or care about any other parts of Spring.
While this couples your code to Spring, it really only couples it to this
small set of utility classes, which are serving as a more capable
replacement for URL
, and can be considered
equivalent to any other library you would use for this purpose.
It is important to note that the
Resource
abstraction does not replace
functionality: it wraps it where possible. For example, a
UrlResource
wraps a URL, and uses the wrapped
URL
to do it's work.
There are a number of Resource
implementations that come supplied straight out of the box in
Spring:
The UrlResource
wraps a
java.net.URL
, and may be used to access any
object that is normally accessible via a URL, such as files, an HTTP
target, an FTP target, etc. All URLs have a standardized
String
representation, such that appropriate
standardized prefixes are used to indicate one URL type from another.
This includes file:
for accessing filesystem paths,
http:
for accessing resources via the HTTP protocol,
ftp:
for accessing resources via FTP, etc.
A UrlResource
is created by Java code
explicitly using the UrlResource
constructor, but
will often be created implicitly when you call an API method which takes
a String
argument which is meant to represent a
path. For the latter case, a JavaBeans
PropertyEditor
will ultimately decide
which type of Resource
to create. If the
path string contains a few well-known (to it, that is) prefixes such as
classpath:
, it will create an appropriate specialized
Resource
for that prefix. However, if it
doesn't recognize the prefix, it will assume the this is just a standard
URL string, and will create a UrlResource
.
This class represents a resource which should be obtained from the classpath. This uses either the thread context class loader, a given class loader, or a given class for loading resources.
This Resource
implementation
supports resolution as java.io.File
if the class
path resource resides in the file system, but not for classpath
resources which reside in a jar and have not been expanded (by the
servlet engine, or whatever the environment is) to the filesystem. To
address this the various Resource
implementations always support resolution as a
java.net.URL
.
A ClassPathResource
is created by Java code
explicitly using the ClassPathResource
constructor, but will often be created implicitly when you call an API
method which takes a String
argument which is
meant to represent a path. For the latter case, a JavaBeans
PropertyEditor
will recognize the special
prefix classpath:
on the string path, and create a
ClassPathResource
in that case.
This is a Resource
implementation
for java.io.File
handles. It obviously supports
resolution as a File
, and as a
URL
.
This is a Resource
implementation
for ServletContext
resources,
interpreting relative paths within the relevant web application's root
directory.
This always supports stream access and URL access, but only allows
java.io.File
access when the web application
archive is expanded and the resource is physically on the filesystem.
Whether or not it's expanded and on the filesystem like this, or
accessed directly from the JAR or somewhere else like a DB (it's
conceivable) is actually dependent on the Servlet container.
A Resource
implementation for a
given InputStream
. This should only be
used if no specific Resource
implementation is applicable. In particular, prefer
ByteArrayResource
or any of the file-based
Resource
implementations where
possible.
In contrast to other Resource
implementations, this is a descriptor for an
already opened resource - therefore returning
true
from isOpen()
. Do not
use it if you need to keep the resource descriptor somewhere, or if you
need to read a stream multiple times.
The ResourceLoader
interface is meant
to be implemented by objects that can return (i.e. load)
Resource
instances.
public interface ResourceLoader { Resource getResource(String location); }
All application contexts implement the
ResourceLoader
interface, and therefore all
application contexts may be used to obtain
Resource
instances.
When you call getResource()
on a specific
application context, and the location path specified doesn't have a
specific prefix, you will get back a
Resource
type that is appropriate to that
particular application context. For example, assume the following snippet
of code was executed against a
ClassPathXmlApplicationContext
instance:
Resource template = ctx.getResource("some/resource/path/myTemplate.txt);
What would be returned would be a
ClassPathResource
; if the same method was executed
against a FileSystemXmlApplicationContext
instance,
you'd get back a FileSystemResource
. For a
WebApplicationContext
, you'd get back a
ServletContextResource
, and so on.
As such, you can load resources in a fashion appropriate to the particular application context.
On the other hand, you may also force
ClassPathResource
to be used, regardless of the
application context type, by specifying the special
classpath:
prefix:
Resource template = ctx.getResource("classpath:some/resource/path/myTemplate.txt);
Similarly, one can force a UrlResource
to be
used by specifying any of the standard java.net.URL
prefixes:
Resource template = ctx.getResource("file:/some/resource/path/myTemplate.txt);
Resource template = ctx.getResource("http://myhost.com/resource/path/myTemplate.txt);
The following table summarizes the strategy for converting
String
s to
Resource
s:
Table 4.1. Resource strings
Prefix | Example | Explanation |
---|---|---|
classpath: | | Loaded from the classpath. |
file: | | Loaded as a |
http: | | Loaded as a
|
(none) | | Depends on the underlying
|
[a] But see also the section entitled Section 4.7.3, “ |
The ResourceLoaderAware
interface is
a special marker interface, identifying objects that expect to be provided
with a ResourceLoader
reference.
public interface ResourceLoaderAware { void setResourceLoader(ResourceLoader resourceLoader); }
When a class implements
ResourceLoaderAware
and is deployed into an
application context (as a Spring-managed bean), it is recognized as
ResourceLoaderAware
by the application
context. The application context will then invoke the
setResourceLoader(ResourceLoader)
, supplying
itself as the argument (remember, all application contexts in Spring
implement the ResourceLoader
interface).
Of course, since an
ApplicationContext
is a
ResourceLoader
, the bean could also
implement the ApplicationContextAware
interface and use the supplied application context directly to load
resources, but in general, it's better to use the specialized
ResourceLoader
interface if that's all
that's needed. The code would just be coupled to the resource loading
interface, which can be considered a utility interface, and not the whole
Spring ApplicationContext
interface.
As of Spring 2.5, you can rely upon autowiring of the
ResourceLoader
as an alternative to
implementing the ResourceLoaderAware
interface.
The "traditional" constructor
and byType
autowiring modes (as described in the section entitled
Section 3.3.5, “Autowiring collaborators”) are now capable of providing a
dependency of type ResourceLoader
for either a
constructor argument or setter method parameter respectively. For more flexibility
(including the ability to autowire fields and multiple parameter methods), consider
using the new annotation-based autowiring features. In that case, the
ResourceLoader
will be autowired into a field,
constructor argument, or method parameter that is expecting the
ResourceLoader
type as long as the field,
constructor, or method in question carries the
@Autowired
annotation. For more information,
see the section entitled Section 3.11.2, “@Autowired
”.
If the bean itself is going to determine and supply the resource
path through some sort of dynamic process, it probably makes sense for the
bean to use the ResourceLoader
interface to
load resources. Consider as an example the loading of a template of some
sort, where the specific resource that is needed depends on the role of
the user. If the resources are static, it makes sense to eliminate the use
of the ResourceLoader
interface completely,
and just have the bean expose the Resource
properties it needs, and expect that they will be injected into it.
What makes it trivial to then inject these properties, is that all
application contexts register and use a special JavaBeans
PropertyEditor
which can convert
String
paths to
Resource
objects. So if
myBean
has a template property of type
Resource
, it can be configured with a
simple string for that resource, as follows:
<bean id="myBean" class="..."> <property name="template" value="some/resource/path/myTemplate.txt"/> </bean>
Note that the resource path has no prefix, so because the
application context itself is going to be used as the
ResourceLoader
, the resource itself will be
loaded via a ClassPathResource
,
FileSystemResource
, or
ServletContextResource
(as appropriate)
depending on the exact type of the context.
If there is a need to force a specific
Resource
type to be used, then a prefix may
be used. The following two examples show how to force a
ClassPathResource
and a
UrlResource
(the latter being used to access a
filesystem file).
<property name="template" value="classpath:some/resource/path/myTemplate.txt">
<property name="template" value="file:/some/resource/path/myTemplate.txt"/>
An application context constructor (for a specific application context type) generally takes a string or array of strings as the location path(s) of the resource(s) such as XML files that make up the definition of the context.
When such a location path doesn't have a prefix, the specific
Resource
type built from that path and
used to load the bean definitions, depends on and is appropriate to the
specific application context. For example, if you create a
ClassPathXmlApplicationContext
as follows:
ApplicationContext ctx = new ClassPathXmlApplicationContext("conf/appContext.xml");
The bean definitions will be loaded from the classpath, as a
ClassPathResource
will be
used. But if you create a
FileSystemXmlApplicationContext
as
follows:
ApplicationContext ctx = new FileSystemXmlApplicationContext("conf/appContext.xml");
The bean definition will be loaded from a filesystem location, in this case relative to the current working directory.
Note that the use of the special classpath prefix or a standard
URL prefix on the location path will override the default type of
Resource
created to load the definition.
So this FileSystemXmlApplicationContext
...
ApplicationContext ctx = new FileSystemXmlApplicationContext("classpath:conf/appContext.xml");
... will actually load it's bean definitions from the classpath.
However, it is still a FileSystemXmlApplicationContext
. If it is
subsequently used as a ResourceLoader
,
any unprefixed paths will still be treated as filesystem paths.
The ClassPathXmlApplicationContext
exposes a number of constructors to enable convenient instantiation.
The basic idea is that one supplies merely a string array containing
just the filenames of the XML files themselves (without the leading
path information), and one also supplies a
Class
; the
ClassPathXmlApplicationContext
will derive the
path information from the supplied class.
An example will hopefully make this clear. Consider a directory layout that looks like this:
com/ foo/ services.xml daos.xml MessengerService.class
A ClassPathXmlApplicationContext
instance
composed of the beans defined in the 'services.xml'
and 'daos.xml'
could be instantiated like
so...
ApplicationContext ctx = new ClassPathXmlApplicationContext( new String[] {"services.xml", "daos.xml"}, MessengerService.class);
Please do consult the Javadocs for the
ClassPathXmlApplicationContext
class for
details of the various constructors.
The resource paths in application context constructor values may
be a simple path (as shown above) which has a one-to-one mapping to a
target Resource, or alternately may contain the special "classpath*:"
prefix and/or internal Ant-style regular expressions (matched using
Spring's PathMatcher
utility). Both of the latter
are effectively wildcards
One use for this mechanism is when doing component-style
application assembly. All components can 'publish' context definition
fragments to a well-known location path, and when the final application
context is created using the same path prefixed via
classpath*:
, all component fragments will be picked
up automatically.
Note that this wildcarding is specific to use of resource paths in
application context constructors (or when using the
PathMatcher
utility class hierarchy directly),
and is resolved at construction time. It has nothing to do with the
Resource
type itself. It's not possible
to use the classpath*:
prefix to construct an actual
Resource
, as a resource points to just
one resource at a time.
When the path location contains an Ant-style pattern, for example:
/WEB-INF/*-context.xml com/mycompany/**/applicationContext.xml file:C:/some/path/*-context.xml classpath:com/mycompany/**/applicationContext.xml
... the resolver follows a more complex but defined procedure to
try to resolve the wildcard. It produces a Resource for the path up to
the last non-wildcard segment and obtains a URL from it. If this URL
is not a "jar:" URL or container-specific variant (e.g.
"zip:
" in WebLogic, "wsjar
" in
WebSphere, etc.), then a java.io.File
is
obtained from it and used to resolve the wildcard by traversing the
filesystem. In the case of a jar URL, the resolver either gets a
java.net.JarURLConnection
from it or manually
parses the jar URL and then traverses the contents of the jar file
to resolve the wildcards.
If the specified path is already a file URL (either
explicitly, or implicitly because the base
ResourceLoader
is a
filesystem one, then wildcarding is guaranteed to work in a
completely portable fashion.
If the specified path is a classpath location, then the
resolver must obtain the last non-wildcard path segment URL via a
Classloader.getResource()
call. Since this
is just a node of the path (not the file at the end) it is actually
undefined (in the ClassLoader
Javadocs)
exactly what sort of a URL is returned in this case. In practice, it
is always a java.io.File
representing the
directory, where the classpath resource resolves to a filesystem
location, or a jar URL of some sort, where the classpath resource
resolves to a jar location. Still, there is a portability concern on
this operation.
If a jar URL is obtained for the last non-wildcard segment,
the resolver must be able to get a
java.net.JarURLConnection
from it, or
manually parse the jar URL, to be able to walk the contents of the
jar, and resolve the wildcard. This will work in most environments,
but will fail in others, and it is strongly recommended that the
wildcard resolution of resources coming from jars be thoroughly
tested in your specific environment before you rely on it.
When constructing an XML-based application context, a location
string may use the special classpath*:
prefix:
ApplicationContext ctx = new ClassPathXmlApplicationContext("classpath*:conf/appContext.xml");
This special prefix specifies that all classpath resources that
match the given name must be obtained (internally, this essentially
happens via a ClassLoader.getResources(...)
call), and then merged to form the final application context
definition.
![]() | Classpath*: portability |
---|---|
The wildcard classpath relies on the |
The "classpath*:
" prefix can also be combined
with a PathMatcher
pattern in the rest of the location path, for
example "classpath*:META-INF/*-beans.xml
". In this
case, the resolution strategy is fairly simple: a
ClassLoader.getResources() call is used on the last non-wildcard path
segment to get all the matching resources in the class loader
hierarchy, and then off each resource the same PathMatcher resoltion
strategy described above is used for the wildcard subpath.
Please note that "classpath*:
" when
combined with Ant-style patterns will only work reliably with at least
one root directory before the pattern starts, unless the actual target
files reside in the file system. This means that a pattern like
"classpath*:*.xml
" will not retrieve files from the
root of jar files but rather only from the root of expanded
directories. This originates from a limitation in the JDK's
ClassLoader.getResources()
method which only
returns file system locations for a passed-in empty string (indicating
potential roots to search).
Ant-style patterns with "classpath:
"
resources are not guaranteed to find matching resources if the root
package to search is available in multiple class path locations. This
is because a resource such as
com/mycompany/package1/service-context.xml
may be in only one location, but when a path such as
classpath:com/mycompany/**/service-context.xml
is used to try to resolve it, the resolver will work off the (first) URL
returned by getResource("com/mycompany")
;. If
this base package node exists in multiple classloader locations, the
actual end resource may not be underneath. Therefore, preferably, use
"classpath*:
" with the same Ant-style pattern in
such a case, which will search all class path locations that contain
the root package.
A FileSystemResource
that is not attached
to a FileSystemApplicationContext
(that is, a
FileSystemApplicationContext
is not the actual
ResourceLoader
) will treat absolute vs.
relative paths as you would expect. Relative paths are relative to the
current working directory, while absolute paths are relative to the root
of the filesystem.
For backwards compatibility (historical) reasons however, this
changes when the FileSystemApplicationContext
is
the ResourceLoader
. The
FileSystemApplicationContext
simply forces all
attached FileSystemResource
instances to treat
all location paths as relative, whether they start with a leading slash
or not. In practice, this means the following are equivalent:
ApplicationContext ctx = new FileSystemXmlApplicationContext("conf/context.xml");
ApplicationContext ctx = new FileSystemXmlApplicationContext("/conf/context.xml");
As are the following: (Even though it would make sense for them to be different, as one case is relative and the other absolute.)
FileSystemXmlApplicationContext ctx = ...; ctx.getResource("some/resource/path/myTemplate.txt");
FileSystemXmlApplicationContext ctx = ...; ctx.getResource("/some/resource/path/myTemplate.txt");
In practice, if true absolute filesystem paths are needed, it is
better to forgo the use of absolute paths with
FileSystemResource
/
FileSystemXmlApplicationContext
, and just force
the use of a UrlResource
, by using the
file:
URL prefix.
// actual context type doesn't matter, the Resource
will always be UrlResource
ctx.getResource("file:/some/resource/path/myTemplate.txt");
// force this FileSystemXmlApplicationContext to load it's definition via a UrlResource
ApplicationContext ctx =
new FileSystemXmlApplicationContext("file:/conf/context.xml");
There are pros and cons for considering validation as business logic,
and Spring offers a design for validation (and data binding) that
does not exclude either one of them. Specifically validation should not be
tied to the web tier, should be easy to localize and it should be
possible to plug in any validator available. Considering the above, Spring
has come up with a Validator
interface that
is both basic and eminently usable in every layer of an application.
Data binding is useful for allowing user input to be dynamically
bound to the domain model of an application (or whatever objects you use
to process user input). Spring provides the so-called
DataBinder
to do exactly that. The
Validator
and the
DataBinder
make up the validation
package,
which is primarily used in but not limited to the MVC framework.
The BeanWrapper
is a fundamental concept in the
Spring Framework and is used in a lot of places. However, you probably
will not ever have the need to use the BeanWrapper
directly. Because this
is reference documentation however, we felt that some explanation might be
in order. We're explaining the BeanWrapper
in this chapter since if you were
going to use it at all, you would probably do so when trying to bind
data to objects, which is strongly related to the BeanWrapper
.
Spring uses PropertyEditors all over the place. The concept of a
PropertyEditor
is part of the JavaBeans specification. Just as the
BeanWrapper
, it's best to explain the use of PropertyEditors in this
chapter as well, since it's closely related to the BeanWrapper
and the
DataBinder
.
Spring's features a Validator
interface that you can
use to validate objects. The Validator
interface works using
an Errors
object so that while validating, validators can report
validation failures to the Errors
object.
Let's consider a small data object:
public class Person {
private String name;
private int age;
// the usual getters and setters...
}
We're going to provide validation behavior for the Person
class by implementing the following two methods of the
org.springframework.validation.Validator
interface:
supports(Class)
- Can this
Validator
validate instances of the supplied
Class
?
validate(Object, org.springframework.validation.Errors)
-
validates the given object and in case of validation errors, registers
those with the given Errors
object
Implementing a Validator
is fairly straightforward,
especially when you know of the ValidationUtils
helper class
that the Spring Framework also provides.
public class PersonValidator implements Validator {
/**
* This Validator
validates just Person
instances
*/
public boolean supports(Class clazz) {
return Person.class.equals(clazz);
}
public void validate(Object obj, Errors e) {
ValidationUtils.rejectIfEmpty(e, "name", "name.empty");
Person p = (Person) obj;
if (p.getAge() < 0) {
e.rejectValue("age", "negativevalue");
} else if (p.getAge() > 110) {
e.rejectValue("age", "too.darn.old");
}
}
}
As you can see, the static
rejectIfEmpty(..)
method on the ValidationUtils
class is used to reject the
'name'
property if it is null
or the empty string.
Have a look at the Javadoc for the ValidationUtils
class to see
what functionality it provides besides the example shown previously.
While it is certainly possible to implement a single
Validator
class to validate each of the nested objects
in a rich object, it may be better to encapsulate the validation logic for each nested
class of object in its own Validator
implementation. A
simple example of a 'rich' object would be a
Customer
that is composed of two String
properties (a first and second name) and a complex Address
object.
Address
objects may be used independently of
Customer
objects, and so a distinct
AddressValidator
has been implemented. If you want your
CustomerValidator
to reuse the logic contained within the
AddressValidator
class without recourse to copy-n-paste you can
dependency-inject or instantiate an AddressValidator
within your
CustomerValidator
, and use it like so:
public class CustomerValidator implements Validator {
private final Validator addressValidator;
public CustomerValidator(Validator addressValidator) {
if (addressValidator == null) {
throw new IllegalArgumentException("The supplied [Validator] is required and must not be null.");
}
if (!addressValidator.supports(Address.class)) {
throw new IllegalArgumentException(
"The supplied [Validator] must support the validation of [Address] instances.");
}
this.addressValidator = addressValidator;
}
/**
* This Validator
validates Customer
instances, and any subclasses of Customer
too
*/
public boolean supports(Class clazz) {
return Customer.class.isAssignableFrom(clazz);
}
public void validate(Object target, Errors errors) {
ValidationUtils.rejectIfEmptyOrWhitespace(errors, "firstName", "field.required");
ValidationUtils.rejectIfEmptyOrWhitespace(errors, "surname", "field.required");
Customer customer = (Customer) target;
try {
errors.pushNestedPath("address");
ValidationUtils.invokeValidator(this.addressValidator, customer.getAddress(), errors);
} finally {
errors.popNestedPath();
}
}
}
Validation errors are reported to the Errors
object passed to the validator. In case of Spring Web MVC you can use
<spring:bind/>
tag to inspect the error messages, but
of course you can also inspect the errors object yourself. More information about
the methods it offers can be found from the Javadoc.
We've talked about databinding and validation. Outputting messages corresponding to
validation errors is the last thing we need to discuss. In the example we've shown
above, we rejected the name
and the age
field.
If we're going to output the error messages by using a MessageSource
,
we will do so using the error code we've given when rejecting the field ('name' and 'age'
in this case). When you call (either directly, or indirectly, using for example the
ValidationUtils
class) rejectValue
or one of
the other reject
methods from the Errors
interface, the underlying implementation will not only register the code you've
passed in, but also a number of additional error codes. What error codes it registers
is determined by the MessageCodesResolver
that is used.
By default, the DefaultMessageCodesResolver
is used, which for example
not only registers a message with the code you gave, but also messages that include the
field name you passed to the reject method. So in case you reject a field using
rejectValue("age", "too.darn.old")
, apart from the
too.darn.old
code, Spring will also register
too.darn.old.age
and too.darn.old.age.int
(so the first will include the field name and the second will include the type of the
field); this is done as a convenience to aid developers in targeting error
messages and suchlike.
More information on the MessageCodesResolver
and the default
strategy can be found online with the Javadocs for
MessageCodesResolver
and
DefaultMessageCodesResolver
respectively.
The org.springframework.beans
package adheres to
the JavaBeans standard provided by Sun. A JavaBean is simply a class with
a default no-argument constructor, which follows a naming convention
where (by way of an example) a property named bingoMadness
would have a setter
method setBingoMadness(..)
and a getter method getBingoMadness()
.
For more information about JavaBeans and the specification, please refer
to Sun's website ( java.sun.com/products/javabeans).
One quite important class in the beans package is the
BeanWrapper
interface and its corresponding
implementation (BeanWrapperImpl
). As quoted from the
Javadoc, the BeanWrapper
offers functionality to set and get property
values (individually or in bulk), get property descriptors, and to query
properties to determine if they are readable or writable. Also, the
BeanWrapper
offers support for nested properties, enabling the setting of
properties on sub-properties to an unlimited depth. Then, the BeanWrapper
supports the ability to add standard JavaBeans
PropertyChangeListeners
and
VetoableChangeListeners
, without the need for
supporting code in the target class. Last but not least, the BeanWrapper
provides support for the setting of indexed properties. The BeanWrapper
usually isn't used by application code directly, but by the
DataBinder
and the
BeanFactory
.
The way the BeanWrapper
works is partly indicated by its name:
it wraps a bean to perform actions on that bean, like
setting and retrieving properties.
Setting and getting properties is done using the
setPropertyValue(s)
and
getPropertyValue(s)
methods that both come with a
couple of overloaded variants. They're all described in more detail in
the Javadoc Spring comes with. What's important to know is that there
are a couple of conventions for indicating properties of an object. A
couple of examples:
Table 5.1. Examples of properties
Expression | Explanation |
---|---|
name | Indicates the property name
corresponding to the methods getName() or
isName() and
setName(..) |
account.name | Indicates the nested property name
of the property account corresponding e.g.
to the methods getAccount().setName() or
getAccount().getName() |
account[2] | Indicates the third element of the
indexed property account . Indexed
properties can be of type array ,
list or other naturally
ordered collection |
account[COMPANYNAME] | Indicates the value of the map entry indexed by the key
COMPANYNAME of the Map property
account |
Below you'll find some examples of working with the BeanWrapper
to
get and set properties.
(This next section is not vitally important to you if you're not
planning to work with the BeanWrapper
directly. If you're
just using the DataBinder
and the
BeanFactory
and their out-of-the-box implementation, you
should skip ahead to the section about
PropertyEditors
.)
Consider the following two classes:
public class Company { private String name; private Employee managingDirector; public String getName() { return this.name; } public void setName(String name) { this.name = name; } public Employee getManagingDirector() { return this.managingDirector; } public void setManagingDirector(Employee managingDirector) { this.managingDirector = managingDirector; } }
public class Employee { private String name; private float salary; public String getName() { return this.name; } public void setName(String name) { this.name = name; } public float getSalary() { return salary; } public void setSalary(float salary) { this.salary = salary; } }
The following code snippets show some examples of how to retrieve
and manipulate some of the properties of instantiated
Companies
and Employees
:
BeanWrapper company = BeanWrapperImpl(new Company()); // setting the company name.. company.setPropertyValue("name", "Some Company Inc."); // ... can also be done like this: PropertyValue value = new PropertyValue("name", "Some Company Inc."); company.setPropertyValue(value); // ok, let's create the director and tie it to the company: BeanWrapper jim = BeanWrapperImpl(new Employee()); jim.setPropertyValue("name", "Jim Stravinsky"); company.setPropertyValue("managingDirector", jim.getWrappedInstance()); // retrieving the salary of the managingDirector through the company Float salary = (Float) company.getPropertyValue("managingDirector.salary");
Spring heavily uses the concept of PropertyEditors
to effect the conversion
between an Object
and a String
. If you think about it,
it sometimes might be handy to be able to represent properties in a different way than the object itself.
For example, a Date
can be represented in a human readable way (as the
String
'2007-14-09
'), while we're still able to convert the
human readable form back to the original date (or even better: convert any date entered in a human readable
form, back to Date
objects). This behavior can be achieved by
registering custom editors, of type java.beans.PropertyEditor
.
Registering custom editors on a BeanWrapper
or alternately in a specific IoC
container as mentioned in the previous chapter, gives it the knowledge of how to convert properties to the
desired type. Read more about PropertyEditors
in the Javadoc of the
java.beans
package provided by Sun.
A couple of examples where property editing is used in Spring:
setting properties on beans is done
using PropertyEditors
. When mentioning
java.lang.String
as the value of a property of
some bean you're declaring in XML file, Spring will (if the setter
of the corresponding property has a Class
-parameter) use the
ClassEditor
to try to resolve the parameter to
a Class
object.
parsing HTTP request parameters in
Spring's MVC framework is done using all kinds of PropertyEditors
that you can manually bind in all subclasses of the
CommandController
.
Spring has a number of built-in PropertyEditors
to make life easy.
Each of those is listed below and they are all located in the
org.springframework.beans.propertyeditors
package. Most, but not all (as indicated below),
are registered by default by BeanWrapperImpl
. Where the property editor is configurable
in some fashion, you can of course still register your own variant to override the default one:
Table 5.2. Built-in PropertyEditors
Class | Explanation |
---|---|
ByteArrayPropertyEditor | Editor for byte arrays. Strings will simply be
converted to their corresponding byte representations.
Registered by default by BeanWrapperImpl . |
ClassEditor | Parses Strings representing classes to actual classes
and the other way around. When a class is not found, an
IllegalArgumentException is thrown. Registered by default by
BeanWrapperImpl . |
CustomBooleanEditor | Customizable property editor for Boolean properties.
Registered by default by BeanWrapperImpl , but, can be
overridden by registering custom instance of it as custom
editor. |
CustomCollectionEditor | Property editor for Collections, converting any source
Collection to a given target Collection type. |
CustomDateEditor | Customizable property editor for java.util.Date, supporting a custom DateFormat. NOT registered by default. Must be user registered as needed with appropriate format. |
CustomNumberEditor | Customizable property editor for any Number subclass
like Integer , Long ,
Float , Double . Registered
by default by BeanWrapperImpl , but can be
overridden by registering custom instance of it as a custom editor. |
FileEditor | Capable of resolving Strings to
java.io.File objects. Registered by default by
BeanWrapperImpl . |
InputStreamEditor | One-way property editor, capable of taking a text
string and producing (via an intermediate ResourceEditor and
Resource ) an
InputStream , so InputStream
properties may be directly set as Strings. Note that the default usage
will not close the InputStream for
you! Registered by default by BeanWrapperImpl . |
LocaleEditor | Capable of resolving Strings to
Locale objects and vice versa (the String
format is [language]_[country]_[variant], which is the same
thing the toString() method of Locale provides). Registered by
default by BeanWrapperImpl . |
PatternEditor | Capable of resolving Strings to JDK 1.5
Pattern objects and vice versa. |
PropertiesEditor | Capable of converting Strings (formatted using the
format as defined in the Javadoc for the java.lang.Properties
class) to Properties objects. Registered by
default by BeanWrapperImpl . |
StringTrimmerEditor | Property editor that trims Strings. Optionally allows
transforming an empty string into a null value. NOT
registered by default; must be user registered as needed. |
URLEditor | Capable of resolving a String representation of a URL
to an actual URL object. Registered by
default by BeanWrapperImpl . |
Spring uses the java.beans.PropertyEditorManager
to set
the search path for property editors that might be needed. The search path also includes
sun.bean.editors
, which includes
PropertyEditor
implementations for types such as
Font
, Color
, and most of the primitive types.
Note also that the standard JavaBeans infrastructure will automatically discover
PropertyEditor
classes (without you having to register them
explicitly) if they are in the same package as the class they handle, and have the same name
as that class, with 'Editor'
appended; for example, one could have the
following class and package structure, which would be sufficient for the
FooEditor
class to be recognized and used as the
PropertyEditor
for Foo
-typed
properties.
com
chank
pop
Foo
FooEditor // the PropertyEditor
for the Foo
class
Note that you can also use the standard BeanInfo
JavaBeans
mechanism here as well (described
in not-amazing-detail here).
Find below an example of using the BeanInfo
mechanism for
explicitly registering one or more PropertyEditor
instances
with the properties of an associated class.
com
chank
pop
Foo
FooBeanInfo // the BeanInfo
for the Foo
class
Here is the Java source code for the referenced FooBeanInfo
class. This
would associate a CustomNumberEditor
with the age
property of the Foo
class.
public class FooBeanInfo extends SimpleBeanInfo { public PropertyDescriptor[] getPropertyDescriptors() { try { final PropertyEditor numberPE = new CustomNumberEditor(Integer.class, true); PropertyDescriptor ageDescriptor = new PropertyDescriptor("age", Foo.class) { public PropertyEditor createPropertyEditor(Object bean) { return numberPE; }; }; return new PropertyDescriptor[] { ageDescriptor }; } catch (IntrospectionException ex) { throw new Error(ex.toString()); } } }
When setting bean properties as a string value, a Spring IoC container
ultimately uses standard JavaBeans PropertyEditors
to convert these
Strings to the complex type of the property. Spring pre-registers a number
of custom PropertyEditors
(for example, to convert a classname expressed
as a string into a real Class
object). Additionally, Java's standard
JavaBeans PropertyEditor
lookup mechanism allows a
PropertyEditor
for a class simply to be named appropriately and
placed in the same package as the class it provides support for, to be found automatically.
If there is a need to register other custom PropertyEditors
, there
are several mechanisms available. The most manual approach, which is not normally convenient or
recommended, is to simply use the registerCustomEditor()
method of the
ConfigurableBeanFactory
interface, assuming you have a
BeanFactory
reference. Another, slightly more convenient, mechanism is to use
a special bean factory post-processor called CustomEditorConfigurer
.
Although bean factory post-processors can be used with BeanFactory
implementations, the CustomEditorConfigurer
has a nested property setup, so it is
strongly recommended that it is used with the ApplicationContext
, where
it may be deployed in similar fashion to any other bean, and automatically detected and applied.
Note that all bean factories and application contexts automatically use a number of built-in property
editors, through their use of something called a BeanWrapper
to handle
property conversions. The standard property editors that the BeanWrapper
registers are listed in the previous section. Additionally,
ApplicationContexts
also override or add an additional number of editors
to handle resource lookups in a manner appropriate to the specific application context type.
Standard JavaBeans PropertyEditor
instances are used to convert
property values expressed as strings to the actual complex type of the property.
CustomEditorConfigurer
, a bean factory post-processor, may be used to conveniently
add support for additional PropertyEditor
instances to an
ApplicationContext
.
Consider a user class ExoticType
, and another class
DependsOnExoticType
which needs ExoticType
set as a property:
package example; public class ExoticType { private String name; public ExoticType(String name) { this.name = name; } } public class DependsOnExoticType { private ExoticType type; public void setType(ExoticType type) { this.type = type; } }
When things are properly set up, we want to be able to assign the type property as a string, which a
PropertyEditor
will behind the scenes convert into an actual
ExoticType
instance:
<bean id="sample" class="example.DependsOnExoticType"> <property name="type" value="aNameForExoticType"/> </bean>
The PropertyEditor
implementation could look similar to this:
// converts string representation to ExoticType
object
package example;
public class ExoticTypeEditor extends PropertyEditorSupport {
private String format;
public void setFormat(String format) {
this.format = format;
}
public void setAsText(String text) {
if (format != null && format.equals("upperCase")) {
text = text.toUpperCase();
}
ExoticType type = new ExoticType(text);
setValue(type);
}
}
Finally, we use CustomEditorConfigurer
to register the new
PropertyEditor
with the ApplicationContext
,
which will then be able to use it as needed:
<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer"> <property name="customEditors"> <map> <entry key="example.ExoticType"> <bean class="example.ExoticTypeEditor"> <property name="format" value="upperCase"/> </bean> </entry> </map> </property> </bean>
Another mechanism for registering property editors with the Spring container is to create and use
a PropertyEditorRegistrar
. This interface is particularly useful when you
need to use the same set of property editors in several different situations: write a corresponding
registrar and reuse that in each case. PropertyEditorRegistrars
work in conjunction
with an interface called PropertyEditorRegistry
, an interface
that is implemented by the Spring BeanWrapper
(and
DataBinder
). PropertyEditorRegistrars
are particularly
convenient when used in conjunction with the CustomEditorConfigurer
(introduced here), which exposes a
property called setPropertyEditorRegistrars(..)
:
PropertyEditorRegistrars
added to a CustomEditorConfigurer
in this
fashion can easily be shared with DataBinder
and Spring MVC
Controllers
. Furthermore, it avoids the need for synchronization on custom
editors: a PropertyEditorRegistrar
is expected to create fresh
PropertyEditor
instances for each bean creation attempt.
Using a PropertyEditorRegistrar
is perhaps best illustrated with an
example. First off, you need to create your own PropertyEditorRegistrar
implementation:
package com.foo.editors.spring;
public final class CustomPropertyEditorRegistrar implements PropertyEditorRegistrar {
public void registerCustomEditors(PropertyEditorRegistry registry) {
// it is expected that new PropertyEditor
instances are created
registry.registerCustomEditor(ExoticType.class, new ExoticTypeEditor());
// you could register as many custom property editors as are required here...
}
}
See also the org.springframework.beans.support.ResourceEditorRegistrar
for an
example PropertyEditorRegistrar
implementation. Notice how in its
implementation of the registerCustomEditors(..)
method it creates new instances
of each property editor.
Next we configure a CustomEditorConfigurer
and inject an
instance of our CustomPropertyEditorRegistrar
into it:
<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer"> <property name="propertyEditorRegistrars"> <list> <ref bean="customPropertyEditorRegistrar"/> </list> </property> </bean> <bean id="customPropertyEditorRegistrar" class="com.foo.editors.spring.CustomPropertyEditorRegistrar"/>
Finally, and in a bit of a departure from the focus of this chapter, for those of you using
Spring's MVC web framework, using PropertyEditorRegistrars
in conjunction with data-binding Controllers
(such as
SimpleFormController
) can be very convenient. Find below an example of using a
PropertyEditorRegistrar
in the implementation of an initBinder(..)
method:
public final class RegisterUserController extends SimpleFormController {
private final PropertyEditorRegistrar customPropertyEditorRegistrar;
public RegisterUserController(PropertyEditorRegistrar propertyEditorRegistrar) {
this.customPropertyEditorRegistrar = propertyEditorRegistrar;
}
protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) throws Exception {
this.customPropertyEditorRegistrar.registerCustomEditors(binder);
}
// other methods to do with registering a User
}
This style of PropertyEditor
registration can lead to concise code (the
implementation of initBinder(..)
is just one line long!), and allows common
PropertyEditor
registration code to be encapsulated in a class and then
shared amongst as many Controllers
as needed.
Aspect-Oriented Programming (AOP) complements Object-Oriented Programming (OOP) by providing another way of thinking about program structure. The key unit of modularity in OOP is the class, whereas in AOP the unit of modularity is the aspect. Aspects enable the modularization of concerns such as transaction management that cut across multiple types and objects. (Such concerns are often termed crosscutting concerns in AOP literature.)
One of the key components of Spring is the AOP framework. While the Spring IoC container does not depend on AOP, meaning you do not need to use AOP if you don't want to, AOP complements Spring IoC to provide a very capable middleware solution.
AOP is used in the Spring Framework to...
... provide declarative enterprise services, especially as a replacement for EJB declarative services. The most important such service is declarative transaction management.
... allow users to implement custom aspects, complementing their use of OOP with AOP.
If you are interested only in generic declarative services
or other pre-packaged declarative middleware services such as pooling, you
do not need to work directly with Spring AOP, and can skip most of this
chapter.
Let us begin by defining some central AOP concepts and terminology. These terms are not Spring-specific... unfortunately, AOP terminology is not particularly intuitive; however, it would be even more confusing if Spring used its own terminology.
Aspect: a modularization of a concern
that cuts across multiple classes. Transaction management is a good
example of a crosscutting concern in J2EE applications. In Spring
AOP, aspects are implemented using regular classes (the schema-based approach) or regular
classes annotated with the @Aspect
annotation (the @AspectJ
style).
Join point: a point during the execution of a program, such as the execution of a method or the handling of an exception. In Spring AOP, a join point always represents a method execution.
Advice: action taken by an aspect at a particular join point. Different types of advice include "around," "before" and "after" advice. (Advice types are discussed below.) Many AOP frameworks, including Spring, model an advice as an interceptor, maintaining a chain of interceptors around the join point.
Pointcut: a predicate that matches join points. Advice is associated with a pointcut expression and runs at any join point matched by the pointcut (for example, the execution of a method with a certain name). The concept of join points as matched by pointcut expressions is central to AOP, and Spring uses the AspectJ pointcut expression language by default.
Introduction: declaring additional
methods or fields on behalf of a type. Spring AOP allows you to
introduce new interfaces (and a corresponding implementation) to any
advised object. For example, you could use an introduction to make a
bean implement an IsModified
interface, to simplify caching. (An introduction is known as an
inter-type declaration in the AspectJ community.)
Target object: object being advised by one or more aspects. Also referred to as the advised object. Since Spring AOP is implemented using runtime proxies, this object will always be a proxied object.
AOP proxy: an object created by the AOP framework in order to implement the aspect contracts (advise method executions and so on). In the Spring Framework, an AOP proxy will be a JDK dynamic proxy or a CGLIB proxy.
Weaving: linking aspects with other application types or objects to create an advised object. This can be done at compile time (using the AspectJ compiler, for example), load time, or at runtime. Spring AOP, like other pure Java AOP frameworks, performs weaving at runtime.
Types of advice:
Before advice: Advice that executes before a join point, but which does not have the ability to prevent execution flow proceeding to the join point (unless it throws an exception).
After returning advice: Advice to be executed after a join point completes normally: for example, if a method returns without throwing an exception.
After throwing advice: Advice to be executed if a method exits by throwing an exception.
After (finally) advice: Advice to be executed regardless of the means by which a join point exits (normal or exceptional return).
Around advice: Advice that surrounds a join point such as a method invocation. This is the most powerful kind of advice. Around advice can perform custom behavior before and after the method invocation. It is also responsible for choosing whether to proceed to the join point or to shortcut the advised method execution by returning its own return value or throwing an exception.
Around advice is the most general kind of advice. Since Spring
AOP, like AspectJ, provides a full range of advice types, we recommend
that you use the least powerful advice type that can implement the
required behavior. For example, if you need only to update a cache with
the return value of a method, you are better off implementing an after
returning advice than an around advice, although an around advice can
accomplish the same thing. Using the most specific advice type provides
a simpler programming model with less potential for errors. For example,
you do not need to invoke the proceed()
method
on the JoinPoint
used for around advice,
and hence cannot fail to invoke it.
In Spring 2.0, all advice parameters are statically typed, so that
you work with advice parameters of the appropriate type (the type of the
return value from a method execution for example) rather than
Object
arrays.
The concept of join points, matched by pointcuts, is the key to AOP which distinguishes it from older technologies offering only interception. Pointcuts enable advice to be targeted independently of the Object-Oriented hierarchy. For example, an around advice providing declarative transaction management can be applied to a set of methods spanning multiple objects (such as all business operations in the service layer).
Spring AOP is implemented in pure Java. There is no need for a special compilation process. Spring AOP does not need to control the class loader hierarchy, and is thus suitable for use in a J2EE web container or application server.
Spring AOP currently supports only method execution join points (advising the execution of methods on Spring beans). Field interception is not implemented, although support for field interception could be added without breaking the core Spring AOP APIs. If you need to advise field access and update join points, consider a language such as AspectJ.
Spring AOP's approach to AOP differs from that of most other AOP frameworks. The aim is not to provide the most complete AOP implementation (although Spring AOP is quite capable); it is rather to provide a close integration between AOP implementation and Spring IoC to help solve common problems in enterprise applications.
Thus, for example, the Spring Framework's AOP functionality is normally used in conjunction with the Spring IoC container. Aspects are configured using normal bean definition syntax (although this allows powerful "autoproxying" capabilities): this is a crucial difference from other AOP implementations. There are some things you cannot do easily or efficiently with Spring AOP, such as advise very fine-grained objects (such as domain objects typically): AspectJ is the best choice in such cases. However, our experience is that Spring AOP provides an excellent solution to most problems in J2EE applications that are amenable to AOP.
Spring AOP will never strive to compete with AspectJ to provide a comprehensive AOP solution. We believe that both proxy-based frameworks like Spring AOP and full-blown frameworks such as AspectJ are valuable, and that they are complementary, rather than in competition. Spring 2.0 seamlessly integrates Spring AOP and IoC with AspectJ, to enable all uses of AOP to be catered for within a consistent Spring-based application architecture. This integration does not affect the Spring AOP API or the AOP Alliance API: Spring AOP remains backward-compatible. See the following chapter for a discussion of the Spring AOP APIs.
![]() | Note |
---|---|
One of the central tenets of the Spring Framework is that of non-invasiveness; this is the idea that you should not be forced to introduce framework-specific classes and interfaces into your business/domain model. However, in some places the Spring Framework does give you the option to introduce Spring Framework-specific dependencies into your codebase: the rationale in giving you such options is because in certain scenarios it might be just plain easier to read or code some specific piece of functionality in such a way. The Spring Framework (almost) always offers you the choice though: you have the freedom to make an informed decision as to which option best suits your particular use case or scenario. One such choice that is relevant to this chapter is that of which AOP framework (and which AOP style) to choose. You have the choice of AspectJ and/or Spring AOP, and you also have the choice of either the @AspectJ annotation-style approach or the Spring XML configuration-style approach. The fact that this chapter chooses to introduce the @AspectJ-style approach first should not be taken as an indication that the Spring team favors the @AspectJ annotation-style approach over the Spring XML configuration-style. See the section entitled Section 6.4, “Choosing which AOP declaration style to use” for a fuller discussion of the whys and wherefores of each style. |
Spring AOP defaults to using standard J2SE dynamic proxies for AOP proxies. This enables any interface (or set of interfaces) to be proxied.
Spring AOP can also use CGLIB proxies. This is necessary to proxy classes, rather than interfaces. CGLIB is used by default if a business object does not implement an interface. As it is good practice to program to interfaces rather than classes, business classes normally will implement one or more business interfaces. It is possible to force the use of CGLIB, in those (hopefully rare) cases where you need to advise a method that is not declared on an interface, or where you need to pass a proxied object to a method as a concrete type.
It is important to grasp the fact that Spring AOP is proxy-based. See the section entitled Section 6.6.1, “Understanding AOP proxies” for a thorough examination of exactly what this implementation detail actually means.
@AspectJ refers to a style of declaring aspects as regular Java classes annotated with Java 5 annotations. The @AspectJ style was introduced by the AspectJ project as part of the AspectJ 5 release. Spring 2.0 interprets the same annotations as AspectJ 5, using a library supplied by AspectJ for pointcut parsing and matching. The AOP runtime is still pure Spring AOP though, and there is no dependency on the AspectJ compiler or weaver.
Using the AspectJ compiler and weaver enables use of the
full AspectJ language, and is discussed in Section 6.8, “Using AspectJ with Spring applications”.
To use @AspectJ aspects in a Spring configuration you need to enable Spring support for configuring Spring AOP based on @AspectJ aspects, and autoproxying beans based on whether or not they are advised by those aspects. By autoproxying we mean that if Spring determines that a bean is advised by one or more aspects, it will automatically generate a proxy for that bean to intercept method invocations and ensure that advice is executed as needed.
The @AspectJ support is enabled by including the following element inside your spring configuration:
<aop:aspectj-autoproxy/>
This assumes that you are using schema support as described in
Appendix A, XML Schema-based configuration. See Section A.2.7, “The aop
schema” for how to import the tags in
the aop namespace.
If you are using the DTD, it is still possible to enable @AspectJ support by adding the following definition to your application context:
<bean class="org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator" />
You will also need two AspectJ libraries on the classpath of your
application: aspectjweaver.jar
and aspectjrt.jar
. These
libraries are available in the 'lib'
directory of an AspectJ installation
(version 1.5.1 or later required), or in the 'lib/aspectj'
directory of the
Spring-with-dependencies distribution.
With the @AspectJ support enabled, any bean defined in your
application context with a class that is an @AspectJ aspect (has the
@Aspect
annotation) will be automatically
detected by Spring and used to configure Spring AOP. The following
example shows the minimal definition required for a not-very-useful
aspect:
A regular bean definition in the application context, pointing to
a bean class that has the @Aspect
annotation:
<bean id="myAspect" class="org.xyz.NotVeryUsefulAspect">
<!-- configure properties of aspect here as normal -->
</bean>
And the NotVeryUsefulAspect
class
definition, annotated with
org.aspectj.lang.annotation.Aspect
annotation;
package org.xyz; import org.aspectj.lang.annotation.Aspect; @Aspect public class NotVeryUsefulAspect { }
Aspects (classes annotated with
@Aspect
) may have methods and fields just
like any other class. They may also contain pointcut, advice, and
introduction (inter-type) declarations.
![]() | Advising aspects |
---|---|
In Spring AOP, it is not possible to have aspects themselves be the target of advice from other aspects. The @Aspect annotation on a class marks it as an aspect, and hence excludes it from auto-proxying. |
Recall that pointcuts determine join points of interest, and thus
enable us to control when advice executes. Spring AOP only
supports method execution join points for Spring beans, so
you can think of a pointcut as matching the execution of methods on
Spring beans. A pointcut declaration has two parts: a signature
comprising a name and any parameters, and a pointcut expression that
determines exactly which method executions we are
interested in. In the @AspectJ annotation-style of AOP, a pointcut
signature is provided by a regular method definition, and the pointcut
expression is indicated using the
@Pointcut
annotation (the method serving
as the pointcut signature must have a
void
return type).
An example will help make this distinction between a pointcut
signature and a pointcut expression clear. The following example defines
a pointcut named 'anyOldTransfer'
that will match the
execution of any method named 'transfer'
:
@Pointcut("execution(* transfer(..))")// the pointcut expression private void anyOldTransfer() {}// the pointcut signature
The pointcut expression that forms the value of the
@Pointcut
annotation is a regular AspectJ
5 pointcut expression. For a full discussion of AspectJ's pointcut
language, see the AspectJ
Programming Guide (and for Java 5 based extensions, the AspectJ
5 Developers Notebook) or one of the books on AspectJ such as
“Eclipse AspectJ” by Colyer et. al. or “AspectJ in
Action” by Ramnivas Laddad.
Spring AOP supports the following AspectJ pointcut designators (PCD) for use in pointcut expressions:
execution - for matching method execution join points, this is the primary pointcut designator you will use when working with Spring AOP
within - limits matching to join points within certain types (simply the execution of a method declared within a matching type when using Spring AOP)
this - limits matching to join points (the execution of methods when using Spring AOP) where the bean reference (Spring AOP proxy) is an instance of the given type
target - limits matching to join points (the execution of methods when using Spring AOP) where the target object (application object being proxied) is an instance of the given type
args - limits matching to join points (the execution of methods when using Spring AOP) where the arguments are instances of the given types
@target
- limits matching to join points (the execution of methods when
using Spring AOP) where the class of the executing object has an
annotation of the given type
@args
-
limits matching to join points (the execution of methods when
using Spring AOP) where the runtime type of the actual arguments
passed have annotations of the given type(s)
@within
- limits matching to join points within types that have the given
annotation (the execution of methods declared in types with the
given annotation when using Spring AOP)
@annotation - limits matching to join points where the subject of the join point (method being executed in Spring AOP) has the given annotation
Because Spring AOP limits matching to only method execution
join points, the discussion of the pointcut designators above gives a
narrower definition than you will find in the AspectJ programming
guide. In addition, AspectJ itself has type-based semantics and at an
execution join point both 'this
' and
'target
' refer to the same object - the object
executing the method. Spring AOP is a proxy-based system and
differentiates between the proxy object itself (bound to
'this
') and the target object behind the proxy
(bound to 'target
').
![]() | Note |
---|---|
Due to the proxy-based nature of Spring's AOP framework, protected methods are by definition not intercepted, neither for JDK proxies (where this isn't applicable) nor for CGLIB proxies (where this is technically possible but not recommendable for AOP purposes). As a consequence, any given pointcut will be matched against public methods only! If your interception needs include protected/private methods or even constructors, consider the use of Spring-driven native AspectJ weaving instead of Spring's proxy-based AOP framework. This constitutes a different mode of AOP usage with different characteristics, so be sure to make yourself familiar with weaving first before making a decision. |
Spring AOP also supports an additional PCD named
'bean
'. This PCD allows you to limit the matching
of join points to a particular named Spring bean, or to a set of named
Spring beans (when using wildcards). The 'bean
' PCD
has the following form:
bean(idOrNameOfBean)
The 'idOrNameOfBean
' token can be the name of
any Spring bean: limited wildcard support using the
'*
' character is provided, so if you establish
some naming conventions for your Spring beans you can quite easily
write a 'bean
' PCD expression to pick them out. As
is the case with other pointcut designators, the
'bean
' PCD can be &&'ed, ||'ed, and !
(negated) too.
![]() | Note |
---|---|
Please note that the ' The ' |
Pointcut expressions can be combined using '&&', '||'
and '!'. It is also possible to refer to pointcut expressions by name.
The following example shows three pointcut expressions:
anyPublicOperation
(which matches if a method
execution join point represents the execution of any public method);
inTrading
(which matches if a method execution is
in the trading module), and tradingOperation
(which
matches if a method execution represents any public method in the
trading module).
@Pointcut("execution(public * *(..))") private void anyPublicOperation() {} @Pointcut("within(com.xyz.someapp.trading..*)") private void inTrading() {} @Pointcut("anyPublicOperation() && inTrading()") private void tradingOperation() {}
It is a best practice to build more complex pointcut expressions out of smaller named components as shown above. When referring to pointcuts by name, normal Java visibility rules apply (you can see private pointcuts in the same type, protected pointcuts in the hierarchy, public pointcuts anywhere and so on). Visibility does not affect pointcut matching.
When working with enterprise applications, you often want to refer to modules of the application and particular sets of operations from within several aspects. We recommend defining a "SystemArchitecture" aspect that captures common pointcut expressions for this purpose. A typical such aspect would look as follows:
package com.xyz.someapp; import org.aspectj.lang.annotation.Aspect; import org.aspectj.lang.annotation.Pointcut; @Aspect public class SystemArchitecture { /** * A join point is in the web layer if the method is defined * in a type in the com.xyz.someapp.web package or any sub-package * under that. */ @Pointcut("within(com.xyz.someapp.web..*)") public void inWebLayer() {} /** * A join point is in the service layer if the method is defined * in a type in thecom.xyz.someapp.service
package or any sub-package * under that. */ @Pointcut("within(com.xyz.someapp.service..*)") public void inServiceLayer() {} /** * A join point is in the data access layer if the method is defined * in a type in thecom.xyz.someapp.dao
package or any sub-package * under that. */ @Pointcut("within(com.xyz.someapp.dao..*)") public void inDataAccessLayer() {} /** * A business service is the execution of any method defined on a service * interface. This definition assumes that interfaces are placed in the * "service" package, and that implementation types are in sub-packages. * * If you group service interfaces by functional area (for example, * in packagescom.xyz.someapp.abc.service
andcom.xyz.def.service
) then * the pointcut expression "execution(* com.xyz.someapp..service.*.*(..))
" * could be used instead. * * Alternatively, you can write the expression using the 'bean
' * PCD, like so "bean(*Service)
". (This assumes that you have * named your Spring service beans in a consistent fashion.) */ @Pointcut("execution(* com.xyz.someapp.service.*.*(..))") public void businessService() {} /** * A data access operation is the execution of any method defined on a * dao interface. This definition assumes that interfaces are placed in the * "dao
" package, and that implementation types are in sub-packages. */ @Pointcut("execution(* com.xyz.someapp.dao.*.*(..))") public void dataAccessOperation() {} }
The pointcuts defined in such an aspect can be referred to anywhere that you need a pointcut expression. For example, to make the service layer transactional, you could write:
<aop:config> <aop:advisor pointcut="com.xyz.someapp.SystemArchitecture.businessService()" advice-ref="tx-advice"/> </aop:config> <tx:advice id="tx-advice"> <tx:attributes> <tx:method name="*" propagation="REQUIRED"/> </tx:attributes> </tx:advice>
The <aop:config>
and
<aop:advisor>
elements are discussed in Section 6.3, “Schema-based AOP support”. The transaction elements are discussed in
Chapter 9, Transaction management.
Spring AOP users are likely to use the
execution
pointcut designator the most often. The
format of an execution expression is:
execution(modifiers-pattern? ret-type-pattern declaring-type-pattern? name-pattern(param-pattern) throws-pattern?)
All parts except the returning type pattern (ret-type-pattern in
the snippet above), name pattern, and parameters pattern are optional.
The returning type pattern determines what the return type of the
method must be in order for a join point to be matched. Most
frequently you will use *
as the returning type
pattern, which matches any return type. A fully-qualified type name
will match only when the method returns the given type. The name
pattern matches the method name. You can use the *
wildcard as all or part of a name pattern. The parameters pattern is
slightly more complex: ()
matches a method that
takes no parameters, whereas (..)
matches any
number of parameters (zero or more). The pattern
(*)
matches a method taking one parameter of any
type, (*,String)
matches a method taking two
parameters, the first can be of any type, the second must be a String.
Consult the
Language Semantics section of the AspectJ Programming Guide
for more information.
Some examples of common pointcut expressions are given below.
the execution of any public method:
execution(public * *(..))
the execution of any method with a name beginning with "set":
execution(* set*(..))
the execution of any method defined by the
AccountService
interface:
execution(* com.xyz.service.AccountService.*(..))
the execution of any method defined in the service package:
execution(* com.xyz.service.*.*(..))
the execution of any method defined in the service package or a sub-package:
execution(* com.xyz.service..*.*(..))
any join point (method execution only in Spring AOP) within the service package:
within(com.xyz.service.*)
any join point (method execution only in Spring AOP) within the service package or a sub-package:
within(com.xyz.service..*)
any join point (method execution only in Spring AOP) where
the proxy implements the
AccountService
interface:
this(com.xyz.service.AccountService)
'this' is more commonly used in a binding form :-
see the following section on advice for how to make the proxy
object available in the advice body.
any join point (method execution only in Spring AOP) where
the target object implements the
AccountService
interface:
target(com.xyz.service.AccountService)
'target' is more commonly used in a binding form :-
see the following section on advice for how to make the target
object available in the advice body.
any join point (method execution only in Spring AOP) which
takes a single parameter, and where the argument passed at runtime
is Serializable
:
args(java.io.Serializable)
'args' is more commonly used in a binding form :- see the following section on advice for how to make the method arguments available in the advice body.
Note that the pointcut given in this example is different to
execution(* *(java.io.Serializable))
: the args
version matches if the argument passed at runtime is Serializable,
the execution version matches if the method signature declares a
single parameter of type
Serializable
.
any join point (method execution only in Spring AOP) where
the target object has an
@Transactional
annotation:
@target(org.springframework.transaction.annotation.Transactional)
'@target' can also be used in a binding form :- see
the following section on advice for how to make the annotation
object available in the advice body.
any join point (method execution only in Spring AOP) where
the declared type of the target object has an
@Transactional
annotation:
@within(org.springframework.transaction.annotation.Transactional)
'@within' can also be used in a binding form :- see
the following section on advice for how to make the annotation
object available in the advice body.
any join point (method execution only in Spring AOP) where
the executing method has an
@Transactional
annotation:
@annotation(org.springframework.transaction.annotation.Transactional)
'@annotation' can also be used in a binding form :-
see the following section on advice for how to make the annotation
object available in the advice body.
any join point (method execution only in Spring AOP) which
takes a single parameter, and where the runtime type of the
argument passed has the @Classified
annotation:
@args(com.xyz.security.Classified)
'@args' can also be used in a binding form :- see
the following section on advice for how to make the annotation
object(s) available in the advice body.
any join point (method execution only in Spring AOP) on a
Spring bean named 'tradeService
':
bean(tradeService)
any join point (method execution only in Spring AOP) on
Spring beans having names that match the wildcard expression
'*Service
':
bean(*Service)
Advice is associated with a pointcut expression, and runs before, after, or around method executions matched by the pointcut. The pointcut expression may be either a simple reference to a named pointcut, or a pointcut expression declared in place.
Before advice is declared in an aspect using the
@Before
annotation:
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
@Aspect
public class BeforeExample {
@Before("com.xyz.myapp.SystemArchitecture.dataAccessOperation()")
public void doAccessCheck() {
// ...
}
}
If using an in-place pointcut expression we could rewrite the above example as:
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
@Aspect
public class BeforeExample {
@Before("execution(* com.xyz.myapp.dao.*.*(..))")
public void doAccessCheck() {
// ...
}
}
After returning advice runs when a matched method execution
returns normally. It is declared using the
@AfterReturning
annotation:
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterReturning;
@Aspect
public class AfterReturningExample {
@AfterReturning("com.xyz.myapp.SystemArchitecture.dataAccessOperation()")
public void doAccessCheck() {
// ...
}
}
Note: it is of course possible to have multiple advice declarations, and other members as well, all inside the same aspect. We're just showing a single advice declaration in these examples to focus on the issue under discussion at the time.
Sometimes you need access in the advice body to the actual value
that was returned. You can use the form of
@AfterReturning
that binds the return
value for this:
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterReturning;
@Aspect
public class AfterReturningExample {
@AfterReturning(
pointcut="com.xyz.myapp.SystemArchitecture.dataAccessOperation()",
returning="retVal")
public void doAccessCheck(Object retVal) {
// ...
}
}
The name used in the returning
attribute must
correspond to the name of a parameter in the advice method. When a
method execution returns, the return value will be passed to the
advice method as the corresponding argument value. A
returning
clause also restricts matching to only
those method executions that return a value of the specified type
(Object
in this case, which will match any
return value).
Please note that it is not possible to return a totally different reference when using after-returning advice.
After throwing advice runs when a matched method execution exits
by throwing an exception. It is declared using the
@AfterThrowing
annotation:
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterThrowing;
@Aspect
public class AfterThrowingExample {
@AfterThrowing("com.xyz.myapp.SystemArchitecture.dataAccessOperation()")
public void doRecoveryActions() {
// ...
}
}
Often you want the advice to run only when exceptions of a given
type are thrown, and you also often need access to the thrown
exception in the advice body. Use the throwing
attribute to both restrict matching (if desired, use
Throwable
as the exception type
otherwise) and bind the thrown exception to an advice
parameter.
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.AfterThrowing;
@Aspect
public class AfterThrowingExample {
@AfterThrowing(
pointcut="com.xyz.myapp.SystemArchitecture.dataAccessOperation()",
throwing="ex")
public void doRecoveryActions(DataAccessException ex) {
// ...
}
}
The name used in the throwing
attribute must
correspond to the name of a parameter in the advice method. When a
method execution exits by throwing an exception, the exception will be
passed to the advice method as the corresponding argument value. A
throwing
clause also restricts matching to only
those method executions that throw an exception of the specified type
(DataAccessException
in this case).
After (finally) advice runs however a matched method execution
exits. It is declared using the @After
annotation. After advice must be prepared to handle both normal and
exception return conditions. It is typically used for releasing
resources, etc.
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.After;
@Aspect
public class AfterFinallyExample {
@After("com.xyz.myapp.SystemArchitecture.dataAccessOperation()")
public void doReleaseLock() {
// ...
}
}
The final kind of advice is around advice. Around advice runs "around" a matched method execution. It has the opportunity to do work both before and after the method executes, and to determine when, how, and even if, the method actually gets to execute at all. Around advice is often used if you need to share state before and after a method execution in a thread-safe manner (starting and stopping a timer for example). Always use the least powerful form of advice that meets your requirements (i.e. don't use around advice if simple before advice would do).
Around advice is declared using the
@Around
annotation. The first parameter
of the advice method must be of type
ProceedingJoinPoint
. Within the body of
the advice, calling proceed()
on the
ProceedingJoinPoint
causes the
underlying method to execute. The proceed
method
may also be called passing in an Object[]
- the
values in the array will be used as the arguments to the method
execution when it proceeds.
The behavior of proceed when called with an
Object[]
is a little different than the
behavior of proceed for around advice compiled by the AspectJ
compiler. For around advice written using the traditional AspectJ
language, the number of arguments passed to proceed must match the
number of arguments passed to the around advice (not the number of
arguments taken by the underlying join point), and the value passed to
proceed in a given argument position supplants the original value at
the join point for the entity the value was bound to (Don't worry if
this doesn't make sense right now!). The approach taken by Spring is
simpler and a better match to its proxy-based, execution only
semantics. You only need to be aware of this difference if you are
compiling @AspectJ aspects written for Spring and using proceed with
arguments with the AspectJ compiler and weaver. There is a way to
write such aspects that is 100% compatible across both Spring AOP and
AspectJ, and this is discussed in the following section on advice
parameters.
import org.aspectj.lang.annotation.Aspect; import org.aspectj.lang.annotation.Around; import org.aspectj.lang.ProceedingJoinPoint; @Aspect public class AroundExample { @Around("com.xyz.myapp.SystemArchitecture.businessService()") public Object doBasicProfiling(ProceedingJoinPoint pjp) throws Throwable { // start stopwatch Object retVal = pjp.proceed(); // stop stopwatch return retVal; } }
The value returned by the around advice will be the return value seen by the caller of the method. A simple caching aspect for example could return a value from a cache if it has one, and invoke proceed() if it does not. Note that proceed may be invoked once, many times, or not at all within the body of the around advice, all of these are quite legal.
Spring 2.0 offers fully typed advice - meaning that you declare
the parameters you need in the advice signature (as we saw for the
returning and throwing examples above) rather than work with
Object[]
arrays all the time. We'll see how to
make argument and other contextual values available to the advice body
in a moment. First let's take a look at how to write generic advice
that can find out about the method the advice is currently
advising.
Any advice method may declare as its first parameter, a
parameter of type
org.aspectj.lang.JoinPoint
(please
note that around advice is required to declare
a first parameter of type
ProceedingJoinPoint
, which is a
subclass of JoinPoint
. The
JoinPoint
interface provides a number
of useful methods such as getArgs()
(returns the
method arguments), getThis()
(returns the
proxy object), getTarget()
(returns the
target object), getSignature()
(returns a
description of the method that is being advised) and
toString()
(prints a useful description of
the method being advised). Please do consult the Javadocs for full
details.
We've already seen how to bind the returned value or exception
value (using after returning and after throwing advice). To make
argument values available to the advice body, you can use the
binding form of args
. If a parameter name is used
in place of a type name in an args expression, then the value of the
corresponding argument will be passed as the parameter value when
the advice is invoked. An example should make this clearer. Suppose
you want to advise the execution of dao operations that take an
Account object as the first parameter, and you need access to the
account in the advice body. You could write the following:
@Before("com.xyz.myapp.SystemArchitecture.dataAccessOperation() &&" +
"args(account,..)")
public void validateAccount(Account account) {
// ...
}
The args(account,..)
part of the pointcut
expression serves two purposes: firstly, it restricts matching to
only those method executions where the method takes at least one
parameter, and the argument passed to that parameter is an instance
of Account
; secondly, it makes the actual
Account
object available to the advice via
the account
parameter.
Another way of writing this is to declare a pointcut that
"provides" the Account
object value when it
matches a join point, and then just refer to the named pointcut from
the advice. This would look as follows:
@Pointcut("com.xyz.myapp.SystemArchitecture.dataAccessOperation() &&" +
"args(account,..)")
private void accountDataAccessOperation(Account account) {}
@Before("accountDataAccessOperation(account)")
public void validateAccount(Account account) {
// ...
}
The interested reader is once more referred to the AspectJ programming guide for more details.
The proxy object (this
), target object
(target
), and annotations (@within,
@target, @annotation, @args
) can all be bound in a similar
fashion. The following example shows how you could match the
execution of methods annotated with an
@Auditable
annotation, and extract
the audit code.
First the definition of the
@Auditable
annotation:
@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD) public @interface Auditable { AuditCode value(); }
And then the advice that matches the execution of
@Auditable
methods:
@Before("com.xyz.lib.Pointcuts.anyPublicMethod() && " +
"@annotation(auditable)")
public void audit(Auditable auditable) {
AuditCode code = auditable.value();
// ...
}
The parameter binding in advice invocations relies on matching names used in pointcut expressions to declared parameter names in (advice and pointcut) method signatures. Parameter names are not available through Java reflection, so Spring AOP uses the following strategies to determine parameter names:
If the parameter names have been specified by the user explicitly, then the specified parameter names are used: both the advice and the pointcut annotations have an optional "argNames" attribute which can be used to specify the argument names of the annotated method - these argument names are available at runtime. For example:
@Before(
value="com.xyz.lib.Pointcuts.anyPublicMethod() && target(bean) && @annotation(auditable)",
argNames="bean,auditable")
public void audit(Object bean, Auditable auditable) {
AuditCode code = auditable.value();
// ... use code and bean
}
If the first parameter is of the
JoinPoint
,
ProceedingJoinPoint
, or
JoinPoint.StaticPart
type, you
may leave out the name of the parameter from the value of the
"argNames" attribute. For example, if you modify the preceding
advice to receive the join point object, the "argNames"
attribute need not include it:
@Before(
value="com.xyz.lib.Pointcuts.anyPublicMethod() && target(bean) && @annotation(auditable)",
argNames="bean,auditable")
public void audit(JoinPoint jp, Object bean, Auditable auditable) {
AuditCode code = auditable.value();
// ... use code, bean, and jp
}
The special treatment given to the first parameter of the
JoinPoint
,
ProceedingJoinPoint
, and
JoinPoint.StaticPart
types is
particularly convenient for advice that do not collect any other
join point context. In such situations, you may simply omit the
"argNames" attribute. For example, the following advice need not
declare the "argNames" attribute:
@Before(
"com.xyz.lib.Pointcuts.anyPublicMethod()")
public void audit(JoinPoint jp) {
// ... use jp
}
Using the 'argNames'
attribute is a
little clumsy, so if the 'argNames'
attribute
has not been specified, then Spring AOP will look at the debug
information for the class and try to determine the parameter
names from the local variable table. This information will be
present as long as the classes have been compiled with debug
information ('-g:vars'
at a minimum). The
consequences of compiling with this flag on are: (1) your code
will be slightly easier to understand (reverse engineer), (2)
the class file sizes will be very slightly bigger (typically
inconsequential), (3) the optimization to remove unused local
variables will not be applied by your compiler. In other words,
you should encounter no difficulties building with this flag
on.
If an @AspectJ aspect has been compiled by the AspectJ
compiler (ajc) even without the debug information then there is
no need to add the argNames
attribute as the
compiler will retain the needed information.
If the code has been compiled without the necessary debug
information, then Spring AOP will attempt to deduce the pairing
of binding variables to parameters (for example, if only one
variable is bound in the pointcut expression, and the advice
method only takes one parameter, the pairing is obvious!). If
the binding of variables is ambiguous given the available
information, then an
AmbiguousBindingException
will be
thrown.
If all of the above strategies fail then an
IllegalArgumentException
will be
thrown.
We remarked earlier that we would describe how to write a proceed call with arguments that works consistently across Spring AOP and AspectJ. The solution is simply to ensure that the advice signature binds each of the method parameters in order. For example:
@Around("execution(List<Account> find*(..)) &&" + "com.xyz.myapp.SystemArchitecture.inDataAccessLayer() && " + "args(accountHolderNamePattern)") public Object preProcessQueryPattern(ProceedingJoinPoint pjp, String accountHolderNamePattern) throws Throwable { String newPattern = preProcess(accountHolderNamePattern); return pjp.proceed(new Object[] {newPattern}); }
In many cases you will be doing this binding anyway (as in the example above).
What happens when multiple pieces of advice all want to run at the same join point? Spring AOP follows the same precedence rules as AspectJ to determine the order of advice execution. The highest precedence advice runs first "on the way in" (so given two pieces of before advice, the one with highest precedence runs first). "On the way out" from a join point, the highest precedence advice runs last (so given two pieces of after advice, the one with the highest precedence will run second).
When two pieces of advice defined in
different aspects both need to run at the same
join point, unless you specify otherwise the order of execution is
undefined. You can control the order of execution by specifying
precedence. This is done in the normal Spring way by either
implementing the
org.springframework.core.Ordered
interface in the aspect class or annotating it with the
Order
annotation. Given two aspects,
the aspect returning the lower value from
Ordered.getValue()
(or the annotation value) has
the higher precedence.
When two pieces of advice defined in the same aspect both need to run at the same join point, the ordering is undefined (since there is no way to retrieve the declaration order via reflection for javac-compiled classes). Consider collapsing such advice methods into one advice method per join point in each aspect class, or refactor the pieces of advice into separate aspect classes - which can be ordered at the aspect level.
Introductions (known as inter-type declarations in AspectJ) enable an aspect to declare that advised objects implement a given interface, and to provide an implementation of that interface on behalf of those objects.
An introduction is made using the
@DeclareParents
annotation. This
annotation is used to declare that matching types have a new parent
(hence the name). For example, given an interface
UsageTracked
, and an implementation of
that interface DefaultUsageTracked
, the following
aspect declares that all implementors of service interfaces also
implement the UsageTracked
interface. (In
order to expose statistics via JMX for example.)
@Aspect public class UsageTracking { @DeclareParents(value="com.xzy.myapp.service.*+", defaultImpl=DefaultUsageTracked.class) public static UsageTracked mixin; @Before("com.xyz.myapp.SystemArchitecture.businessService() &&" + "this(usageTracked)") public void recordUsage(UsageTracked usageTracked) { usageTracked.incrementUseCount(); } }
The interface to be implemented is determined by the type of the
annotated field. The value
attribute of the
@DeclareParents
annotation is an AspectJ
type pattern :- any bean of a matching type will implement the
UsageTracked interface. Note that in the before advice of the above
example, service beans can be directly used as implementations of the
UsageTracked
interface. If accessing a
bean programmatically you would write the following:
UsageTracked usageTracked = (UsageTracked) context.getBean("myService");
(This is an advanced topic, so if you are just starting out with AOP you can safely skip it until later.)
By default there will be a single instance of each aspect within
the application context. AspectJ calls this the singleton instantiation
model. It is possible to define aspects with alternate lifecycles :-
Spring supports AspectJ's perthis
and
pertarget
instantiation models (percflow,
percflowbelow,
and pertypewithin
are not
currently supported).
A "perthis" aspect is declared by specifying a
perthis
clause in the
@Aspect
annotation. Let's look at an
example, and then we'll explain how it works.
@Aspect("perthis(com.xyz.myapp.SystemArchitecture.businessService())")
public class MyAspect {
private int someState;
@Before(com.xyz.myapp.SystemArchitecture.businessService())
public void recordServiceUsage() {
// ...
}
}
The effect of the 'perthis'
clause is that one
aspect instance will be created for each unique service object executing
a business service (each unique object bound to 'this' at join points
matched by the pointcut expression). The aspect instance is created the
first time that a method is invoked on the service object. The aspect
goes out of scope when the service object goes out of scope. Before the
aspect instance is created, none of the advice within it executes. As
soon as the aspect instance has been created, the advice declared within
it will execute at matched join points, but only when the service object
is the one this aspect is associated with. See the AspectJ programming
guide for more information on per-clauses.
The 'pertarget'
instantiation model works in
exactly the same way as perthis, but creates one aspect instance for
each unique target object at matched join points.
Now that you have seen how all the constituent parts work, let's put them together to do something useful!
The execution of business services can sometimes fail due to
concurrency issues (for example, deadlock loser). If the operation is
retried, it is quite likely to succeed next time round. For business
services where it is appropriate to retry in such conditions (idempotent
operations that don't need to go back to the user for conflict
resolution), we'd like to transparently retry the operation to avoid the
client seeing a
PessimisticLockingFailureException
. This is a
requirement that clearly cuts across multiple services in the service
layer, and hence is ideal for implementing via an aspect.
Because we want to retry the operation, we will need to use around advice so that we can call proceed multiple times. Here's how the basic aspect implementation looks:
@Aspect public class ConcurrentOperationExecutor implements Ordered { private static final int DEFAULT_MAX_RETRIES = 2; private int maxRetries = DEFAULT_MAX_RETRIES; private int order = 1; public void setMaxRetries(int maxRetries) { this.maxRetries = maxRetries; } public int getOrder() { return this.order; } public void setOrder(int order) { this.order = order; } @Around("com.xyz.myapp.SystemArchitecture.businessService()") public Object doConcurrentOperation(ProceedingJoinPoint pjp) throws Throwable { int numAttempts = 0; PessimisticLockingFailureException lockFailureException; do { numAttempts++; try { return pjp.proceed(); } catch(PessimisticLockingFailureException ex) { lockFailureException = ex; } } while(numAttempts <= this.maxRetries); throw lockFailureException; } }
Note that the aspect implements the
Ordered
interface so we can set the
precedence of the aspect higher than the transaction advice (we want a
fresh transaction each time we retry). The maxRetries
and order
properties will both be configured by
Spring. The main action happens in the
doConcurrentOperation
around advice. Notice that for
the moment we're applying the retry logic to all
businessService()s
. We try to proceed, and if we fail
with an PessimisticLockingFailureException
we
simply try again unless we have exhausted all of our retry
attempts.
The corresponding Spring configuration is:
<aop:aspectj-autoproxy/> <bean id="concurrentOperationExecutor" class="com.xyz.myapp.service.impl.ConcurrentOperationExecutor"> <property name="maxRetries" value="3"/> <property name="order" value="100"/> </bean>
To refine the aspect so that it only retries idempotent
operations, we might define an Idempotent
annotation:
@Retention(RetentionPolicy.RUNTIME)
public @interface Idempotent {
// marker annotation
}
and use the annotation to annotate the implementation of service
operations. The change to the aspect to only retry idempotent operations
simply involves refining the pointcut expression so that only
@Idempotent
operations match:
@Around("com.xyz.myapp.SystemArchitecture.businessService() && " + "@annotation(com.xyz.myapp.service.Idempotent)") public Object doConcurrentOperation(ProceedingJoinPoint pjp) throws Throwable { ... }
If you are unable to use Java 5, or simply prefer an XML-based format, then Spring 2.0 also offers support for defining aspects using the new "aop" namespace tags. The exact same pointcut expressions and advice kinds are supported as when using the @AspectJ style, hence in this section we will focus on the new syntax and refer the reader to the discussion in the previous section (Section 6.2, “@AspectJ support”) for an understanding of writing pointcut expressions and the binding of advice parameters.
To use the aop namespace tags described in this section, you need to
import the spring-aop schema as described in Appendix A, XML Schema-based configuration. See Section A.2.7, “The aop
schema” for how to import the tags in the
aop namespace.
Within your Spring configurations, all aspect and advisor elements
must be placed within an <aop:config>
element
(you can have more than one <aop:config>
element
in an application context configuration). An
<aop:config>
element can contain pointcut,
advisor, and aspect elements (note these must be declared in that
order).
![]() | Warning |
---|---|
The |
Using the schema support, an aspect is simply a regular Java object defined as a bean in your Spring application context. The state and behavior is captured in the fields and methods of the object, and the pointcut and advice information is captured in the XML.
An aspect is declared using the <aop:aspect> element, and
the backing bean is referenced using the ref
attribute:
<aop:config> <aop:aspect id="myAspect" ref="aBean"> ... </aop:aspect> </aop:config> <bean id="aBean" class="..."> ... </bean>
The bean backing the aspect ("aBean
" in this
case) can of course be configured and dependency injected just like any
other Spring bean.
A named pointcut can be declared inside an <aop:config> element, enabling the pointcut definition to be shared across several aspects and advisors.
A pointcut representing the execution of any business service in the service layer could be defined as follows:
<aop:config> <aop:pointcut id="businessService" expression="execution(* com.xyz.myapp.service.*.*(..))"/> </aop:config>
Note that the pointcut expression itself is using the same AspectJ pointcut expression language as described in Section 6.2, “@AspectJ support”. If you are using the schema based declaration style with Java 5, you can refer to named pointcuts defined in types (@Aspects) within the pointcut expression, but this feature is not available on JDK 1.4 and below (it relies on the Java 5 specific AspectJ reflection APIs). On JDK 1.5 therefore, another way of defining the above pointcut would be:
<aop:config> <aop:pointcut id="businessService" expression="com.xyz.myapp.SystemArchitecture.businessService()"/> </aop:config>
Assuming you have a SystemArchitecture
aspect
as described in Section 6.2.3.3, “Sharing common pointcut definitions”.
Declaring a pointcut inside an aspect is very similar to declaring a top-level pointcut:
<aop:config> <aop:aspect id="myAspect" ref="aBean"> <aop:pointcut id="businessService" expression="execution(* com.xyz.myapp.service.*.*(..))"/> ... </aop:aspect> </aop:config>
Much the same way in an @AspectJ aspect, pointcuts declared using the schema based definition style may collect join point context. For example, the following pointcut collects the 'this' object as the join point context and passes it to advice:
<aop:config> <aop:aspect id="myAspect" ref="aBean"> <aop:pointcut id="businessService" expression="execution(* com.xyz.myapp.service.*.*(..)) && this(service)"/> <aop:before pointcut-ref="businessService" method="monitor"/> ... </aop:aspect> </aop:config>
The advice must be declared to receive the collected join point context by including parameters of the matching names:
public void monitor(Object service) { ... }
When combining pointcut sub-expressions, '&&' is awkward within an XML document, and so the keywords 'and', 'or' and 'not' can be used in place of '&&', '||' and '!' respectively. For example, the previous pointcut may be better written as:
<aop:config>
<aop:aspect id="myAspect" ref="aBean">
<aop:pointcut id="businessService"
expression="execution(* com.xyz.myapp.service.*.*(..)) and this(service)"/>
<aop:before pointcut-ref="businessService" method="monitor"/>
...
</aop:aspect>
</aop:config>
Note that pointcuts defined in this way are referred to by their XML id and cannot be used as named pointcuts to form composite pointcuts. The named pointcut support in the schema based definition style is thus more limited than that offered by the @AspectJ style.
The same five advice kinds are supported as for the @AspectJ style, and they have exactly the same semantics.
Before advice runs before a matched method execution. It is
declared inside an <aop:aspect>
using the
<aop:before> element.
<aop:aspect id="beforeExample" ref="aBean"> <aop:before pointcut-ref="dataAccessOperation" method="doAccessCheck"/> ... </aop:aspect>
Here dataAccessOperation
is the id of a
pointcut defined at the top (<aop:config>
)
level. To define the pointcut inline instead, replace the
pointcut-ref
attribute with a
pointcut
attribute:
<aop:aspect id="beforeExample" ref="aBean"> <aop:before pointcut="execution(* com.xyz.myapp.dao.*.*(..))" method="doAccessCheck"/> ... </aop:aspect>
As we noted in the discussion of the @AspectJ style, using named pointcuts can significantly improve the readability of your code.
The method attribute identifies a method
(doAccessCheck
) that provides the body of the
advice. This method must be defined for the bean referenced by the
aspect element containing the advice. Before a data access operation
is executed (a method execution join point matched by the pointcut
expression), the "doAccessCheck" method on the aspect bean will be
invoked.
After returning advice runs when a matched method execution
completes normally. It is declared inside an
<aop:aspect>
in the same way as before
advice. For example:
<aop:aspect id="afterReturningExample" ref="aBean"> <aop:after-returning pointcut-ref="dataAccessOperation" method="doAccessCheck"/> ... </aop:aspect>
Just as in the @AspectJ style, it is possible to get hold of the return value within the advice body. Use the returning attribute to specify the name of the parameter to which the return value should be passed:
<aop:aspect id="afterReturningExample" ref="aBean"> <aop:after-returning pointcut-ref="dataAccessOperation" returning="retVal" method="doAccessCheck"/> ... </aop:aspect>
The doAccessCheck method must declare a parameter named
retVal
. The type of this parameter constrains
matching in the same way as described for @AfterReturning. For
example, the method signature may be declared as:
public void doAccessCheck(Object retVal) {...
After throwing advice executes when a matched method execution
exits by throwing an exception. It is declared inside an
<aop:aspect>
using the after-throwing
element:
<aop:aspect id="afterThrowingExample" ref="aBean"> <aop:after-throwing pointcut-ref="dataAccessOperation" method="doRecoveryActions"/> ... </aop:aspect>
Just as in the @AspectJ style, it is possible to get hold of the thrown exception within the advice body. Use the throwing attribute to specify the name of the parameter to which the exception should be passed:
<aop:aspect id="afterThrowingExample" ref="aBean"> <aop:after-throwing pointcut-ref="dataAccessOperation" throwing="dataAccessEx" method="doRecoveryActions"/> ... </aop:aspect>
The doRecoveryActions method must declare a parameter named
dataAccessEx
. The type of this parameter constrains
matching in the same way as described for @AfterThrowing. For example,
the method signature may be declared as:
public void doRecoveryActions(DataAccessException dataAccessEx) {...
After (finally) advice runs however a matched method execution
exits. It is declared using the after
element:
<aop:aspect id="afterFinallyExample" ref="aBean"> <aop:after pointcut-ref="dataAccessOperation" method="doReleaseLock"/> ... </aop:aspect>
The final kind of advice is around advice. Around advice runs "around" a matched method execution. It has the opportunity to do work both before and after the method executes, and to determine when, how, and even if, the method actually gets to execute at all. Around advice is often used if you need to share state before and after a method execution in a thread-safe manner (starting and stopping a timer for example). Always use the least powerful form of advice that meets your requirements; don't use around advice if simple before advice would do.
Around advice is declared using the
aop:around
element. The first parameter of the
advice method must be of type
ProceedingJoinPoint
. Within the body of
the advice, calling proceed()
on the
ProceedingJoinPoint
causes the
underlying method to execute. The proceed
method
may also be calling passing in an Object[]
-
the values in the array will be used as the arguments to the method
execution when it proceeds. See Section 6.2.4.5, “Around advice” for notes on calling proceed
with an Object[]
.
<aop:aspect id="aroundExample" ref="aBean"> <aop:around pointcut-ref="businessService" method="doBasicProfiling"/> ... </aop:aspect>
The implementation of the doBasicProfiling
advice would be exactly the same as in the @AspectJ example (minus the
annotation of course):
public Object doBasicProfiling(ProceedingJoinPoint pjp) throws Throwable { // start stopwatch Object retVal = pjp.proceed(); // stop stopwatch return retVal; }
The schema based declaration style supports fully typed advice
in the same way as described for the @AspectJ support - by matching
pointcut parameters by name against advice method parameters. See
Section 6.2.4.6, “Advice parameters” for details. If you
wish to explicitly specify argument names for the advice methods (not
relying on the detection strategies previously described) then this is
done using the arg-names
attribute of the advice
element, which is treated in the same manner to the "argNames"
attribute in an advice annotation as described in Section 6.2.4.6.3, “Determining argument names”. For example:
<aop:before pointcut="com.xyz.lib.Pointcuts.anyPublicMethod() and @annotation(auditable)" method="audit" arg-names="auditable"/>
The arg-names
attribute accepts a
comma-delimited list of parameter names.
Find below a slightly more involved example of the XSD-based approach that illustrates some around advice used in conjunction with a number of strongly typed parameters.
package x.y.service; public interface FooService { Foo getFoo(String fooName, int age); } public class DefaultFooService implements FooService { public Foo getFoo(String name, int age) { return new Foo(name, age); } }
Next up is the aspect. Notice the fact that the
profile(..)
method accepts a number of
strongly-typed parameters, the first of which happens to be the join
point used to proceed with the method call: the presence of this
parameter is an indication that the
profile(..)
is to be used as
around
advice:
package x.y; import org.aspectj.lang.ProceedingJoinPoint; import org.springframework.util.StopWatch; public class SimpleProfiler { public Object profile(ProceedingJoinPoint call, String name, int age) throws Throwable { StopWatch clock = new StopWatch( "Profiling for '" + name + "' and '" + age + "'"); try { clock.start(call.toShortString()); return call.proceed(); } finally { clock.stop(); System.out.println(clock.prettyPrint()); } } }
Finally, here is the XML configuration that is required to effect the execution of the above advice for a particular join point:
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <!-- this is the object that will be proxied by Spring's AOP infrastructure --> <bean id="fooService" class="x.y.service.DefaultFooService"/> <!-- this is the actual advice itself --> <bean id="profiler" class="x.y.SimpleProfiler"/> <aop:config> <aop:aspect ref="profiler"> <aop:pointcut id="theExecutionOfSomeFooServiceMethod" expression="execution(* x.y.service.FooService.getFoo(String,int)) and args(name, age)"/> <aop:around pointcut-ref="theExecutionOfSomeFooServiceMethod" method="profile"/> </aop:aspect> </aop:config> </beans>
If we had the following driver script, we would get output something like this on standard output:
import org.springframework.beans.factory.BeanFactory; import org.springframework.context.support.ClassPathXmlApplicationContext; import x.y.service.FooService; public final class Boot { public static void main(final String[] args) throws Exception { BeanFactory ctx = new ClassPathXmlApplicationContext("x/y/plain.xml"); FooService foo = (FooService) ctx.getBean("fooService"); foo.getFoo("Pengo", 12); } }
StopWatch 'Profiling for 'Pengo' and '12'': running time (millis) = 0 ----------------------------------------- ms % Task name ----------------------------------------- 00000 ? execution(getFoo)
When multiple advice needs to execute at the same join point
(executing method) the ordering rules are as described in Section 6.2.4.7, “Advice ordering”. The precedence between
aspects is determined by either adding the
Order
annotation to the bean backing
the aspect or by having the bean implement the
Ordered
interface.
Introductions (known as inter-type declarations in AspectJ) enable an aspect to declare that advised objects implement a given interface, and to provide an implementation of that interface on behalf of those objects.
An introduction is made using the
aop:declare-parents
element inside an
aop:aspect
This element is used to declare that
matching types have a new parent (hence the name). For example, given an
interface UsageTracked
, and an
implementation of that interface
DefaultUsageTracked
, the following aspect
declares that all implementors of service interfaces also implement the
UsageTracked
interface. (In order to
expose statistics via JMX for example.)
<aop:aspect id="usageTrackerAspect" ref="usageTracking"> <aop:declare-parents types-matching="com.xzy.myapp.service.*+" implement-interface="com.xyz.myapp.service.tracking.UsageTracked" default-impl="com.xyz.myapp.service.tracking.DefaultUsageTracked"/> <aop:before pointcut="com.xyz.myapp.SystemArchitecture.businessService() and this(usageTracked)" method="recordUsage"/> </aop:aspect>
The class backing the usageTracking
bean would
contain the method:
public void recordUsage(UsageTracked usageTracked) { usageTracked.incrementUseCount(); }
The interface to be implemented is determined by
implement-interface
attribute. The value of the
types-matching
attribute is an AspectJ type pattern
:- any bean of a matching type will implement the
UsageTracked
interface. Note that in the
before advice of the above example, service beans can be directly used
as implementations of the UsageTracked
interface. If accessing a bean programmatically you would write the
following:
UsageTracked usageTracked = (UsageTracked) context.getBean("myService");
The only supported instantiation model for schema-defined aspects is the singleton model. Other instantiation models may be supported in future releases.
The concept of "advisors" is brought forward from the AOP support defined in Spring 1.2 and does not have a direct equivalent in AspectJ. An advisor is like a small self-contained aspect that has a single piece of advice. The advice itself is represented by a bean, and must implement one of the advice interfaces described in Section 7.3.2, “Advice types in Spring”. Advisors can take advantage of AspectJ pointcut expressions though.
Spring 2.0 supports the advisor concept with the
<aop:advisor>
element. You will most commonly
see it used in conjunction with transactional advice, which also has its
own namespace support in Spring 2.0. Here's how it looks:
<aop:config> <aop:pointcut id="businessService" expression="execution(* com.xyz.myapp.service.*.*(..))"/> <aop:advisor pointcut-ref="businessService" advice-ref="tx-advice"/> </aop:config> <tx:advice id="tx-advice"> <tx:attributes> <tx:method name="*" propagation="REQUIRED"/> </tx:attributes> </tx:advice>
As well as the pointcut-ref
attribute used in the
above example, you can also use the pointcut
attribute
to define a pointcut expression inline.
To define the precedence of an advisor so that the advice can
participate in ordering, use the order
attribute to
define the Ordered
value of the advisor.
Let's see how the concurrent locking failure retry example from Section 6.2.7, “Example” looks when rewritten using the schema support.
The execution of business services can sometimes fail due to
concurrency issues (for example, deadlock loser). If the operation is
retried, it is quite likely it will succeed next time round. For
business services where it is appropriate to retry in such conditions
(idempotent operations that don't need to go back to the user for
conflict resolution), we'd like to transparently retry the operation to
avoid the client seeing a
PessimisticLockingFailureException
. This is a
requirement that clearly cuts across multiple services in the service
layer, and hence is ideal for implementing via an aspect.
Because we want to retry the operation, we'll need to use around advice so that we can call proceed multiple times. Here's how the basic aspect implementation looks (it's just a regular Java class using the schema support):
public class ConcurrentOperationExecutor implements Ordered { private static final int DEFAULT_MAX_RETRIES = 2; private int maxRetries = DEFAULT_MAX_RETRIES; private int order = 1; public void setMaxRetries(int maxRetries) { this.maxRetries = maxRetries; } public int getOrder() { return this.order; } public void setOrder(int order) { this.order = order; } public Object doConcurrentOperation(ProceedingJoinPoint pjp) throws Throwable { int numAttempts = 0; PessimisticLockingFailureException lockFailureException; do { numAttempts++; try { return pjp.proceed(); } catch(PessimisticLockingFailureException ex) { lockFailureException = ex; } } while(numAttempts <= this.maxRetries); throw lockFailureException; } }
Note that the aspect implements the
Ordered
interface so we can set the
precedence of the aspect higher than the transaction advice (we want a
fresh transaction each time we retry). The maxRetries
and order
properties will both be configured by
Spring. The main action happens in the
doConcurrentOperation
around advice method. We try to
proceed, and if we fail with a
PessimisticLockingFailureException
we simply try
again unless we have exhausted all of our retry attempts.
This class is identical to the one used in the @AspectJ example, but with the annotations removed.
The corresponding Spring configuration is:
<aop:config> <aop:aspect id="concurrentOperationRetry" ref="concurrentOperationExecutor"> <aop:pointcut id="idempotentOperation" expression="execution(* com.xyz.myapp.service.*.*(..))"/> <aop:around pointcut-ref="idempotentOperation" method="doConcurrentOperation"/> </aop:aspect> </aop:config> <bean id="concurrentOperationExecutor" class="com.xyz.myapp.service.impl.ConcurrentOperationExecutor"> <property name="maxRetries" value="3"/> <property name="order" value="100"/> </bean>
Notice that for the time being we assume that all business
services are idempotent. If this is not the case we can refine the
aspect so that it only retries genuinely idempotent operations, by
introducing an Idempotent
annotation:
@Retention(RetentionPolicy.RUNTIME)
public @interface Idempotent {
// marker annotation
}
and using the annotation to annotate the implementation of service
operations. The change to the aspect to retry only idempotent operations
simply involves refining the pointcut expression so that only
@Idempotent
operations match:
<aop:pointcut id="idempotentOperation" expression="execution(* com.xyz.myapp.service.*.*(..)) and @annotation(com.xyz.myapp.service.Idempotent)"/>
Once you have decided that an aspect is the best approach for implementing a given requirement, how do you decide between using Spring AOP or AspectJ, and between the Aspect language (code) style, @AspectJ annotation style, or the Spring XML style? These decisions are influenced by a number of factors including application requirements, development tools, and team familiarity with AOP.
Use the simplest thing that can work. Spring AOP is simpler than using full AspectJ as there is no requirement to introduce the AspectJ compiler / weaver into your development and build processes. If you only need to advise the execution of operations on Spring beans, then Spring AOP is the right choice. If you need to advise objects not managed by the Spring container (such as domain objects typically), then you will need to use AspectJ. You will also need to use AspectJ if you wish to advise join points other than simple method executions (for example, field get or set join points, and so on).
When using AspectJ, you have the choice of the AspectJ language syntax (also known as the "code style") or the @AspectJ annotation style. Clearly, if you are not using Java 5+ then the choice has been made for you... use the code style. If aspects play a large role in your design, and you are able to use the AspectJ Development Tools (AJDT) plugin for Eclipse, then the AspectJ language syntax is the preferred option: it is cleaner and simpler because the language was purposefully designed for writing aspects. If you are not using Eclipse, or have only a few aspects that do not play a major role in your application, then you may want to consider using the @AspectJ style and sticking with a regular Java compilation in your IDE, and adding an aspect weaving phase to your build script.
If you have chosen to use Spring AOP, then you have a choice of @AspectJ or XML style. Clearly if you are not running on Java 5+, then the XML style is the appropriate choice; for Java 5 projects there are various tradeoffs to consider.
The XML style will be most familiar to existing Spring users. It can be used with any JDK level (referring to named pointcuts from within pointcut expressions does still require Java 5+ though) and is backed by genuine POJOs. When using AOP as a tool to configure enterprise services then XML can be a good choice (a good test is whether you consider the pointcut expression to be a part of your configuration you might want to change independently). With the XML style arguably it is clearer from your configuration what aspects are present in the system.
The XML style has two disadvantages. Firstly it does not fully encapsulate the implementation of the requirement it addresses in a single place. The DRY principle says that there should be a single, unambiguous, authoritative representation of any piece of knowledge within a system. When using the XML style, the knowledge of how a requirement is implemented is split across the declaration of the backing bean class, and the XML in the configuration file. When using the @AspectJ style there is a single module - the aspect - in which this information is encapsulated. Secondly, the XML style is slightly more limited in what it can express than the @AspectJ style: only the "singleton" aspect instantiation model is supported, and it is not possible to combine named pointcuts declared in XML. For example, in the @AspectJ style you can write something like:
@Pointcut(execution(* get*())) public void propertyAccess() {} @Pointcut(execution(org.xyz.Account+ *(..)) public void operationReturningAnAccount() {} @Pointcut(propertyAccess() && operationReturningAnAccount()) public void accountPropertyAccess() {}
In the XML style I can declare the first two pointcuts:
<aop:pointcut id="propertyAccess" expression="execution(* get*())"/> <aop:pointcut id="operationReturningAnAccount" expression="execution(org.xyz.Account+ *(..))"/>
The downside of the XML approach is that you cannot define the
'accountPropertyAccess
' pointcut by combining these
definitions.
The @AspectJ style supports additional instantiation models, and richer pointcut composition. It has the advantage of keeping the aspect as a modular unit. It also has the advantage the @AspectJ aspects can be understood (and thus consumed) both by Spring AOP and by AspectJ - so if you later decide you need the capabilities of AspectJ to implement additional requirements then it is very easy to migrate to an AspectJ-based approach. On balance the Spring team prefer the @AspectJ style whenever you have aspects that do more than simple "configuration" of enterprise services.
It is perfectly possible to mix @AspectJ style aspects using the
autoproxying support, schema-defined <aop:aspect>
aspects, <aop:advisor>
declared advisors and even
proxies and interceptors defined using the Spring 1.2 style in the same
configuration. All of these are implemented using the same underlying
support mechanism and will co-exist without any difficulty.
Spring AOP uses either JDK dynamic proxies or CGLIB to create the proxy for a given target object. (JDK dynamic proxies are preferred whenever you have a choice).
If the target object to be proxied implements at least one interface then a JDK dynamic proxy will be used. All of the interfaces implemented by the target type will be proxied. If the target object does not implement any interfaces then a CGLIB proxy will be created.
If you want to force the use of CGLIB proxying (for example, to proxy every method defined for the target object, not just those implemented by its interfaces) you can do so. However, there are some issues to consider:
final
methods cannot be advised, as they
cannot be overriden.
You will need the CGLIB 2 binaries on your classpath, whereas dynamic proxies are available with the JDK. Spring will automatically warn you when it needs CGLIB and the CGLIB library classes are not found on the classpath.
The constructor of your proxied object will be called twice. This is a natural consequence of the CGLIB proxy model whereby a subclass is generated for each proxied object. For each proxied instance, two objects are created: the actual proxied object and an instance of the subclass that implements the advice. This behavior is not exhibited when using JDK proxies. Usually, calling the constructor of the proxied type twice, is not an issue, as there are usually only assignments taking place and no real logic is implemented in the constructor.
To force the use of CGLIB proxies set
the value of the proxy-target-class
attribute of the
<aop:config>
element to true:
<aop:config proxy-target-class="true"> <!-- other beans defined here... --> </aop:config>
To force CGLIB proxying when using the @AspectJ autoproxy support,
set the 'proxy-target-class'
attribute of the
<aop:aspectj-autoproxy>
element to
true
:
<aop:aspectj-autoproxy proxy-target-class="true"/>
![]() | Note |
---|---|
Multiple To be clear: using ' |
Spring AOP is proxy-based. It is vitally important that you grasp the semantics of what that last statement actually means before you write your own aspects or use any of the Spring AOP-based aspects supplied with the Spring Framework.
Consider first the scenario where you have a plain-vanilla, un-proxied, nothing-special-about-it, straight object reference, as illustrated by the following code snippet.
public class SimplePojo implements Pojo { public void foo() { // this next method invocation is a direct call on the 'this' reference this.bar(); } public void bar() { // some logic... } }
If you invoke a method on an object reference, the method is invoked directly on that object reference, as can be seen below.
public class Main {
public static void main(String[] args) {
Pojo pojo = new SimplePojo();
// this is a direct method call on the 'pojo' reference
pojo.foo();
}
}
Things change slightly when the reference that client code has is a proxy. Consider the following diagram and code snippet.
public class Main {
public static void main(String[] args) {
ProxyFactory factory = new ProxyFactory(new SimplePojo());
factory.addInterface(Pojo.class);
factory.addAdvice(new RetryAdvice());
Pojo pojo = (Pojo) factory.getProxy();
// this is a method call on the proxy!
pojo.foo();
}
}
The key thing to understand here is that the client code inside
the main(..)
of the Main
class has a reference to the proxy. This means that
method calls on that object reference will be calls on the proxy, and as
such the proxy will be able to delegate to all of the interceptors
(advice) that are relevant to that particular method call. However, once
the call has finally reached the target object, the
SimplePojo
reference in this case, any method
calls that it may make on itself, such as
this.bar()
or
this.foo()
, are going to be invoked against the
this
reference, and
not the proxy. This has important implications. It
means that self-invocation is not going to result
in the advice associated with a method invocation getting a chance to
execute.
Okay, so what is to be done about this? The best approach (the term best is used loosely here) is to refactor your code such that the self-invocation does not happen. For sure, this does entail some work on your part, but it is the best, least-invasive approach. The next approach is absolutely horrendous, and I am almost reticent to point it out precisely because it is so horrendous. You can (choke!) totally tie the logic within your class to Spring AOP by doing this:
public class SimplePojo implements Pojo { public void foo() { // this works, but... gah! ((Pojo) AopContext.currentProxy()).bar(); } public void bar() { // some logic... } }
This totally couples your code to Spring AOP, and it makes the class itself aware of the fact that it is being used in an AOP context, which flies in the face of AOP. It also requires some additional configuration when the proxy is being created:
public class Main { public static void main(String[] args) { ProxyFactory factory = new ProxyFactory(new SimplePojo()); factory.adddInterface(Pojo.class); factory.addAdvice(new RetryAdvice()); factory.setExposeProxy(true); Pojo pojo = (Pojo) factory.getProxy(); // this is a method call on the proxy! pojo.foo(); } }
Finally, it must be noted that AspectJ does not have this self-invocation issue because it is not a proxy-based AOP framework.
In addition to declaring aspects in your configuration using either
<aop:config>
or
<aop:aspectj-autoproxy>
, it is also possible
programmatically to create proxies that advise target objects. For the
full details of Spring's AOP API, see the next chapter. Here we want to
focus on the ability to automatically create proxies using @AspectJ
aspects.
The class
org.springframework.aop.aspectj.annotation.AspectJProxyFactory
can be used to create a proxy for a target object that is advised by one
or more @AspectJ aspects. Basic usage for this class is very simple, as
illustrated below. See the Javadocs for full information.
// create a factory that can generate a proxy for the given target object AspectJProxyFactory factory = new AspectJProxyFactory(targetObject); // add an aspect, the class must be an @AspectJ aspect // you can call this as many times as you need with different aspects factory.addAspect(SecurityManager.class); // you can also add existing aspect instances, the type of the object supplied must be an @AspectJ aspect factory.addAspect(usageTracker); // now get the proxy object... MyInterfaceType proxy = factory.getProxy();
Everything we've covered so far in this chapter is pure Spring AOP. In this section, we're going to look at how you can use the AspectJ compiler/weaver instead of, or in addition to, Spring AOP if your needs go beyond the facilities offered by Spring AOP alone.
Spring ships with a small AspectJ aspect library, which is available
standalone in your distribution as spring-aspects.jar
; you'll need to add this
to your classpath in order to use the aspects in it. Section 6.8.1, “Using AspectJ to dependency inject domain objects with
Spring” and Section 6.8.2, “Other Spring aspects for AspectJ”
discuss the content of this library and how you can use it. Section 6.8.3, “Configuring AspectJ aspects using Spring IoC” discusses how to dependency inject AspectJ
aspects that are woven using the AspectJ compiler. Finally, Section 6.8.4, “Load-time weaving with AspectJ in the Spring Framework” provides an introduction to load-time weaving for
Spring applications using AspectJ.
The Spring container instantiates and configures beans defined in
your application context. It is also possible to ask a bean factory to
configure a pre-existing object given the name of a
bean definition containing the configuration to be applied. The
spring-aspects.jar
contains an
annotation-driven aspect that exploits this capability to allow
dependency injection of any object. The support is
intended to be used for objects created outside of the control
of any container. Domain objects often fall into this
category because they are often created programmatically using the
new
operator, or by an ORM tool as a result of a
database query.
The @Configurable
annotation marks
a class as eligible for Spring-driven configuration. In the simplest
case it can be used just as a marker annotation:
package com.xyz.myapp.domain;
import org.springframework.beans.factory.annotation.Configurable;
@Configurable
public class Account {
// ...
}
When used as a marker interface in this way, Spring will configure
new instances of the annotated type (Account
in
this case) using a prototype-scoped bean definition with the same name
as the fully-qualified type name
(com.xyz.myapp.domain.Account
). Since the default
name for a bean is the fully-qualified name of its type, a convenient
way to declare the prototype definition is simply to omit the
id
attribute:
<bean class="com.xyz.myapp.domain.Account" scope="prototype"> <property name="fundsTransferService" ref="fundsTransferService"/> </bean>
If you want to explicitly specify the name of the prototype bean definition to use, you can do so directly in the annotation:
package com.xyz.myapp.domain;
import org.springframework.beans.factory.annotation.Configurable;
@Configurable("account")
public class Account {
// ...
}
Spring will now look for a bean definition named
"account
" and use that as the definition to configure
new Account
instances.
You can also use autowiring to avoid having to specify a
prototype-scoped bean definition at all. To have Spring apply autowiring
use the 'autowire
' property of the
@Configurable
annotation: specify either
@Configurable(autowire=Autowire.BY_TYPE)
or
@Configurable(autowire=Autowire.BY_NAME
for
autowiring by type or by name respectively. As an alternative, as of
Spring 2.5 it is preferable to specify explicit, annotation-driven
dependency injection for your @Configurable
beans by using @Autowired
and
@Resource
at the field or method level (see
Section 3.11, “Annotation-based configuration” for further details).
Finally you can enable Spring dependency checking for the object
references in the newly created and configured object by using the
dependencyCheck
attribute (for example:
@Configurable(autowire=Autowire.BY_NAME,dependencyCheck=true)
).
If this attribute is set to true, then Spring will validate after
configuration that all properties (which are not primitives or
collections) have been set.
Using the annotation on its own does nothing of course. It is the
AnnotationBeanConfigurerAspect
in spring-aspects.jar
that acts on the
presence of the annotation. In essence the aspect says "after returning
from the initialization of a new object of a type annotated with
@Configurable
, configure the newly
created object using Spring in accordance with the properties of the
annotation". In this context, initialization refers
to newly instantiated objects (e.g., objects instantiated with the
'new
' operator) as well as to
Serializable
objects that are undergoing
deserialization (e.g., via readResolve()).
![]() | Note |
---|---|
One of the key phrases in the above paragraph is 'in
essence'. For most cases, the exact semantics of
'after returning from the initialization of a new
object' will be fine... in this context, 'after
initialization' means that the dependencies will be
injected after the object has been constructed -
this means that the dependencies will not be available for use in the
constructor bodies of the class. If you want the dependencies to be
injected before the constructor bodies execute,
and thus be available for use in the body of the constructors, then
you need to define this on the
@Configurable(preConstruction=true) You can find out more information about the language semantics of the various pointcut types in AspectJ in this appendix of the AspectJ Programming Guide. |
For this to work the annotated types must be woven with the
AspectJ weaver - you can either use a build-time Ant or Maven task to do
this (see for example the AspectJ
Development Environment Guide) or load-time weaving (see Section 6.8.4, “Load-time weaving with AspectJ in the Spring Framework”). The
AnnotationBeanConfigurerAspect
itself needs
configuring by Spring (in order to obtain a reference to the bean
factory that is to be used to configure new objects). The Spring context
namespace defines a convenient tag for doing this: just include
the following in your application context configuration:
<context:spring-configured/>
If you are using the DTD instead of schema, the equivalent definition is:
<bean class="org.springframework.beans.factory.aspectj.AnnotationBeanConfigurerAspect" factory-method="aspectOf"/>
Instances of @Configurable
objects
created before the aspect has been configured will
result in a warning being issued to the log and no configuration of the
object taking place. An example might be a bean in the Spring
configuration that creates domain objects when it is initialized by
Spring. In this case you can use the "depends-on" bean attribute to
manually specify that the bean depends on the configuration
aspect.
<bean id="myService"
class="com.xzy.myapp.service.MyService"
depends-on="org.springframework.beans.factory.aspectj.AnnotationBeanConfigurerAspect">
<!-- ... -->
</bean>
One of the goals of the
@Configurable
support is to enable
independent unit testing of domain objects without the difficulties
associated with hard-coded lookups. If
@Configurable
types have not been woven
by AspectJ then the annotation has no affect during unit testing, and
you can simply set mock or stub property references in the object
under test and proceed as normal. If
@Configurable
types
have been woven by AspectJ then you can still
unit test outside of the container as normal, but you will see a
warning message each time that you construct an
@Configurable
object indicating that it
has not been configured by Spring.
The AnnotationBeanConfigurerAspect
used
to implement the @Configurable
support
is an AspectJ singleton aspect. The scope of a singleton aspect is the
same as the scope of static
members, that is to say
there is one aspect instance per classloader that defines the type.
This means that if you define multiple application contexts within the
same classloader hierarchy you need to consider where to define the
<aop:spring-configured/>
bean and where to
place spring-aspects.jar
on
the classpath.
Consider a typical Spring web-app configuration with a shared
parent application context defining common business services and
everything needed to support them, and one child application context
per servlet containing definitions particular to that servlet. All of
these contexts will co-exist within the same classloader hierarchy,
and so the AnnotationBeanConfigurerAspect
can only
hold a reference to one of them. In this case we recommend defining
the <aop:spring-configured/>
bean in the
shared (parent) application context: this defines the services that
you are likely to want to inject into domain objects. A consequence is
that you cannot configure domain objects with references to beans
defined in the child (servlet-specific) contexts using the
@Configurable mechanism (probably not something you want to do
anyway!).
When deploying multiple web-apps within the same container,
ensure that each web-application loads the types in spring-aspects.jar
using its own
classloader (for example, by placing spring-aspects.jar
in 'WEB-INF/lib'
). If spring-aspects.jar
is only added to the
container wide classpath (and hence loaded by the shared parent
classloader), all web applications will share the same aspect instance
which is probably not what you want.
In addition to the @Configurable
aspect, spring-aspects.jar
contains an AspectJ aspect that can be used to drive Spring's
transaction management for types and methods annotated with the
@Transactional
annotation. This is
primarily intended for users who want to use the Spring Framework's
transaction support outside of the Spring container.
The aspect that interprets
@Transactional
annotations is the
AnnotationTransactionAspect
. When using this
aspect, you must annotate the implementation class
(and/or methods within that class), not the
interface (if any) that the class implements. AspectJ follows Java's
rule that annotations on interfaces are not
inherited.
A @Transactional
annotation on a
class specifies the default transaction semantics for the execution of
any public operation in the class.
A @Transactional
annotation on a
method within the class overrides the default transaction semantics
given by the class annotation (if present). Methods with
public
, protected
, and default
visibility may all be annotated. Annotating protected
and default visibility methods directly is the only way to get
transaction demarcation for the execution of such methods.
For AspectJ programmers that want to use the Spring configuration
and transaction management support but don't want to (or cannot) use
annotations, spring-aspects.jar
also contains abstract
aspects you can extend to
provide your own pointcut definitions. See the sources for the
AbstractBeanConfigurerAspect
and
AbstractTransactionAspect
aspects for more
information. As an example, the following excerpt shows how you could
write an aspect to configure all instances of objects defined in the
domain model using prototype bean definitions that match the
fully-qualified class names:
public aspect DomainObjectConfiguration extends AbstractBeanConfigurerAspect {
public DomainObjectConfiguration() {
setBeanWiringInfoResolver(new ClassNameBeanWiringInfoResolver());
}
// the creation of a new bean (any object in the domain model)
protected pointcut beanCreation(Object beanInstance) :
initialization(new(..)) &&
SystemArchitecture.inDomainModel() &&
this(beanInstance);
}
When using AspectJ aspects with Spring applications, it is natural
to both want and expect to be able to configure such aspects using
Spring. The AspectJ runtime itself is responsible for aspect creation,
and the means of configuring the AspectJ created aspects via Spring
depends on the AspectJ instantiation model (the
'per-xxx
' clause) used by the aspect.
The majority of AspectJ aspects are singleton
aspects. Configuration of these aspects is very easy: simply create a
bean definition referencing the aspect type as normal, and include the
bean attribute 'factory-method="aspectOf"'
. This
ensures that Spring obtains the aspect instance by asking AspectJ for it
rather than trying to create an instance itself. For example:
<bean id="profiler" class="com.xyz.profiler.Profiler"
factory-method="aspectOf">
<property name="profilingStrategy" ref="jamonProfilingStrategy"/>
</bean>
Non-singleton aspects are harder to configure: however it is
possible to do so by creating prototype bean definitions and using the
@Configurable
support from spring-aspects.jar
to configure the
aspect instances once they have bean created by the AspectJ
runtime.
If you have some @AspectJ aspects that you want to weave with
AspectJ (for example, using load-time weaving for domain model types)
and other @AspectJ aspects that you want to use with Spring AOP, and
these aspects are all configured using Spring, then you will need to
tell the Spring AOP @AspectJ autoproxying support which exact subset of
the @AspectJ aspects defined in the configuration should be used for
autoproxying. You can do this by using one or more
<include/>
elements inside the
<aop:aspectj-autoproxy/>
declaration. Each
<include/>
element specifies a name pattern,
and only beans with names matched by at least one of the patterns will
be used for Spring AOP autoproxy configuration:
<aop:aspectj-autoproxy> <aop:include name="thisBean"/> <aop:include name="thatBean"/> </aop:aspectj-autoproxy>
![]() | Note |
---|---|
Do not be misled by the name of the
|
Load-time weaving (LTW) refers to the process of weaving AspectJ aspects into an application's class files as they are being loaded into the Java virtual machine (JVM). The focus of this section is on configuring and using LTW in the specific context of the Spring Framework: this section is not an introduction to LTW though. For full details on the specifics of LTW and configuring LTW with just AspectJ (with Spring not being involved at all), see the LTW section of the AspectJ Development Environment Guide.
The value-add that the Spring Framework brings to AspectJ LTW is
in enabling much finer-grained control over the weaving process.
'Vanilla' AspectJ LTW is effected using a Java (5+) agent, which is
switched on by specifying a VM argument when starting up a JVM. It is
thus a JVM-wide setting, which may be fine in some situations, but often
is a little too coarse. Spring-enabled LTW enables you to switch on LTW
on a per-ClassLoader
basis,
which obviously is more fine-grained and which can make more sense in a
'single-JVM-multiple-application' environment (such as is found in a
typical application server environment).
Further, in certain environments, this support enables load-time weaving without making any modifications to the application server's launch script that will be needed to add -javaagent:path/to/aspectjweaver.jar or (as we describe later in this section) -javaagent:path/to/spring-agent.jar. Developers simply modify one or more files that form the application context to enable load-time weaving instead of relying on administrators who typically are in charge of the deployment configuration such as the launch script.
Now that the sales pitch is over, let us first walk through a quick example of AspectJ LTW using Spring, followed by detailed specifics about elements introduced in the following example. For a complete example, please see the Petclinic sample application.
Let us assume that you are an application developer who has been tasked with diagnosing the cause of some performance problems in a system. Rather than break out a profiling tool, what we are going to do is switch on a simple profiling aspect that will enable us to very quickly get some performance metrics, so that we can then apply a finer-grained profiling tool to that specific area immediately afterwards.
Here is the profiling aspect. Nothing too fancy, just a quick-and-dirty time-based profiler, using the @AspectJ-style of aspect declaration.
package foo; import org.aspectj.lang.ProceedingJoinPoint; import org.aspectj.lang.annotation.Aspect; import org.aspectj.lang.annotation.Around; import org.aspectj.lang.annotation.Pointcut; import org.springframework.util.StopWatch; import org.springframework.core.annotation.Order; @Aspect public class ProfilingAspect { @Around("methodsToBeProfiled()") public Object profile(ProceedingJoinPoint pjp) throws Throwable { StopWatch sw = new StopWatch(getClass().getSimpleName()); try { sw.start(pjp.getSignature().getName()); return pjp.proceed(); } finally { sw.stop(); System.out.println(sw.prettyPrint()); } } @Pointcut("execution(public * foo..*.*(..))") public void methodsToBeProfiled(){} }
We will also need to create an
'META-INF/aop.xml
' file, to inform the AspectJ
weaver that we want to weave our
ProfilingAspect
into our classes. This file
convention, namely the presence of a file (or files) on the Java
classpath called ' META-INF/aop.xml
' is standard
AspectJ.
<!DOCTYPE aspectj PUBLIC "-//AspectJ//DTD//EN" "http://www.eclipse.org/aspectj/dtd/aspectj.dtd"> <aspectj> <weaver> <!-- only weave classes in our application-specific packages --> <include within="foo.*"/> </weaver> <aspects> <!-- weave in just this aspect --> <aspect name="foo.ProfilingAspect"/> </aspects> </aspectj>
Now to the Spring-specific portion of the configuration. We need
to configure a LoadTimeWeaver
(all
explained later, just take it on trust for now). This load-time weaver
is the essential component responsible for weaving the aspect
configuration in one or more 'META-INF/aop.xml
'
files into the classes in your application. The good thing is that it
does not require a lot of configuration, as can be seen below (there
are some more options that you can specify, but these are detailed
later).
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd"> <!-- a service object; we will be profiling it's methods --> <bean id="entitlementCalculationService" class="foo.StubEntitlementCalculationService"/> <!-- this switches on the load-time weaving --> <context:load-time-weaver/> </beans>
Now that all the required artifacts are in place - the aspect,
the 'META-INF/aop.xml
' file, and the Spring
configuration -, let us create a simple driver class with a
main(..)
method to demonstrate the LTW in
action.
package foo;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public final class Main {
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml", Main.class);
EntitlementCalculationService entitlementCalculationService
= (EntitlementCalculationService) ctx.getBean("entitlementCalculationService");
// the profiling aspect is 'woven' around this method execution
entitlementCalculationService.calculateEntitlement();
}
}
There is one last thing to do. The introduction to this section
did say that one could switch on LTW selectively on a
per-ClassLoader
basis with Spring, and this is
true. However, just for this example, we are going to use a Java agent
(supplied with Spring) to switch on the LTW. This is the command line
we will use to run the above Main
class:
java -javaagent:C:/projects/foo/lib/global/spring-agent.jar foo.Main
The '-javaagent
' is a Java 5+ flag for
specifying and enabling agents
to instrument programs running on the JVM. The Spring
Framework ships with such an agent, the
InstrumentationSavingAgent
, which is packaged
in the spring-agent.jar
that
was supplied as the value of the -javaagent
argument in the above example.
The output from the execution of the Main
program will look something like that below. (I have introduced a
Thread.sleep(..)
statement into the
calculateEntitlement()
implementation so that
the profiler actually captures something other than 0 milliseconds -
the 01234
milliseconds is not
an overhead introduced by the AOP :) )
Calculating entitlement StopWatch 'ProfilingAspect': running time (millis) = 1234 ------ ----- ---------------------------- ms % Task name ------ ----- ---------------------------- 01234 100% calculateEntitlement
Since this LTW is effected using full-blown AspectJ, we are not
just limited to advising Spring beans; the following slight variation
on the Main
program will yield the same
result.
package foo;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public final class Main {
public static void main(String[] args) {
new ClassPathXmlApplicationContext("beans.xml", Main.class);
EntitlementCalculationService entitlementCalculationService =
new StubEntitlementCalculationService();
// the profiling aspect will be 'woven' around this method execution
entitlementCalculationService.calculateEntitlement();
}
}
Notice how in the above program we are simply bootstrapping the
Spring container, and then creating a new instance of the
StubEntitlementCalculationService
totally
outside the context of Spring... the profiling advice still gets woven
in.
The example admittedly is simplistic... however the basics of the LTW support in Spring have all been introduced in the above example, and the rest of this section will explain the 'why' behind each bit of configuration and usage in detail.
![]() | Note |
---|---|
The |
The aspects that you use in LTW have to be AspectJ aspects. They can be written in either the AspectJ language itself or you can write your aspects in the @AspectJ-style. The latter option is of course only an option if you are using Java 5+, but it does mean that your aspects are then both valid AspectJ and Spring AOP aspects. Furthermore, the compiled aspect classes need to be available on the classpath.
The AspectJ LTW infrastructure is configured using one or more
'META-INF/aop.xml
' files, that are on the Java
classpath (either directly, or more typically in jar files).
The structure and contents of this file is detailed in the main
AspectJ reference documentation, and the interested reader is referred
to that resource. (I appreciate that this section is brief,
but the 'aop.xml
' file is 100% AspectJ - there is
no Spring-specific information or semantics that apply to it, and so
there is no extra value that I can contribute either as a result), so
rather than rehash the quite satisfactory section that the AspectJ
developers wrote, I am just directing you there.)
At a minimum you will need the following libraries to use the Spring Framework's support for AspectJ LTW:
spring.jar
(version
2.5 or later)
aspectjrt.jar
(version 1.5 or later)
aspectjweaver.jar
(version 1.5 or later)
If you are using the Spring-provided agent to enable instrumentation, you will also need:
spring-agent.jar
The key component in Spring's LTW support is the
LoadTimeWeaver
interface (in the
org.springframework.instrument.classloading
package), and the numerous implementations of it that ship with the
Spring distribution. A LoadTimeWeaver
is responsible for adding one or more
java.lang.instrument.ClassFileTransformers
to a
ClassLoader
at runtime, which opens the door to
all manner of interesting applications, one of which happens to be the
LTW of aspects.
![]() | Tip |
---|---|
If you are unfamiliar with the idea of runtime class file
transformation, you are encouraged to read the Javadoc API
documentation for the |
Configuring a LoadTimeWeaver
using XML for a particular
ApplicationContext
can be as easy as
adding one line. (Please note that you almost certainly will need to
be using an ApplicationContext
as your
Spring container - typically a
BeanFactory
will not be enough because
the LTW support makes use of
BeanFactoryPostProcessors
.)
To enable the Spring Framework's LTW support, you need to
configure a LoadTimeWeaver
, which
typically is done using the
<context:load-time-weaver/>
element. Find
below a valid <context:load-time-weaver/>
definition that uses default settings.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd"> <context:load-time-weaver/> </beans>
The above <context:load-time-weaver/>
bean definition will define and register a number of LTW-specific
infrastructure beans for you automatically, such as a
LoadTimeWeaver
and an
AspectJWeavingEnabler
. Notice how the
<context:load-time-weaver/>
is defined in the
'context
' namespace; note also that the referenced
XML Schema file is only available in versions of Spring 2.5 and
later.
What the above configuration does is define and register a
default LoadTimeWeaver
bean for you.
The default LoadTimeWeaver
is the
DefaultContextLoadTimeWeaver
class, which
attempts to decorate an automatically detected
LoadTimeWeaver
: the exact type of
LoadTimeWeaver
that will be
'automatically detected' is dependent upon your runtime environment
(summarised in the following table).
Table 6.1. DefaultContextLoadTimeWeaver
LoadTimeWeavers
Runtime Environment | LoadTimeWeaver implementation |
---|---|
Running in BEA's Weblogic 10 |
|
Running in Oracle's OC4J |
|
Running in GlassFish |
|
JVM started with Spring
|
|
Fallback, expecting the underlying ClassLoader to follow common conventions
(e.g. applicable to |
|
Note that these are just the
LoadTimeWeavers
that are autodetected
when using the DefaultContextLoadTimeWeaver
: it
is of course possible to specify exactly which
LoadTimeWeaver
implementation that you
wish to use by specifying the fully-qualified classname as the value
of the 'weaver-class
' attribute of the
<context:load-time-weaver/>
element. Find
below an example of doing just that:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<context:load-time-weaver
weaver-class="org.springframework.instrument.classloading.ReflectiveLoadTimeWeaver"/>
</beans>
The LoadTimeWeaver
that is
defined and registered by the
<context:load-time-weaver/>
element can be
later retrieved from the Spring container using the well-known name
'loadTimeWeaver
'. Remember that the
LoadTimeWeaver
exists just as a
mechanism for Spring's LTW infrastructure to add one or more
ClassFileTransformers
. The actual
ClassFileTransformer
that does the LTW is the
ClassPreProcessorAgentAdapter
(from the
org.aspectj.weaver.loadtime
package) class. See the
class-level Javadoc for the
ClassPreProcessorAgentAdapter
class for further
details, because the specifics of how the weaving is actually effected
is beyond the scope of this section.
There is one final attribute of the
<context:load-time-weaver/>
left to discuss:
the 'aspectj-weaving
' attribute. This is a simple
attribute that controls whether LTW is enabled or not, it is as simple
as that. It accepts one of three possible values, summarised below,
with the default value if the attribute is not present being '
autodetect
'
Table 6.2. 'aspectj-weaving
' attribute values
Attribute Value | Explanation |
---|---|
| AspectJ weaving is on, and aspects will be woven at load-time as appropriate. |
| LTW is off... no aspect will be woven at load-time. |
| If the Spring LTW infrastructure can find at
least one ' |
This last section contains any additional settings and configuration that you will need when using Spring's LTW support in environments such as application servers and web containers.
You may enable Spring's support for LTW in any Java application
(standalone as well as application server based) through the use of
the Spring-provided instrumentation agent. To do so, start
the VM by by specifying the
-javaagent:path/to/spring-agent.jar
option.
Note that this requires modification of the VM launch script
which may prevent you from using this in application server
environments (depending on your operation policies).
For web applications deployed onto Apache Tomcat 5.0 and above,
Spring provides a TomcatInstrumentableClassLoader
to be registered as the web app class loader. The required Tomcat setup
looks as follows, to be included either in Tomcat's central
server.xml
file or in an application-specific
META-INF/context.xml
file within the WAR root.
Spring's spring-tomcat-weaver.jar
needs to be
included in Tomcat's common lib directory in order to make this
setup work.
<Context path="/myWebApp" docBase="/my/webApp/location"> <Loader loaderClass="org.springframework.instrument.classloading.tomcat.TomcatInstrumentableClassLoader" useSystemClassLoaderAsParent="false"/> </Context>
Note: We generally recommend Tomcat 5.5.20 or above
when enabling load-time weaving. Prior versions have known
issues with custom ClassLoader
setup.
Alternatively, consider the use of the Spring-provided generic VM agent, to be specified in Tomcat's launch script (see above). This will make instrumentation available to all deployed web applications, no matter which ClassLoader they happen to run on.
For a more detailed discussion of Tomcat-based weaving setup, check out the Section 12.6.1.3.1, “Tomcat load-time weaving setup (5.0+)” section which discusses specifics of various Tomcat versions. While the primary focus of that section is on JPA persistence provider setup, the Tomcat setup characteristics apply to general load-time weaving as well.
Recent versions of BEA WebLogic (version 10 and above), Oracle
Containers for Java EE (OC4J 10.1.3.1 and above) and Resin (3.1 and above)
provide a ClassLoader that is capable of local instrumentation.
Spring's native LTW leverages such ClassLoaders to enable AspectJ weaving.
You can enable LTW by simply activating context:load-time-weaver
as described earlier. Specifically, you do not
need to modify the launch script to add
-javaagent:path/to/spring-agent.jar
.
GlassFish provides an instrumentation-capable ClassLoader as well, but only in its EAR environment. For GlassFish web applications, follow the Tomcat setup instructions as outlined above.
More information on AspectJ can be found on the AspectJ website.
The book Eclipse AspectJ by Adrian Colyer et. al. (Addison-Wesley, 2005) provides a comprehensive introduction and reference for the AspectJ language.
The book AspectJ in Action by Ramnivas Laddad (Manning, 2003) comes highly recommended; the focus of the book is on AspectJ, but a lot of general AOP themes are explored (in some depth).
The previous chapter described the Spring 2.0 support for AOP using @AspectJ and schema-based aspect definitions. In this chapter we discuss the lower-level Spring AOP APIs and the AOP support used in Spring 1.2 applications. For new applications, we recommend the use of the Spring 2.0 AOP support described in the previous chapter, but when working with existing applications, or when reading books and articles, you may come across Spring 1.2 style examples. Spring 2.0 is fully backwards compatible with Spring 1.2 and everything described in this chapter is fully supported in Spring 2.0.
Let's look at how Spring handles the crucial pointcut concept.
Spring's pointcut model enables pointcut reuse independent of advice types. It's possible to target different advice using the same pointcut.
The org.springframework.aop.Pointcut
interface
is the central interface, used to target advices to particular classes
and methods. The complete interface is shown below:
public interface Pointcut { ClassFilter getClassFilter(); MethodMatcher getMethodMatcher(); }
Splitting the Pointcut
interface into two parts
allows reuse of class and method matching parts, and fine-grained
composition operations (such as performing a "union" with another method
matcher).
The ClassFilter
interface is used to restrict
the pointcut to a given set of target classes. If the
matches()
method always returns true, all target
classes will be matched:
public interface ClassFilter { boolean matches(Class clazz); }
The MethodMatcher
interface is normally more
important. The complete interface is shown below:
public interface MethodMatcher { boolean matches(Method m, Class targetClass); boolean isRuntime(); boolean matches(Method m, Class targetClass, Object[] args); }
The matches(Method, Class)
method is used to
test whether this pointcut will ever match a given method on a target
class. This evaluation can be performed when an AOP proxy is created, to
avoid the need for a test on every method invocation. If the 2-argument
matches method returns true for a given method, and the
isRuntime()
method for the MethodMatcher returns
true, the 3-argument matches method will be invoked on every method
invocation. This enables a pointcut to look at the arguments passed to
the method invocation immediately before the target advice is to
execute.
Most MethodMatchers are static, meaning that their
isRuntime()
method returns false. In this case, the
3-argument matches method will never be invoked.
![]() | Tip |
---|---|
If possible, try to make pointcuts static, allowing the AOP framework to cache the results of pointcut evaluation when an AOP proxy is created. |
Spring supports operations on pointcuts: notably, union and intersection.
Union means the methods that either pointcut matches.
Intersection means the methods that both pointcuts match.
Union is usually more useful.
Pointcuts can be composed using the static methods in the org.springframework.aop.support.Pointcuts class, or using the ComposablePointcut class in the same package. However, using AspectJ pointcut expressions is usually a simpler approach.
Since 2.0, the most important type of pointcut used by Spring is
org.springframework.aop.aspectj.AspectJExpressionPointcut
.
This is a pointcut that uses an AspectJ supplied library to parse an AspectJ
pointcut expression string.
See the previous chapter for a discussion of supported AspectJ pointcut primitives.
Spring provides several convenient pointcut implementations. Some can be used out of the box; others are intended to be subclassed in application-specific pointcuts.
Static pointcuts are based on method and target class, and cannot take into account the method's arguments. Static pointcuts are sufficient - and best - for most usages. It's possible for Spring to evaluate a static pointcut only once, when a method is first invoked: after that, there is no need to evaluate the pointcut again with each method invocation.
Let's consider some static pointcut implementations included with Spring.
One obvious way to specify static pointcuts is regular
expressions. Several AOP frameworks besides Spring make this
possible.
org.springframework.aop.support.Perl5RegexpMethodPointcut
is a generic regular expression pointcut, using Perl 5 regular
expression syntax. The Perl5RegexpMethodPointcut
class depends on Jakarta ORO for regular expression matching. Spring
also provides the JdkRegexpMethodPointcut
class
that uses the regular expression support in JDK 1.4+.
Using the Perl5RegexpMethodPointcut
class,
you can provide a list of pattern Strings. If any of these is a
match, the pointcut will evaluate to true. (So the result is
effectively the union of these pointcuts.)
The usage is shown below:
<bean id="settersAndAbsquatulatePointcut" class="org.springframework.aop.support.Perl5RegexpMethodPointcut"> <property name="patterns"> <list> <value>.*set.*</value> <value>.*absquatulate</value> </list> </property> </bean>
Spring provides a convenience class,
RegexpMethodPointcutAdvisor
, that allows us to
also reference an Advice (remember that an Advice can be an
interceptor, before advice, throws advice etc.). Behind the scenes,
Spring will use the JdkRegexpMethodPointcut
on
J2SE 1.4 or above, and will fall back to
Perl5RegexpMethodPointcut
on older VMs. The use
of Perl5RegexpMethodPointcut
can be forced by
setting the perl5
property to true. Using
RegexpMethodPointcutAdvisor
simplifies wiring, as
the one bean encapsulates both pointcut and advice, as shown
below:
<bean id="settersAndAbsquatulateAdvisor" class="org.springframework.aop.support.RegexpMethodPointcutAdvisor"> <property name="advice"> <ref local="beanNameOfAopAllianceInterceptor"/> </property> <property name="patterns"> <list> <value>.*set.*</value> <value>.*absquatulate</value> </list> </property> </bean>
RegexpMethodPointcutAdvisor can be used with any Advice type.
Dynamic pointcuts are costlier to evaluate than static pointcuts. They take into account method arguments, as well as static information. This means that they must be evaluated with every method invocation; the result cannot be cached, as arguments will vary.
The main example is the control flow
pointcut.
Spring control flow pointcuts are conceptually similar to
AspectJ cflow pointcuts, although less
powerful. (There is currently no way to specify that a pointcut
executes below a join point matched by another pointcut.)
A control flow pointcut matches
the current call stack. For example, it might fire if the join point
was invoked by a method in the com.mycompany.web
package, or by the SomeCaller
class. Control flow
pointcuts are specified using the
org.springframework.aop.support.ControlFlowPointcut
class.
![]() | Note |
---|---|
Control flow pointcuts are significantly more expensive to evaluate at runtime than even other dynamic pointcuts. In Java 1.4, the cost is about 5 times that of other dynamic pointcuts. |
Spring provides useful pointcut superclasses to help you to implement your own pointcuts.
Because static pointcuts are most useful, you'll probably subclass StaticMethodMatcherPointcut, as shown below. This requires implementing just one abstract method (although it's possible to override other methods to customize behavior):
class TestStaticPointcut extends StaticMethodMatcherPointcut { public boolean matches(Method m, Class targetClass) { // return true if custom criteria match } }
There are also superclasses for dynamic pointcuts.
You can use custom pointcuts with any advice type in Spring 1.0 RC2 and above.
Because pointcuts in Spring AOP are Java classes, rather than language features (as in AspectJ) it's possible to declare custom pointcuts, whether static or dynamic. Custom pointcuts in Spring can be arbitrarily complex. However, using the AspectJ pointcut expression language is recommended if possible.
![]() | Note |
---|---|
Later versions of Spring may offer support for "semantic pointcuts" as offered by JAC: for example, "all methods that change instance variables in the target object." |
Let's now look at how Spring AOP handles advice.
Each advice is a Spring bean. An advice instance can be shared across all advised objects, or unique to each advised object. This corresponds to per-class or per-instance advice.
Per-class advice is used most often. It is appropriate for generic advice such as transaction advisors. These do not depend on the state of the proxied object or add new state; they merely act on the method and arguments.
Per-instance advice is appropriate for introductions, to support mixins. In this case, the advice adds state to the proxied object.
It's possible to use a mix of shared and per-instance advice in the same AOP proxy.
Spring provides several advice types out of the box, and is extensible to support arbitrary advice types. Let us look at the basic concepts and standard advice types.
The most fundamental advice type in Spring is interception around advice.
Spring is compliant with the AOP Alliance interface for around advice using method interception. MethodInterceptors implementing around advice should implement the following interface:
public interface MethodInterceptor extends Interceptor { Object invoke(MethodInvocation invocation) throws Throwable; }
The MethodInvocation
argument to the
invoke()
method exposes the method being invoked;
the target join point; the AOP proxy; and the arguments to the method.
The invoke()
method should return the
invocation's result: the return value of the join point.
A simple MethodInterceptor
implementation
looks as follows:
public class DebugInterceptor implements MethodInterceptor { public Object invoke(MethodInvocation invocation) throws Throwable { System.out.println("Before: invocation=[" + invocation + "]"); Object rval = invocation.proceed(); System.out.println("Invocation returned"); return rval; } }
Note the call to the MethodInvocation's
proceed()
method. This proceeds down the
interceptor chain towards the join point. Most interceptors will invoke
this method, and return its return value. However, a
MethodInterceptor, like any around advice, can return a different
value or throw an exception rather than invoke the proceed method.
However, you don't want to do this without good reason!
![]() | Note |
---|---|
MethodInterceptors offer interoperability with other AOP Alliance-compliant AOP implementations. The other advice types discussed in the remainder of this section implement common AOP concepts, but in a Spring-specific way. While there is an advantage in using the most specific advice type, stick with MethodInterceptor around advice if you are likely to want to run the aspect in another AOP framework. Note that pointcuts are not currently interoperable between frameworks, and the AOP Alliance does not currently define pointcut interfaces. |
A simpler advice type is a before
advice. This does not need a
MethodInvocation
object, since it will only be
called before entering the method.
The main advantage of a before advice is that there is no need
to invoke the proceed()
method, and therefore no
possibility of inadvertently failing to proceed down the interceptor
chain.
The MethodBeforeAdvice
interface is shown
below. (Spring's API design would allow for field before advice,
although the usual objects apply to field interception and it's
unlikely that Spring will ever implement it).
public interface MethodBeforeAdvice extends BeforeAdvice { void before(Method m, Object[] args, Object target) throws Throwable; }
Note the return type is void
. Before
advice can insert custom behavior before the join point executes, but
cannot change the return value. If a before advice throws an
exception, this will abort further execution of the interceptor chain.
The exception will propagate back up the interceptor chain. If it is
unchecked, or on the signature of the invoked method, it will be
passed directly to the client; otherwise it will be wrapped in an
unchecked exception by the AOP proxy.
An example of a before advice in Spring, which counts all method invocations:
public class CountingBeforeAdvice implements MethodBeforeAdvice { private int count; public void before(Method m, Object[] args, Object target) throws Throwable { ++count; } public int getCount() { return count; } }
![]() | Tip |
---|---|
Before advice can be used with any pointcut. |
Throws advice is invoked after
the return of the join point if the join point threw an exception.
Spring offers typed throws advice. Note that this means that the
org.springframework.aop.ThrowsAdvice
interface does
not contain any methods: It is a tag interface identifying that the
given object implements one or more typed throws advice methods. These
should be in the form of:
afterThrowing([Method, args, target], subclassOfThrowable)
Only the last argument is required. The method signatures may have either one or four arguments, depending on whether the advice method is interested in the method and arguments. The following classes are examples of throws advice.
The advice below is invoked if a RemoteException
is thrown (including subclasses):
public class RemoteThrowsAdvice implements ThrowsAdvice {
public void afterThrowing(RemoteException ex) throws Throwable {
// Do something with remote exception
}
}
The following advice is invoked if a
ServletException
is thrown. Unlike the above
advice, it declares 4 arguments, so that it has access to the invoked
method, method arguments and target object:
public class ServletThrowsAdviceWithArguments implements ThrowsAdvice {
public void afterThrowing(Method m, Object[] args, Object target, ServletException ex) {
// Do something with all arguments
}
}
The final example illustrates how these two methods could be
used in a single class, which handles both
RemoteException
and
ServletException
. Any number of throws advice
methods can be combined in a single class.
public static class CombinedThrowsAdvice implements ThrowsAdvice { public void afterThrowing(RemoteException ex) throws Throwable { // Do something with remote exception } public void afterThrowing(Method m, Object[] args, Object target, ServletException ex) { // Do something with all arguments } }
Note: If a throws-advice method throws an exception itself, it will override the original exception (i.e. change the exception thrown to the user). The overriding exception will typically be a RuntimeException; this is compatible with any method signature. However, if a throws-advice method throws a checked exception, it will have to match the declared exceptions of the target method and is hence to some degree coupled to specific target method signatures. Do not throw an undeclared checked exception that is incompatible with the target method's signature!
![]() | Tip |
---|---|
Throws advice can be used with any pointcut. |
An after returning advice in Spring must implement the org.springframework.aop.AfterReturningAdvice interface, shown below:
public interface AfterReturningAdvice extends Advice { void afterReturning(Object returnValue, Method m, Object[] args, Object target) throws Throwable; }
An after returning advice has access to the return value (which it cannot modify), invoked method, methods arguments and target.
The following after returning advice counts all successful method invocations that have not thrown exceptions:
public class CountingAfterReturningAdvice implements AfterReturningAdvice { private int count; public void afterReturning(Object returnValue, Method m, Object[] args, Object target) throws Throwable { ++count; } public int getCount() { return count; } }
This advice doesn't change the execution path. If it throws an exception, this will be thrown up the interceptor chain instead of the return value.
![]() | Tip |
---|---|
After returning advice can be used with any pointcut. |
Spring treats introduction advice as a special kind of interception advice.
Introduction requires an IntroductionAdvisor
,
and an IntroductionInterceptor
, implementing the
following interface:
public interface IntroductionInterceptor extends MethodInterceptor { boolean implementsInterface(Class intf); }
The invoke()
method inherited from the AOP
Alliance MethodInterceptor
interface must implement
the introduction: that is, if the invoked method is on an introduced
interface, the introduction interceptor is responsible for handling
the method call - it cannot invoke proceed()
.
Introduction advice cannot be used with any pointcut, as it
applies only at class, rather than method, level. You can only use
introduction advice with the IntroductionAdvisor
,
which has the following methods:
public interface IntroductionAdvisor extends Advisor, IntroductionInfo { ClassFilter getClassFilter(); void validateInterfaces() throws IllegalArgumentException; } public interface IntroductionInfo { Class[] getInterfaces(); }
There is no MethodMatcher
, and hence no
Pointcut
, associated with introduction advice. Only
class filtering is logical.
The getInterfaces()
method returns the
interfaces introduced by this advisor.
validateInterfaces()
method is used internally to see whether or not the introduced interfaces can be implemented by the configured
IntroductionInterceptor
.
Let's look at a simple example from the Spring test suite. Let's suppose we want to introduce the following interface to one or more objects:
public interface Lockable { void lock(); void unlock(); boolean locked(); }
This illustrates a mixin. We
want to be able to cast advised objects to Lockable, whatever their
type, and call lock and unlock methods. If we call the lock() method,
we want all setter methods to throw a
LockedException
. Thus we can add an aspect that
provides the ability to make objects immutable, without them having
any knowledge of it: a good example of AOP.
Firstly, we'll need an
IntroductionInterceptor
that does the heavy
lifting. In this case, we extend the
org.springframework.aop.support.DelegatingIntroductionInterceptor
convenience class. We could implement IntroductionInterceptor
directly, but using
DelegatingIntroductionInterceptor
is best for most
cases.
The DelegatingIntroductionInterceptor
is
designed to delegate an introduction to an actual implementation of
the introduced interface(s), concealing the use of interception to do
so. The delegate can be set to any object using a constructor
argument; the default delegate (when the no-arg constructor is used)
is this. Thus in the example below, the delegate is the
LockMixin
subclass of
DelegatingIntroductionInterceptor
. Given a delegate
(by default itself), a
DelegatingIntroductionInterceptor
instance looks
for all interfaces implemented by the delegate (other than
IntroductionInterceptor), and will support introductions against any
of them. It's possible for subclasses such as
LockMixin
to call the
suppressInterface(Class intf)
method to suppress
interfaces that should not be exposed. However, no matter how many
interfaces an IntroductionInterceptor
is prepared
to support, the IntroductionAdvisor
used will
control which interfaces are actually exposed. An introduced interface
will conceal any implementation of the same interface by the
target.
Thus LockMixin subclasses
DelegatingIntroductionInterceptor
and implements
Lockable itself. The superclass automatically picks up that Lockable
can be supported for introduction, so we don't need to specify that.
We could introduce any number of interfaces in this way.
Note the use of the locked
instance variable.
This effectively adds additional state to that held in the target
object.
public class LockMixin extends DelegatingIntroductionInterceptor implements Lockable { private boolean locked; public void lock() { this.locked = true; } public void unlock() { this.locked = false; } public boolean locked() { return this.locked; } public Object invoke(MethodInvocation invocation) throws Throwable { if (locked() && invocation.getMethod().getName().indexOf("set") == 0) throw new LockedException(); return super.invoke(invocation); } }
Often it isn't necessary to override the invoke()
method: the
DelegatingIntroductionInterceptor
implementation - which calls the delegate method if the method is
introduced, otherwise proceeds towards the join point - is usually
sufficient. In the present case, we need to add a check: no setter
method can be invoked if in locked mode.
The introduction advisor required is simple. All it needs to do
is hold a distinct LockMixin
instance, and specify
the introduced interfaces - in this case, just
Lockable
. A more complex example might take a
reference to the introduction interceptor (which would be defined as a
prototype): in this case, there's no configuration relevant for a
LockMixin
, so we simply create it using
new
.
public class LockMixinAdvisor extends DefaultIntroductionAdvisor { public LockMixinAdvisor() { super(new LockMixin(), Lockable.class); } }
We can apply this advisor very simply: it requires no
configuration. (However, it is necessary: It's
impossible to use an IntroductionInterceptor
without an IntroductionAdvisor.) As usual with
introductions, the advisor must be per-instance, as it is stateful. We
need a different instance of LockMixinAdvisor
, and
hence LockMixin
, for each advised object. The
advisor comprises part of the advised object's state.
We can apply this advisor programmatically, using the
Advised.addAdvisor()
method, or (the recommended
way) in XML configuration, like any other advisor. All proxy creation
choices discussed below, including "auto proxy creators," correctly
handle introductions and stateful mixins.
In Spring, an Advisor is an aspect that contains just a single advice object associated with a pointcut expression.
Apart from the special case of introductions, any advisor can be
used with any advice.
org.springframework.aop.support.DefaultPointcutAdvisor
is the most commonly used advisor class. For example, it can be used with
a MethodInterceptor
, BeforeAdvice
or
ThrowsAdvice
.
It is possible to mix advisor and advice types in Spring in the same AOP proxy. For example, you could use a interception around advice, throws advice and before advice in one proxy configuration: Spring will automatically create the necessary interceptor chain.
If you're using the Spring IoC container (an ApplicationContext or BeanFactory) for your business objects - and you should be! - you will want to use one of Spring's AOP FactoryBeans. (Remember that a factory bean introduces a layer of indirection, enabling it to create objects of a different type.)
![]() | Note |
---|---|
The Spring 2.0 AOP support also uses factory beans under the covers. |
The basic way to create an AOP proxy in Spring is to use the org.springframework.aop.framework.ProxyFactoryBean. This gives complete control over the pointcuts and advice that will apply, and their ordering. However, there are simpler options that are preferable if you don't need such control.
The ProxyFactoryBean
, like other Spring
FactoryBean
implementations, introduces a level of
indirection. If you define a ProxyFactoryBean
with
name foo
, what objects referencing
foo
see is not the
ProxyFactoryBean
instance itself, but an object
created by the ProxyFactoryBean
's implementation of
the getObject()
method. This method will create an
AOP proxy wrapping a target object.
One of the most important benefits of using a
ProxyFactoryBean
or another IoC-aware class to create
AOP proxies, is that it means that advices and pointcuts can also be
managed by IoC. This is a powerful feature, enabling certain approaches
that are hard to achieve with other AOP frameworks. For example, an
advice may itself reference application objects (besides the target,
which should be available in any AOP framework), benefiting from all the
pluggability provided by Dependency Injection.
In common with most FactoryBean
implementations
provided with Spring, the ProxyFactoryBean
class is
itself a JavaBean. Its properties are used to:
Specify the target you want to proxy.
Specify whether to use CGLIB (see below and also the section entitled Section 7.5.3, “JDK- and CGLIB-based proxies”).
Some key properties are inherited from
org.springframework.aop.framework.ProxyConfig
(the
superclass for all AOP proxy factories in Spring). These key properties include:
proxyTargetClass
: true
if the
target class is to be proxied, rather than the target class' interfaces.
If this property value is set to true
, then CGLIB proxies
will be created (but see also below the section entitled
Section 7.5.3, “JDK- and CGLIB-based proxies”).
optimize
: controls whether or not aggressive
optimizations are applied to proxies created via CGLIB.
One should not blithely use this setting unless one fully understands
how the relevant AOP proxy handles optimization. This is currently used only
for CGLIB proxies; it has no effect with JDK dynamic proxies.
frozen
: if a proxy configuration is frozen
,
then changes to the configuration are no longer allowed. This is useful both as
a slight optimization and for those cases when you don't want callers to be able
to manipulate the proxy (via the Advised
interface)
after the proxy has been created. The default value of this property is
false
, so changes such as adding additional advice are allowed.
exposeProxy
: determines whether or not the current
proxy should be exposed in a ThreadLocal
so that
it can be accessed by the target. If a target needs to obtain
the proxy and the exposeProxy
property is set to
true
, the target can use the
AopContext.currentProxy()
method.
aopProxyFactory
: the implementation of
AopProxyFactory
to use. Offers a way of
customizing whether to use dynamic proxies, CGLIB or any other proxy
strategy. The default implementation will choose dynamic proxies or
CGLIB appropriately. There should be no need to use this property;
it is intended to allow the addition of new proxy types in Spring 1.1.
Other properties specific to ProxyFactoryBean
include:
proxyInterfaces
: array of String interface
names. If this isn't supplied, a CGLIB proxy for the target class
will be used (but see also below the section entitled
Section 7.5.3, “JDK- and CGLIB-based proxies”).
interceptorNames
: String array of
Advisor
, interceptor or other advice
names to apply. Ordering is significant, on a first come-first served
basis. That is to say that the first interceptor in the list
will be the first to be able to intercept the invocation.
The names are bean names in the current factory, including
bean names from ancestor factories. You can't mention bean
references here since doing so would result in the
ProxyFactoryBean
ignoring the singleton
setting of the advice.
You can append an interceptor name with an asterisk
(*
). This will result in the application of all
advisor beans with names starting with the part before the asterisk
to be applied. An example of using this feature can be found in
Section 7.5.6, “Using 'global' advisors”.
singleton: whether or not the factory should return a single
object, no matter how often the getObject()
method is called. Several FactoryBean
implementations offer such a method. The default value is
true
. If you want to use stateful advice -
for example, for stateful mixins - use prototype advices along
with a singleton value of false
.
This section serves as the definitive documentation on how the
ProxyFactoryBean
chooses to create one of
either a JDK- and CGLIB-based proxy for a particular target object
(that is to be proxied).
![]() | Note |
---|---|
The behavior of the |
If the class of a target object that is to be proxied (hereafter simply
referred to as the target class) doesn't implement any interfaces, then
a CGLIB-based proxy will be created. This is the easiest scenario, because
JDK proxies are interface based, and no interfaces means JDK proxying
isn't even possible. One simply plugs in the target bean, and specifies the
list of interceptors via the interceptorNames
property.
Note that a CGLIB-based proxy will be created even if the
proxyTargetClass
property of the
ProxyFactoryBean
has been set to false
.
(Obviously this makes no sense, and is best removed from the bean
definition because it is at best redundant, and at worst confusing.)
If the target class implements one (or more) interfaces, then the type of
proxy that is created depends on the configuration of the
ProxyFactoryBean
.
If the proxyTargetClass
property of the
ProxyFactoryBean
has been set to true
,
then a CGLIB-based proxy will be created. This makes sense, and is in
keeping with the principle of least surprise. Even if the
proxyInterfaces
property of the
ProxyFactoryBean
has been set to one or more
fully qualified interface names, the fact that the
proxyTargetClass
property is set to
true
will cause
CGLIB-based proxying to be in effect.
If the proxyInterfaces
property of the
ProxyFactoryBean
has been set to one or more
fully qualified interface names, then a JDK-based proxy will be created.
The created proxy will implement all of the interfaces that were specified
in the proxyInterfaces
property; if the target class
happens to implement a whole lot more interfaces than those specified in
the proxyInterfaces
property, that is all well and
good but those additional interfaces will not be implemented by the
returned proxy.
If the proxyInterfaces
property of the
ProxyFactoryBean
has not been
set, but the target class does implement one (or more)
interfaces, then the ProxyFactoryBean
will auto-detect
the fact that the target class does actually implement at least one interface,
and a JDK-based proxy will be created. The interfaces that are actually
proxied will be all of the interfaces that the target
class implements; in effect, this is the same as simply supplying a list
of each and every interface that the target class implements to the
proxyInterfaces
property. However, it is significantly less
work, and less prone to typos.
Let's look at a simple example of ProxyFactoryBean
in action. This example involves:
A target bean that will be proxied. This is the "personTarget" bean definition in the example below.
An Advisor and an Interceptor used to provide advice.
An AOP proxy bean definition specifying the target object (the personTarget bean) and the interfaces to proxy, along with the advices to apply.
<bean id="personTarget" class="com.mycompany.PersonImpl"> <property name="name"><value>Tony</value></property> <property name="age"><value>51</value></property> </bean> <bean id="myAdvisor" class="com.mycompany.MyAdvisor"> <property name="someProperty"><value>Custom string property value</value></property> </bean> <bean id="debugInterceptor" class="org.springframework.aop.interceptor.DebugInterceptor"> </bean> <bean id="person" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="proxyInterfaces"><value>com.mycompany.Person</value></property> <property name="target"><ref local="personTarget"/></property> <property name="interceptorNames"> <list> <value>myAdvisor</value> <value>debugInterceptor</value> </list> </property> </bean>
Note that the interceptorNames
property takes a
list of String: the bean names of the interceptor or advisors in the
current factory. Advisors, interceptors, before, after returning and
throws advice objects can be used. The ordering of advisors is
significant.
![]() | Note |
---|---|
You might be wondering why the list doesn't hold bean references. The reason for this is that if the ProxyFactoryBean's singleton property is set to false, it must be able to return independent proxy instances. If any of the advisors is itself a prototype, an independent instance would need to be returned, so it's necessary to be able to obtain an instance of the prototype from the factory; holding a reference isn't sufficient. |
The "person" bean definition above can be used in place of a Person implementation, as follows:
Person person = (Person) factory.getBean("person");
Other beans in the same IoC context can express a strongly typed dependency on it, as with an ordinary Java object:
<bean id="personUser" class="com.mycompany.PersonUser"> <property name="person"><ref local="person" /></property> </bean>
The PersonUser
class in this example would
expose a property of type Person. As far as it's concerned, the AOP
proxy can be used transparently in place of a "real" person
implementation. However, its class would be a dynamic proxy class. It
would be possible to cast it to the Advised
interface
(discussed below).
It's possible to conceal the distinction between target and proxy
using an anonymous inner bean, as follows. Only the
ProxyFactoryBean
definition is different; the advice
is included only for completeness:
<bean id="myAdvisor" class="com.mycompany.MyAdvisor"> <property name="someProperty"><value>Custom string property value</value></property> </bean> <bean id="debugInterceptor" class="org.springframework.aop.interceptor.DebugInterceptor"/> <bean id="person" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="proxyInterfaces"><value>com.mycompany.Person</value></property> <!-- Use inner bean, not local reference to target --> <property name="target"> <bean class="com.mycompany.PersonImpl"> <property name="name"><value>Tony</value></property> <property name="age"><value>51</value></property> </bean> </property> <property name="interceptorNames"> <list> <value>myAdvisor</value> <value>debugInterceptor</value> </list> </property> </bean>
This has the advantage that there's only one object of type
Person
: useful if we want to prevent users of the
application context from obtaining a reference to the un-advised object, or
need to avoid any ambiguity with Spring IoC
autowiring. There's also arguably an advantage in
that the ProxyFactoryBean definition is self-contained. However, there
are times when being able to obtain the un-advised target from the
factory might actually be an advantage: for
example, in certain test scenarios.
What if you need to proxy a class, rather than one or more interfaces?
Imagine that in our example above, there was no
Person
interface: we needed to advise a class called
Person
that didn't implement any business interface.
In this case, you can configure Spring to use CGLIB proxying, rather
than dynamic proxies. Simply set the proxyTargetClass
property on the ProxyFactoryBean above to true. While it's best to
program to interfaces, rather than classes, the ability to advise
classes that don't implement interfaces can be useful when working with
legacy code. (In general, Spring isn't prescriptive. While it makes it
easy to apply good practices, it avoids forcing a particular
approach.)
If you want to, you can force the use of CGLIB in any case, even if you do have interfaces.
CGLIB proxying works by generating a subclass of the target class at runtime. Spring configures this generated subclass to delegate method calls to the original target: the subclass is used to implement the Decorator pattern, weaving in the advice.
CGLIB proxying should generally be transparent to users. However, there are some issues to consider:
Final
methods can't be advised, as they
can't be overridden.
You'll need the CGLIB 2 binaries on your classpath; dynamic proxies are available with the JDK.
There's little performance difference between CGLIB proxying and dynamic proxies. As of Spring 1.0, dynamic proxies are slightly faster. However, this may change in the future. Performance should not be a decisive consideration in this case.
By appending an asterisk to an interceptor name, all advisors with bean names matching the part before the asterisk, will be added to the advisor chain. This can come in handy if you need to add a standard set of 'global' advisors:
<bean id="proxy" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="target" ref="service"/> <property name="interceptorNames"> <list> <value>global*</value> </list> </property> </bean> <bean id="global_debug" class="org.springframework.aop.interceptor.DebugInterceptor"/> <bean id="global_performance" class="org.springframework.aop.interceptor.PerformanceMonitorInterceptor"/>
Especially when defining transactional proxies, you may end up with many similar proxy definitions. The use of parent and child bean definitions, along with inner bean definitions, can result in much cleaner and more concise proxy definitions.
First a parent, template, bean definition is created for the proxy:
<bean id="txProxyTemplate" abstract="true" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean"> <property name="transactionManager" ref="transactionManager"/> <property name="transactionAttributes"> <props> <prop key="*">PROPAGATION_REQUIRED</prop> </props> </property> </bean>
This will never be instantiated itself, so may actually be incomplete. Then each proxy which needs to be created is just a child bean definition, which wraps the target of the proxy as an inner bean definition, since the target will never be used on its own anyway.
<bean id="myService" parent="txProxyTemplate"> <property name="target"> <bean class="org.springframework.samples.MyServiceImpl"> </bean> </property> </bean>
It is of course possible to override properties from the parent template, such as in this case, the transaction propagation settings:
<bean id="mySpecialService" parent="txProxyTemplate"> <property name="target"> <bean class="org.springframework.samples.MySpecialServiceImpl"> </bean> </property> <property name="transactionAttributes"> <props> <prop key="get*">PROPAGATION_REQUIRED,readOnly</prop> <prop key="find*">PROPAGATION_REQUIRED,readOnly</prop> <prop key="load*">PROPAGATION_REQUIRED,readOnly</prop> <prop key="store*">PROPAGATION_REQUIRED</prop> </props> </property> </bean>
Note that in the example above, we have explicitly marked the parent bean definition as abstract by using the abstract attribute, as described previously, so that it may not actually ever be instantiated. Application contexts (but not simple bean factories) will by default pre-instantiate all singletons. It is therefore important (at least for singleton beans) that if you have a (parent) bean definition which you intend to use only as a template, and this definition specifies a class, you must make sure to set the abstract attribute to true, otherwise the application context will actually try to pre-instantiate it.
It's easy to create AOP proxies programmatically using Spring. This enables you to use Spring AOP without dependency on Spring IoC.
The following listing shows creation of a proxy for a target object, with one interceptor and one advisor. The interfaces implemented by the target object will automatically be proxied:
ProxyFactory factory = new ProxyFactory(myBusinessInterfaceImpl); factory.addInterceptor(myMethodInterceptor); factory.addAdvisor(myAdvisor); MyBusinessInterface tb = (MyBusinessInterface) factory.getProxy();
The first step is to construct an object of type
org.springframework.aop.framework.ProxyFactory
. You can
create this with a target object, as in the above example, or specify the
interfaces to be proxied in an alternate constructor.
You can add interceptors or advisors, and manipulate them for the life of the ProxyFactory. If you add an IntroductionInterceptionAroundAdvisor you can cause the proxy to implement additional interfaces.
There are also convenience methods on ProxyFactory (inherited from
AdvisedSupport
) which allow you to add other advice types
such as before and throws advice. AdvisedSupport is the superclass of both
ProxyFactory and ProxyFactoryBean.
![]() | Tip |
---|---|
Integrating AOP proxy creation with the IoC framework is best practice in most applications. We recommend that you externalize configuration from Java code with AOP, as in general. |
However you create AOP proxies, you can manipulate them using the
org.springframework.aop.framework.Advised
interface.
Any AOP proxy can be cast to this interface, whichever other interfaces it
implements. This interface includes the following methods:
Advisor[] getAdvisors(); void addAdvice(Advice advice) throws AopConfigException; void addAdvice(int pos, Advice advice) throws AopConfigException; void addAdvisor(Advisor advisor) throws AopConfigException; void addAdvisor(int pos, Advisor advisor) throws AopConfigException; int indexOf(Advisor advisor); boolean removeAdvisor(Advisor advisor) throws AopConfigException; void removeAdvisor(int index) throws AopConfigException; boolean replaceAdvisor(Advisor a, Advisor b) throws AopConfigException; boolean isFrozen();
The getAdvisors()
method will return an Advisor
for every advisor, interceptor or other advice type that has been added to
the factory. If you added an Advisor, the returned advisor at this index
will be the object that you added. If you added an interceptor or other
advice type, Spring will have wrapped this in an advisor with a pointcut
that always returns true. Thus if you added a
MethodInterceptor
, the advisor returned for this index
will be an DefaultPointcutAdvisor
returning your
MethodInterceptor
and a pointcut that matches all
classes and methods.
The addAdvisor()
methods can be used to add any
Advisor. Usually the advisor holding pointcut and advice will be the
generic DefaultPointcutAdvisor
, which can be used with
any advice or pointcut (but not for introductions).
By default, it's possible to add or remove advisors or interceptors even once a proxy has been created. The only restriction is that it's impossible to add or remove an introduction advisor, as existing proxies from the factory will not show the interface change. (You can obtain a new proxy from the factory to avoid this problem.)
A simple example of casting an AOP proxy to the
Advised
interface and examining and manipulating its
advice:
Advised advised = (Advised) myObject; Advisor[] advisors = advised.getAdvisors(); int oldAdvisorCount = advisors.length; System.out.println(oldAdvisorCount + " advisors"); // Add an advice like an interceptor without a pointcut // Will match all proxied methods // Can use for interceptors, before, after returning or throws advice advised.addAdvice(new DebugInterceptor()); // Add selective advice using a pointcut advised.addAdvisor(new DefaultPointcutAdvisor(mySpecialPointcut, myAdvice)); assertEquals("Added two advisors", oldAdvisorCount + 2, advised.getAdvisors().length);
![]() | Note |
---|---|
It's questionable whether it's advisable (no pun intended) to modify advice on a business object in production, although there are no doubt legitimate usage cases. However, it can be very useful in development: for example, in tests. I have sometimes found it very useful to be able to add test code in the form of an interceptor or other advice, getting inside a method invocation I want to test. (For example, the advice can get inside a transaction created for that method: for example, to run SQL to check that a database was correctly updated, before marking the transaction for roll back.) |
Depending on how you created the proxy, you can usually set a
frozen
flag, in which case the
Advised
isFrozen()
method will
return true, and any attempts to modify advice through addition or removal
will result in an AopConfigException
. The ability to
freeze the state of an advised object is useful in some cases, for
example, to prevent calling code removing a security interceptor. It may
also be used in Spring 1.1 to allow aggressive optimization if runtime
advice modification is known not to be required.
So far we've considered explicit creation of AOP proxies using a
ProxyFactoryBean
or similar factory bean.
Spring also allows us to use "autoproxy" bean definitions, which can automatically proxy selected bean definitions. This is built on Spring "bean post processor" infrastructure, which enables modification of any bean definition as the container loads.
In this model, you set up some special bean definitions in your XML
bean definition file to configure the auto proxy infrastructure. This
allows you just to declare the targets eligible for autoproxying: you
don't need to use ProxyFactoryBean
.
There are two ways to do this:
Using an autoproxy creator that refers to specific beans in the current context.
A special case of autoproxy creation that deserves to be considered separately; autoproxy creation driven by source-level metadata attributes.
The org.springframework.aop.framework.autoproxy
package provides the following standard autoproxy creators.
The BeanNameAutoProxyCreator
class is a
BeanPostProcessor
that automatically creates AOP proxies
for beans with names matching literal values or wildcards.
<bean class="org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator"> <property name="beanNames"><value>jdk*,onlyJdk</value></property> <property name="interceptorNames"> <list> <value>myInterceptor</value> </list> </property> </bean>
As with ProxyFactoryBean
, there is an
interceptorNames
property rather than a list of interceptors, to allow
correct behavior for prototype advisors. Named "interceptors" can be
advisors or any advice type.
As with auto proxying in general, the main point of using
BeanNameAutoProxyCreator
is to apply the same
configuration consistently to multiple objects, with minimal
volume of configuration. It is a popular choice for applying
declarative transactions to multiple objects.
Bean definitions whose names match, such as "jdkMyBean" and
"onlyJdk" in the above example, are plain old bean definitions with
the target class. An AOP proxy will be created automatically by the
BeanNameAutoProxyCreator
. The same advice will be
applied to all matching beans. Note that if advisors are used (rather
than the interceptor in the above example), the pointcuts may apply
differently to different beans.
A more general and extremely powerful auto proxy creator is
DefaultAdvisorAutoProxyCreator
. This will
automagically apply eligible advisors in the current context, without
the need to include specific bean names in the autoproxy advisor's
bean definition. It offers the same merit of consistent configuration
and avoidance of duplication as
BeanNameAutoProxyCreator
.
Using this mechanism involves:
Specifying a
DefaultAdvisorAutoProxyCreator
bean
definition.
Specifying any number of Advisors in the same or related contexts. Note that these must be Advisors, not just interceptors or other advices. This is necessary because there must be a pointcut to evaluate, to check the eligibility of each advice to candidate bean definitions.
The DefaultAdvisorAutoProxyCreator
will
automatically evaluate the pointcut contained in each advisor, to see
what (if any) advice it should apply to each business object (such as
"businessObject1" and "businessObject2" in the example).
This means that any number of advisors can be applied automatically to each business object. If no pointcut in any of the advisors matches any method in a business object, the object will not be proxied. As bean definitions are added for new business objects, they will automatically be proxied if necessary.
Autoproxying in general has the advantage of making it impossible for callers or dependencies to obtain an un-advised object. Calling getBean("businessObject1") on this ApplicationContext will return an AOP proxy, not the target business object. (The "inner bean" idiom shown earlier also offers this benefit.)
<bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/> <bean class="org.springframework.transaction.interceptor.TransactionAttributeSourceAdvisor"> <property name="transactionInterceptor" ref="transactionInterceptor"/> </bean> <bean id="customAdvisor" class="com.mycompany.MyAdvisor"/> <bean id="businessObject1" class="com.mycompany.BusinessObject1"> <!-- Properties omitted --> </bean> <bean id="businessObject2" class="com.mycompany.BusinessObject2"/>
The DefaultAdvisorAutoProxyCreator
is very
useful if you want to apply the same advice consistently to many
business objects. Once the infrastructure definitions are in place,
you can simply add new business objects without including specific
proxy configuration. You can also drop in additional aspects very
easily - for example, tracing or performance monitoring aspects - with
minimal change to configuration.
The DefaultAdvisorAutoProxyCreator offers support for filtering
(using a naming convention so that only certain advisors are
evaluated, allowing use of multiple, differently configured,
AdvisorAutoProxyCreators in the same factory) and ordering. Advisors
can implement the org.springframework.core.Ordered
interface to ensure correct ordering if this is an issue. The
TransactionAttributeSourceAdvisor used in the above example has a
configurable order value; the default setting is unordered.
This is the superclass of DefaultAdvisorAutoProxyCreator. You
can create your own autoproxy creators by subclassing this class, in
the unlikely event that advisor definitions offer insufficient
customization to the behavior of the framework
DefaultAdvisorAutoProxyCreator
.
A particularly important type of autoproxying is driven by
metadata. This produces a similar programming model to .NET
ServicedComponents
. Instead of using XML deployment
descriptors as in EJB, configuration for transaction management and
other enterprise services is held in source-level attributes.
In this case, you use the
DefaultAdvisorAutoProxyCreator
, in combination with
Advisors that understand metadata attributes. The metadata specifics are
held in the pointcut part of the candidate advisors, rather than in the
autoproxy creation class itself.
This is really a special case of the
DefaultAdvisorAutoProxyCreator
, but deserves
consideration on its own. (The metadata-aware code is in the pointcuts
contained in the advisors, not the AOP framework itself.)
The /attributes
directory of the JPetStore
sample application shows the use of attribute-driven autoproxying. In
this case, there's no need to use the
TransactionProxyFactoryBean
. Simply defining
transactional attributes on business objects is sufficient, because of
the use of metadata-aware pointcuts. The bean definitions include the
following code, in /WEB-INF/declarativeServices.xml
.
Note that this is generic, and can be used outside the JPetStore:
<bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/> <bean class="org.springframework.transaction.interceptor.TransactionAttributeSourceAdvisor"> <property name="transactionInterceptor" ref="transactionInterceptor"/> </bean> <bean id="transactionInterceptor" class="org.springframework.transaction.interceptor.TransactionInterceptor"> <property name="transactionManager" ref="transactionManager"/> <property name="transactionAttributeSource"> <bean class="org.springframework.transaction.interceptor.AttributesTransactionAttributeSource"> <property name="attributes" ref="attributes"/> </bean> </property> </bean> <bean id="attributes" class="org.springframework.metadata.commons.CommonsAttributes"/>
The DefaultAdvisorAutoProxyCreator
bean
definition (the name is not significant, hence it can even be omitted)
will pick up all eligible pointcuts in the current application context.
In this case, the "transactionAdvisor" bean definition, of type
TransactionAttributeSourceAdvisor
, will apply to
classes or methods carrying a transaction attribute. The
TransactionAttributeSourceAdvisor depends on a TransactionInterceptor,
via constructor dependency. The example resolves this via autowiring.
The AttributesTransactionAttributeSource
depends on
an implementation of the
org.springframework.metadata.Attributes
interface. In
this fragment, the "attributes" bean satisfies this, using the Jakarta
Commons Attributes API to obtain attribute information. (The application
code must have been compiled using the Commons Attributes compilation
task.)
The /annotation
directory of the JPetStore
sample application contains an analogous example for auto-proxying
driven by JDK 1.5+ annotations. The following configuration enables
automatic detection of Spring's Transactional
annotation, leading to implicit proxies for beans containing that
annotation:
<bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/> <bean class="org.springframework.transaction.interceptor.TransactionAttributeSourceAdvisor"> <property name="transactionInterceptor" ref="transactionInterceptor"/> </bean> <bean id="transactionInterceptor" class="org.springframework.transaction.interceptor.TransactionInterceptor"> <property name="transactionManager" ref="transactionManager"/> <property name="transactionAttributeSource"> <bean class="org.springframework.transaction.annotation.AnnotationTransactionAttributeSource"/> </property> </bean>
The TransactionInterceptor
defined here depends
on a PlatformTransactionManager
definition, which is
not included in this generic file (although it could be) because it will
be specific to the application's transaction requirements (typically
JTA, as in this example, or Hibernate, JDO or JDBC):
<bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager"/>
![]() | Tip |
---|---|
If you require only declarative transaction management, using these generic XML definitions will result in Spring automatically proxying all classes or methods with transaction attributes. You won't need to work directly with AOP, and the programming model is similar to that of .NET ServicedComponents. |
This mechanism is extensible. It's possible to do autoproxying based on custom attributes. You need to:
Define your custom attribute.
Specify an Advisor with the necessary advice, including a pointcut that is triggered by the presence of the custom attribute on a class or method. You may be able to use an existing advice, merely implementing a static pointcut that picks up the custom attribute.
It's possible for such advisors to be unique to each advised class
(for example, mixins): they simply need to be defined as prototype,
rather than singleton, bean definitions. For example, the
LockMixin
introduction interceptor from the Spring
test suite, shown above, could be used in conjunction with an
attribute-driven pointcut to target a mixin, as shown here. We use the
generic DefaultPointcutAdvisor
, configured using
JavaBean properties:
<bean id="lockMixin" class="org.springframework.aop.LockMixin" scope="prototype"/> <bean id="lockableAdvisor" class="org.springframework.aop.support.DefaultPointcutAdvisor" scope="prototype"> <property name="pointcut" ref="myAttributeAwarePointcut"/> <property name="advice" ref="lockMixin"/> </bean> <bean id="anyBean" class="anyclass" ...
If the attribute aware pointcut matches any methods in the
anyBean
or other bean definitions, the mixin will be
applied. Note that both lockMixin
and
lockableAdvisor
definitions are prototypes. The
myAttributeAwarePointcut
pointcut can be a singleton
definition, as it doesn't hold state for individual advised
objects.
Spring offers the concept of a TargetSource,
expressed in the org.springframework.aop.TargetSource
interface. This interface is responsible for returning the "target object"
implementing the join point. The TargetSource
implementation is asked for a target instance each time the AOP proxy
handles a method invocation.
Developers using Spring AOP don't normally need to work directly with TargetSources, but this provides a powerful means of supporting pooling, hot swappable and other sophisticated targets. For example, a pooling TargetSource can return a different target instance for each invocation, using a pool to manage instances.
If you do not specify a TargetSource, a default implementation is used that wraps a local object. The same target is returned for each invocation (as you would expect).
Let's look at the standard target sources provided with Spring, and how you can use them.
![]() | Tip |
---|---|
When using a custom target source, your target will usually need to be a prototype rather than a singleton bean definition. This allows Spring to create a new target instance when required. |
The
org.springframework.aop.target.HotSwappableTargetSource
exists to allow the target of an AOP proxy to be switched while allowing
callers to keep their references to it.
Changing the target source's target takes effect immediately. The
HotSwappableTargetSource
is threadsafe.
You can change the target via the swap()
method
on HotSwappableTargetSource as follows:
HotSwappableTargetSource swapper = (HotSwappableTargetSource) beanFactory.getBean("swapper"); Object oldTarget = swapper.swap(newTarget);
The XML definitions required look as follows:
<bean id="initialTarget" class="mycompany.OldTarget"/> <bean id="swapper" class="org.springframework.aop.target.HotSwappableTargetSource"> <constructor-arg ref="initialTarget"/> </bean> <bean id="swappable" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="targetSource" ref="swapper"/> </bean>
The above swap()
call changes the target of the
swappable bean. Clients who hold a reference to that bean will be
unaware of the change, but will immediately start hitting the new
target.
Although this example doesn't add any advice - and it's not
necessary to add advice to use a TargetSource
- of
course any TargetSource
can be used in conjunction
with arbitrary advice.
Using a pooling target source provides a similar programming model to stateless session EJBs, in which a pool of identical instances is maintained, with method invocations going to free objects in the pool.
A crucial difference between Spring pooling and SLSB pooling is that Spring pooling can be applied to any POJO. As with Spring in general, this service can be applied in a non-invasive way.
Spring provides out-of-the-box support for Jakarta Commons Pool
1.3, which provides a fairly efficient pooling implementation. You'll
need the commons-pool Jar on your application's classpath to use this
feature. It's also possible to subclass
org.springframework.aop.target.AbstractPoolingTargetSource
to support any other pooling API.
Sample configuration is shown below:
<bean id="businessObjectTarget" class="com.mycompany.MyBusinessObject" scope="prototype"> ... properties omitted </bean> <bean id="poolTargetSource" class="org.springframework.aop.target.CommonsPoolTargetSource"> <property name="targetBeanName" value="businessObjectTarget"/> <property name="maxSize" value="25"/> </bean> <bean id="businessObject" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="targetSource" ref="poolTargetSource"/> <property name="interceptorNames" value="myInterceptor"/> </bean>
Note that the target object - "businessObjectTarget" in the
example - must be a prototype. This allows the
PoolingTargetSource
implementation to create new
instances of the target to grow the pool as necessary. See the Javadoc
for AbstractPoolingTargetSource
and the concrete
subclass you wish to use for information about it's properties: maxSize
is the most basic, and always guaranteed to be present.
In this case, "myInterceptor" is the name of an interceptor that would need to be defined in the same IoC context. However, it isn't necessary to specify interceptors to use pooling. If you want only pooling, and no other advice, don't set the interceptorNames property at all.
It's possible to configure Spring so as to be able to cast any
pooled object to the
org.springframework.aop.target.PoolingConfig
interface, which exposes information about the configuration and current
size of the pool through an introduction. You'll need to define an
advisor like this:
<bean id="poolConfigAdvisor" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> <property name="targetObject" ref="poolTargetSource"/> <property name="targetMethod" value="getPoolingConfigMixin"/> </bean>
This advisor is obtained by calling a convenience method on the
AbstractPoolingTargetSource
class, hence the use of
MethodInvokingFactoryBean. This advisor's name ("poolConfigAdvisor"
here) must be in the list of interceptors names in the ProxyFactoryBean
exposing the pooled object.
The cast will look as follows:
PoolingConfig conf = (PoolingConfig) beanFactory.getBean("businessObject"); System.out.println("Max pool size is " + conf.getMaxSize());
![]() | Note |
---|---|
Pooling stateless service objects is not usually necessary. We don't believe it should be the default choice, as most stateless objects are naturally thread safe, and instance pooling is problematic if resources are cached. |
Simpler pooling is available using autoproxying. It's possible to set the TargetSources used by any autoproxy creator.
Setting up a "prototype" target source is similar to a pooling TargetSource. In this case, a new instance of the target will be created on every method invocation. Although the cost of creating a new object isn't high in a modern JVM, the cost of wiring up the new object (satisfying its IoC dependencies) may be more expensive. Thus you shouldn't use this approach without very good reason.
To do this, you could modify the
poolTargetSource
definition shown above as follows.
(I've also changed the name, for clarity.)
<bean id="prototypeTargetSource" class="org.springframework.aop.target.PrototypeTargetSource"> <property name="targetBeanName" ref="businessObjectTarget"/> </bean>
There's only one property: the name of the target bean. Inheritance is used in the TargetSource implementations to ensure consistent naming. As with the pooling target source, the target bean must be a prototype bean definition.
ThreadLocal
target sources are useful if you need an object to be
created for each incoming request (per thread that is). The concept of a
ThreadLocal
provide a JDK-wide facility to
transparently store resource alongside a thread. Setting up a
ThreadLocalTargetSource
is pretty much the same as was explained for the
other types of target source:
<bean id="threadlocalTargetSource" class="org.springframework.aop.target.ThreadLocalTargetSource"> <property name="targetBeanName" value="businessObjectTarget"/> </bean>
![]() | Note |
---|---|
ThreadLocals come with serious issues (potentially
resulting in memory leaks) when incorrectly using them in a
multi-threaded and multi-classloader environments. One should always
consider wrapping a threadlocal in some other class and never directly
use the |
Spring AOP is designed to be extensible. While the interception implementation strategy is presently used internally, it is possible to support arbitrary advice types in addition to the out-of-the-box interception around advice, before, throws advice and after returning advice.
The org.springframework.aop.framework.adapter
package is an SPI package allowing support for new custom advice types to
be added without changing the core framework. The only constraint on a
custom Advice
type is that it must implement the
org.aopalliance.aop.Advice
tag interface.
Please refer to the
org.springframework.aop.framework.adapter
package's
Javadocs for further information.
Please refer to the Spring sample applications for further examples of Spring AOP:
The JPetStore's default configuration illustrates the use of the
TransactionProxyFactoryBean
for declarative transaction
management.
The /attributes
directory of the JPetStore
illustrates the use of attribute-driven declarative transaction management.
The Spring team considers developer testing to be an absolutely integral part of enterprise software development. A thorough treatment of testing in the enterprise is beyond the scope of this chapter; rather, the focus here is on the value-add that the adoption of the IoC principle can bring to unit testing and on the benefits that the Spring Framework provides in integration testing.
One of the main benefits of Dependency Injection is that your code
should really depend far less on the container than in traditional J2EE
development. The POJOs that comprise your application should be testable
in JUnit or TestNG tests, with objects simply instantiated using the
new
operator, without Spring or any other
container. You can use mock
objects (in conjunction with many other valuable testing
techniques) to test your code in isolation. If you follow the architecture
recommendations around Spring you will find that the resulting clean
layering and componentization of your codebase will naturally facilitate
easier unit testing. For example, you will be able to
test service layer objects by stubbing or mocking DAO or Repository
interfaces, without any need to access persistent data while running unit
tests.
True unit tests typically will run extremely quickly, as there is no runtime infrastructure to set up, whether application server, database, ORM tool, or whatever. Thus emphasizing true unit tests as part of your development methodology will boost your productivity. The upshot of this is that you often do not need this section of the testing chapter to help you write effective unit tests for your IoC-based applications. For certain unit testing scenarios, however, the Spring Framework provides the following mock objects and testing support classes.
The org.springframework.mock.jndi
package
contains an implementation of the JNDI SPI, which is useful for
setting up a simple JNDI environment for test suites or stand-alone
applications. If, for example, JDBC DataSource
s
get bound to the same JNDI names in test code as within a J2EE
container, both application code and configuration can be reused in
testing scenarios without modification.
The org.springframework.mock.web
package
contains a comprehensive set of Servlet API mock objects, targeted at
usage with Spring's Web MVC framework, which are useful for testing
web contexts and controllers. These mock objects are generally more
convenient to use than dynamic mock objects (e.g., EasyMock) or existing Servlet
API mock objects (e.g., MockObjects).
The org.springframework.test.util
package
contains ReflectionTestUtils
, which is a
collection of reflection-based utility methods for use in unit and
integration testing scenarios in which the developer would benefit
from being able to set a non-public
field or invoke
a non-public
setter method when testing application
code involving, for example:
ORM frameworks such as JPA and Hibernate which condone the
usage of private
or
protected
field access as opposed to
public
setter methods for properties in a
domain entity
Spring's support for annotations such as
@Autowired
and
@Resource
which provides dependency
injection for private
or
protected
fields, setter methods, and
configuration methods
The org.springframework.test.web
package
contains AbstractModelAndViewTests
, which
serves as a convenient base class for JUnit 3.8 based unit tests
dealing with Spring MVC ModelAndView
objects.
When developing against Java 1.4 and higher (e.g., in combination with
JUnit 4+, TestNG, etc.), you have the option of using the
ModelAndViewAssert
class (in the same package)
to test your ModelAndView
related
functionality.
Tip: depending on your testing environment, either extend
AbstractModelAndViewTests
or use
ModelAndViewAssert
directly and then use
MockHttpServletRequest
,
MockHttpSession
, etc. from the org.springframework.mock.web
package to test your Spring MVC Controller
s.
It is important to be able to perform some integration testing without requiring deployment to your application server or connecting to other enterprise infrastructure. This will enable you to test things such as:
The correct wiring of your Spring IoC container contexts.
Data access using JDBC or an ORM tool. This would include such things as the correctness of SQL statements, Hibernate queries, JPA entity mappings, etc.
The Spring Framework provides first class support for integration
testing in the form of the classes that are packaged in the spring-test.jar
library. In this library,
you will find the org.springframework.test
package
which contains valuable classes for integration testing using a Spring
container, while at the same time not being reliant on an application
server or other deployment environment. Such tests will be slower to run
than unit tests but much faster to run than the equivalent Cactus tests
or remote tests relying on deployment to an application server.
Prior to the 2.5 release of the framework, Spring provided integration testing support specific to JUnit 3.8. As of the 2.5 release, Spring offers support for unit and integration testing in the form of the Spring TestContext Framework, which is agnostic of the actual testing framework in use, thus allowing instrumentation of tests in various environments including JUnit 3.8, JUnit 4.4, TestNG, etc. Note that the Spring TestContext Framework requires Java 5+.
The Spring team recommends using the Spring TestContext Framework for
all new unit testing or integration testing involving
ApplicationContext
s or requiring transactional
test fixtures; however, if you are developing in a pre-Java 5
environment, you will need to continue to use the JUnit 3.8 legacy support. In
addition, explicit integration
testing support for JPA which relies on shadow class
loading for JPA class instrumentation is currently only
available with the JUnit 3.8 legacy support. If you are testing against
a JPA provider which does not require class instrumentation, however, it
is recommended that you use the TestContext framework.
The Spring integration testing support frameworks share several common goals, including:
Spring IoC container caching between test execution.
Dependency Injection of test fixture instances (this is nice).
Transaction management appropriate to integration testing (this is even nicer).
Spring-specific support classes that are really useful when writing integration tests.
The following sections outline each of these goals and provide direct links to information specific to the particular support frameworks.
Spring integration testing support frameworks provide consistent
loading of Spring ApplicationContext
s and
caching of those contexts. Support for the caching of loaded contexts
is important, because if you are working on a large project, startup
time may become an issue - not because of the overhead of Spring
itself, but because the objects instantiated by the Spring container
will themselves take time to instantiate. For example, a project with
50-100 Hibernate mapping files might take 10-20 seconds to load the
mapping files, and incurring that cost before running every single
test in every single test fixture will lead to slower overall test
runs that could reduce productivity.
Test classes will generally provide an array containing the
resource locations of XML configuration metadata - typically on the
classpath - used to configure the application. This will be the same,
or nearly the same, as the list of configuration locations specified
in web.xml
or other deployment
configuration.
By default, once loaded, the configured
ApplicationContext
will be reused for
each test. Thus the setup cost will be incurred only once (per test
fixture), and subsequent test execution will be much faster. In the
unlikely case that a test may 'dirty' the application context,
requiring reloading - for example, by changing a bean definition or
the state of an application object - Spring's testing support provides
mechanisms to cause the test fixture to reload the configurations and
rebuild the application context before executing the next test.
Context management and caching with:
When Spring integration testing support frameworks load your
application context, they can optionally configure instances of your
test classes via Dependency Injection. This provides a convenient
mechanism for setting up test fixtures using pre-configured beans from
your application context. A strong benefit here is that you can reuse
application contexts across various testing scenarios (e.g., for
configuring Spring-managed object graphs, transactional proxies,
DataSource
s, etc.), thus avoiding the need to
duplicate complex test fixture set up for individual test
cases.
As an example, consider the scenario where we have a class,
HibernateTitleDao
, that performs data access
logic for say, the Title
domain object. We want
to write integration tests that test all of the following
areas:
The Spring configuration: basically, is everything related
to the configuration of the
HibernateTitleDao
bean correct and
present?
The Hibernate mapping file configuration: is everything mapped correctly and are the correct lazy-loading settings in place?
The logic of the HibernateTitleDao
:
does the configured instance of this class perform as
anticipated?
Dependency Injection of test fixtures with:
One common issue in tests that access a real database is their affect on the state of the persistence store. Even when you're using a development database, changes to the state may affect future tests. Also, many operations - such as inserting to or modifying persistent data - cannot be performed (or verified) outside a transaction.
The Spring integration testing support frameworks meet this
need. By default, they create and roll back a transaction for each
test. You simply write code that can assume the existence of a
transaction. If you call transactionally proxied objects in your
tests, they will behave correctly, according to their transactional
semantics. In addition, if test methods delete the contents of
selected tables while running within a transaction, the transaction
will roll back by default, and the database will return to its state
prior to execution of the test. Transactional support is provided to
your test class via a
PlatformTransactionManager
bean defined in the
test's application context.
If you want a transaction to commit - unusual, but occasionally useful when you want a particular test to populate or modify the database - the Spring integration testing support frameworks can be instructed to cause the transaction to commit instead of roll back either by calling an inherited hook-method or by declaring a specific annotation.
Transaction management with:
The Spring integration testing support frameworks provide
several abstract
support classes that can simplify
writing integration tests. These base test classes provide well
defined hooks into the testing framework as well as convenient
instance variables and methods, allowing access to such things
as:
The ApplicationContext
: useful for
performing explicit bean lookups or testing the state of the
context as a whole.
A JdbcTemplate
or
SimpleJdbcTemplate
: useful for querying to
confirm state. For example, you might query before and after
testing application code that creates an object and persists it
using an ORM tool, to verify that the data appears in the
database. (Spring will ensure that the query runs in the scope of
the same transaction.) You will need to tell your ORM tool to
'flush' its changes for this to work correctly, for example using
the flush()
method on Hibernate's
Session
interface.
Often you will provide an application-wide superclass for integration tests that provides further useful instance variables used in many tests.
Support classes for:
The org.springframework.test.jdbc
package
contains SimpleJdbcTestUtils
, which is a
Java-5-based collection of JDBC related utility functions intended to
simplify standard database testing scenarios. Note that AbstractTransactionalJUnit38SpringContextTests
,
AbstractTransactionalJUnit4SpringContextTests
,
and AbstractTransactionalTestNGSpringContextTests
provide convenience methods which delegate to
SimpleJdbcTestUtils
internally.
The Spring Framework provides a common set of
Spring-specific annotations in the
org.springframework.test.annotation
package that you
can use in your testing if you are developing against Java 5 or
greater.
@IfProfileValue
Indicates that the annotated test is enabled for a specific
testing environment. If the configured
ProfileValueSource
returns a matching
value
for the provided name
,
the test will be enabled. This annotation can be applied to an
entire class or individual methods.
@IfProfileValue(name="java.vendor", value="Sun Microsystems Inc.")
public void testProcessWhichRunsOnlyOnSunJvm() {
// some logic that should run only on Java VMs from Sun Microsystems
}
Alternatively @IfProfileValue
may be configured with a list of values
(with
OR semantics) to achieve TestNG-like support
for test groups in a JUnit environment.
Consider the following example:
@IfProfileValue(name="test-groups", values={"unit-tests", "integration-tests"})
public void testProcessWhichRunsForUnitOrIntegrationTestGroups() {
// some logic that should run only for unit and integration test groups
}
@ProfileValueSourceConfiguration
Class-level annotation which is used to specify what type of
ProfileValueSource
to use when retrieving
profile values configured via the
@IfProfileValue
annotation. If
@ProfileValueSourceConfiguration
is
not declared for a test,
SystemProfileValueSource
will be used by
default.
@ProfileValueSourceConfiguration(CustomProfileValueSource.class)
public class CustomProfileValueSourceTests {
// class body...
}
@DirtiesContext
The presence of this annotation on a test method indicates that the underlying Spring container is 'dirtied' during the execution of the test method, and thus must be rebuilt after the test method finishes execution (regardless of whether the test passed or not).
@DirtiesContext
public void testProcessWhichDirtiesAppCtx() {
// some logic that results in the Spring container being dirtied
}
@ExpectedException
Indicates that the annotated test method is expected to throw an exception during execution. The type of the expected exception is provided in the annotation, and if an instance of the exception is thrown during the test method execution then the test passes. Likewise if an instance of the exception is not thrown during the test method execution then the test fails.
@ExpectedException(SomeBusinessException.class)
public void testProcessRainyDayScenario() {
// some logic that should result in an Exception
being thrown
}
@Timed
Indicates that the annotated test method has to finish execution in a specified time period (in milliseconds). If the text execution time takes longer than the specified time period, the test fails.
Note that the time period includes execution of the test
method itself, any repetitions of the test (see
@Repeat
), as well as any
set up or tear down of the
test fixture.
@Timed(millis=1000)
public void testProcessWithOneSecondTimeout() {
// some logic that should not take longer than 1 second to execute
}
@Repeat
Indicates that the annotated test method must be executed repeatedly. The number of times that the test method is to be executed is specified in the annotation.
Note that the scope of execution to be repeated includes execution of the test method itself as well as any set up or tear down of the test fixture.
@Repeat(10)
public void testProcessRepeatedly() {
// ...
}
@Rollback
Indicates whether or not the transaction for the annotated
test method should be rolled back after the
test method has completed. If true
, the
transaction will be rolled back; otherwise, the transaction will be
committed. Use @Rollback
to override
the default rollback flag configured at the class level.
@Rollback(false)
public void testProcessWithoutRollback() {
// ...
}
@NotTransactional
The presence of this annotation indicates that the annotated test method must not execute in a transactional context.
@NotTransactional
public void testProcessWithoutTransaction() {
// ...
}
Annotation support for:
JUnit 3.8 legacy
support: all common annotations listed above are supported
but must be used in conjunction with
AbstractAnnotationAwareTransactionalTests
in
order for the presence of these annotations to have any
effect.
The TestContext
Framework: supports all of the common annotations listed
above while providing additional TestContext-specific and
transactional annotations (e.g.,
@ContextConfiguration
,
@BeforeTransaction
, etc.). Note,
however, that some of the common annotations are only supported when
used in conjunction with JUnit (e.g., with the SpringJUnit4ClassRunner
or the JUnit
3.8 and JUnit 4.4 base
test classes). Refer to the documentation in the
TestContext Framework section for further
details.
Spring's JUnit 3.8 legacy support is comprised of the classes
found in the org.springframework.test
package. This
package provides valuable JUnit TestCase
superclasses which can be extended for out-of-container integration
tests involving Spring ApplicationContext
s or
requiring transactional support at the test method level.
AbstractSingleSpringContextTests
provides
context management and caching support for JUnit 3.8 based test cases
and exposes a protected
method that subclasses can
override to provide the location of context definition files:
protected String[] getConfigLocations()
Implementations of this method must provide an array containing
the resource locations of XML configuration metadata - typically on
the classpath - used to configure the application. This will be the
same, or nearly the same, as the list of configuration locations
specified in web.xml
or other deployment
configuration. As an alternative you may choose to override one of the
following. See the respective JavaDoc for further details.
protected String[] getConfigPaths()
protected String getConfigPath()
By default, once loaded, the configuration file set will be
reused for each test case. Thus the setup cost will be incurred only
once (per test fixture), and subsequent test execution will be much
faster. In the unlikely case that a test may 'dirty' the application
context, requiring reloading - for example, by changing a bean
definition or the state of an application object - you can call the
setDirty()
method on
AbstractSingleSpringContextTests
to cause the
test fixture to reload the configurations and rebuild the application
context before executing the next test case. As an alternative, if you
are developing against Java 5 or greater and extending AbstractAnnotationAwareTransactionalTests
,
you may annotate your test method with
@DirtiesContext
to achieve the same
effect.
When
AbstractDependencyInjectionSpringContextTests
(and subclasses) load your application context, they can optionally
configure instances of your test classes by Setter Injection. All you
need to do is to define instance variables and the corresponding
setter methods.
AbstractDependencyInjectionSpringContextTests
will automatically locate the corresponding object in the set of
configuration files specified in the
getConfigLocations()
method.
Consider the scenario where we have a class,
HibernateTitleDao
(as outlined in the Common goals section). Let's look
at a JUnit 3.8 based implementation of the test class itself (we will
look at the configuration immediately afterwards).
public final class HibernateTitleDaoTests extends AbstractDependencyInjectionSpringContextTests { // this instance will be (automatically) dependency injected private HibernateTitleDao titleDao; // a setter method to enable DI of the 'titleDao' instance variable public void setTitleDao(HibernateTitleDao titleDao) { this.titleDao = titleDao; } public void testLoadTitle() throws Exception { Title title = this.titleDao.loadTitle(new Long(10)); assertNotNull(title); } // specifies the Spring configuration to load for this test fixture protected String[] getConfigLocations() { return new String[] { "classpath:com/foo/daos.xml" }; } }
The file referenced by the
getConfigLocations()
method (i.e.,
"classpath:com/foo/daos.xml"
) looks like
this:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<!-- this bean will be injected into the HibernateTitleDaoTests
class -->
<bean id="titleDao" class="com.foo.dao.hibernate.HibernateTitleDao">
<property name="sessionFactory" ref="sessionFactory"/>
</bean>
<bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
<!-- dependencies elided for clarity -->
</bean>
</beans>
The
AbstractDependencyInjectionSpringContextTests
classes uses autowire
by type. Thus if you have multiple bean definitions
of the same type, you cannot rely on this approach for those
particular beans. In that case, you can use the inherited
applicationContext
instance variable and perform
explicit lookups using (for example) a call to
applicationContext.getBean("titleDao")
.
If you don't want dependency injection applied to your test
cases, simply don't declare any public
setter
methods. Alternatively, you can extend
AbstractSpringContextTests
- the root of the
JUnit 3.8 integration testing support class hierarchy in the
org.springframework.test
package - which merely
contains convenience methods to load Spring contexts and performs no
Dependency Injection of the test fixture.
If, for whatever reason, you don't fancy having setter methods
in your test fixtures, Spring can inject dependencies into
protected
fields. Find below a reworking of the
previous example to use field level injection (the Spring XML
configuration does not need to change, merely the test
fixture).
public final class HibernateTitleDaoTests extends AbstractDependencyInjectionSpringContextTests { public HibernateTitleDaoTests() { // switch on field level injection setPopulateProtectedVariables(true); } // this instance will be (automatically) dependency injected protected HibernateTitleDao titleDao; public void testLoadTitle() throws Exception { Title title = this.titleDao.loadTitle(new Long(10)); assertNotNull(title); } // specifies the Spring configuration to load for this test fixture protected String[] getConfigLocations() { return new String[] { "classpath:com/foo/daos.xml" }; } }
In the case of field injection, there is no autowiring going
on: the name of a protected
instance variable is
used as the lookup bean name in the configured Spring
container.
AbstractTransactionalSpringContextTests
depends on a PlatformTransactionManager
bean
being defined in the application context. The name doesn't matter due
to the use of autowire by
type.
Typically you will extend the subclass,
AbstractTransactionalDataSourceSpringContextTests
.
This class also requires that a DataSource
bean
definition - again, with any name - be present in the application
context. It creates a JdbcTemplate
instance
variable, that is useful for convenient querying, and provides handy
methods to delete the contents of selected tables (remember that the
transaction will roll back by default, so this is safe to do).
If you want a transaction to commit
programmatically - unusual, but occasionally
useful when you want a particular test to populate the database - you
can call the setComplete()
method inherited
from AbstractTransactionalSpringContextTests
.
This will cause the transaction to commit instead of roll back. As an
alternative, if you are developing against Java 5 or greater and
extending AbstractAnnotationAwareTransactionalTests
,
you may annotate your test method with
@Rollback(false)
to achieve the same
effect through configuration.
There is also the convenient ability to end a transaction before
the test case ends, by calling the
endTransaction()
method. This will roll back
the transaction by default and commit it only if
setComplete()
had previously been called.
This functionality is useful if you want to test the behavior of
'disconnected' data objects, such as Hibernate-mapped entities that
will be used in a web or remoting tier outside a transaction. Often,
lazy loading errors are discovered only through UI testing; if you
call endTransaction()
you can ensure correct
operation of the UI through your JUnit test suite.
When you extend the
AbstractTransactionalDataSourceSpringContextTests
class you will have access to the following
protected
instance variables:
applicationContext
(a
ConfigurableApplicationContext
):
inherited from the
AbstractSingleSpringContextTests
superclass. Use this to perform explicit bean lookup or to test
the state of the context as a whole.
jdbcTemplate
: inherited from
AbstractTransactionalDataSourceSpringContextTests
.
Useful for querying to confirm state. For example, you might query
before and after testing application code that creates an object
and persists it using an ORM tool, to verify that the data appears
in the database. (Spring will ensure that the query runs in the
scope of the same transaction.) You will need to tell your ORM
tool to 'flush' its changes for this to work correctly, for
example using the flush()
method on
Hibernate's Session
interface.
In addition to the aforementioned common
annotations, the
org.springframework.test.annotation
package also
contains an abstract
JUnit
TestCase
class which provides
annotation-driven integration testing support.
The
AbstractAnnotationAwareTransactionalTests
class extends
AbstractTransactionalDataSourceSpringContextTests
and makes text fixtures, which extend it, aware of a number of
(Spring-specific) annotations.
AbstractAnnotationAwareTransactionalTests
supports all annotations listed in the common
annotations section as well as Spring's
@Transactional
annotation for
configuring explicit transactional semantics.
The org.springframework.test.jpa
package
provides support classes for tests based on the Java Persistence API
(JPA).
AbstractJpaTests
is a convenient
support class for JPA-related tests, which offers the same
contract as
AbstractTransactionalDataSourceSpringContextTests
and equally good performance, even when performing the
instrumentation required by the JPA specification. Exposes an
EntityManagerFactory
and a shared
EntityManager
. Requires an
EntityManagerFactory
to be
injected, plus the DataSource
and
JpaTransactionManager
through the
superclass.
AbstractAspectjJpaTests
is a
subclass of AbstractJpaTests
that
activates AspectJ load-time weaving and allows the ability to
specify a custom location for AspectJ's
aop.xml
file.
The Spring TestContext
Framework (located in the
org.springframework.test.context
package) provides
generic, annotation-driven unit and integration testing support that is
agnostic of the testing framework in use, for example JUnit 3.8, JUnit
4.4, TestNG 5.5, etc. The TestContext framework also places a great deal
of importance on convention over configuration with
reasonable defaults that can be overridden via annotation-based
configuration.
In addition to generic testing infrastructure, the TestContext
framework provides explicit support for JUnit 3.8, JUnit 4.4, and TestNG
5.5 in the form of abstract
support classes. For
JUnit 4.4, the framework also provides a custom
Runner
which allows one to write test
classes that are not required to extend a particular class
hierarchy.
The following section provides an overview of the internals of the TestContext framework. If you are only interested in using the framework and not necessarily interested in extending it with your own custom listeners, feel free to skip ahead to the configuration (context management, dependency injection, transaction management), support classes, and annotation support sections.
The core of the framework consists of the
TestContext
and
TestContextManager
classes and the
TestExecutionListener
interface. A
TestContextManager
is created on a per-test
basis. The TestContextManager
in turn manages a
TestContext
which is responsible for holding
the context of the current test. The
TestContextManager
is also responsible for
updating the state of the TestContext
as the
test progresses and delegating to
TestExecutionListener
s, which
instrument the actual test execution (e.g., providing dependency
injection, managing transactions, etc.). Consult the JavaDoc and the
Spring test suite for further information and examples of various
configurations.
TestContext
: encapsulates the context
in which a test is executed, agnostic of the actual testing
framework in use.
TestContextManager
: the main entry
point into the Spring TestContext Framework,
which is responsible for managing a single
TestContext
and signaling events to all
registered TestExecutionListener
s
at well defined test execution points: test instance preparation,
prior to any before methods of a particular
testing framework, and after any after
methods of a particular testing framework.
TestExecutionListener
:
defines a listener API for reacting to test
execution events published by the
TestContextManager
with which the listener
is registered.
Spring provides three
TestExecutionListener
implementations which are configured by default (via the
@TestExecutionListeners
annotation):
DependencyInjectionTestExecutionListener
,
DirtiesContextTestExecutionListener
, and
TransactionalTestExecutionListener
, which
provide support for dependency injection of the test instance,
handling of the @DirtiesContext
annotation, and transactional test execution support with default
rollback semantics, respectively.
The following three sections explain how to configure the
TestContext
framework via annotations and
provide working examples of how to actually write unit and integration
tests with the framework.
Each TestContext
provides context
management and caching support for the test instance for which it is
responsible. Test instances do not automatically receive access to the
configured ApplicationContext
; however, if a
test class implements the
ApplicationContextAware
interface, a
reference to the ApplicationContext
will be
supplied to the test instance (provided the
DependencyInjectionTestExecutionListener
has
been configured, which is the default). Note that
AbstractJUnit38SpringContextTests
,
AbstractJUnit4SpringContextTests
, and
AbstractTestNGSpringContextTests
already
implement ApplicationContextAware
and
therefore provide this functionality out-of-the-box.
In contrast to the JUnit 3.8 legacy support, test classes which
use the TestContext framework do not need to override any
protected
instance methods to configure their
application context. Rather, configuration is achieved merely by
declaring the @ContextConfiguration
annotation at the class level. If your test class does not explicitly
declare any application context resource locations
,
the configured ContextLoader
will
determine how and whether or not to load a context from a default set
of locations. For example,
GenericXmlContextLoader
- which is the default
ContextLoader
- will generate a default
location based on the name of the test class. If your class is named
com.example.MyTest
,
GenericXmlContextLoader
will load your
application context from
"classpath:/com/example/MyTest-context.xml"
.
package com.example;
@RunWith(SpringJUnit4ClassRunner.class)
// ApplicationContext will be loaded from "classpath:/com/example/MyTest-context.xml"
@ContextConfiguration
public class MyTest {
// class body...
}
If the default location does not suit your needs, you are free
to explicitly configure the locations
attribute of
@ContextConfiguration
(see code listing
below) with an array containing the resource locations of XML
configuration metadata (assuming an XML-capable
ContextLoader
has been configured) -
typically on the classpath - used to configure the application. This
will be the same, or nearly the same, as the list of configuration
locations specified in web.xml
or other deployment
configuration. As an alternative you may choose to implement and
configure your own custom
ContextLoader
.
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from"/applicationContext.xml"
and"/applicationContext-test.xml"
// in the root of the classpath @ContextConfiguration(locations={"/applicationContext.xml", "/applicationContext-test.xml"}) public class MyTest { // class body... }
@ContextConfiguration
also
supports a boolean inheritLocations
attribute which
denotes whether or not resource locations from superclasses should be
inherited. The default value is
true
, which means that an annotated class will
inherit the resource locations defined by an
annotated superclass. Specifically, the resource locations for an
annotated class will be appended to the list of resource locations
defined by an annotated superclass. Thus, subclasses have the option
of extending the list of resource locations. In
the following example, the
ApplicationContext
for
ExtendedTest
will be loaded from
"/base-context.xml" and
"/extended-context.xml", in that order. Beans defined in
"/extended-context.xml" may therefore override those defined in
"/base-context.xml".
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from"/base-context.xml"
in the root of the classpath @ContextConfiguration(locations={"/base-context.xml"}) public class BaseTest { // class body... } // ApplicationContext will be loaded from"/base-context.xml"
and"/extended-context.xml"
// in the root of the classpath @ContextConfiguration(locations={"/extended-context.xml"}) public class ExtendedTest extends BaseTest { // class body... }
If inheritLocations
is set to
false
, the resource locations for the annotated
class will shadow and effectively replace any
resource locations defined by a superclass.
By default, once loaded, the configured
ApplicationContext
will be reused for
each test. Thus the setup cost will be incurred only once (per test
fixture), and subsequent test execution will be much faster. In the
unlikely case that a test may dirty the
application context, requiring reloading - for example, by changing a
bean definition or the state of an application object - you may
annotate your test method with
@DirtiesContext
(assuming
DirtiesContextTestExecutionListener
has been
configured, which is the default) to cause the test fixture to reload
the configurations and rebuild the application context before
executing the next test.
When you configure the
DependencyInjectionTestExecutionListener
-
which is configured by default - via the
@TestExecutionListeners
annotation, the
dependencies of your test instances will be
injected from beans in the application context
you configured via
@ContextConfiguration
by Setter
Injection, Field Injection, or both, depending on which annotations
you choose and whether you place them on setter methods or fields. For
consistency with annotation support in Spring 2.5, you may choose
either Spring's @Autowired
annotation
or the @Resource
annotation from JSR
250. The semantics for both are consistent throughout the Spring
Framework. For example, if you prefer autowiring by
type, annotate your setter methods or fields with
@Autowired
. On the other hand, if you
prefer to have your dependencies injected by
name, annotate your setter methods or fields with
@Resource
.
![]() | Tip |
---|---|
The TestContext framework does not instrument the manner in
which a test instance is instantiated. Thus the use of
|
Since @Autowired
performs autowiring by
type, if you have multiple bean definitions of the
same type, you cannot rely on this approach for those particular
beans. In that case, you can use
@Resource
for injection by
name. Alternatively, if your test class implements
ApplicationContextAware
, you can directly
access the ApplicationContext
supplied to your
test and perform an explicit lookup using (for example) a call to
applicationContext.getBean("titleDao")
.
If you don't want dependency injection applied to your test
instances, simply don't annotate any fields or setter methods with
@Autowired
or
@Resource
. Alternatively, you can
disable dependency injection altogether by explicitly configuring your
class with @TestExecutionListeners
and
omitting
DependencyInjectionTestExecutionListener.class
from
the list of listeners.
Consider the scenario where we have a class,
HibernateTitleDao
(as outlined in the common goals section). First,
let's look at a JUnit 4.4 based implementation of the test class
itself which uses @Autowired
for field
injection (we will look at the application context configuration after
all sample code listings). Note: The dependency injection
behavior in the following code listings is not in any way specific to
JUnit 4.4. The same DI techniques can be used in conjunction with any
testing framework.
@RunWith(SpringJUnit4ClassRunner.class) // specifies the Spring configuration to load for this test fixture @ContextConfiguration(locations={"daos.xml"}) public final class HibernateTitleDaoTests { // this instance will be dependency injected by type @Autowired private HibernateTitleDao titleDao; public void testLoadTitle() throws Exception { Title title = this.titleDao.loadTitle(new Long(10)); assertNotNull(title); } }
Alternatively, we can configure the class to use
@Autowired
for setter injection.
@RunWith(SpringJUnit4ClassRunner.class) // specifies the Spring configuration to load for this test fixture @ContextConfiguration(locations={"daos.xml"}) public final class HibernateTitleDaoTests { // this instance will be dependency injected by type private HibernateTitleDao titleDao; @Autowired public void setTitleDao(HibernateTitleDao titleDao) { this.titleDao = titleDao; } public void testLoadTitle() throws Exception { Title title = this.titleDao.loadTitle(new Long(10)); assertNotNull(title); } }
Now let's take a look at an example using
@Resource
for field injection.
@RunWith(SpringJUnit4ClassRunner.class) // specifies the Spring configuration to load for this test fixture @ContextConfiguration(locations={"daos.xml"}) public final class HibernateTitleDaoTests { // this instance will be dependency injected by name @Resource private HibernateTitleDao titleDao; public void testLoadTitle() throws Exception { Title title = this.titleDao.loadTitle(new Long(10)); assertNotNull(title); } }
Finally, here is an example using
@Resource
for setter injection.
@RunWith(SpringJUnit4ClassRunner.class) // specifies the Spring configuration to load for this test fixture @ContextConfiguration(locations={"daos.xml"}) public final class HibernateTitleDaoTests { // this instance will be dependency injected by name private HibernateTitleDao titleDao; @Resource public void setTitleDao(HibernateTitleDao titleDao) { this.titleDao = titleDao; } public void testLoadTitle() throws Exception { Title title = this.titleDao.loadTitle(new Long(10)); assertNotNull(title); } }
The above code listings use the same XML context file referenced
by the @ContextConfiguration
annotation
(i.e., "daos.xml"
) which looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<!-- this bean will be injected into the HibernateTitleDaoTests
class -->
<bean id="titleDao" class="com.foo.dao.hibernate.HibernateTitleDao">
<property name="sessionFactory" ref="sessionFactory"/>
</bean>
<bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
<!-- dependencies elided for clarity -->
</bean>
</beans>
![]() | Note |
---|---|
If you are extending from a Spring-provided test base class that happens
to use ...
@Override @Autowired
public void setDataSource(@Qualifier("myDataSource") DataSource dataSource) {
super.setDataSource(dataSource);
}
... The specified qualifier value indicates the specific
Alternatively, consider using the ...
@Override @Resource("myDataSource")
public void setDataSource(DataSource dataSource) {
super.setDataSource(dataSource);
}
... |
In the TestContext framework, transactions are managed by the
TransactionalTestExecutionListener
, which is
configured via the
@TestExecutionListeners
annotation by
default, even if you do not explicitly declare
@TestExecutionListeners
on your test
class. To enable support for transactions, however, you must provide a
PlatformTransactionManager
bean in the
application context loaded via
@ContextConfiguration
semantics. In
addition, you must declare
@Transactional
either at the class or
method level.
For class-level transaction configuration (i.e., setting the
bean name for the transaction manager and the default rollback flag),
see the @TransactionConfiguration
entry
in the TestContext framework
annotation support section.
There are several options for configuring transactions for
individual test methods. If transactions are not enabled for the
entire test class, methods may be explicitly annotated with
@Transactional
. Similarly, if
transactions are enabled for the entire test
class, methods may be explicitly flagged not to run within a
transaction by annotating them with
@NotTransactional
. To control whether
or not a transaction should commit for a particular test method, you
may use the @Rollback
annotation to
override the class-level default rollback setting.
Note that AbstractTransactionalJUnit38SpringContextTests
,
AbstractTransactionalJUnit4SpringContextTests
,
and AbstractTransactionalTestNGSpringContextTests
are pre-configured for transactional support at the class level.
You will occasionally find that you need to execute certain code
before or after a transactional test method but outside the
transactional context, for example to verify the initial database
state prior to execution of your test or to verify expected
transactional commit behavior after test execution (e.g., if the test
was configured not to roll back the transaction).
TransactionalTestExecutionListener
supports the
@BeforeTransaction
and
@AfterTransaction
annotations exactly
for such scenarios. Simply annotate any public void
method in your test class with one of these annotations, and the
TransactionalTestExecutionListener
will ensure
that your before transaction method or
after transaction method is executed at the
appropriate time.
![]() | Tip |
---|---|
Any before methods (e.g., methods
annotated with JUnit 4's @Before) and any after
methods (e.g., methods annotated with JUnit 4's @After)
will be executed within a
transaction. In addition, methods annotated with
|
The following JUnit 4 based example displays a fictitious integration testing scenario highlighting several of the transaction-related annotations. Consult the TestContext framework annotation support section of the reference manual for further information and configuration examples.
@RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration @TransactionConfiguration(transactionManager="txMgr", defaultRollback=false) @Transactional public class FictitiousTransactionalTest { @BeforeTransaction public void verifyInitialDatabaseState() { // logic to verify the initial state before a transaction is started } @Before public void setUpTestDataWithinTransaction() { // set up test data within the transaction } @Test // overrides the class-level defaultRollback setting @Rollback(true) public void modifyDatabaseWithinTransaction() { // logic which uses the test data and modifies database state } @After public void tearDownWithinTransaction() { // execute "tear down" logic within the transaction } @AfterTransaction public void verifyFinalDatabaseState() { // logic to verify the final state after transaction has rolled back } @Test @NotTransactional public void performNonDatabaseRelatedAction() { // logic which does not modify database state } }
The
org.springframework.test.context.junit38
package
provides support classes for JUnit 3.8 based test cases.
AbstractJUnit38SpringContextTests
:
Abstract TestCase
which integrates
the Spring TestContext Framework with
explicit ApplicationContext
testing
support in a JUnit 3.8 environment. When you extend the
AbstractJUnit38SpringContextTests
class
you will have access to the following
protected
instance variables:
applicationContext
: use this to
perform explicit bean lookups or to test the state of the
context as a whole.
AbstractTransactionalJUnit38SpringContextTests
:
Abstract transactional extension of
AbstractJUnit38SpringContextTests
that
also adds some convenience functionality for JDBC access.
Expects a javax.sql.DataSource
bean and a
PlatformTransactionManager
bean
to be defined in the ApplicationContext
.
When you extend the
AbstractTransactionalJUnit38SpringContextTests
class you will have access to the following
protected
instance variables:
applicationContext
: inherited from
the AbstractJUnit38SpringContextTests
superclass. Use this to perform explicit bean lookups or to
test the state of the context as a whole.
simpleJdbcTemplate
: useful for
querying to confirm state. For example, you might query
before and after testing application code that creates an
object and persists it using an ORM tool, to verify that the
data appears in the database. (Spring will ensure that the
query runs in the scope of the same transaction.) You will
need to tell your ORM tool to 'flush' its changes for this
to work correctly, for example using the
flush()
method on Hibernate's
Session
interface.
The org.springframework.test.context.junit4
package provides support classes for JUnit 4.4 based test
cases.
AbstractJUnit4SpringContextTests
:
Abstract base test class which integrates the
Spring TestContext Framework with explicit
ApplicationContext
testing support in a
JUnit 4.4 environment.
When you extend
AbstractJUnit4SpringContextTests
you will
have access to the following protected
instance variables:
applicationContext
: use this to
perform explicit bean lookups or to test the state of the
context as a whole.
AbstractTransactionalJUnit4SpringContextTests
:
Abstract transactional extension of
AbstractJUnit4SpringContextTests
that
also adds some convenience functionality for JDBC access.
Expects a javax.sql.DataSource
bean and a
PlatformTransactionManager
bean
to be defined in the
ApplicationContext
.
When you extend
AbstractTransactionalJUnit4SpringContextTests
you will have access to the following
protected
instance variables:
applicationContext
: inherited from
the AbstractJUnit4SpringContextTests
superclass. Use this to perform explicit bean lookups or to
test the state of the context as a whole.
simpleJdbcTemplate
: useful for
querying to confirm state. For example, you might query
before and after testing application code that creates an
object and persists it using an ORM tool, to verify that the
data appears in the database. (Spring will ensure that the
query runs in the scope of the same transaction.) You will
need to tell your ORM tool to 'flush' its changes for this
to work correctly, for example using the
flush()
method on Hibernate's
Session
interface.
![]() | Tip |
---|---|
These classes serve only as a convenience for extension. If
you do not wish for your test classes to be tied to a
Spring-specific class hierarchy - for example, if you wish to
directly extend the class you are testing - you may configure your
own custom test classes by using
|
The Spring TestContext Framework offers
full integration with JUnit 4.4 via a custom runner. By annotating
test classes with
@Runwith(SpringJUnit4ClassRunner.class)
,
developers can implement standard JUnit 4.4 unit and integration
tests and simultaneously reap the benefits of the TestContext
framework such as support for loading application contexts,
dependency injection of test instances, transactional test method
execution, etc. The following code listing displays the minimal
requirements for configuring a test class to run with the custom
Spring Runner. Note that
@TestExecutionListeners
has been
configured with an empty list in order to disable the default
listeners, which would otherwise require that an
ApplicationContext
be configured via
@ContextConfiguration
.
@RunWith(SpringJUnit4ClassRunner.class)
@TestExecutionListeners({})
public class SimpleTest {
@Test
public void testMethod() {
// execute test logic...
}
}
The org.springframework.test.context.testng
package provides support classes for TestNG based test cases.
AbstractTestNGSpringContextTests
:
Abstract base test class which integrates the
Spring TestContext Framework with explicit
ApplicationContext
testing support in a
TestNG environment.
When you extend
AbstractTestNGSpringContextTests
you will
have access to the following protected
instance variables:
applicationContext
: use this to
perform explicit bean lookups or to test the state of the
context as a whole.
AbstractTransactionalTestNGSpringContextTests
:
Abstract transactional extension of
AbstractTestNGSpringContextTests
that
adds some convenience functionality for JDBC access. Expects a
javax.sql.DataSource
bean and a
PlatformTransactionManager
bean
to be defined in the
ApplicationContext
.
When you extend
AbstractTransactionalTestNGSpringContextTests
you will have access to the following
protected
instance variables:
applicationContext
: inherited from
the AbstractTestNGSpringContextTests
superclass. Use this to perform explicit bean lookups or to
test the state of the context as a whole.
simpleJdbcTemplate
: useful for
querying to confirm state. For example, you might query
before and after testing application code that creates an
object and persists it using an ORM tool, to verify that the
data appears in the database. (Spring will ensure that the
query runs in the scope of the same transaction.) You will
need to tell your ORM tool to 'flush' its changes for this
to work correctly, for example using the
flush()
method on Hibernate's
Session
interface.
![]() | Tip |
---|---|
These classes serve only as a convenience for extension. If
you do not wish for your test classes to be tied to a
Spring-specific class hierarchy - for example, if you wish to
directly extend the class you are testing - you may configure your
own custom test classes by using
|
The Spring TestContext Framework supports all annotations as outlined in the common annotations section. The following annotations, however, are only supported when used in conjunction with JUnit (e.g., with the SpringJUnit4ClassRunner or the JUnit 3.8 and JUnit 4.4 support classes.
@IfProfileValue
@ProfileValueSourceConfiguration
@ExpectedException
Using Spring's
@ExpectedException
annotation in
conjunction with JUnit 4's
@Test(expected=...)
configuration
would lead to an unresolvable conflict. Developers must therefore
choose one or the other when integrating with JUnit 4, in which
case it is generally preferable to use the explicit JUnit 4
configuration.
@Timed
Spring's @Timed
annotation
has different semantics than JUnit 4's
@Test(timeout=...)
support.
Specifically, due to the manner in which JUnit 4 handles test
execution timeouts (i.e., by executing the test method in a
separate Thread
),
@Test(timeout=...)
applies to
each iteration in the case of repetitions
and preemptively fails the test if the test takes too long.
Spring's @Timed
, on the other hand,
times the total test execution time
(including all repetitions) and does not preemptively fail the test
but rather waits for the test to actually complete before failing.
@Repeat
The following non-test-specific annotations are also supported by the Spring TestContext Framework with their standard semantics.
@Autowired
@Qualifier
@Resource
(javax.annotation)
if JSR-250 is present
@PersistenceContext
(javax.persistence) if JPA is present
@PersistenceUnit
(javax.persistence) if JPA is present
@Required
@Transactional
The following list includes all annotations specific to the Spring TestContext Framework. Refer to the respective JavaDoc for further information, including default attribute values, etc.
@ContextConfiguration
Defines class-level metadata which is used to determine how
to load and configure an
ApplicationContext
. Specifically,
@ContextConfiguration defines the application context resource
locations
to load as well as the
ContextLoader
strategy to use for
loading the context.
@ContextConfiguration(locations={"example/test-context.xml"}, loader=CustomContextLoader.class)
public class CustomConfiguredApplicationContextTests {
// class body...
}
Note: @ContextConfiguration
provides support for inherited resource
locations by default. See the Context management and
caching section and JavaDoc for an example and further
details.
@TestExecutionListeners
Defines class-level metadata for configuring which
TestExecutionListener
s should be
registered with a TestContextManager
.
Typically, @TestExecutionListeners
will be used in conjunction with
@ContextConfiguration
.
@ContextConfiguration
@TestExecutionListeners({CustomTestExecutionListener.class, AnotherTestExecutionListener.class})
public class CustomTestExecutionListenerTests {
// class body...
}
Note: @TestExecutionListeners
provides support for inherited listeners by
default. See the JavaDoc for an example and further
details.
@TransactionConfiguration
Defines class-level metadata for configuring transactional
tests. Specifically, the bean name of the
PlatformTransactionManager
that is
to be used to drive transactions can be explicitly configured if
the bean name of the desired PlatformTransactionManager is not
"transactionManager". In addition, the
defaultRollback
flag can optionally be changed
to false
. Typically,
@TransactionConfiguration
will be
used in conjunction with
@ContextConfiguration
.
@ContextConfiguration
@TransactionConfiguration(transactionManager="txMgr", defaultRollback=false)
public class CustomConfiguredTransactionalTests {
// class body...
}
@BeforeTransaction
Indicates that the annotated public void
method should be executed before a
transaction is started for test methods configured to run within a
transaction via the @Transactional
annotation.
@BeforeTransaction
public void beforeTransaction() {
// logic to be executed before a transaction is started
}
@AfterTransaction
Indicates that the annotated public void
method should be executed after a transaction
has been ended for test methods configured to run within a
transaction via the @Transactional
annotation.
@AfterTransaction
public void afterTransaction() {
// logic to be executed after a transaction has ended
}
The PetClinic sample application included with the full Spring
distribution illustrates several features of the Spring
TestContext Framework in a JUnit 4.4 environment. Most test
functionality is included in the
AbstractClinicTests
, for which a partial listing
is shown below:
@ContextConfiguration public abstract class AbstractClinicTests extends AbstractTransactionalJUnit4SpringContextTests { @Autowired protected Clinic clinic; @Test public void getVets() { Collection<Vet> vets = this.clinic.getVets(); assertEquals("JDBC query must show the same number of vets", super.countRowsInTable("VETS"), vets.size()); Vet v1 = EntityUtils.getById(vets, Vet.class, 2); assertEquals("Leary", v1.getLastName()); assertEquals(1, v1.getNrOfSpecialties()); assertEquals("radiology", (v1.getSpecialties().get(0)).getName()); // ... } // ... }
Notes:
This test case extends the
AbstractTransactionalJUnit4SpringContextTests
class, from which it inherits configuration for Dependency Injection
(via the
DependencyInjectionTestExecutionListener
) and
transactional behavior (via the
TransactionalTestExecutionListener
).
The clinic
instance variable - the
application object being tested - is set by Dependency Injection via
@Autowired
semantics.
The testGetVets()
method illustrates
how the inherited countRowsInTable()
method
can be used to easily verify the number of rows in a given table,
thus testing correct behavior of the application code being tested.
This allows for stronger tests and lessens dependency on the exact
test data. For example, you can add additional rows in the database
without breaking tests.
Like many integration tests using a database, most of the
tests in AbstractClinicTests
depend on a
minimum amount of data already in the database before the test cases
run. You might, however, choose to populate the database in your
test cases also - again, within the same transaction.
The PetClinic application supports three data access technologies
- JDBC, Hibernate, and JPA. By declaring
@ContextConfiguration
without any
specific resource locations, the
AbstractClinicTests
class will have its
application context loaded from the default location,
"AbstractClinicTests-context.xml"
, which declares a
common DataSource
. Subclasses specify additional
context locations which must declare a
PlatformTransactionManager
and a concrete
implementation of Clinic
.
For example, the Hibernate implementation of the PetClinic tests
contains the following implementation. Note that for this example,
HibernateClinicTests
does not contain a single
line of code: we only need to declare
@ContextConfiguration
, and the tests are
inherited from AbstractClinicTests
. Since
@ContextConfiguration
is declared without
any specific resource locations, the Spring TestContext
Framework will load an application context from all the beans
defined in "AbstractClinicTests-context.xml"
(i.e.,
the inherited locations) and
"HibernateClinicTests-context.xml"
, with
"HibernateClinicTests-context.xml"
possibly
overriding beans defined in
"AbstractClinicTests-context.xml"
.
@ContextConfiguration
public class HibernateClinicTests extends AbstractClinicTests { }
As you can see in the PetClinic application, the Spring
configuration is split across multiple files. As is typical of large
scale applications, configuration locations will often be specified in a
common base class for all application-specific integration tests. Such a
base class may also add useful instance variables - populated by
Dependency Injection, naturally - such as a
HibernateTemplate
, in the case of an application
using Hibernate.
As far as possible, you should have exactly the same Spring
configuration files in your integration tests as in the deployed
environment. One likely point of difference concerns database connection
pooling and transaction infrastructure. If you are deploying to a
full-blown application server, you will probably use its connection pool
(available through JNDI) and JTA implementation. Thus in production you
will use a JndiObjectFactoryBean
for the
DataSource
and
JtaTransactionManager
. JNDI and JTA will not be
available in out-of-container integration tests, so you should use a
combination like the Commons DBCP BasicDataSource
and DataSourceTransactionManager
or
HibernateTransactionManager
for them. You can
factor out this variant behavior into a single XML file, having the
choice between application server and 'local' configuration separated
from all other configuration, which will not vary between the test and
production environments. In addition, it is advisable to use properties
files for connection settings: see the PetClinic application for an
example.
This section contains links to further resources about testing in general.
The JUnit homepage. The Spring Framework's unit test suite is written using JUnit 3.8 as the testing framework.
The TestNG homepage. TestNG is a testing framework inspired by JUnit 3.8 with added support for Java 5 annotations, test groups, data-driven testing, distributed testing, etc.
The Mock Objects homepage. About Mock Objects, a technique for improving the design of code within Test-Driven Development.
The EasyMock homepage. The Spring Framework uses EasyMock extensively in it's test suite.
The JMock homepage. JMock is a library that supports test-driven development of Java code with mock objects.
The DbUnit homepage. DbUnit is a JUnit extension (also usable with Ant) targeted for database-driven projects that, among other things, puts your database into a known state between test runs.
The Grinder homepage. The Grinder is a Java load-testing framework.
This part of the reference documentation is concerned with the middle tier, and specifically the data access responsibilities of said tier.
Spring's comprehensive transaction management support is covered in some detail, followed by thorough coverage of the various middle tier data access frameworks and technologies that the Spring Framework integrates with.
One of the most compelling reasons to use the Spring Framework is the comprehensive transaction support. The Spring Framework provides a consistent abstraction for transaction management that delivers the following benefits:
Provides a consistent programming model across different transaction APIs such as JTA, JDBC, Hibernate, JPA, and JDO.
Supports declarative transaction management.
Provides a simpler API for programmatic transaction management than a number of complex transaction APIs such as JTA.
Integrates very well with Spring's various data access abstractions.
This chapter is divided up into a number of sections, each detailing one of the value-adds or technologies of the Spring Framework's transaction support. The chapter closes up with some discussion of best practices surrounding transaction management (for example, choosing between declarative and programmatic transaction management).
The first section, entitled Motivations, describes why one would want to use the Spring Framework's transaction abstraction as opposed to EJB CMT or driving transactions via a proprietary API such as Hibernate.
The second section, entitled
Key abstractions
outlines the core classes in the Spring Framework's transaction support,
as well as how to configure and obtain DataSource
instances from a variety of sources.
The third section, entitled Declarative transaction management, covers the Spring Framework's support for declarative transaction management.
The fourth section, entitled Programmatic transaction management, covers the Spring Framework's support for programmatic (that is, explicitly coded) transaction management.
Traditionally, J2EE developers have had two choices for transaction management: global or local transactions. Global transactions are managed by the application server, using the Java Transaction API (JTA). Local transactions are resource-specific: the most common example would be a transaction associated with a JDBC connection. This choice has profound implications. For instance, global transactions provide the ability to work with multiple transactional resources (typically relational databases and message queues). With local transactions, the application server is not involved in transaction management and cannot help ensure correctness across multiple resources. (It is worth noting that most applications use a single transaction resource.)
Global Transactions. Global transactions have a significant downside, in that code needs
to use JTA, and JTA is a cumbersome API to use (partly due to its exception
model). Furthermore, a JTA UserTransaction
normally needs to be sourced from JNDI: meaning that we need to use
both JNDI and JTA to use JTA.
Obviously all use of global transactions limits the reusability of application
code, as JTA is normally only available in an application server environment. Previously, the preferred way to use global transactions was via EJB
CMT (Container Managed Transaction):
CMT is a form of declarative transaction management
(as distinguished from programmatic transaction management).
EJB CMT removes the need for transaction-related JNDI lookups - although of course
the use of EJB itself necessitates the use of JNDI. It removes most of the need (although
not entirely) to write Java code to control transactions. The significant
downside is that CMT is tied to JTA and an application server
environment. Also, it is only available if one chooses to implement
business logic in EJBs, or at least behind a transactional EJB facade. The
negatives around EJB in general are so great that this is not an
attractive proposition, especially in the face of compelling alternatives for
declarative transaction management.
Local Transactions. Local transactions may be easier to use, but have significant disadvantages: they cannot work across multiple transactional resources. For example, code that manages transactions using a JDBC connection cannot run within a global JTA transaction. Another downside is that local transactions tend to be invasive to the programming model.
Spring resolves these problems. It enables application developers to use a consistent programming model in any environment. You write your code once, and it can benefit from different transaction management strategies in different environments. The Spring Framework provides both declarative and programmatic transaction management. Declarative transaction management is preferred by most users, and is recommended in most cases.
With programmatic transaction management, developers work with the Spring Framework transaction abstraction, which can run over any underlying transaction infrastructure. With the preferred declarative model, developers typically write little or no code related to transaction management, and hence don't depend on the Spring Framework's transaction API (or indeed on any other transaction API).
The key to the Spring transaction abstraction is the notion of a
transaction strategy. A transaction strategy is
defined by the
org.springframework.transaction.PlatformTransactionManager
interface, shown below:
public interface PlatformTransactionManager { TransactionStatus getTransaction(TransactionDefinition definition) throws TransactionException; void commit(TransactionStatus status) throws TransactionException; void rollback(TransactionStatus status) throws TransactionException; }
This is primarily an SPI interface, although it can be used
programmatically.
Note that in keeping with the Spring Framework's philosophy,
PlatformTransactionManager
is
an interface, and can thus be easily mocked or stubbed
as necessary. Nor is it tied to a lookup strategy such as JNDI:
PlatformTransactionManager
implementations
are defined like any other object (or bean) in the Spring Framework's IoC container.
This benefit alone makes it a worthwhile abstraction even when working
with JTA: transactional code can be tested much more easily than if it
used JTA directly.
Again in keeping with Spring's philosophy, the TransactionException
that can be thrown by any of the PlatformTransactionManager
interface's methods is unchecked (that is it extends the
java.lang.RuntimeException
class). Transaction infrastructure
failures are almost invariably fatal. In rare cases where application code can actually
recover from a transaction failure, the application developer can still choose to catch
and handle TransactionException
. The salient point is
that developers are not forced to do so.
The getTransaction(..)
method returns a
TransactionStatus
object, depending on a
TransactionDefinition
parameter. The returned
TransactionStatus
might represent a new or
existing transaction (if there were a matching transaction in the current
call stack - with the implication being that (as with J2EE transaction contexts)
a TransactionStatus
is associated with a
thread of execution).
The TransactionDefinition
interface specifies:
Isolation: the degree of isolation this transaction has from the work of other transactions. For example, can this transaction see uncommitted writes from other transactions?
Propagation: normally all code executed within a transaction scope will run in that transaction. However, there are several options specifying behavior if a transactional method is executed when a transaction context already exists: for example, simply continue running in the existing transaction (the common case); or suspending the existing transaction and creating a new transaction. Spring offers all of the transaction propagation options familiar from EJB CMT. (Some details regarding the semantics of transaction propagation in Spring can be found in the section entitled Section 9.5.7, “Transaction propagation”.
Timeout: how long this transaction may run before timing out (and automatically being rolled back by the underlying transaction infrastructure).
Read-only status: a read-only transaction does not modify any data. Read-only transactions can be a useful optimization in some cases (such as when using Hibernate).
These settings reflect standard transactional concepts. If necessary, please refer to a resource discussing transaction isolation levels and other core transaction concepts because understanding such core concepts is essential to using the Spring Framework or indeed any other transaction management solution.
The TransactionStatus
interface provides a simple
way for transactional code to control transaction execution and query
transaction status. The concepts should be familiar, as they are common to
all transaction APIs:
public interface TransactionStatus { boolean isNewTransaction(); void setRollbackOnly(); boolean isRollbackOnly(); }
Regardless of whether you opt for declarative or programmatic transaction
management in Spring, defining the correct
PlatformTransactionManager
implementation is
absolutely essential. In good Spring fashion, this important definition typically
is made using via Dependency Injection.
PlatformTransactionManager
implementations
normally require knowledge of the environment in which they work: JDBC, JTA,
Hibernate, etc The following examples from the
dataAccessContext-local.xml
file from Spring's
jPetStore sample application show how a local
PlatformTransactionManager
implementation can be
defined. (This will work with plain JDBC.)
We must define a JDBC DataSource
, and
then use the Spring DataSourceTransactionManager
, giving
it a reference to the DataSource
.
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="${jdbc.driverClassName}" /> <property name="url" value="${jdbc.url}" /> <property name="username" value="${jdbc.username}" /> <property name="password" value="${jdbc.password}" /> </bean>
The related PlatformTransactionManager
bean
definition will look like this:
<bean id="txManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"> <property name="dataSource" ref="dataSource"/> </bean>
If we use JTA in a J2EE container, as in the 'dataAccessContext-jta.xml'
file from the same sample application, we use a container DataSource
,
obtained via JNDI, in conjunction with Spring's JtaTransactionManager
.
The JtaTransactionManager
doesn't need to know about the
DataSource
, or any other specific resources, as
it will use the container's global transaction management infrastructure.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jee="http://www.springframework.org/schema/jee"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-2.5.xsd">
<jee:jndi-lookup id="dataSource" jndi-name="jdbc/jpetstore"/>
<bean id="txManager" class="org.springframework.transaction.jta.JtaTransactionManager" />
<!-- other <bean/>
definitions here -->
</beans>
![]() | Note |
---|---|
The above definition of the |
We can also use Hibernate local transactions easily, as shown in the
following examples from the Spring Framework's PetClinic
sample application. In this case, we need to define a Hibernate
LocalSessionFactoryBean
, which application code will
use to obtain Hibernate Session
instances.
The DataSource
bean definition will be
similar to the one shown previously (and thus is not shown). If the
DataSource
is managed by the JEE container it should
be non-transactional as the Spring Framework, rather than the JEE container, will
manage transactions.
The 'txManager'
bean in this case is of the
HibernateTransactionManager
type. In the same way as the
DataSourceTransactionManager
needs a reference to the
DataSource
, the
HibernateTransactionManager
needs a reference to the
SessionFactory
.
<bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"> <property name="dataSource" ref="dataSource" /> <property name="mappingResources"> <list> <value>org/springframework/samples/petclinic/hibernate/petclinic.hbm.xml</value> </list> </property> <property name="hibernateProperties"> <value> hibernate.dialect=${hibernate.dialect} </value> </property> </bean> <bean id="txManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager"> <property name="sessionFactory" ref="sessionFactory" /> </bean>
With Hibernate and JTA transactions, we can simply use the
JtaTransactionManager
as with JDBC or any other resource strategy.
<bean id="txManager" class="org.springframework.transaction.jta.JtaTransactionManager"/>
Note that this is identical to JTA configuration for any resource, as these are global transactions, which can enlist any transactional resource.
In all these cases, application code will not need to change at
all. We can change how transactions are managed merely by changing
configuration, even if that change means moving from local to global
transactions or vice versa.
It should now be clear how different transaction managers are
created, and how they are linked to related resources which need to be
synchronized to transactions (for example DataSourceTransactionManager
to a JDBC DataSource
,
HibernateTransactionManager
to a Hibernate
SessionFactory
, and so forth). There remains the question
however of how the application code, directly or indirectly using a
persistence API (such as JDBC, Hibernate, and JDO), ensures that these resources
are obtained and handled properly in terms of proper
creation/reuse/cleanup and trigger (optionally) transaction
synchronization via the relevant PlatformTransactionManager
.
The preferred approach is to use Spring's highest level
persistence integration APIs. These do not replace the native APIs, but
internally handle resource creation/reuse, cleanup, optional
transaction synchronization of the resources and exception mapping so
that user data access code doesn't have to worry about these concerns at
all, but can concentrate purely on non-boilerplate persistence logic.
Generally, the same template approach is used
for all persistence APIs, with examples including the
JdbcTemplate
, HibernateTemplate
,
and JdoTemplate
classes (detailed in subsequent chapters
of this reference documentation.
At a lower level exist classes such as
DataSourceUtils
(for JDBC),
SessionFactoryUtils
(for Hibernate),
PersistenceManagerFactoryUtils
(for JDO), and so on.
When it is preferable for application code to deal directly with the
resource types of the native persistence APIs, these classes ensure that
proper Spring Framework-managed instances are obtained, transactions are
(optionally) synchronized, and exceptions which happen in the process
are properly mapped to a consistent API.
For example, in the case of JDBC, instead of the traditional JDBC approach of
calling the getConnection()
method on the
DataSource
, you would instead use Spring's
org.springframework.jdbc.datasource.DataSourceUtils
class as follows:
Connection conn = DataSourceUtils.getConnection(dataSource);
If an existing transaction exists, and already has a connection
synchronized (linked) to it, that instance will be returned. Otherwise,
the method call will trigger the creation of a new connection, which
will be (optionally) synchronized to any existing transaction, and
made available for subsequent reuse in that same transaction. As mentioned,
this has the added advantage that any SQLException
will be wrapped in a Spring Framework
CannotGetJdbcConnectionException
- one of the Spring
Framework's hierarchy of unchecked DataAccessExceptions. This gives you more
information than can easily be obtained from the
SQLException
, and ensures portability across
databases: even across different persistence technologies.
It should be noted that this will also work fine without Spring transaction management (transaction synchronization is optional), so you can use it whether or not you are using Spring for transaction management.
Of course, once you've used Spring's JDBC support or Hibernate
support, you will generally prefer not to use
DataSourceUtils
or the other helper classes, because
you'll be much happier working via the Spring abstraction than directly
with the relevant APIs. For example, if you use the Spring
JdbcTemplate
or jdbc.object
package to simplify your use of JDBC, correct connection retrieval happens
behind the scenes and you won't need to write any special code.
At the very lowest level exists the
TransactionAwareDataSourceProxy
class. This is a
proxy for a target DataSource
, which wraps the
target DataSource
to add awareness of Spring-managed
transactions. In this respect, it is similar to a transactional JNDI
DataSource
as provided by a J2EE server.
It should almost never be necessary or desirable to use this
class, except when existing code exists which must be called and passed
a standard JDBC DataSource
interface implementation.
In that case, it's possible to still have this code be usable, but
participating in Spring managed transactions. It is preferable to write
your new code using the higher level abstractions mentioned
above.
Most users of the Spring Framework choose declarative transaction management. It is the option with the least impact on application code, and hence is most consistent with the ideals of a non-invasive lightweight container.
The Spring Framework's declarative transaction management is made possible with Spring AOP, although, as the transactional aspects code comes with the Spring Framework distribution and may be used in a boilerplate fashion, AOP concepts do not generally have to be understood to make effective use of this code.
It may be helpful to begin by considering EJB CMT and explaining the
similarities and differences with the Spring Framework's declarative transaction
management. The basic approach is similar: it is possible to specify
transaction behavior (or lack of it) down to individual method level. It is
possible to make a setRollbackOnly()
call within a
transaction context if necessary. The differences are:
Unlike EJB CMT, which is tied to JTA, the Spring Framework's declarative transaction management works in any environment. It can work with JDBC, JDO, Hibernate or other transactions under the covers, with configuration changes only.
The Spring Framework enables declarative transaction management to be applied to any class, not merely special classes such as EJBs.
The Spring Framework offers declarative rollback rules: this is a feature with no EJB equivalent. Both programmatic and declarative support for rollback rules is provided.
The Spring Framework gives you an opportunity to customize transactional
behavior, using AOP. For example, if you want to insert custom
behavior in the case of transaction rollback, you can. You can also
add arbitrary advice, along with the transactional advice. With EJB
CMT, you have no way to influence the container's transaction
management other than setRollbackOnly()
.
The Spring Framework does not support propagation of transaction contexts across remote calls, as do high-end application servers. If you need this feature, we recommend that you use EJB. However, consider carefully before using such a feature, because normally, one does not want transactions to span remote calls.
The concept of rollback rules is important: they enable us to
specify which exceptions (and throwables) should cause automatic roll
back. We specify this declaratively, in configuration, not in Java code.
So, while we can still call setRollbackOnly()
on the
TransactionStatus
object to roll the current
transaction back programmatically, most often we can specify a rule that
MyApplicationException
must always result in
rollback. This has the significant advantage that business objects don't need
to depend on the transaction infrastructure. For example, they typically
don't need to import any Spring APIs, transaction or other.
While the EJB default behavior is for the EJB container to
automatically roll back the transaction on a system
exception (usually a runtime exception), EJB CMT does not roll
back the transaction automatically on an application exception
(that is, a checked exception other than java.rmi.RemoteException
).
While the Spring default behavior for declarative transaction management follows
EJB convention (roll back is automatic only on unchecked exceptions), it is often
useful to customize this.
The aim of this section is to dispel the mystique that is sometimes associated
with the use of declarative transactions. It is all very well for this reference
documentation simply to tell you to annotate your classes with the
@Transactional
annotation, add the line
('<tx:annotation-driven/>'
) to your configuration,
and then expect you to understand how it all works. This section will explain the
inner workings of the Spring Framework's declarative transaction infrastructure to
help you navigate your way back upstream to calmer waters in the event of
transaction-related issues.
The most important concepts to grasp with regard to the Spring Framework's
declarative transaction support are that this support is enabled
via AOP proxies,
and that the transactional advice is driven by metadata (currently
XML- or annotation-based). The combination of AOP with transactional metadata yields
an AOP proxy that uses a TransactionInterceptor
in conjunction
with an appropriate PlatformTransactionManager
implementation
to drive transactions around method invocations.
![]() | Note |
---|---|
Although knowledge of Spring AOP is not required to use Spring's declarative transaction support, it can help. Spring AOP is thoroughly covered in the chapter entitled Chapter 6, Aspect Oriented Programming with Spring. |
Conceptually, calling a method on a transactional proxy looks like this...
Consider the following interface, and its attendant implementation.
(The intent is to convey the concepts, and using the rote Foo
and
Bar
tropes means that you can concentrate on the transaction
usage and not have to worry about the domain model.)
// the service interface that we want to make transactional
package x.y.service;
public interface FooService {
Foo getFoo(String fooName);
Foo getFoo(String fooName, String barName);
void insertFoo(Foo foo);
void updateFoo(Foo foo);
}
// an implementation of the above interface
package x.y.service;
public class DefaultFooService implements FooService {
public Foo getFoo(String fooName) {
throw new UnsupportedOperationException();
}
public Foo getFoo(String fooName, String barName) {
throw new UnsupportedOperationException();
}
public void insertFoo(Foo foo) {
throw new UnsupportedOperationException();
}
public void updateFoo(Foo foo) {
throw new UnsupportedOperationException();
}
}
(For the purposes of this example, the fact that the
DefaultFooService
class throws
UnsupportedOperationException
instances in the body
of each implemented method is good; it will allow us to see transactions being created
and then rolled back in response to the UnsupportedOperationException
instance being thrown.)
Let's assume that the first two methods of the FooService
interface (getFoo(String)
and getFoo(String, String)
)
have to execute in the context of a transaction with read-only semantics, and that
the other methods (insertFoo(Foo)
and
updateFoo(Foo)
) have to execute in the context of a transaction
with read-write semantics. Don't worry about taking the following configuration in
all at once; everything will be explained in detail in the next few paragraphs.
<!-- from the file'context.xml'
--> <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <!-- this is the service object that we want to make transactional --> <bean id="fooService" class="x.y.service.DefaultFooService"/> <!-- the transactional advice (what 'happens'; see the<aop:advisor/>
bean below) --> <tx:advice id="txAdvice" transaction-manager="txManager"> <!-- the transactional semantics... --> <tx:attributes> <!-- all methods starting with'get'
are read-only --> <tx:method name="get*" read-only="true"/> <!-- other methods use the default transaction settings (see below) --> <tx:method name="*"/> </tx:attributes> </tx:advice> <!-- ensure that the above transactional advice runs for any execution of an operation defined by theFooService
interface --> <aop:config> <aop:pointcut id="fooServiceOperation" expression="execution(* x.y.service.FooService.*(..))"/> <aop:advisor advice-ref="txAdvice" pointcut-ref="fooServiceOperation"/> </aop:config> <!-- don't forget theDataSource
--> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="oracle.jdbc.driver.OracleDriver"/> <property name="url" value="jdbc:oracle:thin:@rj-t42:1521:elvis"/> <property name="username" value="scott"/> <property name="password" value="tiger"/> </bean> <!-- similarly, don't forget thePlatformTransactionManager
--> <bean id="txManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"> <property name="dataSource" ref="dataSource"/> </bean> <!-- other<bean/>
definitions here --> </beans>
Let's pick apart the above configuration. We have a service object
(the 'fooService'
bean) that we want to make transactional.
The transaction semantics that we want to apply are encapsulated in the
<tx:advice/>
definition. The
<tx:advice/>
definition reads as
“... all methods on starting with 'get'
are to execute
in the context of a read-only transaction, and all other methods are to execute
with the default transaction semantics”. The
'transaction-manager'
attribute of the
<tx:advice/>
tag is set to the
name of the PlatformTransactionManager
bean
that is going to actually drive the transactions (in this
case the 'txManager'
bean).
![]() | Tip |
---|---|
You can actually omit the |
The <aop:config/>
definition ensures that the transactional
advice defined by the 'txAdvice'
bean actually executes at the appropriate
points in the program. First we define a pointcut that matches the execution of any
operation defined in the FooService
interface
('fooServiceOperation'
). Then we associate the pointcut with the
'txAdvice'
using an advisor. The result indicates that at the execution
of a 'fooServiceOperation'
, the advice defined by 'txAdvice'
will be run.
The expression defined within the <aop:pointcut/>
element is an AspectJ pointcut expression; see the chapter entitled Chapter 6, Aspect Oriented Programming with Spring
for more details on pointcut expressions in Spring 2.0.
A common requirement is to make an entire service layer transactional. The best way to do this is simply to change the pointcut expression to match any operation in your service layer. For example:
<aop:config> <aop:pointcut id="fooServiceMethods" expression="execution(* x.y.service.*.*(..))"/> <aop:advisor advice-ref="txAdvice" pointcut-ref="fooServiceMethods"/> </aop:config>
(This example assumes that all your service interfaces are defined
in the 'x.y.service'
package; see the chapter entitled
Chapter 6, Aspect Oriented Programming with Spring for more details.)
Now that we've analyzed the configuration, you may be asking yourself, “Okay... but what does all this configuration actually do?”.
The above configuration is going to effect the creation of a
transactional proxy around the object that is created from the
'fooService'
bean definition. The proxy will be configured
with the transactional advice, so that when an appropriate method is invoked
on the proxy, a transaction may
be started, suspended, be marked as read-only, etc., depending on the
transaction configuration associated with that method. Consider the following
program that test drives the above configuration.
public final class Boot { public static void main(final String[] args) throws Exception { ApplicationContext ctx = new ClassPathXmlApplicationContext("context.xml", Boot.class); FooService fooService = (FooService) ctx.getBean("fooService"); fooService.insertFoo (new Foo()); } }
The output from running the above program will look something
like this. (Please note that the Log4J output and the stacktrace
from the UnsupportedOperationException
thrown by the
insertFoo(..)
method of the
DefaultFooService
class have been truncated in
the interest of clarity.)
<!-- the Spring container is starting up... --> [AspectJInvocationContextExposingAdvisorAutoProxyCreator] - Creating implicit proxy for bean 'fooService' with 0 common interceptors and 1 specific interceptors <!-- theDefaultFooService
is actually proxied --> [JdkDynamicAopProxy] - Creating JDK dynamic proxy for [x.y.service.DefaultFooService] <!-- ... theinsertFoo(..)
method is now being invoked on the proxy --> [TransactionInterceptor] - Getting transaction for x.y.service.FooService.insertFoo <!-- the transactional advice kicks in here... --> [DataSourceTransactionManager] - Creating new transaction with name [x.y.service.FooService.insertFoo] [DataSourceTransactionManager] - Acquired Connection [org.apache.commons.dbcp.PoolableConnection@a53de4] for JDBC transaction <!-- theinsertFoo(..)
method fromDefaultFooService
throws an exception... --> [RuleBasedTransactionAttribute] - Applying rules to determine whether transaction should rollback on java.lang.UnsupportedOperationException [TransactionInterceptor] - Invoking rollback for transaction on x.y.service.FooService.insertFoo due to throwable [java.lang.UnsupportedOperationException] <!-- and the transaction is rolled back (by default,RuntimeException
instances cause rollback) --> [DataSourceTransactionManager] - Rolling back JDBC transaction on Connection [org.apache.commons.dbcp.PoolableConnection@a53de4] [DataSourceTransactionManager] - Releasing JDBC Connection after transaction [DataSourceUtils] - Returning JDBC Connection to DataSource Exception in thread "main" java.lang.UnsupportedOperationException at x.y.service.DefaultFooService.insertFoo(DefaultFooService.java:14) <!-- AOP infrastructure stack trace elements removed for clarity --> at $Proxy0.insertFoo(Unknown Source) at Boot.main(Boot.java:11)
The previous section outlined the basics of how to specify the transactional settings for the classes, typically service layer classes, in your application in a declarative fashion. This section describes how you can control the rollback of transactions in a simple declarative fashion.
The recommended way to indicate to the Spring Framework's
transaction infrastructure that a transaction's work is to be rolled back is to
throw an Exception
from code that is currently
executing in the context of a transaction. The Spring Framework's
transaction infrastructure code will catch any unhandled
Exception
as it bubbles up the call stack, and will
mark the transaction for rollback.
Note however that the Spring Framework's transaction infrastructure
code will, by default, only mark a transaction for rollback in
the case of runtime, unchecked exceptions; that is, when the thrown exception is an
instance or subclass of RuntimeException
.
(Errors
will also - by default - result in a rollback.) Checked
exceptions that are thrown from a transactional method will
not result in the transaction being rolled back.
Exactly which Exception
types mark a transaction
for rollback can be configured. Find below a snippet of XML configuration that
demonstrates how one would configure rollback for a checked, application-specific
Exception
type.
<tx:advice id="txAdvice" transaction-manager="txManager">
<tx:attributes>
<tx:method name="get*" read-only="true" rollback-for="NoProductInStockException"/>
<tx:method name="*"/>
</tx:attributes>
</tx:advice>
It is also possible to specify 'no rollback rules', for those times when you do
not want a transaction to be marked for rollback when an exception is thrown.
In the example configuration below, we effectively are telling the Spring Framework's transaction
infrastructure to commit the attendant transaction even in the face of an unhandled
InstrumentNotFoundException
.
<tx:advice id="txAdvice">
<tx:attributes>
<tx:method name="updateStock" no-rollback-for="InstrumentNotFoundException"/>
<tx:method name="*"/>
</tx:attributes>
</tx:advice>
When the Spring Framework's transaction infrastructure has caught an exception and is consulting
any configured rollback rules to determine whether or not to mark the transaction for rollback, the
strongest matching rule wins. So in the case of the following configuration,
any exception other than an InstrumentNotFoundException
would result in the
attendant transaction being marked for rollback.
<tx:advice id="txAdvice"> <tx:attributes> <tx:method name="*" rollback-for="Throwable" no-rollback-for="InstrumentNotFoundException"/> </tx:attributes> </tx:advice>
The second way to indicate that a rollback is required is to do so programmatically. Although very simple, this way is quite invasive, and tightly couples your code to the Spring Framework's transaction infrastructure, as can be seen below:
public void resolvePosition() { try { // some business logic... } catch (NoProductInStockException ex) { // trigger rollback programmatically TransactionAspectSupport.currentTransactionStatus().setRollbackOnly(); } }
You are strongly encouraged to use the declarative approach to rollback if at all possible. Programmatic rollback is available should you absolutely need it, but its usage flies in the face of achieving a nice, clean POJO-based architecture.
Consider the scenario where you have a number of service layer objects,
and you want to apply totally different transactional configuration
to each of them. This is achieved by defining distinct <aop:advisor/>
elements with differing 'pointcut'
and 'advice-ref'
attribute values.
Let's assume that all of your service layer classes are defined in a root
'x.y.service'
package. To make all beans that are instances of classes
defined in that package (or in subpackages) and that have names ending in
'Service'
have the default transactional configuration, you would write
the following:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd">
<aop:config>
<aop:pointcut id="serviceOperation"
expression="execution(* x.y.service..*Service.*(..))"/>
<aop:advisor pointcut-ref="serviceOperation" advice-ref="txAdvice"/>
</aop:config>
<!-- these two beans will be transactional... -->
<bean id="fooService" class="x.y.service.DefaultFooService"/>
<bean id="barService" class="x.y.service.extras.SimpleBarService"/>
<!-- ... and these two beans won't -->
<bean id="anotherService" class="org.xyz.SomeService"/> <!-- (not in the right package) -->
<bean id="barManager" class="x.y.service.SimpleBarManager"/> <!-- (doesn't end in 'Service') -->
<tx:advice id="txAdvice">
<tx:attributes>
<tx:method name="get*" read-only="true"/>
<tx:method name="*"/>
</tx:attributes>
</tx:advice>
<!-- other transaction infrastructure beans such as a PlatformTransactionManager
omitted... -->
</beans>
Find below an example of configuring two distinct beans with totally different transactional settings.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <aop:config> <aop:pointcut id="defaultServiceOperation" expression="execution(* x.y.service.*Service.*(..))"/> <aop:pointcut id="noTxServiceOperation" expression="execution(* x.y.service.ddl.DefaultDdlManager.*(..))"/> <aop:advisor pointcut-ref="defaultServiceOperation" advice-ref="defaultTxAdvice"/> <aop:advisor pointcut-ref="noTxServiceOperation" advice-ref="noTxAdvice"/> </aop:config> <!-- this bean will be transactional (see the'defaultServiceOperation'
pointcut) --> <bean id="fooService" class="x.y.service.DefaultFooService"/> <!-- this bean will also be transactional, but with totally different transactional settings --> <bean id="anotherFooService" class="x.y.service.ddl.DefaultDdlManager"/> <tx:advice id="defaultTxAdvice"> <tx:attributes> <tx:method name="get*" read-only="true"/> <tx:method name="*"/> </tx:attributes> </tx:advice> <tx:advice id="noTxAdvice"> <tx:attributes> <tx:method name="*" propagation="NEVER"/> </tx:attributes> </tx:advice> <!-- other transaction infrastructure beans such as aPlatformTransactionManager
omitted... --> </beans>
This section summarises the various transactional settings that can be specified
using the <tx:advice/>
tag. The default
<tx:advice/>
settings are:
The propagation setting is REQUIRED
The isolation level is DEFAULT
The transaction is read/write
The transaction timeout defaults to the default timeout of the underlying transaction system, or or none if timeouts are not supported
Any RuntimeException
will trigger
rollback, and any checked Exception
will not
These default settings can be changed; the various
attributes of the <tx:method/>
tags that are nested within
<tx:advice/>
and <tx:attributes/>
tags are summarized below:
Table 9.1. <tx:method/>
settings
Attribute | Required? | Default | Description |
---|---|---|---|
name | Yes |
The method name(s) with which the transaction attributes
are to be associated. The wildcard (*) character can be used to
associate the same transaction attribute settings with a number
of methods; for example, | |
propagation | No | REQUIRED | The transaction propagation behavior |
isolation | No | DEFAULT | The transaction isolation level |
timeout | No | -1 | The transaction timeout value (in seconds) |
read-only | No | false | Is this transaction read-only? |
rollback-for | No |
The | |
no-rollback-for | No |
The |
At the time of writing it is not possible to have explicit control over the
name of a transaction, where 'name' means the transaction name that will be shown
in a transaction monitor, if applicable (for example, WebLogic's transaction
monitor), and in logging output. For declarative transactions, the transaction
name is always the fully-qualified class name + "." + method name of the
transactionally-advised class. For example
'com.foo.BusinessService.handlePayment'
.
![]() | Note |
---|---|
The functionality offered by the |
In addition to the XML-based declarative approach to transaction configuration, you can also use an annotation-based approach to transaction configuration. Declaring transaction semantics directly in the Java source code puts the declarations much closer to the affected code, and there is generally not much danger of undue coupling, since code that is meant to be used transactionally is almost always deployed that way anyway.
The ease-of-use afforded by the use of the @Transactional
annotation is best illustrated with an example, after which all of the details
will be explained. Consider the following class definition:
// the service class that we want to make transactional @Transactional public class DefaultFooService implements FooService { Foo getFoo(String fooName); Foo getFoo(String fooName, String barName); void insertFoo(Foo foo); void updateFoo(Foo foo); }
When the above POJO is defined as a bean in a Spring IoC container, the bean instance can be made transactional by adding merely one line of XML configuration, like so:
<!-- from the file'context.xml'
--> <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <!-- this is the service object that we want to make transactional --> <bean id="fooService" class="x.y.service.DefaultFooService"/> <!-- enable the configuration of transactional behavior based on annotations --> <tx:annotation-driven transaction-manager="txManager"/> <!-- aPlatformTransactionManager
is still required --> <bean id="txManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"> <!-- (this dependency is defined somewhere else) --> <property name="dataSource" ref="dataSource"/> </bean> <!-- other<bean/>
definitions here --> </beans>
![]() | Tip |
---|---|
You can actually omit the |
The @Transactional
annotation may be placed
before an interface definition, a method on an interface, a class definition, or a
public method on a class. However, please note that the mere
presence of the @Transactional
annotation is not
enough to actually turn on the transactional behavior - the
@Transactional
annotation is simply metadata
that can be consumed by something that is @Transactional
-aware
and that can use the metadata to configure the appropriate beans with transactional
behavior. In the case of the above example, it is the presence of the
<tx:annotation-driven/>
element that
switches on the transactional behavior.
The Spring team's recommendation is that you only annotate concrete
classes with the @Transactional
annotation,
as opposed to annotating interfaces. You certainly can place the
@Transactional
annotation on an interface (or
an interface method), but this will only work as you would expect it to if
you are using interface-based proxies. The fact that annotations are
not inherited means that if you are using class-based
proxies (proxy-target-class="true"
) or the weaving-based aspect
(mode="aspectj"
) then the transaction settings will not be
recognised by the proxying/weaving infrastructure and the object will not be
wrapped in a transactional proxy (which would be decidedly bad).
So please do take the Spring team's advice and only annotate concrete classes
(and the methods of concrete classes) with the
@Transactional
annotation.
Note: In proxy mode (which is the default), only 'external'
method calls coming in through the proxy will be intercepted.
This means that 'self-invocation', i.e. a method within the target object
calling some other method of the target object, won't lead to an actual
transaction at runtime even if the invoked method is marked with
@Transactional
!
Consider the use of AspectJ mode (see below) if you expect
self-invocations to be wrapped with transactions as well. In this case,
there won't be a proxy in the first place; instead, the target class
will be 'weaved' (i.e. its byte code will be modified) in order to
turn @Transactional
into runtime behavior
on any kind of method.
Table 9.2. <tx:annotation-driven/>
settings
Attribute | Default | Description |
---|---|---|
transaction-manager | transactionManager | The name of transaction manager to use. Only required
if the name of the transaction manager is not |
mode | proxy | The default mode "proxy" will process annotated beans to be proxied using Spring's AOP framework (following proxy semantics, as discussed above, applying to method calls coming in through the proxy only). The alternative mode "aspectj" will instead weave the affected classes with Spring's AspectJ transaction aspect (modifying the target class byte code in order to apply to any kind of method call). AspectJ weaving requires spring-aspects.jar on the classpath as well as load-time weaving (or compile-time weaving) enabled. (See the section entitled Section 6.8.4.5, “Spring configuration” for details on how to set up load-time weaving.) |
proxy-target-class | false | Applies to proxy mode only. Controls what type
of transactional proxies are created for classes annotated
with the |
order | Ordered.LOWEST_PRECEDENCE | Defines the order of the transaction advice that will be applied to
beans annotated with |
![]() | Note |
---|---|
The " |
The most derived location takes precedence when evaluating the transactional
settings for a method. In the case of the following example, the
DefaultFooService
class is annotated at the class level
with the settings for a read-only transaction, but the
@Transactional
annotation on the
updateFoo(Foo)
method in the same class takes precedence
over the transactional settings defined at the class level.
@Transactional(readOnly = true) public class DefaultFooService implements FooService { public Foo getFoo(String fooName) { // do something } // these settings have precedence for this method @Transactional(readOnly = false, propagation = Propagation.REQUIRES_NEW) public void updateFoo(Foo foo) { // do something } }
The @Transactional
annotation is
metadata that specifies that an interface, class, or method must have
transactional semantics; for example, “start a brand new read-only
transaction when this method is invoked, suspending any existing
transaction”. The default
@Transactional
settings are:
The propagation setting is PROPAGATION_REQUIRED
The isolation level is ISOLATION_DEFAULT
The transaction is read/write
The transaction timeout defaults to the default timeout of the underlying transaction system, or or none if timeouts are not supported
Any RuntimeException
will trigger
rollback, and any checked Exception
will not
These default settings can be changed; the various
properties of the @Transactional
annotation
are summarized in the following table:
Table 9.3. @Transactional
properties
Property | Type | Description |
---|---|---|
propagation
| enum: Propagation | optional propagation setting |
isolation
| enum: Isolation | optional isolation level |
readOnly
| boolean | read/write vs. read-only transaction |
timeout
| int (in seconds granularity) | the transaction timeout |
rollbackFor
| an array of Class objects, which
must be derived from Throwable | an optional array of exception classes which must cause rollback |
rollbackForClassname
| an array of class names. Classes
must be derived from Throwable | an optional array of names of exception classes that must cause rollback |
noRollbackFor
| an array of Class objects, which
must be derived from Throwable | an optional array of exception classes that must not cause rollback. |
noRollbackForClassname
| an array of String class names, which
must be derived from Throwable | an optional array of names of exception classes that must not cause rollback |
Currently it is not possible to have explicit control over the name of a transaction, where
'name' means the transaction name that will be shown in a transaction monitor, if applicable (for
example, WebLogic's transaction monitor), and in logging output. For declarative transactions, the
transaction name is always the fully-qualified class name + "." + method name of the
transactionally-advised class. For example, if the handlePayment(..)
method of the BusinessService
class started a transaction, the name of the
transaction would be:
com.foo.BusinessService.handlePayment
Please note that this section of the Spring reference documentation is not an introduction to transaction propagation proper; rather it details some of the semantics regarding transaction propagation in Spring.
In the case of Spring-managed transactions, please be aware of the difference between physical and logical transactions, and how the propagation setting applies to this difference.
PROPAGATION_REQUIRED
When the propagation setting is PROPAGATION_REQUIRED
, a
logical transaction scope is created for each method that it gets applied to. Each
such logical transaction scope can individually decide on rollback-only status, with an outer
transaction scope being logically independent from the inner transaction scope. Of course, in case of
standard PROPAGATION_REQUIRED
behavior, they will be mapped to the same physical
transaction. So a rollback-only marker set in the inner transaction scope does affect the outer
transactions chance to actually commit (as you would expect it to).
However, in the case where an inner transaction scopes sets the rollback-only marker, the outer
transaction itself has not decided on the rollback itself, and so the rollback (silently triggered by
the inner transaction scope) is unexpected: a corresponding
UnexpectedRollbackException
will be thrown at that point. This is
expected behavior so that the caller of a transaction can never be misled to assume
that a commit was performed when it really was not. So if an inner transaction (that the outer caller is
not aware of) silently marks a transaction as rollback-only, the outer caller would still innocently
call commit - and needs to receive an UnexpectedRollbackException
to indicate
clearly that a rollback was performed instead.
PROPAGATION_REQUIRES_NEW
PROPAGATION_REQUIRES_NEW
, in contrast, uses a completely
independent transaction for each affected transaction scope. In that case, the underlying physical
transactions will be different and hence can commit or rollback independently, with an outer transaction
not affected by an inner transaction's rollback status.
PROPAGATION_NESTED
is different again in that it uses a
single physical transaction with multiple savepoints that it can roll back to.
Such partial rollbacks allow an inner transaction scope to trigger a rollback
for its scope, with the outer transaction being able to continue the physical
transaction despite some operations having been rolled back. This is typically mapped onto JDBC
savepoints, so will only work with JDBC resource transactions (see Spring's
DataSourceTransactionManager
).
Consider the situation where you would like to execute
both transactional and
(to keep things simple) some basic profiling advice. How do you
effect this in the context of using
<tx:annotation-driven/>
?
What we want to see when we invoke the updateFoo(Foo)
method is:
the configured profiling aspect starting up,
then the transactional advice executing,
then the method on the advised object executing
then the transaction committing (we'll assume a sunny day scenario here),
and then finally the profiling aspect reporting (somehow) exactly how long the whole transactional method invocation took
![]() | Note |
---|---|
This chapter is not concerned with explaining AOP in any great detail (except as it applies to transactions). Please see the chapter entitled Chapter 6, Aspect Oriented Programming with Spring for detailed coverage of the various bits and pieces of the following AOP configuration (and AOP in general). |
Here is the code for a simple profiling aspect. The
ordering of advice is controlled via the Ordered
interface. For full details on advice ordering, see Section 6.2.4.7, “Advice ordering”.
package x.y; import org.aspectj.lang.ProceedingJoinPoint; import org.springframework.util.StopWatch; import org.springframework.core.Ordered; public class SimpleProfiler implements Ordered { private int order; // allows us to control the ordering of advice public int getOrder() { return this.order; } public void setOrder(int order) { this.order = order; } // this method is the around advice public Object profile(ProceedingJoinPoint call) throws Throwable { Object returnValue; StopWatch clock = new StopWatch(getClass().getName()); try { clock.start(call.toShortString()); returnValue = call.proceed(); } finally { clock.stop(); System.out.println(clock.prettyPrint()); } return returnValue; } }
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <bean id="fooService" class="x.y.service.DefaultFooService"/> <!-- this is the aspect --> <bean id="profiler" class="x.y.SimpleProfiler"> <!-- execute before the transactional advice (hence the lower order number) --> <property name="order" value="1"/> </bean> <tx:annotation-driven transaction-manager="txManager" order="200"/> <aop:config> <!-- this advice will execute around the transactional advice --> <aop:aspect id="profilingAspect" ref="profiler"> <aop:pointcut id="serviceMethodWithReturnValue" expression="execution(!void x.y..*Service.*(..))"/> <aop:around method="profile" pointcut-ref="serviceMethodWithReturnValue"/> </aop:aspect> </aop:config> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="oracle.jdbc.driver.OracleDriver"/> <property name="url" value="jdbc:oracle:thin:@rj-t42:1521:elvis"/> <property name="username" value="scott"/> <property name="password" value="tiger"/> </bean> <bean id="txManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"> <property name="dataSource" ref="dataSource"/> </bean> </beans>
The result of the above configuration will be a 'fooService'
bean that has profiling and transactional aspects applied to it
in that order. The configuration of any number of additional
aspects is effected in a similar fashion.
Finally, find below some example configuration for effecting the same setup as above, but using the purely XML declarative approach.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <bean id="fooService" class="x.y.service.DefaultFooService"/> <!-- the profiling advice --> <bean id="profiler" class="x.y.SimpleProfiler"> <!-- execute before the transactional advice (hence the lower order number) --> <property name="order" value="1"/> </bean> <aop:config> <aop:pointcut id="entryPointMethod" expression="execution(* x.y..*Service.*(..))"/> <!-- will execute after the profiling advice (c.f. the order attribute) --> <aop:advisor advice-ref="txAdvice" pointcut-ref="entryPointMethod" order="2"/> <!-- order value is higher than the profiling aspect --> <aop:aspect id="profilingAspect" ref="profiler"> <aop:pointcut id="serviceMethodWithReturnValue" expression="execution(!void x.y..*Service.*(..))"/> <aop:around method="profile" pointcut-ref="serviceMethodWithReturnValue"/> </aop:aspect> </aop:config> <tx:advice id="txAdvice" transaction-manager="txManager"> <tx:attributes> <tx:method name="get*" read-only="true"/> <tx:method name="*"/> </tx:attributes> </tx:advice> <!-- other <bean/> definitions such as aDataSource
and aPlatformTransactionManager
here --> </beans>
The result of the above configuration will be a 'fooService'
bean that has profiling and transactional aspects applied to it
in that order. If we wanted the profiling advice to execute
after the transactional advice on the way in, and
before the transactional advice on the way out, then we would
simply swap the value of the profiling aspect bean's 'order'
property such that it was higher than the transactional advice's order value.
The configuration of any number of additional aspects is achieved in a similar fashion.
It is also possible to use the Spring Framework's
@Transactional
support outside of a Spring container
by means of an AspectJ aspect. To use this support you must first
annotate your classes (and optionally your classes' methods with the
@Transactional
annotation, and then you must link
(weave) your application with the
org.springframework.transaction.aspectj.AnnotationTransactionAspect
defined in the spring-aspects.jar
file.
The aspect must also be configured with a transaction manager. You could of course
use the Spring Framework's IoC container to take care of dependency injecting the
aspect. The simplest way to
configure the transaction management aspect is to use the
'<tx:annotation-driven/>'
element and specify the
mode
attribute to asepctj
as described in
Section 9.5.6, “Using @Transactional
”.
Since we're focusing here on applications running outside of a Spring
container, we'll show you how to do it programmatically.
![]() | Note |
---|---|
Prior to continuing, you may well want to read the previous sections entitled
Section 9.5.6, “Using |
// construct an appropriate transaction manager
DataSourceTransactionManager txManager = new DataSourceTransactionManager(getDataSource());
// configure the AnnotationTransactionAspect
to use it; this must be done before executing any transactional methods
AnnotationTransactionAspect.aspectOf().setTransactionManager(txManager);
![]() | Note |
---|---|
When using this aspect, you must annotate the implementation class (and/or methods within that class), not the interface (if any) that the class implements. AspectJ follows Java's rule that annotations on interfaces are not inherited. |
The @Transactional
annotation on a class specifies
the default transaction semantics for the execution of any method in the class.
The @Transactional
annotation on a method within
the class overrides the default transaction semantics given by the class annotation
(if present). Any method may be annotated, regardless of visibility.
To weave your applications with the AnnotationTransactionAspect
you must either build your application with AspectJ (see the
AspectJ Development Guide)
or use load-time weaving. See the section entitled Section 6.8.4, “Load-time weaving with AspectJ in the Spring Framework” for a
discussion of load-time weaving with AspectJ.
The Spring Framework provides two means of programmatic transaction management:
Using the TransactionTemplate
.
Using a PlatformTransactionManager
implementation directly.
If you are going to use programmatic transaction management, the Spring
team generally recommends using the TransactionTemplate
.
The second approach is similar to using the JTA UserTransaction
API (although exception handling is less cumbersome).
The TransactionTemplate
adopts the same
approach as other Spring templates such as the
JdbcTemplate
. It uses a callback approach, to
free application code from having to do the boilerplate acquisition
and release of transactional resources, and results in code that is
intention driven, in that the code that is written focuses solely
on what the developer wants to do.
![]() | Note |
---|---|
As you will immediately see in the examples that follow, using
the |
Application code that must execute in a transactional context,
and that will use the TransactionTemplate
explicitly,
looks like this. You, as an application developer, will write a
TransactionCallback
implementation (typically
expressed as an anonymous inner class) that will contain all of the code
that you need to have execute in the context of a transaction. You will then
pass an instance of your custom TransactionCallback
to the execute(..)
method exposed on the
TransactionTemplate
.
public class SimpleService implements Service { // singleTransactionTemplate
shared amongst all methods in this instance private final TransactionTemplate transactionTemplate; // use constructor-injection to supply thePlatformTransactionManager
public SimpleService(PlatformTransactionManager transactionManager) { Assert.notNull(transactionManager, "The 'transactionManager' argument must not be null."); this.transactionTemplate = new TransactionTemplate(transactionManager); } public Object someServiceMethod() { return transactionTemplate.execute(new TransactionCallback() { // the code in this method executes in a transactional context public Object doInTransaction(TransactionStatus status) { updateOperation1(); return resultOfUpdateOperation2(); } }); } }
If there is no return value, use the convenient
TransactionCallbackWithoutResult
class via an
anonymous class like so:
transactionTemplate.execute(new TransactionCallbackWithoutResult() {
protected void doInTransactionWithoutResult(TransactionStatus status) {
updateOperation1();
updateOperation2();
}
});
Code within the callback can roll the transaction back by calling
the setRollbackOnly()
method on the supplied
TransactionStatus
object.
transactionTemplate.execute(new TransactionCallbackWithoutResult() {
protected void doInTransactionWithoutResult(TransactionStatus status) {
try {
updateOperation1();
updateOperation2();
} catch (SomeBusinessExeption ex) {
status.setRollbackOnly();
}
}
});
Transaction settings such as the propagation mode, the isolation level,
the timeout, and so forth can be set on the TransactionTemplate
either programmatically or in configuration. TransactionTemplate
instances by default have the default transactional settings.
Find below an example of programmatically customizing the
transactional settings for a specific TransactionTemplate
.
public class SimpleService implements Service { private final TransactionTemplate transactionTemplate; public SimpleService(PlatformTransactionManager transactionManager) { Assert.notNull(transactionManager, "The 'transactionManager' argument must not be null."); this.transactionTemplate = new TransactionTemplate(transactionManager); // the transaction settings can be set here explicitly if so desired this.transactionTemplate.setIsolationLevel(TransactionDefinition.ISOLATION_READ_UNCOMMITTED); this.transactionTemplate.setTimeout(30); // 30 seconds // and so forth... } }
Find below an example of defining a TransactionTemplate
with some custom
transactional settings, using Spring XML configuration. The 'sharedTransactionTemplate
'
can then be injected into as many services as are required.
<bean id="sharedTransactionTemplate" class="org.springframework.transaction.support.TransactionTemplate"> <property name="isolationLevelName" value="ISOLATION_READ_UNCOMMITTED"/> <property name="timeout" value="30"/> </bean>"
Finally, instances of the TransactionTemplate
class are
threadsafe, in that instances do not maintain any conversational state.
TransactionTemplate
instances do
however maintain configuration state, so while a number of classes
may choose to share a single instance of a TransactionTemplate
, if a class needed
to use a TransactionTemplate
with different settings
(for example, a different isolation level), then two distinct
TransactionTemplate
instances would need to be
created and used.
You can also use the
org.springframework.transaction.PlatformTransactionManager
directly to manage your transaction. Simply pass the implementation of
the PlatformTransactionManager
you're
using to your bean via a bean reference. Then, using the
TransactionDefinition
and
TransactionStatus
objects you can
initiate transactions, rollback and commit.
DefaultTransactionDefinition def = new DefaultTransactionDefinition(); // explicitly setting the transaction name is something that can only be done programmatically def.setName("SomeTxName"); def.setPropagationBehavior(TransactionDefinition.PROPAGATION_REQUIRED); TransactionStatus status = txManager.getTransaction(def); try { // execute your business logic here } catch (MyException ex) { txManager.rollback(status); throw ex; } txManager.commit(status);
Programmatic transaction management is usually a good idea only if
you have a small number of transactional operations. For example, if you
have a web application that require transactions only for certain update
operations, you may not want to set up transactional proxies using Spring
or any other technology. In this case, using the TransactionTemplate
may be a good approach. Being able to set the transaction name
explicitly is also something that can only be done using the programmatic
approach to transaction management.
On the other hand, if your application has numerous transactional operations, declarative transaction management is usually worthwhile. It keeps transaction management out of business logic, and is not difficult to configure. When using the Spring Framework, rather than EJB CMT, the configuration cost of declarative transaction management is greatly reduced.
Spring's transaction abstraction generally is application server
agnostic. Additionally, Spring's JtaTransactionManager
class,
which can optionally perform a JNDI lookup for the JTA
UserTransaction
and
TransactionManager
objects, autodetects
the location for the latter object, which varies by application server. Having
access to the JTA TransactionManager
allows for
enhanced transaction semantics, in particular supporting transaction suspension.
Please see the JtaTransactionManager
Javadocs for details.
Spring's JtaTransactionManager
is the standard
choice when running on J2EE application servers, known to work on all common
servers. Its advanced functionality such as transaction suspension is known to
work on many servers as well - including GlassFish, JBoss, Geronimo and Oracle
OC4J - without any special configuration required. However, for fully supported
transaction suspension and further advanced integration, Spring ships special
adapters for IBM WebSphere and BEA WebLogic and also for Oracle OC4J.
We'll discuss these adapters in the following sections.
For standard scenarios, including WebLogic, WebSphere and OC4J,
consider using the convenient '<tx:jta-transaction-manager/>'
configuration element. This will automatically detect the underlying
server and choose the best transaction manager available for the platform.
This means that you won't have to configure server-specific adapter classes
(as discussed in the following sections) explicitly; they will rather be chosen
automatically, with the standard JtaTransactionManager
as default fallback.
On WebSphere 6.0 and above, the recommended Spring JTA transaction
manager to use is WebSphereUowTransactionManager
.
This special adapter leverages IBM's UOWManager
API which is available in WebSphere Application Server 6.0.2.19 or above
and 6.1.0.9 or above. With this adapter, Spring-driven transaction suspension
(suspend/resume as initiated by PROPAGATION_REQUIRES_NEW
)
is officially supported by IBM!
In a WebSphere 5.1 environment, you may wish to use
Spring's WebSphereTransactionManagerFactoryBean
class. This is a factory bean which retrieves the JTA
TransactionManager
in a WebSphere environment, which
is done via WebSphere's static
access methods.
Once the JTA TransactionManager
instance has
been obtained via this factory bean, Spring's
JtaTransactionManager
may be configured with a
reference to it, for enhanced transaction semantics over the use of only
the JTA UserTransaction
object.
Please see the Javadocs for full details.
Note that WebSphereTransactionManagerFactoryBean
usage is known to work on WAS 5.1 and 6.0 but is not officially supported
by IBM. Prefer WebSphereUowTransactionManager
when running on WAS 6.0 or higher (see above).
On WebLogic 8.1 or above, you will generally prefer to use
the WebLogicJtaTransactionManager
instead
of the stock JtaTransactionManager
class.
This special WebLogic-specific subclass of the normal
JtaTransactionManager
supports the full power of
Spring's transaction definitions in a WebLogic-managed transaction environment,
beyond standard JTA semantics: Features include transaction names, per-transaction
isolation levels, and proper resuming of transactions in all cases.
Spring ships a special adapter class for OC4J 10.1.3 or above:
OC4JJtaTransactionManager
. This is analogous to
the WebLogicJtaTransactionManager
class discussed
in the previous section, providing similar value-adds on OC4J:
transaction names and per-transaction isolation levels.
Note that the full JTA functionality, including transaction suspension,
works fine with Spring's JtaTransactionManager
on
OC4J as well. The special OC4JJtaTransactionManager
adapter simply provides value-adds beyond standard JTA.
You should take care to use the correct
PlatformTransactionManager
implementation for their requirements. Used properly, the Spring Framework
merely provides a straightforward and portable abstraction. If you are using
global transactions, you must use the
org.springframework.transaction.jta.JtaTransactionManager
class
(or an
application server-specific subclass
of it) for all your transactional operations. Otherwise the transaction infrastructure
will attempt to perform local transactions on resources such as container
DataSource
instances. Such local transactions
do not make sense, and a good application server will treat them as errors.
Find below links to further resources about the Spring Framework's transaction support.
Java Transaction Design Strategies is a book available from InfoQ that provides a well-paced introduction to transactions in Java. It also includes side-by-side examples of how to configure and use transactions using both the Spring Framework and EJB3.
The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access technologies like JDBC, Hibernate or JDO in a consistent way. This allows one to switch between the aforementioned persistence technologies fairly easily and it also allows one to code without worrying about catching exceptions that are specific to each technology.
Spring provides a convenient translation from technology-specific
exceptions like SQLException
to its own
exception class hierarchy with the
DataAccessException
as the root exception.
These exceptions wrap the original exception so there is never
any risk that one might lose any information as to what might
have gone wrong.
In addition to JDBC exceptions, Spring can also wrap Hibernate-specific exceptions, converting them from proprietary, checked exceptions (in the case of versions of Hibernate prior to Hibernate 3.0), to a set of focused runtime exceptions (the same is true for JDO and JPA exceptions). This allows one to handle most persistence exceptions, which are non-recoverable, only in the appropriate layers, without having annoying boilerplate catch-and-throw blocks and exception declarations in one's DAOs. (One can still trap and handle exceptions anywhere one needs to though.) As mentioned above, JDBC exceptions (including database-specific dialects) are also converted to the same hierarchy, meaning that one can perform some operations with JDBC within a consistent programming model.
The above holds true for the various template classes in Springs
support for various ORM frameworks. If one uses the interceptor-based
classes then the application must care about handling
HibernateExceptions
and
JDOExceptions
itself, preferably via delegating
to SessionFactoryUtils
'
convertHibernateAccessException(..)
or
convertJdoAccessException
methods respectively.
These methods convert the exceptions to ones that are compatible
with the exceptions in the org.springframework.dao
exception hierarchy. As JDOExceptions
are
unchecked, they can simply get thrown too, sacrificing generic DAO
abstraction in terms of exceptions though.
The exception hierarchy that Spring provides can be seen below.
(Please note that the class hierarchy detailed in the image
shows only a subset of the entire
DataAccessException
hierarchy.)
To make it easier to work with a variety of data access technologies
such as JDBC, JDO and Hibernate in a consistent way, Spring provides
a set of abstract
DAO classes that one can extend.
These abstract classes have methods for providing the data source and
any other configuration settings that are specific to the relevant
data-access technology.
JdbcDaoSupport
- superclass for JDBC data
access objects. Requires a DataSource
to be provided; in turn, this class provides a
JdbcTemplate
instance initialized from the
supplied DataSource
to subclasses.
HibernateDaoSupport
- superclass for
Hibernate data access objects. Requires a
SessionFactory
to be provided;
in turn, this class provides a
HibernateTemplate
instance initialized
from the supplied SessionFactory
to subclasses. Can alternatively be initialized directly via a
HibernateTemplate
, to reuse the latters
settings like SessionFactory
,
flush mode, exception translator, and so forth.
JdoDaoSupport
- super class for JDO data
access objects. Requires a
PersistenceManagerFactory
to be provided; in turn, this class provides a
JdoTemplate
instance initialized from the
supplied PersistenceManagerFactory
to subclasses.
JpaDaoSupport
- super class for JPA data
access objects. Requires a
EntityManagerFactory
to be provided;
in turn, this class provides a JpaTemplate
instance initialized from the supplied
EntityManagerFactory
to subclasses.
The value-add provided by the Spring Framework's JDBC abstraction framework is perhaps best shown by the following list (note that only the italicized lines need to be coded by an application developer):
Define connection parameters
Open the connection
Specify the statement
Prepare and execute the statement
Set up the loop to iterate through the results (if any)
Do the work for each iteration
Process any exception
Handle transactions
Close the connection
The Spring Framework takes care of all the grungy, low-level details that can make JDBC such a tedious API to develop with.
There are a number of options for selecting an approach to form the basis for your JDBC database access. There are three flavors of the JdbcTemplate, a new "SimpleJdbc" approach taking advantage of database metadata, and there is also the "RDBMS Object" style for a more object oriented approach similar in style to the JDO Query design. We'll briefly list the primary reasons why you would pick one of these approaches. Keep in mind that even if you start using one of these approaches, you can still mix and match if there is a feature in a different approach that you would like to take advantage of. All approaches requires a JDBC 2.0 compliant driver and some advanced features require a JDBC 3.0 driver.
JdbcTemplate - this is the classic Spring JDBC approach and the most widely used. This is the "lowest level" approach and all other approaches use a JdbcTemplate under the covers. Works well in a JDK 1.4 and higher environment.
NamedParameterJdbcTemplate - wraps a JdbcTemplate to provide more convenient usage with named parameters instead of the traditional JDBC "?" place holders. This provides better documentation and ease of use when you have multiple parameters for an SQL statement. Works with JDK 1.4 and up.
SimpleJdbcTemplate - this class combines the most frequently used features of both JdbcTemplate and NamedParameterJdbcTemplate plus it adds additional convenience by taking advantage of some Java 5 features like varargs, autoboxing and generics to provide an easier to use API. Requires JDK 5 or higher.
SimpleJdbcInsert and SimpleJdbcCall - designed to take advantage of database metadata to limit the amount of configuration needed. This will simplify the coding to a point where you only need to provide the name of the table or procedure and provide a Map of parameters matching the column names. Designed to work together with the SimpleJdbcTemplate. Requires JDK 5 or higher and a database that provides adequate metadata.
RDBMS Objects including MappingSqlQuery, SqlUpdate and StoredProcedure - an approach where you create reusable and thread safe objects during initialization of your data access layer. This approach is modeled after JDO Query where you define your query string, declare parameters and compile the query. Once that is done any execute methods can be called multiple times with various parameter values passed in. Works with JDK 1.4 and higher.
The Spring Framework's JDBC abstraction framework consists of four
different packages, namely core
,
datasource
, object
, and
support
.
The org.springframework.jdbc.core
package
contains the JdbcTemplate
class and its various
callback interfaces, plus a variety of related classes. A sub-package
named org.springframework.jdbc.core.simple
contains
the SimpleJdbcTemplate
class and the related
SimpleJdbcInsert
and
SimpleJdbcCall
classes. Another sub-package named
org.springframework.jdbc.core.namedparam
contains the
NamedParameterJdbcTemplate
class and the related
support classes.
The org.springframework.jdbc.datasource
package
contains a utility class for easy
DataSource
access, and various simple
DataSource
implementations that can be
used for testing and running unmodified JDBC code outside of a J2EE
container. The utility class provides static methods to obtain
connections from JNDI and to close connections if necessary. It has
support for thread-bound connections, e.g. for use with
DataSourceTransactionManager
.
Next, the org.springframework.jdbc.object
package contains classes that represent RDBMS queries, updates, and
stored procedures as thread safe, reusable objects. This approach is
modeled by JDO, although of course objects returned by queries are
“disconnected” from the database. This higher level of JDBC
abstraction depends on the lower-level abstraction in the
org.springframework.jdbc.core
package.
Finally the org.springframework.jdbc.support
package is where you find the SQLException
translation functionality and some utility classes.
Exceptions thrown during JDBC processing are translated to
exceptions defined in the org.springframework.dao
package. This means that code using the Spring JDBC abstraction layer
does not need to implement JDBC or RDBMS-specific error handling. All
translated exceptions are unchecked giving you the option of catching
the exceptions that you can recover from while allowing other exceptions
to be propagated to the caller.
The JdbcTemplate
class is the central class
in the JDBC core package. It simplifies the use of JDBC since it handles
the creation and release of resources. This helps to avoid common errors
such as forgetting to always close the connection. It executes the core
JDBC workflow like statement creation and execution, leaving application
code to provide SQL and extract results. This class executes SQL
queries, update statements or stored procedure calls, imitating
iteration over ResultSet
s and extraction
of returned parameter values. It also catches JDBC exceptions and
translates them to the generic, more informative, exception hierarchy
defined in the org.springframework.dao
package.
Code using the JdbcTemplate
only need to
implement callback interfaces, giving them a clearly defined contract.
The PreparedStatementCreator
callback
interface creates a prepared statement given a
Connection
provided by this class,
providing SQL and any necessary parameters. The same is true for the
CallableStatementCreator
interface which
creates callable statement. The
RowCallbackHandler
interface extracts
values from each row of a
ResultSet
.
The JdbcTemplate
can be used within a DAO
implementation via direct instantiation with a
DataSource
reference, or be configured in
a Spring IOC container and given to DAOs as a bean reference. Note: the
DataSource
should always be configured as
a bean in the Spring IoC container, in the first case given to the
service directly, in the second case to the prepared template.
Finally, all of the SQL issued by this class is logged at the
'DEBUG'
level under the category corresponding to the
fully qualified class name of the template instance (typically
JdbcTemplate
, but it may be different if a custom
subclass of the JdbcTemplate
class is being
used).
Find below some examples of using the
JdbcTemplate
class. (These examples are not an
exhaustive list of all of the functionality exposed by the
JdbcTemplate
; see the attendant Javadocs for
that).
A simple query for getting the number of rows in a relation.
int rowCount = this.jdbcTemplate.queryForInt("select count(0) from t_accrual");
A simple query using a bind variable.
int countOfActorsNamedJoe = this.jdbcTemplate.queryForInt( "select count(0) from t_actors where first_name = ?", new Object[]{"Joe"});
Querying for a String
.
String surname = (String) this.jdbcTemplate.queryForObject( "select surname from t_actor where id = ?", new Object[]{new Long(1212)}, String.class);
Querying and populating a single domain object.
Actor actor = (Actor) this.jdbcTemplate.queryForObject( "select first_name, surname from t_actor where id = ?", new Object[]{new Long(1212)}, new RowMapper() { public Object mapRow(ResultSet rs, int rowNum) throws SQLException { Actor actor = new Actor(); actor.setFirstName(rs.getString("first_name")); actor.setSurname(rs.getString("surname")); return actor; } });
Querying and populating a number of domain objects.
Collection actors = this.jdbcTemplate.query( "select first_name, surname from t_actor", new RowMapper() { public Object mapRow(ResultSet rs, int rowNum) throws SQLException { Actor actor = new Actor(); actor.setFirstName(rs.getString("first_name")); actor.setSurname(rs.getString("surname")); return actor; } });
If the last two snippets of code actually existed in the same
application, it would make sense to remove the duplication present
in the two RowMapper
anonymous inner
classes, and extract them out into a single class (typically a
static
inner class) that can then be referenced
by DAO methods as needed. For example, the last code snippet might
be better off written like so:
public Collection findAllActors() { return this.jdbcTemplate.query( "select first_name, surname from t_actor", new ActorMapper()); } private static final class ActorMapper implements RowMapper { public Object mapRow(ResultSet rs, int rowNum) throws SQLException { Actor actor = new Actor(); actor.setFirstName(rs.getString("first_name")); actor.setSurname(rs.getString("surname")); return actor; } }
this.jdbcTemplate.update( "insert into t_actor (first_name, surname) values (?, ?)", new Object[] {"Leonor", "Watling"});
this.jdbcTemplate.update( "update t_actor set weapon = ? where id = ?", new Object[] {"Banjo", new Long(5276)});
this.jdbcTemplate.update( "delete from actor where id = ?", new Object[] {new Long.valueOf(actorId)});
The execute(..)
method can be used to
execute any arbitrary SQL, and as such is often used for DDL
statements. It is heavily overloaded with variants taking callback
interfaces, binding variable arrays, and suchlike.
this.jdbcTemplate.execute("create table mytable (id integer, name varchar(100))");
Invoking a simple stored procedure (more sophisticated stored procedure support is covered later).
this.jdbcTemplate.update( "call SUPPORT.REFRESH_ACTORS_SUMMARY(?)", new Object[]{Long.valueOf(unionId)});
Instances of the JdbcTemplate
class are
threadsafe once configured. This is important
because it means that you can configure a single instance of a
JdbcTemplate
and then safely inject this
shared reference into multiple DAOs (or
repositories). To be clear, the JdbcTemplate
is
stateful, in that it maintains a reference to a
DataSource
, but this state is
not conversational state.
A common idiom when using the
JdbcTemplate
class (and the associated SimpleJdbcTemplate
and NamedParameterJdbcTemplate
classes) is to configure a DataSource
in your Spring configuration file, and then dependency inject that
shared DataSource
bean into your DAO
classes; the JdbcTemplate
is created in the
setter for the DataSource
. This leads
to DAOs that look in part like this:
public class JdbcCorporateEventDao implements CorporateEventDao {
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
// JDBC-backed implementations of the methods on the CorporateEventDao
follow...
}
The attendant configuration might look like this.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="corporateEventDao" class="com.example.JdbcCorporateEventDao">
<property name="dataSource" ref="dataSource"/>
</bean>
<!-- the DataSource
(parameterized for configuration via a PropertyPlaceHolderConfigurer
) -->
<bean id="dataSource" destroy-method="close" class="org.apache.commons.dbcp.BasicDataSource">
<property name="driverClassName" value="${jdbc.driverClassName}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</bean>
</beans>
If you are using Spring's JdbcDaoSupport
class, and your various JDBC-backed DAO classes extend from it, then
you inherit a setDataSource(..)
method for
free from said superclass. It is totally up to you as to whether or
not you inherit from said class, you certainly are not forced to. If
you look at the source for the JdbcDaoSupport
class you will see that there is not a whole lot to it... it is
provided as a convenience only.
Regardless of which of the above template initialization styles
you choose to use (or not), there is (almost) certainly no need to
create a brand new instance of a JdbcTemplate
class each and every time you wish to execute some SQL... remember,
once configured, a JdbcTemplate
instance is
threadsafe. A reason for wanting multiple
JdbcTemplate
instances would be when you have
an application that accesses multiple databases, which requires
multiple DataSources
, and subsequently
multiple differently configured
JdbcTemplates
.
The NamedParameterJdbcTemplate
class adds
support for programming JDBC statements using named parameters (as
opposed to programming JDBC statements using only classic placeholder
('?'
) arguments. The
NamedParameterJdbcTemplate
class wraps a
JdbcTemplate
, and delegates to the wrapped
JdbcTemplate
to do much of its work. This section
will describe only those areas of the
NamedParameterJdbcTemplate
class that differ from
the JdbcTemplate
itself; namely, programming JDBC
statements using named parameters.
// some JDBC-backed DAO class...
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
}
public int countOfActorsByFirstName(String firstName) {
String sql = "select count(0) from T_ACTOR where first_name = :first_name";
SqlParameterSource namedParameters = new MapSqlParameterSource("first_name", firstName);
return namedParameterJdbcTemplate.queryForInt(sql, namedParameters);
}
Notice the use of the named parameter notation in the value
assigned to the 'sql'
variable, and the corresponding
value that is plugged into the 'namedParameters'
variable (of type MapSqlParameterSource
).
If you like, you can also pass along named parameters (and their
corresponding values) to a
NamedParameterJdbcTemplate
instance using the
(perhaps more familiar) Map
-based style.
(The rest of the methods exposed by the
NamedParameterJdbcOperations
- and
implemented by the NamedParameterJdbcTemplate
class) follow a similar pattern and will not be covered here.)
// some JDBC-backed DAO class...
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
}
public int countOfActorsByFirstName(String firstName) {
String sql = "select count(0) from T_ACTOR where first_name = :first_name";
Map namedParameters = Collections.singletonMap("first_name", firstName);
return this.namedParameterJdbcTemplate.queryForInt(sql, namedParameters);
}
Another nice feature related to the
NamedParameterJdbcTemplate
(and existing in the
same Java package) is the
SqlParameterSource
interface. You have
already seen an example of an implementation of this interface in one of
the preceding code snippets (the
MapSqlParameterSource
class). The entire point of
the SqlParameterSource
is to serve as a
source of named parameter values to a
NamedParameterJdbcTemplate
. The
MapSqlParameterSource
class is a very simple
implementation, that is simply an adapter around a
java.util.Map
, where the keys are the
parameter names and the values are the parameter values.
Another SqlParameterSource
implementation is the
BeanPropertySqlParameterSource
class. This class
wraps an arbitrary JavaBean (that is, an instance of a class that
adheres to the JavaBean
conventions), and uses the properties of the wrapped JavaBean as
the source of named parameter values.
public class Actor {
private Long id;
private String firstName;
private String lastName;
public String getFirstName() {
return this.firstName;
}
public String getLastName() {
return this.lastName;
}
public Long getId() {
return this.id;
}
// setters omitted...
}
// some JDBC-backed DAO class...
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
}
public int countOfActors(Actor exampleActor) {
// notice how the named parameters match the properties of the above 'Actor
' class
String sql = "select count(0) from T_ACTOR where first_name = :firstName and last_name = :lastName";
SqlParameterSource namedParameters = new BeanPropertySqlParameterSource(exampleActor);
return this.namedParameterJdbcTemplate.queryForInt(sql, namedParameters);
}
Remember that the
NamedParameterJdbcTemplate
class
wraps a classic JdbcTemplate
template; if you need access to the wrapped
JdbcTemplate
instance (to access some of the
functionality only present in the JdbcTemplate
class), then you can use the
getJdbcOperations()
method to access the
wrapped JdbcTemplate
via the
JdbcOperations
interface.
See also the section entitled Section 11.2.1.2, “JdbcTemplate
idioms (best
practices)” for some advice on how to best use
the NamedParameterJdbcTemplate
class in the
context of an application.
![]() | Note |
---|---|
The functionality offered by the
|
The SimpleJdbcTemplate
class is a wrapper
around the classic JdbcTemplate
that takes
advantage of Java 5 language features such as varargs and autoboxing.
The SimpleJdbcTemplate
class is somewhat of a sop
to the syntactic-sugar-like features of Java 5, but as anyone who has
developed on Java 5 and then had to move back to developing on a
previous version of the JDK will know, those syntactic-sugar-like
features sure are nice.
The value-add of the SimpleJdbcTemplate
class in the area of syntactic-sugar is best illustrated with a
'before and after' example. The following code
snippet shows first some data access code using the classic
JdbcTemplate
, followed immediately thereafter by
a code snippet that does the same job, only this time using the
SimpleJdbcTemplate
.
// classic JdbcTemplate
-style...
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
public Actor findActor(long id) {
String sql = "select id, first_name, last_name from T_ACTOR where id = ?";
RowMapper mapper = new RowMapper() {
public Object mapRow(ResultSet rs, int rowNum) throws SQLException {
Actor actor = new Actor();
actor.setId(rs.getLong("id"));
actor.setFirstName(rs.getString("first_name"));
actor.setLastName(rs.getString("last_name"));
return actor;
}
};
// notice the cast, the wrapping up of the 'id' argument
// in an array, and the boxing of the 'id' argument as a reference type
return (Actor) jdbcTemplate.queryForObject(sql, mapper, new Object[] {Long.valueOf(id)});
}
Here is the same method, only this time using the
SimpleJdbcTemplate
; notice how much 'cleaner' the
code is.
// SimpleJdbcTemplate
-style...
private SimpleJdbcTemplate simpleJdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
}
public Actor findActor(long id) {
String sql = "select id, first_name, last_name from T_ACTOR where id = ?";
ParameterizedRowMapper<Actor> mapper = new ParameterizedRowMapper<Actor>() {
// notice the return type with respect to Java 5 covariant return types
public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {
Actor actor = new Actor();
actor.setId(rs.getLong("id"));
actor.setFirstName(rs.getString("first_name"));
actor.setLastName(rs.getString("last_name"));
return actor;
}
};
return this.simpleJdbcTemplate.queryForObject(sql, mapper, id);
}
See also the section entitled Section 11.2.1.2, “JdbcTemplate
idioms (best
practices)” for some advice on how to best use
the SimpleJdbcTemplate
class in the context of an
application.
![]() | Note |
---|---|
The |
In order to work with data from a database, one needs to obtain a
connection to the database. The way Spring does this is through a
DataSource
. A
DataSource
is part of the JDBC
specification and can be seen as a generalized connection factory. It
allows a container or a framework to hide connection pooling and
transaction management issues from the application code. As a developer,
you don not need to know any details about how to connect to the
database, that is the responsibility for the administrator that sets up
the datasource. You will most likely have to fulfill both roles while
you are developing and testing you code though, but you will not
necessarily have to know how the production data source is
configured.
When using Spring's JDBC layer, you can either obtain a data
source from JNDI or you can configure your own, using an implementation
that is provided in the Spring distribution. The latter comes in handy
for unit testing outside of a web container. We will use the
DriverManagerDataSource
implementation for this
section but there are several additional implementations that will be
covered later on. The DriverManagerDataSource
works the same way that you probably are used to work when you obtain a
JDBC connection. You have to specify the fully qualified class name of
the JDBC driver that you are using so that the
DriverManager
can load the driver class. Then you
have to provide a URL that varies between JDBC drivers. You have to
consult the documentation for your driver for the correct value to use
here. Finally you must provide a username and a password that will be
used to connect to the database. Here is an example of how to configure
a DriverManagerDataSource
:
DriverManagerDataSource dataSource = new DriverManagerDataSource(); dataSource.setDriverClassName("org.hsqldb.jdbcDriver"); dataSource.setUrl("jdbc:hsqldb:hsql://localhost:"); dataSource.setUsername("sa"); dataSource.setPassword("");
SQLExceptionTranslator
is an
interface to be implemented by classes that can translate between
SQLExceptions
and Spring's own
data-access-strategy-agnostic
org.springframework.dao.DataAccessException
.
Implementations can be generic (for example, using SQLState codes for
JDBC) or proprietary (for example, using Oracle error codes) for greater
precision.
SQLErrorCodeSQLExceptionTranslator
is the
implementation of SQLExceptionTranslator
that is used by default. This implementation uses specific vendor codes.
More precise than SQLState
implementation, but vendor
specific. The error code translations are based on codes held in a
JavaBean type class named SQLErrorCodes
. This
class is created and populated by an
SQLErrorCodesFactory
which as the name suggests
is a factory for creating SQLErrorCodes
based on
the contents of a configuration file named 'sql-error-codes.xml'
. This file is
populated with vendor codes and based on the DatabaseProductName taken
from the DatabaseMetaData
, the codes for
the current database are used.
The SQLErrorCodeSQLExceptionTranslator
applies the following matching rules:
Try custom translation implemented by any subclass. Note that this class is concrete and is typically used itself, in which case this rule does not apply.
Apply error code matching. Error codes are obtained from the
SQLErrorCodesFactory
by default. This looks
up error codes from the classpath and keys into them from the
database name from the database metadata.
Use the fallback translator.
SQLStateSQLExceptionTranslator
is the
default fallback translator.
SQLErrorCodeSQLExceptionTranslator
can be
extended the following way:
public class MySQLErrorCodesTranslator extends SQLErrorCodeSQLExceptionTranslator { protected DataAccessException customTranslate(String task, String sql, SQLException sqlex) { if (sqlex.getErrorCode() == -12345) { return new DeadlockLoserDataAccessException(task, sqlex); } return null; } }
In this example the specific error code
'-12345'
is translated and any other errors are
simply left to be translated by the default translator implementation.
To use this custom translator, it is necessary to pass it to the
JdbcTemplate
using the method
setExceptionTranslator
and to use this
JdbcTemplate
for all of the data access
processing where this translator is needed. Here is an example of how
this custom translator can be used:
// create aJdbcTemplate
and set data source JdbcTemplate jt = new JdbcTemplate(); jt.setDataSource(dataSource); // create a custom translator and set theDataSource
for the default translation lookup MySQLErrorCodesTransalator tr = new MySQLErrorCodesTransalator(); tr.setDataSource(dataSource); jt.setExceptionTranslator(tr); // use theJdbcTemplate
for thisSqlUpdate
SqlUpdate su = new SqlUpdate(); su.setJdbcTemplate(jt); su.setSql("update orders set shipping_charge = shipping_charge * 1.05"); su.compile(); su.update();
The custom translator is passed a data source because we still
want the default translation to look up the error codes in
sql-error-codes.xml
.
To execute an SQL statement, there is very little code needed. All
you need is a DataSource
and a
JdbcTemplate
. Once you have that, you can use a
number of convenience methods that are provided with the
JdbcTemplate
. Here is a short example showing
what you need to include for a minimal but fully functional class that
creates a new table.
import javax.sql.DataSource; import org.springframework.jdbc.core.JdbcTemplate; public class ExecuteAStatement { private JdbcTemplate jdbcTemplate; public void setDataSource(DataSource dataSource) { this.jdbcTemplate = new JdbcTemplate(dataSource); } public void doExecute() { this.jdbcTemplate.execute("create table mytable (id integer, name varchar(100))"); } }
In addition to the execute methods, there is a large number of
query methods. Some of these methods are intended to be used for queries
that return a single value. Maybe you want to retrieve a count or a
specific value from one row. If that is the case then you can use
queryForInt(..)
,
queryForLong(..)
or
queryForObject(..)
. The latter will convert the
returned JDBC Type
to the Java class that is
passed in as an argument. If the type conversion is invalid, then an
InvalidDataAccessApiUsageException
will
be thrown. Here is an example that contains two query methods, one for
an int
and one that queries for a
String
.
import javax.sql.DataSource; import org.springframework.jdbc.core.JdbcTemplate; public class RunAQuery { private JdbcTemplate jdbcTemplate; public void setDataSource(DataSource dataSource) { this.jdbcTemplate = new JdbcTemplate(dataSource); } public int getCount() { return this.jdbcTemplate.queryForInt("select count(*) from mytable"); } public String getName() { return (String) this.jdbcTemplate.queryForObject("select name from mytable", String.class); } public void setDataSource(DataSource dataSource) { this.dataSource = dataSource; } }
In addition to the single results query methods there are several
methods that return a List with an entry for each row that the query
returned. The most generic method is
queryForList(..)
which returns a
List
where each entry is a
Map
with each entry in the map
representing the column value for that row. If we add a method to the
above example to retrieve a list of all the rows, it would look like
this:
private JdbcTemplate jdbcTemplate; public void setDataSource(DataSource dataSource) { this.jdbcTemplate = new JdbcTemplate(dataSource); } public List getList() { return this.jdbcTemplate.queryForList("select * from mytable"); }
The list returned would look something like this:
[{name=Bob, id=1}, {name=Mary, id=2}]
There are also a number of update methods that you can use. Find below an example where a column is updated for a certain primary key. In this example an SQL statement is used that has place holders for row parameters. Note that the parameter values are passed in as an array of objects (and thus primitives have to be wrapped in the primitive wrapper classes).
import javax.sql.DataSource; import org.springframework.jdbc.core.JdbcTemplate; public class ExecuteAnUpdate { private JdbcTemplate jdbcTemplate; public void setDataSource(DataSource dataSource) { this.jdbcTemplate = new JdbcTemplate(dataSource); } public void setName(int id, String name) { this.jdbcTemplate.update( "update mytable set name = ? where id = ?", new Object[] {name, new Integer(id)}); } }
One of the update
convenience methods
provides support for acquiring the primary keys generated by the
database (part of the JDBC 3.0 standard - see chapter 13.6 of the
specification for details). The method takes a
PreparedStatementCreator
as its first argument,
and this is the way the required insert statement is specified. The
other argument is a KeyHolder
, which will contain
the generated key on successful return from the update. There is not a
standard single way to create an appropriate
PreparedStatement
(which explains why the method
signature is the way it is). An example that works on Oracle and may not
work on other platforms is:
final String INSERT_SQL = "insert into my_test (name) values(?)";
final String name = "Rob";
KeyHolder keyHolder = new GeneratedKeyHolder();
jdbcTemplate.update(
new PreparedStatementCreator() {
public PreparedStatement createPreparedStatement(Connection connection) throws SQLException {
PreparedStatement ps =
connection.prepareStatement(INSERT_SQL, new String[] {"id"});
ps.setString(1, name);
return ps;
}
},
keyHolder);
// keyHolder.getKey() now contains the generated key
The DataSourceUtils
class is a convenient
and powerful helper class that provides static
methods to obtain connections from JNDI and close connections if
necessary. It has support for thread-bound connections, for example for
use with DataSourceTransactionManager
.
The SmartDataSource
interface is to
be implemented by classes that can provide a connection to a relational
database. Extends the DataSource
interface to allow classes using it to query whether or not the
connection should be closed after a given operation. This can sometimes
be useful for efficiency, in the cases where one knows that one wants to
reuse a connection.
This is an abstract
base class for Spring's
DataSource
implementations, that takes
care of the "uninteresting" glue. This is the class one would extend if
one was writing one's own DataSource
implementation.
The SingleConnectionDataSource
class is an
implementation of the SmartDataSource
interface that wraps a single
Connection
that is
not closed after use. Obviously, this is not
multi-threading capable.
If client code will call close in the assumption of a pooled
connection, like when using persistence tools, set
suppressClose
to true
. This will
return a close-suppressing proxy instead of the physical connection. Be
aware that you will not be able to cast this to a native Oracle
Connection
or the like anymore.
This is primarily a test class. For example, it enables easy
testing of code outside an application server, in conjunction with a
simple JNDI environment. In contrast to
DriverManagerDataSource
, it reuses the same
connection all the time, avoiding excessive creation of physical
connections.
The DriverManagerDataSource
class is an
implementation of the standard DataSource
interface that configures a plain old JDBC Driver via bean properties, and
returns a new Connection
every time.
This is potentially useful for test or standalone environments
outside of a J2EE container, either as a
DataSource
bean in a Spring IoC
container, or in conjunction with a simple JNDI environment.
Pool-assuming Connection.close()
calls will simply
close the connection, so any
DataSource
-aware persistence code should
work. However, using JavaBean style connection pools such as
commons-dbcp is so easy, even in a test environment, that it is almost
always preferable to use such a connection pool over
DriverManagerDataSource
.
TransactionAwareDataSourceProxy
is a proxy
for a target DataSource
, which wraps that
target DataSource
to add awareness of
Spring-managed transactions. In this respect it is similar to a
transactional JNDI DataSource
as provided
by a J2EE server.
![]() | Note |
---|---|
It should almost never be necessary or desirable to use this
class, except when existing code exists which must be called and
passed a standard JDBC |
(See the
TransactionAwareDataSourceProxy
Javadocs for more
details.)
The DataSourceTransactionManager
class is a
PlatformTransactionManager
implementation
for single JDBC datasources. It binds a JDBC connection from the
specified data source to the currently executing thread, potentially
allowing for one thread connection per data source.
Application code is required to retrieve the JDBC connection via
DataSourceUtils.getConnection(DataSource)
instead of
J2EE's standard DataSource.getConnection
. This is
recommended anyway, as it throws unchecked
org.springframework.dao
exceptions instead of checked
SQLExceptions
. All framework classes like
JdbcTemplate
use this strategy implicitly. If not
used with this transaction manager, the lookup strategy behaves exactly
like the common one - it can thus be used in any case.
The DataSourceTransactionManager
class
supports custom isolation levels, and timeouts that get applied as
appropriate JDBC statement query timeouts. To support the latter,
application code must either use JdbcTemplate
or
call DataSourceUtils.applyTransactionTimeout(..)
method for each created statement.
This implementation can be used instead of
JtaTransactionManager
in the single resource
case, as it does not require the container to support JTA. Switching
between both is just a matter of configuration, if you stick to the
required connection lookup pattern. Note that JTA does not support
custom isolation levels!
There are times when we need to access vendor specific JDBC
methods that differ from the standard JDBC API. This can be problematic
if we are running in an application server or with a
DataSource
that wraps the
Connection
, Statement
and
ResultSet
objects with its own wrapper objects.
To gain access to the native objects you can configure your
JdbcTemplate
or
OracleLobHandler
with a
NativeJdbcExtractor
.
The NativeJdbcExtractor comes in a variety of flavors to match your execution environment:
SimpleNativeJdbcExtractor
C3P0NativeJdbcExtractor
CommonsDbcpNativeJdbcExtractor
JBossNativeJdbcExtractor
WebLogicNativeJdbcExtractor
WebSphereNativeJdbcExtractor
XAPoolNativeJdbcExtractor
Usually the SimpleNativeJdbcExtractor
is
sufficient for unwrapping a Connection
object in
most environments. See the Java Docs for more details.
Most JDBC drivers provide improved performance if you batch multiple calls to the same prepared statement. By grouping updates into batches you limit the number of round trips to the database. This section will cover batch processing using both the JdbcTemplate and the SimpleJdbcTemplate.
Using the JdbcTemplate batch processing is accomplished by
implementing a special interface,
BatchPreparedStatementSetter
, and passing that in
as the second parameter in your batchUpdate
method call. This interface has two methods you must implement. One is
named getBatchSize
and here you provide the size
of the current batch. The other method is
setValues
and it allows you to set the values for
the parameters of the prepared statement and. This method will get
called the number of times that you specified in the
getBatchSize
call. Here is an example of this
where we update the actor table based on entries in a list. The entire
list is used as the batch in his example.
public class JdbcActorDao implements ActorDao { private JdbcTemplate jdbcTemplate; public void setDataSource(DataSource dataSource) { this.jdbcTemplate = new JdbcTemplate(dataSource); } public int[] batchUpdate(final List actors) { int[] updateCounts = jdbcTemplate.batchUpdate( "update t_actor set first_name = ?, last_name = ? where id = ?", new BatchPreparedStatementSetter() { public void setValues(PreparedStatement ps, int i) throws SQLException { ps.setString(1, ((Actor)actors.get(i)).getFirstName()); ps.setString(2, ((Actor)actors.get(i)).getLastName()); ps.setLong(3, ((Actor)actors.get(i)).getId().longValue()); } public int getBatchSize() { return actors.size(); } } ); return updateCounts; } // ... additional methods }
If you are processing stream of updates or reading from a
file then you might have a preferred batch size, but the last batch
might not have that number of entries. In this case you can use the
InterruptibleBatchPreparedStatementSetter
interface which allows you to interrupt a batch once the input source is
exhausted. The isBatchExhausted
method allows you
to signal the end of the batch.
The SimpleJdbcTemplate
provides an
alternate way of providing the batch update. Instead of implementing a
special batch interface, you simply provide all parameter values in the
call and the framework will loop over these values and use an internal
prepared statement setter. The API varies depending on whether you use
named parameters or not. For the named parameters you provide an array
of SqlParameterSource
, one entry for each member
of the batch. You can use the
SqlParameterSource.createBatch
method to create
this array, passing in either an array of JavaBeans or an array of Maps
containing the parameter values.
This example shows a batch update using named parameters:
public class JdbcActorDao implements ActorDao { private SimpleJdbcTemplate simpleJdbcTemplate; public void setDataSource(DataSource dataSource) { this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource); } public int[] batchUpdate(final List<Actor> actors) { SqlParameterSource[] batch = SqlParameterSourceUtils.createBatch(actors.toArray()); int[] updateCounts = simpleJdbcTemplate.batchUpdate( "update t_actor set first_name = :firstName, last_name = :lastName where id = :id", batch); return updateCounts; } // ... additional methods }
For an SQL statement using the classic "?" place holders you pass in a List containing an object array with the update values. This object array must have one entry for each placeholder in the SQL statement and they must be in the same order as they are defined in the SQL statement.
The same example using classic JDBC "?" place holders:
public class JdbcActorDao implements ActorDao { private SimpleJdbcTemplate simpleJdbcTemplate; public void setDataSource(DataSource dataSource) { this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource); } public int[] batchUpdate(final List<Actor> actors) { List<Object[]> batch = new ArrayList<Object[]>(); for (Actor actor : actors) { Object[] values = new Object[] { actor.getFirstName(), actor.getLastName(), actor.getId()}; batch.add(values); } int[] updateCounts = simpleJdbcTemplate.batchUpdate( "update t_actor set first_name = ?, last_name = ? where id = ?", batch); return updateCounts; } // ... additional methods }
All batch update methods return an int array containing the number of affected rows for each batch entry. This count is reported by the JDBC driver and it's not always available in which case the JDBC driver simply returns a -2 value.
The SimpleJdbcInsert
and
SimpleJdbcCall
classes provide simplified
configuration by taking advantage of database metadata that can be
retrieved via the JDBC driver. This means there is less to configure up
front, although you can override or turn off the metadata processing if
you prefer to provide all the details in your code.
Let's start by looking at the
SimpleJdbcInsert
class first. We will use the
minimal amount of configuration options to start with. The
SimpleJdbcInsert
should be instantiated in the
data access layer's initialization method. For this example, the
initializing method is the setDataSource
method.
There is no need to subclass the SimpleJdbcInsert
class, just create a new instance and set the table name using the
withTableName
method. Configuration methods for
this class follows the "fluid" style returning the instance of the
SimpleJdbcInsert
which allows you to chain all
configuration methods. In this case there is only one configuration
method used but we will see examples of multiple ones soon.
public class JdbcActorDao implements ActorDao { private SimpleJdbcTemplate simpleJdbcTemplate; private SimpleJdbcInsert insertActor; public void setDataSource(DataSource dataSource) { this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource); this.insertActor = new SimpleJdbcInsert(dataSource).withTableName("t_actor"); } public void add(Actor actor) { Map<String, Object> parameters = new HashMap<String, Object>(3); parameters.put("id", actor.getId()); parameters.put("first_name", actor.getFirstName()); parameters.put("last_name", actor.getLastName()); insertActor.execute(parameters); } // ... additional methods }
The execute method used here takes a plain
java.utils.Map
as it's only parameter. The
important thing to note here is that the keys used for the Map must
match the column names of the table as defined in the database. This is
because we read the metadata in order to construct the actual insert
statement.
Next we'll look at the same insert, but instead of passing in the
id we will retrieve the auto-generated key and set it on the new Actor
object. When we create the SimpleJdbcInsert
, in
addition to specifying the table name, we specify the name of the
generated key column using the
usingGeneratedKeyColumns
method.
public class JdbcActorDao implements ActorDao { private SimpleJdbcTemplate simpleJdbcTemplate; private SimpleJdbcInsert insertActor; public void setDataSource(DataSource dataSource) { this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource); this.insertActor = new SimpleJdbcInsert(dataSource) .withTableName("t_actor") .usingGeneratedKeyColumns("id"); } public void add(Actor actor) { Map<String, Object> parameters = new HashMap<String, Object>(2); parameters.put("first_name", actor.getFirstName()); parameters.put("last_name", actor.getLastName()); Number newId = insertActor.executeAndReturnKey(parameters); actor.setId(newId.longValue()); } // ... additional methods }
Here we can see the main difference when executing the
insert is that we don't add the id to the Map and we call the
executeReturningKey
method. This returns a
java.lang.Number
object that we can use to create an
instance of the numerical type that is used in our domain class. It's
important to note that we can't rely on all databases to return a
specific Java class here, java.lang.Number
is the
base class that we can rely on. If you have multiple auto-generated
columns or the generated values are non-numeric then you can use a
KeyHolder
that is returned from the
executeReturningKeyHolder
method.
It's possible to limit the columns used for the insert by
specifying a list of column names to be used. This is accomplished using
the usingColumns
method.
public class JdbcActorDao implements ActorDao { private SimpleJdbcTemplate simpleJdbcTemplate; private SimpleJdbcInsert insertActor; public void setDataSource(DataSource dataSource) { this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource); this.insertActor = new SimpleJdbcInsert(dataSource) .withTableName("t_actor") .usingColumns("first_name", "last_name") .usingGeneratedKeyColumns("id"); } public void add(Actor actor) { Map<String, Object> parameters = new HashMap<String, Object>(2); parameters.put("first_name", actor.getFirstName()); parameters.put("last_name", actor.getLastName()); Number newId = insertActor.executeAndReturnKey(parameters); actor.setId(newId.longValue()); } // ... additional methods }
The execution of the insert is the same as if we had relied on the metadata for determining what columns to use.
Using a Map to provide parameter values works fine, but it's not
the most convenient class to use. Spring provides a couple of
implementations of the SqlParameterSource
interface that can be used instead. The first one we'll look at is
BeanPropertySqlParameterSource
which is a very
convenient class as long as you have a JavaBean compliant class that
contains your values. It will use the corresponding getter method to
extract the parameter values. Here is an example:
public class JdbcActorDao implements ActorDao { private SimpleJdbcTemplate simpleJdbcTemplate; private SimpleJdbcInsert insertActor; public void setDataSource(DataSource dataSource) { this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource); this.insertActor = new SimpleJdbcInsert(dataSource) .withTableName("t_actor") .usingGeneratedKeyColumns("id"); } public void add(Actor actor) { SqlParameterSource parameters = new BeanPropertySqlParameterSource(actor); Number newId = insertActor.executeAndReturnKey(parameters); actor.setId(newId.longValue()); } // ... additional methods }
Another option is the
MapSqlParameterSource
that resembles a Map but
provides a more convenient addValue
method that
can be chained.
public class JdbcActorDao implements ActorDao { private SimpleJdbcTemplate simpleJdbcTemplate; private SimpleJdbcInsert insertActor; public void setDataSource(DataSource dataSource) { this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource); this.insertActor = new SimpleJdbcInsert(dataSource) .withTableName("t_actor") .usingGeneratedKeyColumns("id"); } public void add(Actor actor) { SqlParameterSource parameters = new MapSqlParameterSource() .addValue("first_name", actor.getFirstName()) .addValue("last_name", actor.getLastName()); Number newId = insertActor.executeAndReturnKey(parameters); actor.setId(newId.longValue()); } // ... additional methods }
As you can see, the configuration is the same, it;s just the executing code that has to change to use these alternative input classes.
Let's now turn our attention to calling stored procedures using
the SimpleJdbcCall
class. This class is designed
to make it as simple as possible to call a stored procedure. It takes
advantage of metadata present in the database to look up names of in and
out parameters. This means that you don't have to explicitly declare
parameters. You can of course still declare them if you prefer to do
that or if you have parameters that don't have an automatic mapping to a
Java class like ARRAY or STRUCT parameters. In our first example we will
look at a plain vanilla procedure that only returns scalar values in
form of VARCHAR and DATE. I have added a birthDate property to the Actor
class to get some variety in terms of return values. The example
procedure reads a specified actor entry and returns first_name,
last_name, and birth_date columns in the form of out parameters. Here is
the source for the procedure as it would look when using MySQL as the
database:
CREATE PROCEDURE read_actor ( IN in_id INTEGER, OUT out_first_name VARCHAR(100), OUT out_last_name VARCHAR(100), OUT out_birth_date DATE) BEGIN SELECT first_name, last_name, birth_date INTO out_first_name, out_last_name, out_birth_date FROM t_actor where id = in_id; END;
As you can see there are four parameters. One is an in parameter "in_id" containing the id of the Actor we are looking up. The remaining parameters are out parameters and they will be used to return the data read from the table.
The SimpleJdbcCall
is declared in a similar
manner to the SimpleJdbcInsert
, no need to
subclass and we declare it in the initialization method. For this
example, all we need to specify is the name of the procedure.
public class JdbcActorDao implements ActorDao { private SimpleJdbcTemplate simpleJdbcTemplate; private SimpleJdbcCall procReadActor; public void setDataSource(DataSource dataSource) { this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource); this.procReadActor = new SimpleJdbcCall(dataSource) .withProcedureName("read_actor"); } public Actor readActor(Long id) { SqlParameterSource in = new MapSqlParameterSource() .addValue("in_id", id); Map out = procReadActor.execute(in); Actor actor = new Actor(); actor.setId(id); actor.setFirstName((String) out.get("out_first_name")); actor.setLastName((String) out.get("out_last_name")); actor.setBirthDate((Date) out.get("out_birth_date")); return actor; } // ... additional methods }
The execution of the call involves creating an
SqlParameterSource
containing the in parameter.
It's important to match the name of the parameter declared in the stored
procedure. The case doesn't have to match since we use metadata to
determine how database objects should be referred to - what you specify
in your source for the stored procedure is not necessarily the way it is
stored in the database, some databases transform names to all upper case
while others use lower case or the case as specified.
The execute
method takes the in parameters
and returns a Map containing any out parameters keyed by the name as
specified in the stored procedure. In this case they are
out_first_name, out_last_name
and
out_birth_date
.
The last part of the execute
method just
creates an Actor instance to use to return the data retrieved. Again,
it's important to match the names of the out parameters here. Also, the
case used for the names of the out parameters stored in the results map
are as they were defined in the database. You will either have to do a
case-insensitive lookup or instruct Spring to use a
CaseInsensitiveMap
from the Jakarta Commons
project. The way you do that is by creating your own
JdbcTemplate
and setting the
setResultsMapCaseInsensitive
property to
true
. Then you pass this customized
JdbcTemplate
instance into the constructor of
your SimpleJdbcCall
. You also have to include the
commons-collections.jar
on your classpath for
this to work. Here is an example of this configuration:
public class JdbcActorDao implements ActorDao { private SimpleJdbcCall procReadActor; public void setDataSource(DataSource dataSource) { JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource); jdbcTemplate.setResultsMapCaseInsensitive(true); this.procReadActor = new SimpleJdbcCall(jdbcTemplate) .withProcedureName("read_actor"); } // ... additional methods }
By doing this, you don't have to worry about the case used for the names of your returned out parameters.
We have seen how the parameters are deduced based on metadata, but
you can declare then explicitly if you wish. This is done when the
SimpleJdbcCall
is created and configured using
the declareParameters
method that takes a
variable number of SqlParameter
objects as input.
See the next section for details on how to define an
SqlParameter
.
We can opt to declare one, some or all of the parameters
explicitly. The parameter metadata is still being used. By calling the
method withoutProcedureColumnMetaDataAccess
we
can specify that we would like to bypass any processing of the metadata
lookups for potential parameters and only use the declared ones. Another
situation that can arise is that one or more in parameters have default
values and we would like to leave them out of the call. To do that we
will just call the useInParameterNames
to specify
the list of in parameter names to include.
This is what a fully declared procedure call declaration of our earlier example would look like:
public class JdbcActorDao implements ActorDao { private SimpleJdbcCall procReadActor; public void setDataSource(DataSource dataSource) { JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource); jdbcTemplate.setResultsMapCaseInsensitive(true); this.procReadActor = new SimpleJdbcCall(jdbcTemplate) .withProcedureName("read_actor") .withoutProcedureColumnMetaDataAccess() .useInParameterNames("in_id") .declareParameters( new SqlParameter("in_id", Types.NUMERIC), new SqlOutParameter("out_first_name", Types.VARCHAR), new SqlOutParameter("out_last_name", Types.VARCHAR), new SqlOutParameter("out_birth_date", Types.DATE) ); } // ... additional methods }
The execution and end results are the same, we are just specifying all the details explicitly rather than relying on metadata. This will be necessary if the database we use is not part of the supported databases. Currently we support metadata lookup of stored procedure calls for the following databases: Apache Derby, DB2, MySQL, Microsoft SQL Server, Oracle and Sybase. We also support metadata lookup of stored functions for: MySQL, Microsoft SQL Server and Oracle.
To define a parameter to be used for the SimpleJdbc classes, and
also for the RDBMS operations classes covered in the following section,
you use an SqlParameter
or one of its subclasses.
You typically specify the parameter name and SQL type in the
constructor. The SQL type is specified using the
java.sql.Types
constants. We have already seen
declarations like:
new SqlParameter("in_id", Types.NUMERIC), new SqlOutParameter("out_first_name", Types.VARCHAR),
The first line with the SqlParameter
declares an in parameter. In parameters can be used for both stored
procedure calls and for queries using the
SqlQuery
and its subclasses covered in the
following section.
The second line with the SqlOutParameter
declares an out parameter to be used in a stored procedure call. There
is also an SqlInOutParameter
for inout
parameters, parameters that provide an in value to the procedure and
that also return a value
![]() | Note |
---|---|
Only parameters declared as |
In addition to the name and the SQL type you can specify
additional options. For in parameters you can specify a scale for
numeric data or a type name for custom database types. For out
parameters you can provide a RowMapper
to handle
mapping of rows returned from a REF cursor. Another option is to specify
an SqlReturnType
that provides and opportunity to
define customized handling of the return values.
Calling a stored function is done almost exactly the same way as
calling a stored procedure. The only difference is that you need to
provide a function name rather than a procedure name. This is done by
using the withFunctionName
method. Using this
method indicates that your call is to a function and the corresponding
call string for a function call will be generated. There is also a
specialized execute call executeFunction
that
will return the function return value as an object of a specified type.
This way you don't have to retrieve the return value from the results
map. A similar convenience method named
executeObject
is also available for stored
procedures that only have one out parameter. The following example is
based on a stored function named get_actor_name
that returns an actor's full name. Here is the MySQL source for this
function:
CREATE FUNCTION get_actor_name (in_id INTEGER) RETURNS VARCHAR(200) READS SQL DATA BEGIN DECLARE out_name VARCHAR(200); SELECT concat(first_name, ' ', last_name) INTO out_name FROM t_actor where id = in_id; RETURN out_name; END;
To call this function we again create a
SimpleJdbcCall
in the initialization
method.
public class JdbcActorDao implements ActorDao { private SimpleJdbcTemplate simpleJdbcTemplate; private SimpleJdbcCall funcGetActorName; public void setDataSource(DataSource dataSource) { this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource); JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource); jdbcTemplate.setResultsMapCaseInsensitive(true); this.funcGetActorName = new SimpleJdbcCall(jdbcTemplate) .withFunctionName("get_actor_name"); } public String getActorName(Long id) { SqlParameterSource in = new MapSqlParameterSource() .addValue("in_id", id); String name = funcGetActorName.executeFunction(String.class, in); return name; } // ... additional methods }
The execute method used returns a
String
containing the return value from the
function call.
Calling a stored procedure or function that returns a result set
has always been a bit tricky. Some databases return result sets during
the JDBC results processing while others require an explicitly
registered out parameter of a specific type. Both approaches still needs
some additional processing to loop over the result set and process the
returned rows. With the SimpleJdbcCall
you use
the returningResultSet
method and declare a
RowMapper
implementation to be used for a
specific parameter. In the case where the result set is returned during
the results processing, there are no names defined, so the returned
results will have to match the order you declare the
RowMapper
implementations. The name specified
will still be used to store the processed list of results in the results
map returned from the execute statement.
For this example we will use a stored procedure that takes no in parameters and returns all rows from the t_actor table. Here is the MySQL source for this procedure:
CREATE PROCEDURE read_all_actors() BEGIN SELECT a.id, a.first_name, a.last_name, a.birth_date FROM t_actor a; END;
In order to call this procedure we need to declare the
RowMapper
to be used. Since the class we want to
map to follows the JavaBean rules, we can use a
ParameterizedBeanPropertyRowMapper
that is
created by passing in the required class to map to in the
newInstance
method.
public class JdbcActorDao implements ActorDao { private SimpleJdbcTemplate simpleJdbcTemplate; private SimpleJdbcCall procReadAllActors; public void setDataSource(DataSource dataSource) { this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource); JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource); jdbcTemplate.setResultsMapCaseInsensitive(true); this.procReadAllActors = new SimpleJdbcCall(jdbcTemplate) .withProcedureName("read_all_actors") .returningResultSet("actors", ParameterizedBeanPropertyRowMapper.newInstance(Actor.class)); } public List getActorsList() { Map m = procReadAllActors.execute(new HashMap<String, Object>(0)); return (List) m.get("actors"); } // ... additional methods }
The execute call passes in an empty Map since this call doesn't take any parameters. The list of Actors is then retrieved from the results map and returned to the caller.
The org.springframework.jdbc.object
package
contains classes that allow one to access the database in a more
object-oriented manner. By way of an example, one can execute queries and
get the results back as a list containing business objects with the
relational column data mapped to the properties of the business object.
One can also execute stored procedures and run update, delete and insert
statements.
![]() | Note |
---|---|
There is a view borne from experience acquired in the field
amongst some of the Spring developers that the various RDBMS operation
classes described below (with the exception of the It must be stressed however that this is just a view... if you feel that you are getting measurable value from using the RDBMS operation classes, feel free to continue using these classes. |
SqlQuery
is a reusable, threadsafe class
that encapsulates an SQL query. Subclasses must implement the
newRowMapper(..)
method to provide a
RowMapper
instance that can create one
object per row obtained from iterating over the
ResultSet
that is created during the
execution of the query. The SqlQuery
class is
rarely used directly since the MappingSqlQuery
subclass provides a much more convenient implementation for mapping rows
to Java classes. Other implementations that extend
SqlQuery
are
MappingSqlQueryWithParameters
and
UpdatableSqlQuery
.
MappingSqlQuery
is a reusable query in
which concrete subclasses must implement the abstract
mapRow(..)
method to convert each row of the
supplied ResultSet
into an object. Find
below a brief example of a custom query that maps the data from the
customer relation to an instance of the Customer
class.
private class CustomerMappingQuery extends MappingSqlQuery { public CustomerMappingQuery(DataSource ds) { super(ds, "SELECT id, name FROM customer WHERE id = ?"); super.declareParameter(new SqlParameter("id", Types.INTEGER)); compile(); } public Object mapRow(ResultSet rs, int rowNumber) throws SQLException { Customer cust = new Customer(); cust.setId((Integer) rs.getObject("id")); cust.setName(rs.getString("name")); return cust; } }
We provide a constructor for this customer query that takes the
DataSource
as the only parameter. In this
constructor we call the constructor on the superclass with the
DataSource
and the SQL that should be
executed to retrieve the rows for this query. This SQL will be used to
create a PreparedStatement
so it may
contain place holders for any parameters to be passed in during
execution. Each parameter must be declared using the
declareParameter
method passing in an
SqlParameter
. The
SqlParameter
takes a name and the JDBC type as
defined in java.sql.Types
. After all parameters
have been defined we call the compile()
method so the
statement can be prepared and later be executed.
public Customer getCustomer(Integer id) { CustomerMappingQuery custQry = new CustomerMappingQuery(dataSource); Object[] parms = new Object[1]; parms[0] = id; List customers = custQry.execute(parms); if (customers.size() > 0) { return (Customer) customers.get(0); } else { return null; } }
The method in this example retrieves the customer with the id that
is passed in as the only parameter. After creating an instance of the
CustomerMappingQuery
class we create an array of
objects that will contain all parameters that are passed in. In this
case there is only one parameter and it is passed in as an
Integer
. Now we are ready to execute the query
using this array of parameters and we get a List
that
contains a Customer
object for each row that was
returned for our query. In this case it will only be one entry if there
was a match.
The SqlUpdate
class encapsulates an SQL
update. Like a query, an update object is reusable, and like all
RdbmsOperation
classes, an update can have
parameters and is defined in SQL. This class provides a number of
update(..)
methods analogous to the
execute(..)
methods of query objects. This
class is concrete. Although it can be subclassed (for example to add a
custom update method) it can easily be parameterized by setting SQL and
declaring parameters.
import java.sql.Types;
import javax.sql.DataSource;
import org.springframework.jdbc.core.SqlParameter;
import org.springframework.jdbc.object.SqlUpdate;
public class UpdateCreditRating extends SqlUpdate {
public UpdateCreditRating(DataSource ds) {
setDataSource(ds);
setSql("update customer set credit_rating = ? where id = ?");
declareParameter(new SqlParameter(Types.NUMERIC));
declareParameter(new SqlParameter(Types.NUMERIC));
compile();
}
/**
* @param id for the Customer to be updated
* @param rating the new value for credit rating
* @return number of rows updated
*/
public int run(int id, int rating) {
Object[] params =
new Object[] {
new Integer(rating),
new Integer(id)};
return update(params);
}
}
The StoredProcedure
class is a superclass
for object abstractions of RDBMS stored procedures. This class is
abstract
, and its various
execute(..)
methods have protected
access, preventing use other than through a subclass that offers tighter
typing.
The inherited sql
property will be the name of
the stored procedure in the RDBMS.
To define a parameter to be used for the StoredProcedure classe,
you use an SqlParameter
or one of its subclasses.
You must specify the parameter name and SQL type in the constructor. The
SQL type is specified using the java.sql.Types
constants. We have already seen declarations like:
new SqlParameter("in_id", Types.NUMERIC), new SqlOutParameter("out_first_name", Types.VARCHAR),
The first line with the SqlParameter
declares an in parameter. In parameters can be used for both stored
procedure calls and for queries using the
SqlQuery
and its subclasses covered in the
following section.
The second line with the SqlOutParameter
declares an out parameter to be used in the stored procedure call. There
is also an SqlInOutParameter
for inout
parameters, parameters that provide an in value to the procedure and
that also return a value
![]() | Note |
---|---|
Parameters declared as |
In addition to the name and the SQL type you can specify
additional options. For in parameters you can specify a scale for
numeric data or a type name for custom database types. For out
parameters you can provide a RowMapper
to handle
mapping of rows returned from a REF cursor. Another option is to specify
an SqlReturnType
that provides and opportunity to
define customized handling of the return values.
Here is an example of a program that calls a function,
sysdate()
, that comes with any Oracle database. To
use the stored procedure functionality one has to create a class that
extends StoredProcedure
. There are no input
parameters, but there is an output parameter that is declared as a date
type using the class SqlOutParameter
. The
execute()
method returns a map with an entry for each
declared output parameter using the parameter name as the key.
import java.sql.Types;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import javax.sql.DataSource;
import org.springframework.jdbc.core.SqlOutParameter;
import org.springframework.jdbc.datasource.*;
import org.springframework.jdbc.object.StoredProcedure;
public class TestStoredProcedure {
public static void main(String[] args) {
TestStoredProcedure t = new TestStoredProcedure();
t.test();
System.out.println("Done!");
}
void test() {
DriverManagerDataSource ds = new DriverManagerDataSource();
ds.setDriverClassName("oracle.jdbc.OracleDriver");
ds.setUrl("jdbc:oracle:thin:@localhost:1521:mydb");
ds.setUsername("scott");
ds.setPassword("tiger");
MyStoredProcedure sproc = new MyStoredProcedure(ds);
Map results = sproc.execute();
printMap(results);
}
private class MyStoredProcedure extends StoredProcedure {
private static final String SQL = "sysdate";
public MyStoredProcedure(DataSource ds) {
setDataSource(ds);
setFunction(true);
setSql(SQL);
declareParameter(new SqlOutParameter("date", Types.DATE));
compile();
}
public Map execute() {
// the 'sysdate' sproc has no input parameters, so an empty Map is supplied...
return execute(new HashMap());
}
}
private static void printMap(Map results) {
for (Iterator it = results.entrySet().iterator(); it.hasNext(); ) {
System.out.println(it.next());
}
}
}
Find below an example of a StoredProcedure
that has two output parameters (in this case Oracle REF cursors).
import oracle.jdbc.driver.OracleTypes;
import org.springframework.jdbc.core.SqlOutParameter;
import org.springframework.jdbc.object.StoredProcedure;
import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;
public class TitlesAndGenresStoredProcedure extends StoredProcedure {
private static final String SPROC_NAME = "AllTitlesAndGenres";
public TitlesAndGenresStoredProcedure(DataSource dataSource) {
super(dataSource, SPROC_NAME);
declareParameter(new SqlOutParameter("titles", OracleTypes.CURSOR, new TitleMapper()));
declareParameter(new SqlOutParameter("genres", OracleTypes.CURSOR, new GenreMapper()));
compile();
}
public Map execute() {
// again, this sproc has no input parameters, so an empty Map is supplied...
return super.execute(new HashMap());
}
}
Notice how the overloaded variants of the
declareParameter(..)
method that have been used in
the TitlesAndGenresStoredProcedure
constructor
are passed RowMapper
implementation
instances; this is a very convenient and powerful way to reuse existing
functionality. (The code for the two
RowMapper
implementations is provided
below in the interest of completeness.)
Firstly the TitleMapper
class, which simply
maps a ResultSet
to a
Title
domain object for each row in the supplied
ResultSet
.
import com.foo.sprocs.domain.Title; import org.springframework.jdbc.core.RowMapper; import java.sql.ResultSet; import java.sql.SQLException; public final class TitleMapper implements RowMapper { public Object mapRow(ResultSet rs, int rowNum) throws SQLException { Title title = new Title(); title.setId(rs.getLong("id")); title.setName(rs.getString("name")); return title; } }
Secondly, the GenreMapper
class, which
again simply maps a ResultSet
to a
Genre
domain object for each row in the supplied
ResultSet
.
import org.springframework.jdbc.core.RowMapper; import java.sql.ResultSet; import java.sql.SQLException; import com.foo.domain.Genre; public final class GenreMapper implements RowMapper { public Object mapRow(ResultSet rs, int rowNum) throws SQLException { return new Genre(rs.getString("name")); } }
If one needs to pass parameters to a stored procedure (that is the
stored procedure has been declared as having one or more input
parameters in its definition in the RDBMS), one would code a strongly
typed execute(..)
method which would delegate to the
superclass' (untyped) execute(Map parameters)
(which
has protected
access); for example:
import oracle.jdbc.driver.OracleTypes; import org.springframework.jdbc.core.SqlOutParameter; import org.springframework.jdbc.object.StoredProcedure; import javax.sql.DataSource; import java.util.HashMap; import java.util.Map; public class TitlesAfterDateStoredProcedure extends StoredProcedure { private static final String SPROC_NAME = "TitlesAfterDate"; private static final String CUTOFF_DATE_PARAM = "cutoffDate"; public TitlesAfterDateStoredProcedure(DataSource dataSource) { super(dataSource, SPROC_NAME); declareParameter(new SqlParameter(CUTOFF_DATE_PARAM, Types.DATE); declareParameter(new SqlOutParameter("titles", OracleTypes.CURSOR, new TitleMapper())); compile(); } public Map execute(Date cutoffDate) { Map inputs = new HashMap(); inputs.put(CUTOFF_DATE_PARAM, cutoffDate); return super.execute(inputs); } }
The SqlFunction
RDBMS operation class
encapsulates an SQL "function" wrapper for a query that returns a single
row of results. The default behavior is to return an
int
, but that can be overridden by using the methods
with an extra return type parameter. This is similar to using the
queryForXxx
methods of the
JdbcTemplate
. The advantage with
SqlFunction
is that you don't have to create the
JdbcTemplate
, it is done behind the
scenes.
This class is intended to use to call SQL functions that return a
single result using a query like "select user()" or "select sysdate from
dual". It is not intended for calling more complex stored functions or
for using a CallableStatement
to invoke a stored
procedure or stored function. (Use the
StoredProcedure
or SqlCall
classes for this type of processing).
SqlFunction
is a concrete class, and there
is typically no need to subclass it. Code using this package can create
an object of this type, declaring SQL and parameters, and then invoke
the appropriate run method repeatedly to execute the function. Here is
an example of retrieving the count of rows from a table:
public int countRows() { SqlFunction sf = new SqlFunction(dataSource, "select count(*) from mytable"); sf.compile(); return sf.run(); }
There are some issues involving parameters and data values that are common across all the different approaches provided by the Spring JDBC Framework.
Most of the time Spring will assume the SQL type of the parameters based on the type of parameter passed in. It is possible to explicitly provide the SQL type to be used when setting parameter values. This is sometimes necessary to correctly set NULL values.
There are a few different ways this can be accomplished:
Many of the update and query methods of the
JdbcTemplate
take an additional parameter in
the form of an int array. This array should contain the SQL type
using constant values from the java.sql.Types
class. There must be one entry for each parameter.
You can wrap the parameter value that needs this additional
information using the SqlParameterValue
class. Create a new instance for each value and pass in the SQL type
and parameter value in the constructor. You can also provide an
optional scale parameter for numeric values.
For methods working with named parameters, you can use the
SqlParameterSource
classes
BeanPropertySqlParameterSource
or
MapSqlParameterSource
. They both have methods
for registering the SQL type for any of the named parameter
values.
You can store images and other binary objects as well and large
chunks of text. These large object are called BLOB for binary data and
CLOB for character data. Spring lets you handle these large objects
using the JdbcTemplate directly and also when using the higher
abstractions provided by RDBMS Objects and the SimpleJdbc classes. All
of these approaches use an implementation of the
LobHandler
interface for the actual management of
the LOB data. The LobHandler
provides access to a
LobCreator
, via the
getLobCreator
method, for creating new LOB
objects to be inserted.
The LobCreator/LobHandler
provides the
following support for LOB in- and output:
BLOB
byte[] – getBlobAsBytes and setBlobAsBytes
InputStream – getBlobAsBinaryStream and setBlobAsBinaryStream
CLOB
String – getClobAsString and setClobAsString
InputStream – getClobAsAsciiStream and setClobAsAsciiStream
Reader – getClobAsCharacterStream and setClobAsCharacterStream
We will now show an example of how to create and insert a BLOB. We will later see how to read it back from the database.
This example uses a JdbcTemplate and an implementation of the AbstractLobCreatingPreparedStatementCallback. There is one method that must be implemented and it is "setValues". In this method you will be provided with a LobCreator that can be used to set the values for the LOB columns in your SQL insert statement.
We are assuming that we have a variable named 'lobHandler' that
already is set to an instance of a
DefaultLobHandler
. This is typically done using
dependency injection.
final File blobIn = new File("spring2004.jpg"); final InputStream blobIs = new FileInputStream(blobIn); final File clobIn = new File("large.txt"); final InputStream clobIs = new FileInputStream(clobIn); final InputStreamReader clobReader = new InputStreamReader(clobIs); jdbcTemplate.execute( "INSERT INTO lob_table (id, a_clob, a_blob) VALUES (?, ?, ?)", new AbstractLobCreatingPreparedStatementCallback(lobhandler) {protected void setValues(PreparedStatement ps, LobCreator lobCreator) throws SQLException { ps.setLong(1, 1L); lobCreator.setClobAsCharacterStream(ps, 2, clobReader, (int)clobIn.length());
lobCreator.setBlobAsBinaryStream(ps, 3, blobIs, (int)blobIn.length());
} } ); blobIs.close(); clobReader.close();
![]() | Here we use the lobHandler that in this example is a plain
|
![]() | Using the method |
![]() | Using the method
|
Now it's time to read the LOB data from the database. Again, we
use a JdbcTempate and we have the same instance variable 'lobHandler'
with a reference to a DefaultLobHandler
.
List l = jdbcTemplate.query("select id, a_clob, a_blob from lob_table", new RowMapper() { public Object mapRow(ResultSet rs, int i) throws SQLException { Map results = new HashMap(); String clobText = lobHandler.getClobAsString(rs, "a_clob");results.put("CLOB", clobText); byte[] blobBytes = lobHandler.getBlobAsBytes(rs, "a_blob");
results.put("BLOB", blobBytes); return results; } });
![]() | Using the method |
![]() | Using the method |
The SQL standard allows for selecting rows based on an expression
that includes a variable list of values. A typical example would be
"select * from T_ACTOR where id in (1, 2, 3)". This variable list is not
directly supported for prepared statements by the JDBC standard - there
is no way of declaring a variable number of place holders. You would
have to either have a number of variations with the desired number of
place holders prepared or you would have to dynamically generate the SQL
string once you know how many place holders are required. The named
parameter support provided in the
NamedParameterJdbcTemplate
and
SimpleJdbcTemplate
takes the latter approach.
When you pass in the values you should pass them in as a
java.util.List
of primitive objects. This list
will be used to insert the required place holders and pass in the values
during the statement execution.
![]() | Note |
---|---|
You need to be careful when passing in a large number of values. The JDBC standard doesn't guarantee that you can use more than 100 values for an IN expression list. Various databases exceed this number, but they usually have a hard limit for how many values are allowed. Oracle's limit for instance is 1000. |
In addition to the primitive values in the value list, you can
create a java.util.List
of object arrays. This
would support a case where there are multiple expressions defined for
the IN clause like "select * from T_ACTOR where (id, last_name) in ((1,
'Johnson'), (2, 'Harrop'))". This of course requires that your database
supports this syntax.
When calling stored procedures it's sometimes possible to use
complex types specific to the database. To accommodate these types
Spring provides a SqlReturnType
for handling them
when they are returned from the stored procedure call and
SqlTypeValue
when they are passed in as a
parameter to the stored procedure.
Here is an example of returning the value of an Oracle STRUCT
object of the user declared type "ITEM_TYPE". The
SqlReturnType
interface has a single method named
"getTypeValue
" that must be implemented. This
interface is used as part of the declaration of an
SqlOutParameter
.
declareParameter(new SqlOutParameter("item", OracleTypes.STRUCT, "ITEM_TYPE", new SqlReturnType() { public Object getTypeValue(CallableStatement cs, int colIndx, int sqlType, String typeName) throws SQLException { STRUCT struct = (STRUCT)cs.getObject(colIndx); Object[] attr = struct.getAttributes(); TestItem item = new TestItem(); item.setId(((Number) attr[0]).longValue()); item.setDescription((String)attr[1]); item.setExpirationDate((java.util.Date)attr[2]); return item; } }));
Going from Java to the database and passing in the
value of a TestItem
into a stored procedure is
done using the SqlTypeValue
. The
SqlTypeValue
interface has a single method named
"createTypeValue
" that must be implemented. The
active connection is passed in and can be used to create database
specific objects like StructDescriptor
s or
ArrayDescriptor
s
SqlTypeValue value = new AbstractSqlTypeValue() { protected Object createTypeValue(Connection conn, int sqlType, String typeName) throws SQLException { StructDescriptor itemDescriptor = new StructDescriptor(typeName, conn); Struct item = new STRUCT(itemDescriptor, conn, new Object[] { testItem.getId(), testItem.getDescription(), new java.sql.Date(testItem.getExpirationDate().getTime()) }); return item; } };
This SqlTypeValue
can now be added
to the Map containing the input parameters for the execute call of the
stored procedure.
The Spring Framework provides integration with Hibernate, JDO, Oracle TopLink, iBATIS SQL Maps and JPA: in terms of resource management, DAO implementation support, and transaction strategies. For example for Hibernate, there is first-class support with lots of IoC convenience features, addressing many typical Hibernate integration issues. All of these support packages for O/R (Object Relational) mappers comply with Spring's generic transaction and DAO exception hierarchies. There are usually two integration styles: either using Spring's DAO 'templates' or coding DAOs against plain Hibernate/JDO/TopLink/etc APIs. In both cases, DAOs can be configured through Dependency Injection and participate in Spring's resource and transaction management.
Spring adds significant support when using the O/R mapping layer of your choice to create data access applications. First of all, you should know that once you started using Spring's support for O/R mapping, you don't have to go all the way. No matter to what extent, you're invited to review and leverage the Spring approach, before deciding to take the effort and risk of building a similar infrastructure in-house. Much of the O/R mapping support, no matter what technology you're using may be used in a library style, as everything is designed as a set of reusable JavaBeans. Usage inside a Spring IoC container does provide additional benefits in terms of ease of configuration and deployment; as such, most examples in this section show configuration inside a Spring container.
Some of the benefits of using the Spring Framework to create your ORM DAOs include:
Ease of testing. Spring's IoC approach
makes it easy to swap the implementations and config locations of
Hibernate SessionFactory
instances,
JDBC DataSource
instances, transaction
managers, and mappes object implementations (if needed). This makes it
much easier to isolate and test each piece of persistence-related code
in isolation.
Common data access exceptions. Spring can wrap exceptions from your O/R mapping tool of choice, converting them from proprietary (potentially checked) exceptions to a common runtime DataAccessException hierarchy. This allows you to handle most persistence exceptions, which are non-recoverable, only in the appropriate layers, without annoying boilerplate catches/throws, and exception declarations. You can still trap and handle exceptions anywhere you need to. Remember that JDBC exceptions (including DB specific dialects) are also converted to the same hierarchy, meaning that you can perform some operations with JDBC within a consistent programming model.
General resource management. Spring
application contexts can handle the location and configuration of
Hibernate SessionFactory
instances,
JDBC DataSource
instances, iBATIS SQL
Maps configuration objects, and other related resources. This makes
these values easy to manage and change. Spring offers efficient, easy
and safe handling of persistence resources. For example: related code
using Hibernate generally needs to use the same Hibernate
Session
for efficiency and proper
transaction handling. Spring makes it easy to transparently create and
bind a Session
to the current thread,
either by using an explicit 'template' wrapper class at the Java code
level or by exposing a current Session
through the Hibernate SessionFactory
(for DAOs based on plain Hibernate API). Thus Spring solves many of
the issues that repeatedly arise from typical Hibernate usage, for any
transaction environment (local or JTA).
Integrated transaction management. Spring allows you to wrap your O/R mapping code with either a declarative, AOP style method interceptor, or an explicit 'template' wrapper class at the Java code level. In either case, transaction semantics are handled for you, and proper transaction handling (rollback, etc) in case of exceptions is taken care of. As discussed below, you also get the benefit of being able to use and swap various transaction managers, without your Hibernate/JDO related code being affected: for example, between local transactions and JTA, with the same full services (such as declarative transactions) available in both scenarios. As an additional benefit, JDBC-related code can fully integrate transactionally with the code you use to do O/R mapping. This is useful for data access that's not suitable for O/R mapping, such as batch processing or streaming of BLOBs, which still needs to share common transactions with ORM operations.
The PetClinic sample in the Spring distribution offers alternative DAO implementations and application context configurations for JDBC, Hibernate, Oracle TopLink, and JPA. PetClinic can therefore serve as working sample app that illustrates the use of Hibernate, TopLink and JPA in a Spring web application. It also leverages declarative transaction demarcation with different transaction strategies.
The JPetStore sample illustrates the use of iBATIS SQL Maps in a Spring environment. It also features two web tier versions: one based on Spring Web MVC, one based on Struts.
Beyond the samples shipped with Spring, there are a variety of Spring-based O/R mapping samples provided by specific vendors: for example, the JDO implementations JPOX (http://www.jpox.org/) and Kodo (http://www.bea.com/kodo/).
We will start with a coverage of Hibernate 3 in a Spring environment, using it to demonstrate the approach that Spring takes towards integrating O/R mappers. This section will cover many issues in detail and show different variations of DAO implementations and transaction demarcation. Most of these patterns can be directly translated to all other supported ORM tools. The following sections in this chapter will then cover the other ORM technologies, showing briefer examples there.
Note: As of Spring 2.5, Spring requires Hibernate 3.1 or higher. Neither Hibernate 2.1 nor Hibernate 3.0 are supported anymore.
Typical business applications are often cluttered with repetitive
resource management code. Many projects try to invent their own
solutions for this issue, sometimes sacrificing proper handling of
failures for programming convenience. Spring advocates strikingly simple
solutions for proper resource handling, namely IoC via templating; for
example infrastructure classes with callback interfaces, or applying AOP
interceptors. The infrastructure cares for proper resource handling, and
for appropriate conversion of specific API exceptions to an unchecked
infrastructure exception hierarchy. Spring introduces a DAO exception
hierarchy, applicable to any data access strategy. For direct JDBC, the
JdbcTemplate
class mentioned in a previous
section cares for connection handling, and for proper conversion of
SQLException
to the
DataAccessException
hierarchy, including
translation of database-specific SQL error codes to meaningful exception
classes. It supports both JTA and JDBC transactions, via respective
Spring transaction managers.
Spring also offers Hibernate and JDO support, consisting of a
HibernateTemplate
/
JdoTemplate
analogous to
JdbcTemplate
, a
HibernateInterceptor
/
JdoInterceptor
, and a Hibernate / JDO transaction
manager. The major goal is to allow for clear application layering, with
any data access and transaction technology, and for loose coupling of
application objects. No more business service dependencies on the data
access or transaction strategy, no more hard-coded resource lookups, no
more hard-to-replace singletons, no more custom service registries. One
simple and consistent approach to wiring up application objects, keeping
them as reusable and free from container dependencies as possible. All
the individual data access features are usable on their own but
integrate nicely with Spring's application context concept, providing
XML-based configuration and cross-referencing of plain JavaBean
instances that don't need to be Spring-aware. In a typical Spring
application, many important objects are JavaBeans: data access
templates, data access objects (that use the templates), transaction
managers, business services (that use the data access objects and
transaction managers), web view resolvers, web controllers (that use the
business services),and so on.
To avoid tying application objects to hard-coded resource lookups,
Spring allows you to define resources such as a JDBC
DataSource
or a Hibernate
SessionFactory
as beans in the Spring
container. Application objects that need to access resources just
receive references to such pre-defined instances via bean references
(the DAO definition in the next section illustrates this). The following
excerpt from an XML application context definition shows how to set up a
JDBC DataSource
and a Hibernate
SessionFactory
on top of it:
<beans> <bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="org.hsqldb.jdbcDriver"/> <property name="url" value="jdbc:hsqldb:hsql://localhost:9001"/> <property name="username" value="sa"/> <property name="password" value=""/> </bean> <bean id="mySessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"> <property name="dataSource" ref="myDataSource"/> <property name="mappingResources"> <list> <value>product.hbm.xml</value> </list> </property> <property name="hibernateProperties"> <value> hibernate.dialect=org.hibernate.dialect.HSQLDialect </value> </property> </bean> </beans>
Note that switching from a local Jakarta Commons DBCP
BasicDataSource
to a JNDI-located
DataSource
(usually managed by an
application server) is just a matter of configuration:
<beans> <bean id="myDataSource" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="java:comp/env/jdbc/myds"/> </bean> </beans>
You can also access a JNDI-located
SessionFactory
, using Spring's
JndiObjectFactoryBean
to retrieve and expose it.
However, that is typically not common outside of an EJB context.
The basic programming model for templating looks as follows, for
methods that can be part of any custom data access object or business
service. There are no restrictions on the implementation of the
surrounding object at all, it just needs to provide a Hibernate
SessionFactory
. It can get the latter
from anywhere, but preferably as bean reference from a Spring IoC
container - via a simple setSessionFactory(..)
bean property setter. The following snippets show a DAO definition in a
Spring container, referencing the above defined
SessionFactory
, and an example for a DAO
method implementation.
<beans> <bean id="myProductDao" class="product.ProductDaoImpl"> <property name="sessionFactory" ref="mySessionFactory"/> </bean> </beans>
public class ProductDaoImpl implements ProductDao { private HibernateTemplate hibernateTemplate; public void setSessionFactory(SessionFactory sessionFactory) { this.hibernateTemplate = new HibernateTemplate(sessionFactory); } public Collection loadProductsByCategory(String category) throws DataAccessException { return this.hibernateTemplate.find("from test.Product product where product.category=?", category); } }
The HibernateTemplate
class provides many
methods that mirror the methods exposed on the Hibernate
Session
interface, in addition to a
number of convenience methods such as the one shown above. If you need
access to the Session
to invoke methods
that are not exposed on the HibernateTemplate
,
you can always drop down to a callback-based approach like so.
public class ProductDaoImpl implements ProductDao { private HibernateTemplate hibernateTemplate; public void setSessionFactory(SessionFactory sessionFactory) { this.hibernateTemplate = new HibernateTemplate(sessionFactory); } public Collection loadProductsByCategory(final String category) throws DataAccessException { return this.hibernateTemplate.execute(new HibernateCallback() { public Object doInHibernate(Session session) { Criteria criteria = session.createCriteria(Product.class); criteria.add(Expression.eq("category", category)); criteria.setMaxResults(6); return criteria.list(); } }; } }
A callback implementation effectively can be used for any
Hibernate data access. HibernateTemplate
will
ensure that Session
instances are
properly opened and closed, and automatically participate in
transactions. The template instances are thread-safe and reusable, they
can thus be kept as instance variables of the surrounding class. For
simple single step actions like a single find, load, saveOrUpdate, or
delete call, HibernateTemplate
offers alternative
convenience methods that can replace such one line callback
implementations. Furthermore, Spring provides a convenient
HibernateDaoSupport
base class that provides a
setSessionFactory(..)
method for receiving a
SessionFactory
, and
getSessionFactory()
and
getHibernateTemplate()
for use by subclasses. In
combination, this allows for very simple DAO implementations for typical
requirements:
public class ProductDaoImpl extends HibernateDaoSupport implements ProductDao { public Collection loadProductsByCategory(String category) throws DataAccessException { return this.getHibernateTemplate().find( "from test.Product product where product.category=?", category); } }
As alternative to using Spring's
HibernateTemplate
to implement DAOs, data access
code can also be written in a more traditional fashion, without wrapping
the Hibernate access code in a callback, while still respecting and
participating in Spring's generic
DataAccessException
hierarchy. The
HibernateDaoSupport
base class offers methods to
access the current transactional Session
and to convert exceptions in such a scenario; similar methods are also
available as static helpers on the
SessionFactoryUtils
class. Note that such code
will usually pass 'false
' as the value of the
getSession(..)
methods
'allowCreate
' argument, to enforce running within a
transaction (which avoids the need to close the returned
Session
, as its lifecycle is managed by
the transaction).
public class HibernateProductDao extends HibernateDaoSupport implements ProductDao { public Collection loadProductsByCategory(String category) throws DataAccessException, MyException { Session session = getSession(false); try { Query query = session.createQuery("from test.Product product where product.category=?"); query.setString(0, category); List result = query.list(); if (result == null) { throw new MyException("No search results."); } return result; } catch (HibernateException ex) { throw convertHibernateAccessException(ex); } } }
The advantage of such direct Hibernate access code is that it
allows any checked application exception to be
thrown within the data access code; contrast this to the
HibernateTemplate
class which is restricted to
throwing only unchecked exceptions within the callback. Note that you
can often defer the corresponding checks and the throwing of application
exceptions to after the callback, which still allows working with
HibernateTemplate
. In general, the
HibernateTemplate
class' convenience methods are
simpler and more convenient for many scenarios.
Hibernate 3 provides a feature called "contextual Sessions", where
Hibernate itself manages one current
Session
per transaction. This is roughly
equivalent to Spring's synchronization of one Hibernate
Session
per transaction. A corresponding
DAO implementation looks like as follows, based on the plain Hibernate
API:
public class ProductDaoImpl implements ProductDao { private SessionFactory sessionFactory; public void setSessionFactory(SessionFactory sessionFactory) { this.sessionFactory = sessionFactory; } public Collection loadProductsByCategory(String category) { return this.sessionFactory.getCurrentSession() .createQuery("from test.Product product where product.category=?") .setParameter(0, category) .list(); } }
This style is very similar to what you will find in the Hibernate
reference documentation and examples, except for holding the
SessionFactory
in an instance variable.
We strongly recommend such an instance-based setup over the old-school
static
HibernateUtil
class
from Hibernate's CaveatEmptor sample application. (In general, do not
keep any resources in static
variables unless
absolutely necessary.)
The above DAO follows the Dependency Injection pattern: it fits
nicely into a Spring IoC container, just like it would if coded against
Spring's HibernateTemplate
. Of course, such a DAO
can also be set up in plain Java (for example, in unit tests): simply
instantiate it and call setSessionFactory(..)
with the desired factory reference. As a Spring bean definition, it
would look as follows:
<beans> <bean id="myProductDao" class="product.ProductDaoImpl"> <property name="sessionFactory" ref="mySessionFactory"/> </bean> </beans>
The main advantage of this DAO style is that it depends on Hibernate API only; no import of any Spring class is required. This is of course appealing from a non-invasiveness perspective, and will no doubt feel more natural to Hibernate developers.
However, the DAO throws plain
HibernateException
(which is unchecked, so does
not have to be declared or caught), which means that callers can only
treat exceptions as generally fatal - unless they want to depend on
Hibernate's own exception hierarchy. Catching specific causes such as an
optimistic locking failure is not possible without tieing the caller to
the implementation strategy. This tradeoff might be acceptable to
applications that are strongly Hibernate-based and/or do not need any
special exception treatment.
Fortunately, Spring's
LocalSessionFactoryBean
supports Hibernate's
SessionFactory.getCurrentSession()
method for
any Spring transaction strategy, returning the current Spring-managed
transactional Session
even with
HibernateTransactionManager
. Of course, the
standard behavior of that method remains: returning the current
Session
associated with the ongoing JTA
transaction, if any (no matter whether driven by Spring's
JtaTransactionManager
, by EJB CMT, or by
JTA).
In summary: DAOs can be implemented based on the plain Hibernate 3 API, while still being able to participate in Spring-managed transactions.
Transactions can be demarcated in a higher level of the
application, on top of such lower-level data access services spanning
any number of operations. There are no restrictions on the
implementation of the surrounding business service here as well, it just
needs a Spring PlatformTransactionManager
. Again,
the latter can come from anywhere, but preferably as bean reference via
a setTransactionManager(..)
method - just like
the productDAO
should be set via a
setProductDao(..)
method. The following
snippets show a transaction manager and a business service definition in
a Spring application context, and an example for a business method
implementation.
<beans> <bean id="myTxManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager"> <property name="sessionFactory" ref="mySessionFactory"/> </bean> <bean id="myProductService" class="product.ProductServiceImpl"> <property name="transactionManager" ref="myTxManager"/> <property name="productDao" ref="myProductDao"/> </bean> </beans>
public class ProductServiceImpl implements ProductService {
private TransactionTemplate transactionTemplate;
private ProductDao productDao;
public void setTransactionManager(PlatformTransactionManager transactionManager) {
this.transactionTemplate = new TransactionTemplate(transactionManager);
}
public void setProductDao(ProductDao productDao) {
this.productDao = productDao;
}
public void increasePriceOfAllProductsInCategory(final String category) {
this.transactionTemplate.execute(new TransactionCallbackWithoutResult() {
public void doInTransactionWithoutResult(TransactionStatus status) {
List productsToChange = this.productDao.loadProductsByCategory(category);
// do the price increase...
}
}
);
}
}
Alternatively, one can use Spring's declarative transaction support, which essentially enables you to replace explicit transaction demarcation API calls in your Java code with an AOP transaction interceptor configured in a Spring container. This allows you to keep business services free of repetitive transaction demarcation code, and allows you to focus on adding business logic which is where the real value of your application lies. Furthermore, transaction semantics like propagation behavior and isolation level can be changed in a configuration file and do not affect the business service implementations.
<beans>
<bean id="myTxManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
<property name="sessionFactory" ref="mySessionFactory"/>
</bean>
<bean id="myProductService" class="org.springframework.aop.framework.ProxyFactoryBean">
<property name="proxyInterfaces" value="product.ProductService"/>
<property name="target">
<bean class="product.DefaultProductService">
<property name="productDao" ref="myProductDao"/>
</bean>
</property>
<property name="interceptorNames">
<list>
<value>myTxInterceptor</value> <!-- the transaction interceptor (configured elsewhere) -->
</list>
</property>
</bean>
</beans>
public class ProductServiceImpl implements ProductService { private ProductDao productDao; public void setProductDao(ProductDao productDao) { this.productDao = productDao; } // notice the absence of transaction demarcation code in this method // Spring's declarative transaction infrastructure will be demarcating transactions on your behalf public void increasePriceOfAllProductsInCategory(final String category) { List productsToChange = this.productDao.loadProductsByCategory(category); // ... } }
Spring's TransactionInterceptor
allows any
checked application exception to be thrown with the callback code, while
TransactionTemplate
is restricted to unchecked
exceptions within the callback.
TransactionTemplate
will trigger a rollback in
case of an unchecked application exception, or if the transaction has
been marked rollback-only by the application (via
TransactionStatus
).
TransactionInterceptor
behaves the same way by
default but allows configurable rollback policies per method.
The following higher level approach to declarative transactions
doesn't use the ProxyFactoryBean
, and as such may
be easier to use if you have a large number of service objects that you
wish to make transactional.
![]() | Note |
---|---|
You are strongly encouraged to read the section entitled Section 9.5, “Declarative transaction management” if you have not done so already prior to continuing. |
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd">
<!-- SessionFactory
, DataSource
, etc. omitted -->
<bean id="myTxManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
<property name="sessionFactory" ref="mySessionFactory"/>
</bean>
<aop:config>
<aop:pointcut id="productServiceMethods" expression="execution(* product.ProductService.*(..))"/>
<aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/>
</aop:config>
<tx:advice id="txAdvice" transaction-manager="myTxManager">
<tx:attributes>
<tx:method name="increasePrice*" propagation="REQUIRED"/>
<tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/>
<tx:method name="*" propagation="SUPPORTS" read-only="true"/>
</tx:attributes>
</tx:advice>
<bean id="myProductService" class="product.SimpleProductService">
<property name="productDao" ref="myProductDao"/>
</bean>
</beans>
Both TransactionTemplate
and
TransactionInterceptor
delegate the actual
transaction handling to a
PlatformTransactionManager
instance, which can be
a HibernateTransactionManager
(for a single
Hibernate SessionFactory
, using a
ThreadLocal
Session
under the hood) or a
JtaTransactionManager
(delegating to the JTA
subsystem of the container) for Hibernate applications. You could even
use a custom PlatformTransactionManager
implementation. So switching from native Hibernate transaction
management to JTA, such as when facing distributed transaction
requirements for certain deployments of your application, is just a
matter of configuration. Simply replace the Hibernate transaction
manager with Spring's JTA transaction implementation. Both transaction
demarcation and data access code will work without changes, as they just
use the generic transaction management APIs.
For distributed transactions across multiple Hibernate session
factories, simply combine JtaTransactionManager
as a transaction strategy with multiple
LocalSessionFactoryBean
definitions. Each of your
DAOs then gets one specific
SessionFactory
reference passed into it's
respective bean property. If all underlying JDBC data sources are
transactional container ones, a business service can demarcate
transactions across any number of DAOs and any number of session
factories without special regard, as long as it is using
JtaTransactionManager
as the strategy.
<beans> <bean id="myDataSource1" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName value="java:comp/env/jdbc/myds1"/> </bean> <bean id="myDataSource2" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="java:comp/env/jdbc/myds2"/> </bean> <bean id="mySessionFactory1" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"> <property name="dataSource" ref="myDataSource1"/> <property name="mappingResources"> <list> <value>product.hbm.xml</value> </list> </property> <property name="hibernateProperties"> <value> hibernate.dialect=org.hibernate.dialect.MySQLDialect hibernate.show_sql=true </value> </property> </bean> <bean id="mySessionFactory2" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"> <property name="dataSource" ref="myDataSource2"/> <property name="mappingResources"> <list> <value>inventory.hbm.xml</value> </list> </property> <property name="hibernateProperties"> <value> hibernate.dialect=org.hibernate.dialect.OracleDialect </value> </property> </bean> <bean id="myTxManager" class="org.springframework.transaction.jta.JtaTransactionManager"/> <bean id="myProductDao" class="product.ProductDaoImpl"> <property name="sessionFactory" ref="mySessionFactory1"/> </bean> <bean id="myInventoryDao" class="product.InventoryDaoImpl"> <property name="sessionFactory" ref="mySessionFactory2"/> </bean> <!-- this shows the Spring 1.x style of declarative transaction configuration --> <!-- it is totally supported, 100% legal in Spring 2.x, but see also above for the sleeker, Spring 2.0 style --> <bean id="myProductService" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean"> <property name="transactionManager" ref="myTxManager"/> <property name="target"> <bean class="product.ProductServiceImpl"> <property name="productDao" ref="myProductDao"/> <property name="inventoryDao" ref="myInventoryDao"/> </bean> </property> <property name="transactionAttributes"> <props> <prop key="increasePrice*">PROPAGATION_REQUIRED</prop> <prop key="someOtherBusinessMethod">PROPAGATION_REQUIRES_NEW</prop> <prop key="*">PROPAGATION_SUPPORTS,readOnly</prop> </props> </property> </bean> </beans>
Both HibernateTransactionManager
and
JtaTransactionManager
allow for proper JVM-level
cache handling with Hibernate - without container-specific transaction
manager lookup or JCA connector (as long as not using EJB to initiate
transactions).
HibernateTransactionManager
can export the
JDBC Connection
used by Hibernate to
plain JDBC access code, for a specific
DataSource
. This allows for high-level
transaction demarcation with mixed Hibernate/JDBC data access completely
without JTA, as long as you are just accessing one database!
HibernateTransactionManager
will automatically
expose the Hibernate transaction as JDBC transaction if the passed-in
SessionFactory
has been set up with a
DataSource
(through the "dataSource"
property of the LocalSessionFactoryBean
class).
Alternatively, the DataSource
that the
transactions are supposed to be exposed for can also be specified
explicitly, through the "dataSource" property of the
HibernateTransactionManager
class.
Spring's resource management allows for simple switching between a
JNDI SessionFactory
and a local one,
without having to change a single line of application code. The decision
as to whether to keep the resource definitions in the container or
locally within the application, is mainly a matter of the transaction
strategy being used. Compared to a Spring-defined local
SessionFactory
, a manually registered
JNDI SessionFactory
does not provide any
benefits. Deploying a SessionFactory
through Hibernate's JCA connector provides the added value of
participating in the J2EE server's management infrastructure, but does
not add actual value beyond that.
An important benefit of Spring's transaction support is that it
isn't bound to a container at all. Configured to any other strategy than
JTA, it will work in a standalone or test environment too. Especially
for the typical case of single-database transactions, this is a very
lightweight and powerful alternative to JTA. When using local EJB
Stateless Session Beans to drive transactions, you depend both on an EJB
container and JTA - even if you just access a single database anyway,
and just use SLSBs for declarative transactions via CMT. The alternative
of using JTA programmatically requires a J2EE environment as well. JTA
does not just involve container dependencies in terms of JTA itself and
of JNDI DataSource
instances. For
non-Spring JTA-driven Hibernate transactions, you have to use the
Hibernate JCA connector, or extra Hibernate transaction code with the
TransactionManagerLookup
being configured
for proper JVM-level caching.
Spring-driven transactions can work with a locally defined
Hibernate SessionFactory
nicely, just
like with a local JDBC DataSource
- if
accessing a single database, of course. Therefore you just have to fall
back to Spring's JTA transaction strategy when actually facing
distributed transaction requirements. Note that a JCA connector needs
container-specific deployment steps, and obviously JCA support in the
first place. This is far more hassle than deploying a simple web app
with local resource definitions and Spring-driven transactions. And you
often need the Enterprise Edition of your container, as for example
WebLogic Express does not provide JCA. A Spring application with local
resources and transactions spanning one single database will work in any
J2EE web container (without JTA, JCA, or EJB) - like Tomcat, Resin, or
even plain Jetty. Additionally, such a middle tier can be reused in
desktop applications or test suites easily.
All things considered: if you do not use EJB, stick with local
SessionFactory
setup and Spring's
HibernateTransactionManager
or
JtaTransactionManager
. You will get all of the
benefits including proper transactional JVM-level caching and
distributed transactions, without any container deployment hassle. JNDI
registration of a Hibernate
SessionFactory
via the JCA connector
really only adds value when used in conjunction with EJBs.
In some JTA environments with very strict
XADataSource
implementations -- currently
only some WebLogic and WebSphere versions -- when using Hibernate
configured without any awareness of the JTA
PlatformTransactionManager
object for
that environment, it is possible for spurious warning or exceptions to
show up in the application server log. These warnings or exceptions will
say something to the effect that the connection being accessed is no
longer valid, or JDBC access is no longer valid, possibly because the
transaction is no longer active. As an example, here is an actual
exception from WebLogic:
java.sql.SQLException: The transaction is no longer active - status: 'Committed'. No further JDBC access is allowed within this transaction.
This warning is easy to resolve by simply making Hibernate aware
of the JTA PlatformTransactionManager
instance, to which it will also synchronize (along with Spring). This
may be done in two ways:
If in your application context you are already directly
obtaining the JTA
PlatformTransactionManager
object
(presumably from JNDI via JndiObjectFactoryBean
)
and feeding it for example to Spring's
JtaTransactionManager
, then the easiest way
is to simply specify a reference to this as the value of
LocalSessionFactoryBean
's
jtaTransactionManager property. Spring will
then make the object available to Hibernate.
More likely you do not already have the JTA
PlatformTransactionManager
instance
(since Spring's JtaTransactionManager
can
find it itself) so you need to instead configure Hibernate to also
look it up directly. This is done by configuring an AppServer
specific TransactionManagerLookup
class in the
Hibernate configuration, as described in the Hibernate
manual.
It is not necessary to read any more for proper usage, but the
full sequence of events with and without Hibernate being aware of the
JTA PlatformTransactionManager
will now
be described.
When Hibernate is not configured with any awareness of the JTA
PlatformTransactionManager
, the sequence
of events when a JTA transaction commits is as follows:
JTA transaction commits
Spring's JtaTransactionManager
is
synchronized to the JTA transaction, so it is called back via an
afterCompletion callback by the JTA transaction
manager.
Among other activities, this can trigger a callback by Spring
to Hibernate, via Hibernate's
afterTransactionCompletion
callback (used to
clear the Hibernate cache), followed by an explicit
close()
call on the Hibernate Session, which
results in Hibernate trying to close()
the JDBC
Connection.
In some environments, this
Connection.close()
call then triggers the
warning or error, as the application server no longer considers the
Connection
usable at all, since the
transaction has already been committed.
When Hibernate is configured with awareness of the JTA
PlatformTransactionManager
, the sequence
of events when a JTA transaction commits is instead as follows:
JTA transaction is ready to commit
Spring's JtaTransactionManager
is
synchronized to the JTA transaction, so it is called back via a
beforeCompletion callback by the JTA
transaction manager.
Spring is aware that Hibernate itself is synchronized to the
JTA transaction, and behaves differently than in the previous
scenario. Assuming the Hibernate
Session
needs to be closed at all,
Spring will close it now.
JTA Transaction commits
Hibernate is synchronized to the JTA transaction, so it is called back via an afterCompletion callback by the JTA transaction manager, and can properly clear its cache.
Spring supports the standard JDO 2.0/2.1 API as data access
strategy, following the same style as the Hibernate support. The
corresponding integration classes reside in the
org.springframework.orm.jdo
package.
Spring provides a
LocalPersistenceManagerFactoryBean
class that
allows for defining a local JDO
PersistenceManagerFactory
within a Spring
application context:
<beans> <bean id="myPmf" class="org.springframework.orm.jdo.LocalPersistenceManagerFactoryBean"> <property name="configLocation" value="classpath:kodo.properties"/> </bean> </beans>
Alternatively, a
PersistenceManagerFactory
can also be set
up through direct instantiation of a
PersistenceManagerFactory
implementation
class. A JDO PersistenceManagerFactory
implementation class is supposed to follow the JavaBeans pattern, just
like a JDBC DataSource
implementation
class, which is a natural fit for a Spring bean definition. This setup
style usually supports a Spring-defined JDBC
DataSource
, passed into the
"connectionFactory" property. For example, for the open source JDO
implementation JPOX (http://www.jpox.org):
<beans> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="${jdbc.driverClassName}"/> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </bean> <bean id="myPmf" class="org.jpox.PersistenceManagerFactoryImpl" destroy-method="close"> <property name="connectionFactory" ref="dataSource"/> <property name="nontransactionalRead" value="true"/> </bean> </beans>
A JDO PersistenceManagerFactory
can
also be set up in the JNDI environment of a J2EE application server,
usually through the JCA connector provided by the particular JDO
implementation. Spring's standard
JndiObjectFactoryBean
can be used to retrieve and
expose such a PersistenceManagerFactory
.
However, outside an EJB context, there is often no compelling benefit in
holding the PersistenceManagerFactory
in
JNDI: only choose such setup for a good reason. See "container resources
versus local resources" in the Hibernate section for a discussion; the
arguments there apply to JDO as well.
Each JDO-based DAO will then receive the
PersistenceManagerFactory
through
dependency injection. Such a DAO could be coded against plain JDO API,
working with the given
PersistenceManagerFactory
, but will
usually rather be used with the Spring Framework's
JdoTemplate
:
<beans> <bean id="myProductDao" class="product.ProductDaoImpl"> <property name="persistenceManagerFactory" ref="myPmf"/> </bean> </beans>
public class ProductDaoImpl implements ProductDao {
private JdoTemplate jdoTemplate;
public void setPersistenceManagerFactory(PersistenceManagerFactory pmf) {
this.jdoTemplate = new JdoTemplate(pmf);
}
public Collection loadProductsByCategory(final String category) throws DataAccessException {
return (Collection) this.jdoTemplate.execute(new JdoCallback() {
public Object doInJdo(PersistenceManager pm) throws JDOException {
Query query = pm.newQuery(Product.class, "category = pCategory");
query.declareParameters("String pCategory");
List result = query.execute(category);
// do some further stuff with the result list
return result;
}
});
}
}
A callback implementation can effectively be used for any JDO data
access. JdoTemplate
will ensure that
PersistenceManager
s are properly opened and
closed, and automatically participate in transactions. The template
instances are thread-safe and reusable, they can thus be kept as
instance variables of the surrounding class. For simple single-step
actions such as a single find
,
load
, makePersistent
, or
delete
call, JdoTemplate
offers alternative convenience methods that can replace such one line
callback implementations. Furthermore, Spring provides a convenient
JdoDaoSupport
base class that provides a
setPersistenceManagerFactory(..)
method for receiving
a PersistenceManagerFactory
, and
getPersistenceManagerFactory()
and
getJdoTemplate()
for use by subclasses. In
combination, this allows for very simple DAO implementations for typical
requirements:
public class ProductDaoImpl extends JdoDaoSupport implements ProductDao { public Collection loadProductsByCategory(String category) throws DataAccessException { return getJdoTemplate().find( Product.class, "category = pCategory", "String category", new Object[] {category}); } }
As alternative to working with Spring's
JdoTemplate
, you can also code Spring-based DAOs
at the JDO API level, explicitly opening and closing a
PersistenceManager
. As elaborated in the
corresponding Hibernate section, the main advantage of this approach is
that your data access code is able to throw checked exceptions.
JdoDaoSupport
offers a variety of support methods
for this scenario, for fetching and releasing a transactional
PersistenceManager
as well as for
converting exceptions.
DAOs can also be written against plain JDO API, without any Spring
dependencies, directly using an injected
PersistenceManagerFactory
. A
corresponding DAO implementation looks like as follows:
public class ProductDaoImpl implements ProductDao { private PersistenceManagerFactory persistenceManagerFactory; public void setPersistenceManagerFactory(PersistenceManagerFactory pmf) { this.persistenceManagerFactory = pmf; } public Collection loadProductsByCategory(String category) { PersistenceManager pm = this.persistenceManagerFactory.getPersistenceManager(); try { Query query = pm.newQuery(Product.class, "category = pCategory"); query.declareParameters("String pCategory"); return query.execute(category); } finally { pm.close(); } } }
As the above DAO still follows the Dependency Injection pattern,
it still fits nicely into a Spring container, just like it would if
coded against Spring's JdoTemplate
:
<beans> <bean id="myProductDao" class="product.ProductDaoImpl"> <property name="persistenceManagerFactory" ref="myPmf"/> </bean> </beans>
The main issue with such DAOs is that they always get a new
PersistenceManager
from the factory. To
still access a Spring-managed transactional
PersistenceManager
, consider defining a
TransactionAwarePersistenceManagerFactoryProxy
(as included in Spring) in front of your target
PersistenceManagerFactory
, passing the
proxy into your DAOs.
<beans> <bean id="myPmfProxy" class="org.springframework.orm.jdo.TransactionAwarePersistenceManagerFactoryProxy"> <property name="targetPersistenceManagerFactory" ref="myPmf"/> </bean> <bean id="myProductDao" class="product.ProductDaoImpl"> <property name="persistenceManagerFactory" ref="myPmfProxy"/> </bean> </beans>
Your data access code will then receive a transactional
PersistenceManager
(if any) from the
PersistenceManagerFactory.getPersistenceManager()
method that it calls. The latter method call goes through the proxy,
which will first check for a current transactional
PersistenceManager
before getting a new
one from the factory. close()
calls on the
PersistenceManager
will be ignored in
case of a transactional
PersistenceManager
.
If your data access code will always run within an active
transaction (or at least within active transaction synchronization), it
is safe to omit the PersistenceManager.close()
call and thus the entire finally
block, which you
might prefer to keep your DAO implementations concise:
public class ProductDaoImpl implements ProductDao { private PersistenceManagerFactory persistenceManagerFactory; public void setPersistenceManagerFactory(PersistenceManagerFactory pmf) { this.persistenceManagerFactory = pmf; } public Collection loadProductsByCategory(String category) { PersistenceManager pm = this.persistenceManagerFactory.getPersistenceManager(); Query query = pm.newQuery(Product.class, "category = pCategory"); query.declareParameters("String pCategory"); return query.execute(category); } }
With such DAOs that rely on active transactions, it is recommended
to enforce active transactions through turning
TransactionAwarePersistenceManagerFactoryProxy
's
"allowCreate" flag off:
<beans> <bean id="myPmfProxy" class="org.springframework.orm.jdo.TransactionAwarePersistenceManagerFactoryProxy"> <property name="targetPersistenceManagerFactory" ref="myPmf"/> <property name="allowCreate" value="false"/> </bean> <bean id="myProductDao" class="product.ProductDaoImpl"> <property name="persistenceManagerFactory" ref="myPmfProxy"/> </bean> </beans>
The main advantage of this DAO style is that it depends on JDO API only; no import of any Spring class is required. This is of course appealing from a non-invasiveness perspective, and might feel more natural to JDO developers.
However, the DAO throws plain
JDOException
(which is unchecked, so does
not have to be declared or caught), which means that callers can only
treat exceptions as generally fatal - unless they want to depend on
JDO's own exception structure. Catching specific causes such as an
optimistic locking failure is not possible without tying the caller to
the implementation strategy. This tradeoff might be acceptable to
applications that are strongly JDO-based and/or do not need any special
exception treatment.
In summary: DAOs can be implemented based on plain JDO API, while
still being able to participate in Spring-managed transactions. This
might in particular appeal to people already familiar with JDO, feeling
more natural to them. However, such DAOs will throw plain
JDOException
; conversion to Spring's
DataAccessException
would have to happen
explicitly (if desired).
To execute service operations within transactions, you can use Spring's common declarative transaction facilities. For example:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <bean id="myTxManager" class="org.springframework.orm.jdo.JdoTransactionManager"> <property name="persistenceManagerFactory" ref="myPmf"/> </bean> <bean id="myProductService" class="product.ProductServiceImpl"> <property name="productDao" ref="myProductDao"/> </bean> <tx:advice id="txAdvice" transaction-manager="txManager"> <tx:attributes> <tx:method name="increasePrice*" propagation="REQUIRED"/> <tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/> <tx:method name="*" propagation="SUPPORTS" read-only="true"/> </tx:attributes> </tx:advice> <aop:config> <aop:pointcut id="productServiceMethods" expression="execution(* product.ProductService.*(..))"/> <aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/> </aop:config> </beans>
Note that JDO requires an active transaction when modifying a
persistent object. There is no concept like a non-transactional flush in
JDO, in contrast to Hibernate. For this reason, the chosen JDO
implementation needs to be set up for a specific environment: in
particular, it needs to be explicitly set up for JTA synchronization, to
detect an active JTA transaction itself. This is not necessary for local
transactions as performed by Spring's
JdoTransactionManager
, but it is necessary for
participating in JTA transactions (whether driven by Spring's
JtaTransactionManager
or by EJB CMT / plain
JTA).
JdoTransactionManager
is capable of
exposing a JDO transaction to JDBC access code that accesses the same
JDBC DataSource
, provided that the
registered JdoDialect
supports retrieval of the
underlying JDBC Connection
. This is
the case for JDBC-based JDO 2.0 implementations by default.
As an advanced feature, both JdoTemplate
and interfacename
support a custom
JdoDialect
, to be passed into the
"jdoDialect" bean property. In such a scenario, the DAOs won't receive a
PersistenceManagerFactory
reference but
rather a full JdoTemplate
instance instead (for
example, passed into JdoDaoSupport
's
"jdoTemplate" property). A JdoDialect
implementation can enable some advanced features supported by Spring,
usually in a vendor-specific manner:
applying specific transaction semantics (such as custom isolation level or transaction timeout)
retrieving the transactional JDBC
Connection
(for exposure to
JDBC-based DAOs)
applying query timeouts (automatically calculated from Spring-managed transaction timeout)
eagerly flushing a
PersistenceManager
(to make
transactional changes visible to JDBC-based data access code)
advanced translation of JDOExceptions
to
Spring DataAccessExceptions
See the JdoDialect
Javadoc for more details
on its operations and how they are used within Spring's JDO support.
Since Spring 1.2, Spring supports Oracle TopLink (http://www.oracle.com/technology/products/ias/toplink) as
data access strategy, following the same style as the Hibernate support.
Both TopLink 9.0.4 (the production version as of Spring 1.2) and 10.1.3
(still in beta as of Spring 1.2) are supported. The corresponding
integration classes reside in the
org.springframework.orm.toplink
package.
Spring's TopLink support has been co-developed with the Oracle TopLink team. Many thanks to the TopLink team, in particular to Jim Clark who helped to clarify details in all areas!
TopLink itself does not ship with a SessionFactory abstraction.
Instead, multi-threaded access is based on the concept of a central
ServerSession
, which in turn is able to spawn
ClientSession
instances for single-threaded usage.
For flexible setup options, Spring defines a
SessionFactory
abstraction for TopLink,
enabling to switch between different
Session
creation strategies.
As a one-stop shop, Spring provides a
LocalSessionFactoryBean
class that allows for
defining a TopLink SessionFactory
with
bean-style configuration. It needs to be configured with the location of
the TopLink session configuration file, and usually also receives a
Spring-managed JDBC DataSource
to
use.
<beans> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="${jdbc.driverClassName}"/> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </bean> <bean id="mySessionFactory" class="org.springframework.orm.toplink.LocalSessionFactoryBean"> <property name="configLocation" value="toplink-sessions.xml"/> <property name="dataSource" ref="dataSource"/> </bean> </beans>
<toplink-configuration> <session> <name>Session</name> <project-xml>toplink-mappings.xml</project-xml> <session-type> <server-session/> </session-type> <enable-logging>true</enable-logging> <logging-options/> </session> </toplink-configuration>
Usually, LocalSessionFactoryBean
will hold
a multi-threaded TopLink ServerSession
underneath and
create appropriate client Session
s for
it: either a plain Session
(typical), a
managed ClientSession
, or a transaction-aware
Session
(the latter are mainly used
internally by Spring's TopLink support). It might also hold a
single-threaded TopLink DatabaseSession
; this is
rather unusual, though.
Each TopLink-based DAO will then receive the
SessionFactory
through dependency
injection, i.e. through a bean property setter or through a constructor
argument. Such a DAO could be coded against plain TopLink API, fetching
a Session
from the given
SessionFactory
, but will usually rather
be used with Spring's TopLinkTemplate
:
<beans> <bean id="myProductDao" class="product.ProductDaoImpl"> <property name="sessionFactory" ref="mySessionFactory"/> </bean> </beans>
public class TopLinkProductDao implements ProductDao {
private TopLinkTemplate tlTemplate;
public void setSessionFactory(SessionFactory sessionFactory) {
this.tlTemplate = new TopLinkTemplate(sessionFactory);
}
public Collection loadProductsByCategory(final String category) throws DataAccessException {
return (Collection) this.tlTemplate.execute(new TopLinkCallback() {
public Object doInTopLink(Session session) throws TopLinkException {
ReadAllQuery findOwnersQuery = new ReadAllQuery(Product.class);
findOwnersQuery.addArgument("Category");
ExpressionBuilder builder = this.findOwnersQuery.getExpressionBuilder();
findOwnersQuery.setSelectionCriteria(
builder.get("category").like(builder.getParameter("Category")));
Vector args = new Vector();
args.add(category);
List result = session.executeQuery(findOwnersQuery, args);
// do some further stuff with the result list
return result;
}
});
}
}
A callback implementation can effectively be used for any TopLink
data access. TopLinkTemplate
will ensure that
Session
s are properly opened and closed,
and automatically participate in transactions. The template instances
are thread-safe and reusable, they can thus be kept as instance
variables of the surrounding class. For simple single-step actions such
as a single executeQuery
, readAll
,
readById
, or merge
call,
JdoTemplate
offers alternative convenience
methods that can replace such one line callback implementations.
Furthermore, Spring provides a convenient
TopLinkDaoSupport
base class that provides a
setSessionFactory(..)
method for receiving a
SessionFactory
, and
getSessionFactory()
and
getTopLinkTemplate()
for use by subclasses. In
combination, this allows for simple DAO implementations for typical
requirements:
public class ProductDaoImpl extends TopLinkDaoSupport implements ProductDao { public Collection loadProductsByCategory(String category) throws DataAccessException { ReadAllQuery findOwnersQuery = new ReadAllQuery(Product.class); findOwnersQuery.addArgument("Category"); ExpressionBuilder builder = this.findOwnersQuery.getExpressionBuilder(); findOwnersQuery.setSelectionCriteria( builder.get("category").like(builder.getParameter("Category"))); return getTopLinkTemplate().executeQuery(findOwnersQuery, new Object[] {category}); } }
Side note: TopLink query objects are thread-safe and can be cached within the DAO, i.e. created on startup and kept in instance variables.
As alternative to working with Spring's
TopLinkTemplate
, you can also code your TopLink
data access based on the raw TopLink API, explicitly opening and closing
a Session
. As elaborated in the
corresponding Hibernate section, the main advantage of this approach is
that your data access code is able to throw checked exceptions.
TopLinkDaoSupport
offers a variety of support
methods for this scenario, for fetching and releasing a transactional
Session
as well as for converting
exceptions.
DAOs can also be written against plain TopLink API, without any
Spring dependencies, directly using an injected TopLink
Session
. The latter will usually be based
on a SessionFactory
defined by a
LocalSessionFactoryBean
, exposed for bean
references of type Session
through
Spring's TransactionAwareSessionAdapter
.
The getActiveSession()
method defined on
TopLink's Session
interface will return
the current transactional Session
in such
a scenario. If there is no active transaction, it will return the shared
TopLink ServerSession
as-is, which is only supposed
to be used directly for read-only access. There is also an analogous
getActiveUnitOfWork()
method, returning the
TopLink UnitOfWork
associated with the
current transaction, if any (returning null
else).
A corresponding DAO implementation looks like as follows:
public class ProductDaoImpl implements ProductDao { private Session session; public void setSession(Session session) { this.session = session; } public Collection loadProductsByCategory(String category) { ReadAllQuery findOwnersQuery = new ReadAllQuery(Product.class); findOwnersQuery.addArgument("Category"); ExpressionBuilder builder = this.findOwnersQuery.getExpressionBuilder(); findOwnersQuery.setSelectionCriteria( builder.get("category").like(builder.getParameter("Category"))); Vector args = new Vector(); args.add(category); return session.getActiveSession().executeQuery(findOwnersQuery, args); } }
As the above DAO still follows the Dependency Injection pattern,
it still fits nicely into a Spring application context, analogous to
like it would if coded against Spring's
TopLinkTemplate
. Spring's
TransactionAwareSessionAdapter
is used to expose a
bean reference of type Session
, to be
passed into the DAO:
<beans> <bean id="mySessionAdapter" class="org.springframework.orm.toplink.support.TransactionAwareSessionAdapter"> <property name="sessionFactory" ref="mySessionFactory"/> </bean> <bean id="myProductDao" class="product.ProductDaoImpl"> <property name="session" ref="mySessionAdapter"/> </bean> </beans>
The main advantage of this DAO style is that it depends on TopLink API only; no import of any Spring class is required. This is of course appealing from a non-invasiveness perspective, and might feel more natural to TopLink developers.
However, the DAO throws plain
TopLinkException
(which is unchecked, so
does not have to be declared or caught), which means that callers can
only treat exceptions as generally fatal - unless they want to depend on
TopLink's own exception structure. Catching specific causes such as an
optimistic locking failure is not possible without tying the caller to
the implementation strategy. This tradeoff might be acceptable to
applications that are strongly TopLink-based and/or do not need any
special exception treatment.
A further disadvantage of that DAO style is that TopLink's
standard getActiveSession()
feature just works
within JTA transactions. It does not work with any
other transaction strategy out-of-the-box, in particular not with local
TopLink transactions.
Fortunately, Spring's
TransactionAwareSessionAdapter
exposes a
corresponding proxy for the TopLink ServerSession
which supports TopLink's Session.getActiveSession()
and Session.getActiveUnitOfWork()
methods for any
Spring transaction strategy, returning the current Spring-managed
transactional Session
even with
TopLinkTransactionManager
. Of course, the standard
behavior of that method remains: returning the current
Session
associated with the ongoing JTA
transaction, if any (no matter whether driven by Spring's
JtaTransactionManager
, by EJB CMT, or by plain
JTA).
In summary: DAOs can be implemented based on plain TopLink API,
while still being able to participate in Spring-managed transactions.
This might in particular appeal to people already familiar with TopLink,
feeling more natural to them. However, such DAOs will throw plain
TopLinkException
; conversion to Spring's
DataAccessException
would have to happen
explicitly (if desired).
To execute service operations within transactions, you can use Spring's common declarative transaction facilities. For example:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <bean id="myTxManager" class="org.springframework.orm.toplink.TopLinkTransactionManager"> <property name="sessionFactory" ref="mySessionFactory"/> </bean> <bean id="myProductService" class="product.ProductServiceImpl"> <property name="productDao" ref="myProductDao"/> </bean> <aop:config> <aop:pointcut id="productServiceMethods" expression="execution(* product.ProductService.*(..))"/> <aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/> </aop:config> <tx:advice id="txAdvice" transaction-manager="myTxManager"> <tx:attributes> <tx:method name="increasePrice*" propagation="REQUIRED"/> <tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/> <tx:method name="*" propagation="SUPPORTS" read-only="true"/> </tx:attributes> </tx:advice> </beans>
Note that TopLink requires an active
UnitOfWork
for modifying a persistent
object. (You should never modify objects returned by a plain TopLink
Session
- those are usually read-only
objects, directly taken from the second-level cache!) There is no
concept like a non-transactional flush in TopLink, in contrast to
Hibernate. For this reason, TopLink needs to be set up for a specific
environment: in particular, it needs to be explicitly set up for JTA
synchronization, to detect an active JTA transaction itself and expose a
corresponding active Session
and
UnitOfWork
. This is not necessary for
local transactions as performed by Spring's
TopLinkTransactionManager
, but it is necessary for
participating in JTA transactions (whether driven by Spring's
JtaTransactionManager
or by EJB CMT / plain
JTA).
Within your TopLink-based DAO code, use the
Session.getActiveUnitOfWork()
method to access the
current UnitOfWork
and perform write
operations through it. This will only work within an active transaction
(both within Spring-managed transactions and plain JTA transactions).
For special needs, you can also acquire separate
UnitOfWork
instances that won't
participate in the current transaction; this is hardly needed,
though.
TopLinkTransactionManager
is capable of
exposing a TopLink transaction to JDBC access code that accesses the
same JDBC DataSource
, provided that
TopLink works with JDBC in the backend and is thus able to expose the
underlying JDBC Connection
. The
DataSource
to expose the transactions for
needs to be specified explicitly; it won't be autodetected.
The iBATIS support in the Spring Framework much resembles the JDBC / Hibernate support in that it supports the same template style programming and just as with JDBC or Hibernate, the iBATIS support works with Spring's exception hierarchy and let's you enjoy the all IoC features Spring has.
Transaction management can be handled through Spring's standard
facilities. There are no special transaction strategies for iBATIS, as
there is no special transactional resource involved other than a JDBC
Connection
. Hence, Spring's standard JDBC
DataSourceTransactionManager
or
JtaTransactionManager
are perfectly
sufficient.
![]() | Note |
---|---|
Spring does actually support both iBatis 1.x and 2.x. However, only support for iBatis 2.x is actually shipped with the core Spring distribution. The iBatis 1.x support classes were moved to the Spring Modules project as of Spring 2.0, and you are directed there for documentation. |
If we want to map the previous Account class with iBATIS 2.x we
need to create the following SQL map
'Account.xml'
:
<sqlMap namespace="Account"> <resultMap id="result" class="examples.Account"> <result property="name" column="NAME" columnIndex="1"/> <result property="email" column="EMAIL" columnIndex="2"/> </resultMap> <select id="getAccountByEmail" resultMap="result"> select ACCOUNT.NAME, ACCOUNT.EMAIL from ACCOUNT where ACCOUNT.EMAIL = #value# </select> <insert id="insertAccount"> insert into ACCOUNT (NAME, EMAIL) values (#name#, #email#) </insert> </sqlMap>
The configuration file for iBATIS 2 looks like this:
<sqlMapConfig> <sqlMap resource="example/Account.xml"/> </sqlMapConfig>
Remember that iBATIS loads resources from the class path, so be
sure to add the 'Account.xml'
file to the class
path.
We can use the SqlMapClientFactoryBean
in
the Spring container. Note that with iBATIS SQL Maps 2.x, the JDBC
DataSource
is usually specified on the
SqlMapClientFactoryBean
, which enables lazy
loading.
<beans> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="${jdbc.driverClassName}"/> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </bean> <bean id="sqlMapClient" class="org.springframework.orm.ibatis.SqlMapClientFactoryBean"> <property name="configLocation" value="WEB-INF/sqlmap-config.xml"/> <property name="dataSource" ref="dataSource"/> </bean> </beans>
The SqlMapClientDaoSupport
class offers a
supporting class similar to the SqlMapDaoSupport
.
We extend it to implement our DAO:
public class SqlMapAccountDao extends SqlMapClientDaoSupport implements AccountDao { public Account getAccount(String email) throws DataAccessException { return (Account) getSqlMapClientTemplate().queryForObject("getAccountByEmail", email); } public void insertAccount(Account account) throws DataAccessException { getSqlMapClientTemplate().update("insertAccount", account); } }
In the DAO, we use the pre-configured
SqlMapClientTemplate
to execute the queries,
after setting up the SqlMapAccountDao
in the
application context and wiring it with our
SqlMapClient
instance:
<beans> <bean id="accountDao" class="example.SqlMapAccountDao"> <property name="sqlMapClient" ref="sqlMapClient"/> </bean> </beans>
Note that a SqlMapTemplate
instance could
also be created manually, passing in the SqlMapClient
as constructor argument. The SqlMapClientDaoSupport
base class simply pre-initializes a
SqlMapClientTemplate
instance for us.
The SqlMapClientTemplate
also offers a
generic execute
method, taking a custom
SqlMapClientCallback
implementation as argument. This
can, for example, be used for batching:
public class SqlMapAccountDao extends SqlMapClientDaoSupport implements AccountDao { public void insertAccount(Account account) throws DataAccessException { getSqlMapClientTemplate().execute(new SqlMapClientCallback() { public Object doInSqlMapClient(SqlMapExecutor executor) throws SQLException { executor.startBatch(); executor.update("insertAccount", account); executor.update("insertAddress", account.getAddress()); executor.executeBatch(); } }); } }
In general, any combination of operations offered by the native
SqlMapExecutor
API can be used in such a callback.
Any SQLException
thrown will automatically get
converted to Spring's generic DataAccessException
hierarchy.
DAOs can also be written against plain iBATIS API, without any
Spring dependencies, directly using an injected
SqlMapClient
. A corresponding DAO implementation
looks like as follows:
public class SqlMapAccountDao implements AccountDao { private SqlMapClient sqlMapClient; public void setSqlMapClient(SqlMapClient sqlMapClient) { this.sqlMapClient = sqlMapClient; } public Account getAccount(String email) { try { return (Account) this.sqlMapClient.queryForObject("getAccountByEmail", email); } catch (SQLException ex) { throw new MyDaoException(ex); } } public void insertAccount(Account account) throws DataAccessException { try { this.sqlMapClient.update("insertAccount", account); } catch (SQLException ex) { throw new MyDaoException(ex); } } }
In such a scenario, the SQLException
thrown by
the iBATIS API needs to be handled in a custom fashion: usually,
wrapping it in your own application-specific DAO exception. Wiring in
the application context would still look like before, due to the fact
that the plain iBATIS-based DAO still follows the Dependency Injection
pattern:
<beans> <bean id="accountDao" class="example.SqlMapAccountDao"> <property name="sqlMapClient" ref="sqlMapClient"/> </bean> </beans>
Spring JPA (available under the
org.springframework.orm.jpa
package) offers
comprehensive support for the Java
Persistence API in a similar manner to the integration with
Hibernate or JDO, while being aware of the underlying implementation in
order to provide additional features.
Spring JPA offers three ways of setting up JPA
EntityManagerFactory
:
The LocalEntityManagerFactoryBean
creates
an EntityManagerFactory
suitable for
environments which solely use JPA for data access. The factory bean
will use the JPA PersistenceProvider
autodetection mechanism (according to JPA's Java SE bootstrapping)
and, in most cases, requires only the persistence unit name to be
specified:
<beans> <bean id="myEmf" class="org.springframework.orm.jpa.LocalEntityManagerFactoryBean"> <property name="persistenceUnitName" value="myPersistenceUnit"/> </bean> </beans>
This is the simplest but also most limited form of JPA
deployment. There is no way to link to an existing JDBC
DataSource
and no support for global
transactions, for example. Furthermore, weaving (byte-code
transformation) of persistent classes is provider-specific, often
requiring a specific JVM agent to specified on startup. All in all,
this option is only really sufficient for standalone applications and
test environments (which is exactly what the JPA specification
designed it for).
Only use this option in simple deployment environments like standalone applications and integration tests.
Obtaining an EntityManagerFactory
from JNDI (for example in a Java EE 5 environment), is just a matter
of changing the XML configuration:
<beans> <jee:jndi-lookup id="myEmf" jndi-name="persistence/myPersistenceUnit"/> </beans>
This assumes standard Java EE 5 bootstrapping, with the Java EE
server autodetecting persistence units (i.e.
META-INF/persistence.xml
files in application jars)
and persistence-unit-ref
entries in the Java EE
deployment descriptor (e.g. web.xml
) defining
environment naming context locations for those persistence
units.
In such a scenario, the entire persistence unit deployment,
including the weaving (byte-code transformation) of persistent
classes, is up to the Java EE server. The JDBC
DataSource
is defined through a JNDI
location in the META-INF/persistence.xml
file;
EntityManager transactions are integrated with the server's JTA
subsystem. Spring merely uses the obtained
EntityManagerFactory
, passing it on to
application objects via dependency injection, and managing
transactions for it (typically through
JtaTransactionManager
).
Note that, in case of multiple persistence units used in the
same application, the bean names of such a JNDI-retrieved persistence
units should match the persistence unit names that the application
uses to refer to them (e.g. in @PersistenceUnit
and
@PersistenceContext
annotations).
Use this option when deploying to a Java EE 5 server. Check your server's documentation on how to deploy a custom JPA provider into your server, allowing for a different provider than the server's default.
The
LocalContainerEntityManagerFactoryBean
gives
full control over EntityManagerFactory
configuration and is appropriate for environments where fine-grained
customization is required. The
LocalContainerEntityManagerFactoryBean
will
create a PersistenceUnitInfo
based on
the persistence.xml
file, the supplied
dataSourceLookup
strategy and the specified
loadTimeWeaver
. It is thus possible to work with
custom DataSources outside of JNDI and to control the weaving
process.
<beans> <bean id="myEmf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> <property name="dataSource" ref="someDataSource"/> <property name="loadTimeWeaver"> <bean class="org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver"/> </property> </bean> </beans>
A typical persistence.xml
file looks as follows:
<persistence xmlns="http://java.sun.com/xml/ns/persistence" version="1.0"> <persistence-unit name="myUnit" transaction-type="RESOURCE_LOCAL"> <mapping-file>META-INF/orm.xml</mapping-file> <exclude-unlisted-classes/> </persistence-unit> </persistence>
NOTE: The "exclude-unlisted-classes" element always
indicates that NO scanning for annotated entity classes is supposed
to happen, in order to support the
<exclude-unlisted-classes/>
shortcut.
This is in line with the JPA specification (which suggests that shortcut)
but unfortunately in conflict with the JPA XSD (which implies "false"
for that shortcut). As a consequence,
"<exclude-unlisted-classes> false </exclude-unlisted-classes/>
"
is not supported! Simply omit the "exclude-unlisted-classes" element if
you would like entity class scanning to actually happen.
This is the most powerful JPA setup option, allowing for
flexible local configuration within the application. It supports links
to an existing JDBC DataSource
,
supports both local and global transactions, etc. However, it also
imposes requirements onto the runtime environment, such as the
availability of a weaving-capable ClassLoader if the persistence
provider demands byte-code transformation.
Note that this option may conflict with the built-in JPA
capabilities of a Java EE 5 server. So when running in a full Java EE
5 environment, consider obtaining your
EntityManagerFactory
from JNDI.
Alternatively, specify a custom "persistenceXmlLocation" on your
LocalContainerEntityManagerFactoryBean
definition, e.g. "META-INF/my-persistence.xml", and only include a
descriptor with that name in your application jar files. Since the
Java EE 5 server will only look for default
META-INF/persistence.xml
files, it will ignore such
custom persistence units and hence avoid conflicts with a
Spring-driven JPA setup upfront. (This applies to Resin 3.1, for
example.)
Use this option for full JPA capabilities in a Spring-based application environment. This includes web containers such as Tomcat as well as standalone applications and integration tests with sophisticated persistence requirements.
The LoadTimeWeaver
interface is a
Spring-provided class that allows JPA
ClassTransformer
instances to be
plugged in a specific manner depending on the environment (web
container/application server). Hooking
ClassTransformers
through a Java 5 agent
is typically not efficient - the agents work against the
entire virtual machine and inspect
every class that is loaded - something that is
typically undesirable in a production server enviroment.
Spring provides a number of
LoadTimeWeaver
implementations for
various environments, allowing
ClassTransformer
instances to be
applied only per ClassLoader and not per VM.
The following sections will discuss typical JPA weaving setup on Tomcat as well as using Spring's VM agent. See the AOP chapter section entitled Section 6.8.4.5, “Spring configuration” for details on how to set up general load-time weaving, covering Tomcat and the VM agent as well as WebLogic, OC4J, GlassFish and Resin.
Apache
Tomcat's default ClassLoader does not support class
transformation but allows custom ClassLoaders to be used. Spring
offers the TomcatInstrumentableClassLoader
(inside the
org.springframework.instrument.classloading.tomcat
package) which extends the Tomcat ClassLoader
(WebappClassLoader
) and allows JPA
ClassTransformer
instances to 'enhance' all
classes loaded by it. In short, JPA transformers will be applied
only inside a specific web application (which uses the
TomcatInstrumentableClassLoader
).
In order to use the custom ClassLoader on:
Copy spring-tomcat-weaver.jar
into
$CATALINA_HOME/server/lib (where
$CATALINA_HOME represents the root of the
Tomcat installation).
Instruct Tomcat to use the custom ClassLoader (instead of the default one) by editing the web application context file:
<Context path="/myWebApp" docBase="/my/webApp/location"> <Loader loaderClass="org.springframework.instrument.classloading.tomcat.TomcatInstrumentableClassLoader"/> </Context>
Tomcat 5.0.x and 5.5.x series support several context locations: server configuration file ($CATALINA_HOME/conf/server.xml), the default context configuration ($CATALINA_HOME/conf/context.xml) that affects all deployed web applications and per-webapp configurations, deployed on the server ($CATALINA_HOME/conf/[enginename]/[hostname]/my-webapp-context.xml) side or along with the webapp (your-webapp.war/META-INF/context.xml). For efficiency, inside the web-app configuration style is recommended since only applications which use JPA will use the custom ClassLoader. See the Tomcat 5.x documentation for more details about available context locations.
Note that versions prior to 5.5.20 contained a bug in
the XML configuration parsing preventing usage of
Loader
tag inside
server.xml (no matter if a ClassLoader is
specified or not (be it the official or a custom one). See
Tomcat's bugzilla for more
details.
If you are using Tomcat 5.5.20+ you can set
useSystemClassLoaderAsParent to
false
to fix the problem:
<Context path="/myWebApp" docBase="/my/webApp/location"> <Loader loaderClass="org.springframework.instrument.classloading.tomcat.TomcatInstrumentableClassLoader" useSystemClassLoaderAsParent="false"/> </Context>
Copy spring-tomcat-weaver.jar
into
$CATALINA_HOME/lib (where
$CATALINA_HOME represents the root of the
Tomcat installation).
Instruct Tomcat to use the custom ClassLoader (instead of the default one) by editing the web application context file:
<Context path="/myWebApp" docBase="/my/webApp/location"> <Loader loaderClass="org.springframework.instrument.classloading.tomcat.TomcatInstrumentableClassLoader"/> </Context>
Tomcat 6.0.x (similar to 5.0.x/5.5.x) series support several context locations: server configuration file ($CATALINA_HOME/conf/server.xml), the default context configuration ($CATALINA_HOME/conf/context.xml) that affects all deployed web applications and per-webapp configurations, deployed on the server ($CATALINA_HOME/conf/[enginename]/[hostname]/my-webapp-context.xml) side or along with the webapp (your-webapp.war/META-INF/context.xml). For efficiency, inside the web-app configuration style is recommended since only applications which use JPA will use the custom ClassLoader. See the Tomcat 5.x documentation for more details about available context locations.
Tomcat 5.0.x/5.5.x
Tomcat 6.0.x
The last step required on all Tomcat versions, is to use the
appropriate the LoadTimeWeaver
when
configuring
LocalContainerEntityManagerFactoryBean
:
<bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> <property name="loadTimeWeaver"> <bean class="org.springframework.instrument.classloading.ReflectiveLoadTimeWeaver"/> </property> </bean>
Using this technique, JPA applications relying on instrumentation, can run in Tomcat without the need of an agent. This is important especially when hosting applications which rely on different JPA implementations since the JPA transformers are applied only at ClassLoader level and thus, are isolated from each other.
![]() | Note |
---|---|
If TopLink is being used a JPA provider under Tomcat, please place the toplink-essentials jar under $CATALINA_HOME/shared/lib folder instead of your war. |
For environments where class instrumentation is required but
are not supported by the existing LoadTimeWeaver implementations, a
JDK agent can be the only solution. For such cases, Spring provides
InstrumentationLoadTimeWeaver
which requires
a Spring-specific (but very general) VM agent (spring-agent.jar
):
<bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> <property name="loadTimeWeaver"> <bean class="org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver"/> </property> </bean>
Note that the virtual machine has to be started with the Spring agent, by supplying the following JVM options:
-javaagent:/path/to/spring-agent.jar
Since Spring 2.5, a context-wide LoadTimeWeaver
can be configured using the context:load-time-weaver
configuration
element. Such a 'global' weaver will be picked up by all JPA
LocalContainerEntityManagerFactoryBeans
automatically.
This is the preferred way of setting up a load-time weaver, delivering autodetection of the platform (WebLogic, OC4J, GlassFish, Tomcat, Resin, VM agent) as well as automatic propagation of the weaver to all weaver-aware beans.
<context:load-time-weaver/> <bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> ... </bean>
See the section entitled Section 6.8.4.5, “Spring configuration” for details on how to set up general load-time weaving, covering Tomcat and the VM agent as well as WebLogic, OC4J, GlassFish and Resin.
For applications that rely on multiple persistence units
locations (stored in various jars in the classpath for example),
Spring offers the
PersistenceUnitManager
to act as a
central repository and avoid the (potentially expensive) persistence
units discovery process. The default implementation allows multiple
locations to be specified (by default, the classpath is searched for
'META-INF/persistence.xml'
files) which are
parsed and later on retrieved through the persistence unit
name:
<bean id="pum" class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager">
<property name="persistenceXmlLocation">
<list>
<value>org/springframework/orm/jpa/domain/persistence-multi.xml</value>
<value>classpath:/my/package/**/custom-persistence.xml</value>
<value>classpath*:META-INF/persistence.xml</value>
</list>
</property>
<property name="dataSources">
<map>
<entry key="localDataSource" value-ref="local-db"/>
<entry key="remoteDataSource" value-ref="remote-db"/>
</map>
</property>
<!-- if no datasource is specified, use this one -->
<property name="defaultDataSource" ref="remoteDataSource"/>
</bean>
<bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="persistenceUnitManager" ref="pum"/>
</bean>
Note that the default implementation allows customization of the
persistence unit infos before feeding them to the JPA provider
declaratively through its properties (which affect all
hosted units) or programmatically, through the
PersistenceUnitPostProcessor
(which allows persistence unit selection). If no
PersistenceUnitManager
is
specified, one will be created and used internally by
LocalContainerEntityManagerFactoryBean
.
Each JPA-based DAO will then receive a
EntityManagerFactory
via dependency
injection. Such a DAO can be coded against plain JPA and work with the
given EntityManagerFactory
or through
Spring's JpaTemplate
:
<beans> <bean id="myProductDao" class="product.ProductDaoImpl"> <property name="entityManagerFactory" ref="myEmf"/> </bean> </beans>
public class JpaProductDao implements ProductDao {
private JpaTemplate jpaTemplate;
public void setEntityManagerFactory(EntityManagerFactory emf) {
this.jpaTemplate = new JpaTemplate(emf);
}
public Collection loadProductsByCategory(final String category) throws DataAccessException {
return (Collection) this.jpaTemplate.execute(new JpaCallback() {
public Object doInJpa(EntityManager em) throws PersistenceException {
Query query = em.createQuery("from Product as p where p.category = :category");
query.setParameter("category", category);
List result = query.getResultList();
// do some further processing with the result list
return result;
}
});
}
}
The JpaCallback
implementation
allows any type of JPA data access. The
JpaTemplate
will ensure that
EntityManager
s are properly opened and
closed and automatically participate in transactions. Moreover, the
JpaTemplate
properly handles exceptions, making
sure resources are cleaned up and the appropriate transactions rolled
back. The template instances are thread-safe and reusable and they can
be kept as instance variable of the enclosing class. Note that
JpaTemplate
offers single-step actions such as
find, load, merge, etc along with alternative convenience methods that
can replace one line callback implementations.
Furthermore, Spring provides a convenient
JpaDaoSupport
base class that provides the
get/setEntityManagerFactory
and
getJpaTemplate()
to be used by
subclasses:
public class ProductDaoImpl extends JpaDaoSupport implements ProductDao { public Collection loadProductsByCategory(String category) throws DataAccessException { Map<String, String> params = new HashMap<String, String>(); params.put("category", category); return getJpaTemplate().findByNamedParams("from Product as p where p.category = :category", params); } }
Besides working with Spring's JpaTemplate
,
one can also code Spring-based DAOs against the JPA, doing one's own
explicit EntityManager
handling. As also
elaborated in the corresponding Hibernate section, the main advantage of
this approach is that your data access code is able to throw checked
exceptions. JpaDaoSupport
offers a variety of
support methods for this scenario, for retrieving and releasing a
transaction EntityManager
, as well as for
converting exceptions.
JpaTemplate mainly exists as a sibling of JdoTemplate
and HibernateTemplate, offering the same style for people used to it.
For newly started projects, consider adopting the native JPA style of
coding data access objects instead, based on a "shared EntityManager"
reference obtained through the JPA
@PersistenceContext
annotation (using Spring's
PersistenceAnnotationBeanPostProcessor
; see below
for details.)
![]() | Note |
---|---|
While |
It is possible to write code against the plain JPA without using
any Spring dependencies, using an injected
EntityManagerFactory
or
EntityManager
. Note that Spring can
understand @PersistenceUnit
and
@PersistenceContext
annotations both at
field and method level if a
PersistenceAnnotationBeanPostProcessor
is
enabled. A corresponding DAO implementation might look like this:
public class ProductDaoImpl implements ProductDao { private EntityManagerFactory emf; @PersistenceUnit public void setEntityManagerFactory(EntityManagerFactory emf) { this.emf = emf; } public Collection loadProductsByCategory(String category) { EntityManager em = this.emf.createEntityManager(); try { Query query = em.createQuery("from Product as p where p.category = ?1"); query.setParameter(1, category); return query.getResultList(); } finally { if (em != null) { em.close(); } } } }
The DAO above has no dependency on Spring and still fits nicely
into a Spring application context, just like it would if coded against
Spring's JpaTemplate
. Moreover, the DAO takes
advantage of annotations to require the injection of the default
EntityManagerFactory
:
<beans>
<!-- bean post-processor for JPA annotations -->
<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor"/>
<bean id="myProductDao" class="product.ProductDaoImpl"/>
</beans>
Note: As alternative to defining a
PersistenceAnnotationBeanPostProcessor
explicitly, consider using Spring 2.5's
context:annotation-config
XML element in your
application context configuration. This will automatically register all
of Spring's standard post-processors for annotation-based configuration
(including CommonAnnotationBeanPostProcessor
etc).
<beans>
<!-- post-processors for all standard config annotations -->
<context:annotation-config/>
<bean id="myProductDao" class="product.ProductDaoImpl"/>
</beans>
The main issue with such a DAO is that it always creates a new
EntityManager
via the factory. This can
be easily overcome by requesting a transactional
EntityManager
(also called "shared
EntityManager", since it is a shared, thread-safe proxy for the actual
transactional EntityManager) to be injected instead of the
factory:
public class ProductDaoImpl implements ProductDao { @PersistenceContext private EntityManager em; public Collection loadProductsByCategory(String category) { Query query = em.createQuery("from Product as p where p.category = :category"); query.setParameter("category", category); return query.getResultList(); } }
Note that the @PersistenceContext
annotation
has an optional attribute type
, which defaults to
PersistenceContextType.TRANSACTION
. This default is
what you need to receive a "shared EntityManager" proxy. The
alternative, PersistenceContextType.EXTENDED
, is a
completely different affair: This results in a so-called "extended
EntityManager", which is not thread-safe and hence
must not be used in a concurrently accessed component such as a
Spring-managed singleton bean. Extended EntityManagers are only supposed
to be used in stateful components that, for example, reside in a
session, with the lifecycle of the EntityManager not tied to a current
transaction but rather being completely up to the application.
The injected EntityManager
is
Spring-managed (aware of the ongoing transaction). It is important to
note that even though the new implementation prefers method level
injection (of an EntityManager
instead of
an EntityManagerFactory)
, no change is
required in the application context XML due to annotation usage.
The main advantage of this DAO style is that it depends on Java Persistence API; no import of any Spring class is required. Moreover, as the JPA annotations are understood, the injections are applied automatically by the Spring container. This is of course appealing from a non-invasiveness perspective, and might feel more natural to JPA developers.
However, the DAO throws the plain
PersistenceException
exception class (which is
unchecked, and so does not have to be declared or caught) but also
IllegalArgumentException
and
IllegalStateException
, which means that callers
can only treat exceptions as generally fatal - unless they want to
depend on JPA's own exception structure. Catching specific causes such
as an optimistic locking failure is not possible without tying the
caller to the implementation strategy. This tradeoff might be acceptable
to applications that are strongly JPA-based and/or do not need any
special exception treatment. However, Spring offers a solution allowing
exception translation to be applied transparently through the
@Repository
annotation:
@Repository
public class ProductDaoImpl implements ProductDao {
// class body here...
}
<beans>
<!-- Exception
translation bean post processor -->
<bean class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor"/>
<bean id="myProductDao" class="product.ProductDaoImpl"/>
</beans>
The postprocessor will automatically look for all exception
translators (implementations of the
PersistenceExceptionTranslator
interface)
and advise all beans marked with the
@Repository
annotation so that the
discovered translators can intercept and apply the appropriate
translation on the thrown exceptions.
In summary: DAOs can be implemented based on the plain Java Persistence API and annotations, while still being able to benefit from Spring-managed transactions, dependency injection, and transparent exception conversion (if desired) to Spring's custom exception hierarchies.
To execute service operations within transactions, you can use Spring's common declarative transaction facilities. For example:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <bean id="myTxManager" class="org.springframework.orm.jpa.JpaTransactionManager"> <property name="entityManagerFactory" ref="myEmf"/> </bean> <bean id="myProductService" class="product.ProductServiceImpl"> <property name="productDao" ref="myProductDao"/> </bean> <aop:config> <aop:pointcut id="productServiceMethods" expression="execution(* product.ProductService.*(..))"/> <aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/> </aop:config> <tx:advice id="txAdvice" transaction-manager="myTxManager"> <tx:attributes> <tx:method name="increasePrice*" propagation="REQUIRED"/> <tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/> <tx:method name="*" propagation="SUPPORTS" read-only="true"/> </tx:attributes> </tx:advice> </beans>
Spring JPA allows a configured
JpaTransactionManager
to expose a JPA transaction
to JDBC access code that accesses the same JDBC
DataSource
, provided that the registered
JpaDialect
supports retrieval of the
underlying JDBC Connection
. Out of the box,
Spring provides dialects for the Toplink, Hibernate and OpenJPA JPA
implementations. See the next section for details on the
JpaDialect
mechanism.
As an advanced feature JpaTemplate
,
JpaTransactionManager
and subclasses of
AbstractEntityManagerFactoryBean
support a custom
JpaDialect
, to be passed into the
"jpaDialect" bean property. In such a scenario, the DAOs won't receive an
EntityManagerFactory
reference but rather a
full JpaTemplate
instance instead (for example,
passed into JpaDaoSupport
's "jpaTemplate"
property). A JpaDialect
implementation can
enable some advanced features supported by Spring, usually in a
vendor-specific manner:
applying specific transaction semantics (such as custom isolation level or transaction timeout)
retrieving the transactional JDBC
Connection
(for exposure to JDBC-based
DAOs)
advanced translation of PersistenceExceptions
to Spring DataAccessExceptions
This is particularly valuable for special transaction semantics and
for advanced translation of exception. Note that the default
implementation used (DefaultJpaDialect
) doesn't
provide any special capabilities and if the above features are required,
the appropriate dialect has to be specified.
See the JpaDialect
Javadoc for more
details of its operations and how they are used within Spring's JPA
support.
This part of the reference documentation covers the Spring Framework's support for the presentation tier (and specifically web-based presentation tiers).
The Spring Framework's own web framework, Spring Web MVC, is covered in the first couple of chapters. A number of the remaining chapters in this part of the reference documentation are concerned with the Spring Framework's integration with other web technologies, such as Struts and JSF (to name but two).
This section concludes with coverage of Spring's MVC portlet framework.
Spring's Web MVC framework is designed around a
DispatcherServlet
that dispatches requests to
handlers, with configurable handler mappings, view resolution, locale and
theme resolution as well as support for upload files. The default handler
is a very simple Controller
interface, just
offering a ModelAndView handleRequest(request,response)
method. This can already be used for application controllers, but you will
prefer the included implementation hierarchy, consisting of, for example
AbstractController
,
AbstractCommandController
and
SimpleFormController
. Application controllers will
typically be subclasses of those. Note that you can choose an appropriate
base class: if you don't have a form, you don't need a form controller.
This is a major difference to Struts.
![]() | Tip |
---|---|
Since Spring 2.5, an annotated controller style is available
for Java 5+ users. This is a compelling alternative to implementing
traditional |
Spring Web MVC allows you to use any object as a command or form
object - there is no need to implement a framework-specific interface or
base class. Spring's data binding is highly flexible: for example, it
treats type mismatches as validation errors that can be evaluated by the
application, not as system errors. All this means that you don't need to
duplicate your business objects' properties as simple, untyped strings in
your form objects just to be able to handle invalid submissions, or to
convert the Strings properly. Instead, it is often preferable to bind
directly to your business objects. This is another major difference to
Struts which is built around required base classes such as
Action
and
ActionForm
.
Compared to WebWork, Spring has more differentiated object roles. It
supports the notion of a Controller
, an
optional command or form object, and a model that gets passed to the view.
The model will normally include the command or form object but also
arbitrary reference data; instead, a WebWork
Action
combines all those roles into one
single object. WebWork does allow you to use existing business objects as
part of your form, but only by making them bean properties of the
respective Action
class. Finally, the same
Action
instance that handles the request is
used for evaluation and form population in the view. Thus, reference data
needs to be modeled as bean properties of the
Action
too. These are (arguably) too many
roles for one object.
Spring's view resolution is extremely flexible. A
Controller
implementation can even write a
view directly to the response (by returning null
for
the ModelAndView
). In the normal case, a
ModelAndView
instance consists of a view name and a
model Map
, which contains bean names and
corresponding objects (like a command or form, containing reference data).
View name resolution is highly configurable, either via bean names, via a
properties file, or via your own
ViewResolver
implementation. The fact that
the model (the M in MVC) is based on the
Map
interface allows for the complete
abstraction of the view technology. Any renderer can be integrated
directly, whether JSP, Velocity, or any other rendering technology. The
model Map
is simply transformed into an
appropriate format, such as JSP request attributes or a Velocity template
model.
There are several reasons why some projects will prefer to use other MVC implementations. Many teams expect to leverage their existing investment in skills and tools. In addition, there is a large body of knowledge and experience available for the Struts framework. Thus, if you can live with Struts' architectural flaws, it can still be a viable choice for the web layer; the same applies to WebWork and other web MVC frameworks.
If you don't want to use Spring's web MVC, but intend to leverage
other solutions that Spring offers, you can integrate the web MVC
framework of your choice with Spring easily. Simply start up a Spring
root application context via its
ContextLoaderListener
, and access it via its
ServletContext
attribute (or Spring's
respective helper method) from within a Struts or WebWork action. Note
that there aren't any "plug-ins" involved, so no dedicated integration
is necessary. From the web layer's point of view, you'll simply use
Spring as a library, with the root application context instance as the
entry point.
All your registered beans and all of Spring's services can be at your fingertips even without Spring's Web MVC. Spring doesn't compete with Struts or WebWork in this scenario, it just addresses the many areas that the pure web MVC frameworks don't, from bean configuration to data access and transaction handling. So you are able to enrich your application with a Spring middle tier and/or data access tier, even if you just want to use, for example, the transaction abstraction with JDBC or Hibernate.
Spring's web module provides a wealth of unique web support features, including:
Clear separation of roles - controller, validator, command
object, form object, model object,
DispatcherServlet
, handler mapping, view
resolver, etc. Each role can be fulfilled by a specialized
object.
Powerful and straightforward configuration of both framework and application classes as JavaBeans, including easy referencing across contexts, such as from web controllers to business objects and validators.
Adaptability, non-intrusiveness. Use whatever controller subclass you need (plain, command, form, wizard, multi-action, or a custom one) for a given scenario instead of deriving from a single controller for everything.
Reusable business code - no need for duplication. You can use existing business objects as command or form objects instead of mirroring them in order to extend a particular framework base class.
Customizable binding and validation - type mismatches as application-level validation errors that keep the offending value, localized date and number binding, etc instead of String-only form objects with manual parsing and conversion to business objects.
Customizable handler mapping and view resolution - handler mapping and view resolution strategies range from simple URL-based configuration, to sophisticated, purpose-built resolution strategies. This is more flexible than some web MVC frameworks which mandate a particular technique.
Flexible model transfer - model transfer via a name/value
Map
supports easy integration with
any view technology.
Customizable locale and theme resolution, support for JSPs with or without Spring tag library, support for JSTL, support for Velocity without the need for extra bridges, etc.
A simple yet powerful JSP tag library known as the Spring tag library that provides support for features such as data binding and themes. The custom tags allow for maximum flexibility in terms of markup code. For information on the tag library descriptor, see the appendix entitled Appendix D, spring.tld
A JSP form tag library, introduced in Spring 2.0, that makes writing forms in JSP pages much easier. For information on the tag library descriptor, see the appendix entitled Appendix E, spring-form.tld
Beans whose lifecycle is scoped to the current HTTP request or
HTTP Session
. This is not a specific
feature of Spring MVC itself, but rather of the
WebApplicationContext
container(s)
that Spring MVC uses. These bean scopes are described in detail in
the section entitled Section 3.4.4, “The other scopes”
Spring's web MVC framework is, like many other web MVC frameworks,
request-driven, designed around a central servlet that dispatches requests
to controllers and offers other functionality facilitating the development
of web applications. Spring's DispatcherServlet
however, does more than just that. It is completely integrated with the
Spring IoC container and as such allows you to use every other feature
that Spring has.
The request processing workflow of the Spring Web MVC
DispatcherServlet
is illustrated in the following
diagram. The pattern-savvy reader will recognize that the
DispatcherServlet
is an expression of the
“Front Controller” design pattern (this is a pattern that
Spring Web MVC shares with many other leading web frameworks).
The requesting processing workflow in Spring Web MVC (high level)
The DispatcherServlet
is
an actual Servlet
(it inherits from the
HttpServlet
base class), and as such is declared in
the web.xml
of your web application. Requests that you
want the DispatcherServlet
to handle will have to
be mapped using a URL mapping in the same web.xml
file.
This is standard J2EE servlet configuration; an example of such a
DispatcherServlet
declaration and mapping can be
found below.
<web-app> <servlet> <servlet-name>example</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>example</servlet-name> <url-pattern>*.form</url-pattern> </servlet-mapping> </web-app>
In the example above, all requests ending with
.form
will be handled by the
'example'
DispatcherServlet
.
This is only the first step in setting up Spring Web MVC... the various
beans used by the Spring Web MVC framework (over and above the
DispatcherServlet
itself) now need to be
configured.
As detailed in the section entitled Section 3.8, “The ApplicationContext
”,
ApplicationContext
instances in Spring can
be scoped. In the web MVC framework, each
DispatcherServlet
has its own
WebApplicationContext
, which inherits all
the beans already defined in the root
WebApplicationContext
. These inherited
beans defined can be overridden in the servlet-specific scope, and new
scope-specific beans can be defined local to a given servlet
instance.
Context hierarchy in Spring Web MVC
The framework will, on initialization of a
DispatcherServlet
, look for a file named
[servlet-name]-servlet.xml
in the
WEB-INF
directory of your web application and create
the beans defined there (overriding the definitions of any beans defined
with the same name in the global scope).
Consider the following DispatcherServlet
servlet configuration (in the 'web.xml'
file.)
<web-app> <servlet> <servlet-name>golfing</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>golfing</servlet-name> <url-pattern>*.do</url-pattern> </servlet-mapping> </web-app>
With the above servlet configuration in place, you will need to have
a file called '/WEB-INF/golfing-servlet.xml'
in your application;
this file will contain all of your Spring Web
MVC-specific components (beans). The exact location of this
configuration file can be changed via a servlet initialization parameter
(see below for details).
The WebApplicationContext
is an
extension of the plain ApplicationContext
that has some extra features necessary for web applications. It differs
from a normal ApplicationContext
in that it
is capable of resolving themes (see Section 13.7, “Using themes”),
and that it knows which servlet it is associated with (by having a link to
the ServletContext
). The
WebApplicationContext
is bound in the
ServletContext
, and by using static methods
on the RequestContextUtils
class you can always
lookup the WebApplicationContext
in case
you need access to it.
The Spring DispatcherServlet
has a couple of
special beans it uses in order to be able to process requests and render
the appropriate views. These beans are included in the Spring framework
and can be configured in the
WebApplicationContext
, just as any other
bean would be configured. Each of those beans is described in more detail
below. Right now, we'll just mention them, just to let you know they exist
and to enable us to go on talking about the
DispatcherServlet
. For most of the beans, sensible
defaults are provided so you don't (initially) have to worry about
configuring them.
Table 13.1. Special beans in the
WebApplicationContext
Bean type | Explanation |
---|---|
Controllers | Controllers are the
components that form the 'C' part of the
MVC. |
Handler mappings | Handler mappings handle the execution of a list of pre- and post-processors and controllers that will be executed if they match certain criteria (for instance a matching URL specified with the controller) |
View resolvers | View resolvers are components capable of resolving view names to views |
Locale resolver | A locale resolver is a component capable of resolving the locale a client is using, in order to be able to offer internationalized views |
Theme resolver | A theme resolver is capable of resolving themes your web application can use, for example, to offer personalized layouts |
multipart file resolver | A multipart file resolver offers the functionality to process file uploads from HTML forms |
Handler exception resolver(s) | Handler exception resolvers offer functionality to map exceptions to views or implement other more complex exception handling code |
When a DispatcherServlet
is set up for use
and a request comes in for that specific
DispatcherServlet
, said
DispatcherServlet
starts processing the request.
The list below describes the complete process a request goes through when
handled by a DispatcherServlet
:
The WebApplicationContext
is
searched for and bound in the request as an attribute in order for the
controller and other elements in the process to use. It is bound by
default under the key
DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE
.
The locale resolver is bound to the request to let elements in the process resolve the locale to use when processing the request (rendering the view, preparing data, etc.) If you don't use the resolver, it won't affect anything, so if you don't need locale resolving, you don't have to use it.
The theme resolver is bound to the request to let elements such as views determine which theme to use. The theme resolver does not affect anything if you don't use it, so if you don't need themes you can just ignore it.
If a multipart resolver is specified, the request is inspected
for multiparts; if multiparts are found, the request is wrapped in a
MultipartHttpServletRequest
for further
processing by other elements in the process. (See the section entitled
Section 13.8.2, “Using the
MultipartResolver
” for further information
about multipart handling).
An appropriate handler is searched for. If a handler is found, the execution chain associated with the handler (preprocessors, postprocessors, and controllers) will be executed in order to prepare a model (for rendering).
If a model is returned, the view is rendered. If no model is returned (which could be due to a pre- or postprocessor intercepting the request, for example, for security reasons), no view is rendered, since the request could already have been fulfilled.
Exceptions that are thrown during processing of the request get
picked up by any of the handler exception resolvers that are declared in
the WebApplicationContext
. Using these
exception resolvers allows you to define custom behaviors in case such
exceptions get thrown.
The Spring DispatcherServlet
also has support
for returning the last-modification-date, as
specified by the Servlet API. The process of determining the last
modification date for a specific request is straightforward: the
DispatcherServlet
will first lookup an appropriate
handler mapping and test if the handler that is found implements
the interface LastModified
interface. If so, the value of the long
getLastModified(request)
method of the
LastModified
interface is returned to the
client.
You can customize Spring's DispatcherServlet
by adding context parameters in the web.xml
file or
servlet initialization parameters. The possibilities are listed
below.
Table 13.2. DispatcherServlet
initialization
parameters
Parameter | Explanation |
---|---|
contextClass | Class that implements
WebApplicationContext , which will
be used to instantiate the context used by this servlet. If this
parameter isn't specified, the
XmlWebApplicationContext will be
used. |
contextConfigLocation | String which is passed to the context instance (specified
by contextClass ) to indicate where context(s)
can be found. The string is potentially split up into multiple
strings (using a comma as a delimiter) to support multiple
contexts (in case of multiple context locations, of beans that are
defined twice, the latest takes precedence). |
namespace | the namespace of the
WebApplicationContext . Defaults to
[servlet-name]-servlet . |
The notion of a controller is part of the MVC design pattern (more specifically, it is the 'C' in MVC). Controllers provide access to the application behavior which is typically defined by a service interface. Controllers interpret user input and transform such input into a sensible model which will be represented to the user by the view. Spring has implemented the notion of a controller in a very abstract way enabling a wide variety of different kinds of controllers to be created. Spring contains form-specific controllers, command-based controllers, and controllers that execute wizard-style logic, to name but a few.
Spring's basis for the controller architecture is the
org.springframework.web.servlet.mvc.Controller
interface, the source code for which is listed below.
public interface Controller { /** * Process the request and return a ModelAndView object which the DispatcherServlet * will render. */ ModelAndView handleRequest( HttpServletRequest request, HttpServletResponse response) throws Exception; }
As you can see, the Controller
interface defines a single method that is responsible for handling a
request and returning an appropriate model and view. These three concepts
are the basis for the Spring MVC implementation -
ModelAndView
and
Controller
. While the
Controller
interface is quite abstract,
Spring offers a lot of Controller
implementations out of the box that already contain a lot of the
functionality you might need. The
Controller
interface just defines the most
basic responsibility required of every controller; namely handling a
request and returning a model and a view.
To provide a basic infrastructure, all of Spring's various
Controller
inherit from
AbstractController
, a class offering caching
support and, for example, the setting of the mimetype.
Table 13.3. Features offered by the
AbstractController
Feature | Explanation |
---|---|
supportedMethods | indicates what methods this controller should accept.
Usually this is set to both GET and
POST , but you can modify this to reflect the
method you want to support. If a request is received with a
method that is not supported by the controller, the client will
be informed of this (expedited by the throwing of a
ServletException ). |
requireSession | indicates whether or not this controller requires a HTTP
session to do its work. If a session is not present when such a
controller receives a request, the user is informed of this by a
ServletException being thrown. |
synchronizeOnSession | use this if you want handling by this controller to be synchronized on the user's HTTP session. |
cacheSeconds | when you want a controller to generate a caching directive in the HTTP response, specify a positive integer here. By default the value of this property is set to -1 so no caching directives will be included in the generated response. |
useExpiresHeader | tweaks your controllers to specify the HTTP 1.0
compatible "Expires" header in the
generated response. By default the value of this property is
true . |
useCacheHeader | tweaks your controllers to specify the HTTP 1.1
compatible "Cache-Control" header in the
generated response. By default the value of this property is
true . |
When using the AbstractController
as the
baseclass for your controllers you only have to override the
handleRequestInternal(HttpServletRequest,
HttpServletResponse)
method, implement your logic, and return
a ModelAndView
object. Here is short example
consisting of a class and a declaration in the web application
context.
package samples; public class SampleController extends AbstractController { public ModelAndView handleRequestInternal( HttpServletRequest request, HttpServletResponse response) throws Exception { ModelAndView mav = new ModelAndView("hello"); mav.addObject("message", "Hello World!"); return mav; } }
<bean id="sampleController" class="samples.SampleController"> <property name="cacheSeconds" value="120"/> </bean>
The above class and the declaration in the web application context is all you need besides setting up a handler mapping (see the section entitled Section 13.4, “Handler mappings”) to get this very simple controller working. This controller will generate caching directives telling the client to cache things for 2 minutes before rechecking. This controller also returns a hard-coded view (which is typically considered bad practice).
Although you can extend AbstractController
,
Spring provides a number of concrete implementations which offer
functionality that is commonly used in simple MVC applications. The
ParameterizableViewController
is basically the
same as the example above, except for the fact that you can specify the
view name that it will return in the web application context (and thus
remove the need to hard-code the viewname in the Java class).
The UrlFilenameViewController
inspects the
URL and retrieves the filename of the file request and uses that as a
viewname. For example, the filename of
http://www.springframework.org/index.html
request is
index
.
Spring offers a MultiActionController
class
that supports the aggregation of multiple request-handling methods into
one controller, which then allows you to group related functionality
together. (If you are a Struts veteran you might recognize the
similarity between the Struts DispatchAction
and
the Spring MVC MultiActionController
.) The
MultiActionController
class is defined in a
distinct package -
org.springframework.web.servlet.mvc.multiaction
- and
it is capable of mapping requests to method names and then invoking the
correct method to handle a particular request. Using the
MultiActionController
is especially handy when
you have a lot of related functionality that would perhaps be nice to
define all in a single class without having to implement one
Controller
for each bit of functionality.
The MultiActionController
typically is not
appropriate for capturing very complex request-handling logic or use
cases that address totally-different areas of functionality, and you are
encouraged to stick with the standard 'one
piece-of-functionality maps to one
Controller
' for such
cases.
There are two usage-styles for the
MultiActionController
. Either you subclass the
MultiActionController
and specify the methods
that will be resolved by the
MethodNameResolver
on your subclass, or
you define a delegate object, on which methods resolved by the
MethodNameResolver
will be invoked. If
you choose the former style, you do not need to set a delegate, but for
the latter style, you will need to inject your delegate object into the
MultiActionController
as a collaborator (either
as a single constructor argument or via the
'setDelegate
' method).
The MultiActionController
needs some
strategy to determine which method to invoke when handling an incoming
request: this strategy is defined by the
MethodNameResolver
interface. The
MultiActionController
class exposes the
'methodNameResolver
' property so that you can inject
a MethodNameResolver
that is capable of
doing that. The methods that you define on a
MultiActionController
(or on the class of the
injected delegate object) must conform to the following
signature:
// 'anyMeaningfulName
' can be replaced by any method name
public [ModelAndView | Map | void] anyMeaningfulName(HttpServletRequest, HttpServletResponse [,HttpSession] [,AnyObject])
The full details of this method signature are covered in the
class-level
Javadoc of the MultiActionController
source itself. If you are planning to use the
MultiActionController
, you are highly encouraged
to consult that Javadoc. However, below you will find some basic
examples of valid MultiActionController
method
signatures.
The standard signature (mirrors the
Controller
interface method).
public ModelAndView displayCatalog(HttpServletRequest, HttpServletResponse)
This signature accepts a Login
argument
that will be populated (bound) with parameters retrieved from the
request.
public ModelAndView login(HttpServletRequest, HttpServletResponse, Login)
This signature requires that the request already have a valid session.
public ModelAndView viewCart(HttpServletRequest, HttpServletResponse, HttpSession)
This signature accepts a Product
argument
that will be populated (bound) with parameters retrieved from the
request and requires that the request already have
a valid session. Note that the order of arguments is important: the
session must be the third argument, and an object to be bound must
always be the final argument (fourth when a session is specified, or
third otherwise).
public ModelAndView updateCart(HttpServletRequest, HttpServletResponse, HttpSession, Product)
This signature has a void
return type
indicating that the handler method assumes the responsibility of writing
the response.
public void home(HttpServletRequest, HttpServletResponse)
This signature has a Map
return
type indicating that a view name translator will be responsible for
providing the view name based upon the request, and the model will
consist of the Map's
entries (see the
section entitled Section 13.10, “Convention over configuration” below).
public Map list(HttpServletRequest, HttpServletResponse)
The MethodNameResolver
is
responsible for resolving method names based on the specifics of the
incoming HttpServletRequest
. A number of
MethodNameResolver
implementations are
provided for you, and of course you can always write your own. Please
also note that the InternalPathMethodNameResolver
is the default MethodNameResolver
that
will be used if you don't inject one explicitly.
InternalPathMethodNameResolver
-
interprets the final filename from the request path and uses that as
the method name/
For example,
'http://www.sf.net/testing.view
' will result in
the method testing(HttpServletRequest,
HttpServletResponse)
being invoked.
ParameterMethodNameResolver
-
interprets a request parameter as the name of the method that is to
be invoked.
For example,
'http://www.sf.net/index.view?method=testIt
' will
result in the method testIt(HttpServletRequest,
HttpServletResponse)
being invoked. The
'paramName
' property specifies the name of the
request parameter that is to be used.
PropertiesMethodNameResolver
- uses a
user-defined Properties
object with request
URLs mapped to method names. For example, when the
Properties
contain
'/index/welcome.html=doIt
' and a request to
/index/welcome.html
comes in, the
doIt(HttpServletRequest,
HttpServletResponse)
method will be invoked. This
particular MethodNameResolver
uses
the Spring PathMatcher
class internally, so
if the Properties
contained
'/**/welcom?.html
', the example would also have
worked.
You may also declare custom methods for handling
Exceptions
that occur during request handling.
The valid signature for such a method is similar to the request handling
methods in that the HttpServletRequest
and HttpServletResponse
must be provided
as the first and second parameters respectively. Unlike request handling
methods however, the method's name is irrelevant. Instead, when
determining which Exception
handling method to
invoke, the decision is based upon the most specific possible match
among the methods whose third argument is some type of
Exception
. Here is an example signature for one
such Exception
handling method.
public ModelAndView processException(HttpServletRequest, HttpServletResponse, IllegalArgumentException)
Let's look at an example showing the delegate-style of
MultiActionController
usage in conjunction with
the ParameterMethodNameResolver
.
<bean id="paramMultiController" class="org.springframework.web.servlet.mvc.multiaction.MultiActionController"> <property name="methodNameResolver"> <bean class="org.springframework.web.servlet.mvc.multiaction.ParameterMethodNameResolver"> <property name="paramName" value="method"/> </bean> </property> <property name="delegate"> <bean class="samples.SampleDelegate"/> </property> </bean> }
public class SampleDelegate { public ModelAndView retrieveIndex(HttpServletRequest req, HttpServletResponse resp) { return new ModelAndView("index", "date", new Long(System.currentTimeMillis())); } }
When using the delegate shown above, we could also configure the
PropertiesMethodNameResolver
to match any number
couple of URLs to the method we defined:
<bean id="propsResolver" class="org....mvc.multiaction.PropertiesMethodNameResolver"> <property name="mappings"> <value> /index/welcome.html=retrieveIndex /**/notwelcome.html=retrieveIndex /*/user?.html=retrieveIndex </value> </property> </bean> <bean id="paramMultiController" class="org....mvc.multiaction.MultiActionController"> <property name="methodNameResolver" ref="propsResolver"/> <property name="delegate"> <bean class="samples.SampleDelegate"/> </property> </bean>
Spring's command controllers are a
fundamental part of the Spring Web MVC package. Command controllers
provide a way to interact with data objects and dynamically bind
parameters from the HttpServletRequest
to
the data object specified. They perform a somewhat similar role to the
Struts ActionForm
, but in Spring, your data
objects don't have to implement a framework-specific interface. First,
lets examine what command controllers are available straight out of the
box.
AbstractCommandController
- a command
controller you can use to create your own command controller,
capable of binding request parameters to a data object you specify.
This class does not offer form functionality; it does however offer
validation features and lets you specify in the controller itself
what to do with the command object that has been populated with
request parameter values.
AbstractFormController
- an abstract
controller offering form submission support. Using this controller
you can model forms and populate them using a command object you
retrieve in the controller. After a user has filled the form, the
AbstractFormController
binds the fields,
validates the command object, and hands the object back to the
controller to take the appropriate action. Supported features are:
invalid form submission (resubmission), validation, and normal form
workflow. You implement methods to determine which views are used
for form presentation and success. Use this controller if you need
forms, but don't want to specify what views you're going to show the
user in the application context.
SimpleFormController
- a form
controller that provides even more support when creating a form with
a corresponding command object. The
SimpleFormController
let's you specify a
command object, a viewname for the form, a viewname for page you
want to show the user when form submission has succeeded, and
more.
AbstractWizardFormController
- as the
class name suggests, this is an abstract class - your wizard
controller should extend it. This means you have to implement the
validatePage()
,
processFinish()
and
processCancel()
methods.
You probably also want to write a contractor, which should at
the very least call setPages()
and
setCommandName()
. The former takes as its
argument an array of type String. This array is the list of views
which comprise your wizard. The latter takes as its argument a
String, which will be used to refer to your command object from
within your views.
As with any instance of
AbstractFormController
, you are required to
use a command object - a JavaBean which will be populated with the
data from your forms. You can do this in one of two ways: either
call setCommandClass()
from the constructor with
the class of your command object, or implement the
formBackingObject()
method.
AbstractWizardFormController
has a
number of concrete methods that you may wish to override. Of these,
the ones you are likely to find most useful are:
referenceData(..)
which you can use to pass model
data to your view in the form of a
Map
;
getTargetPage()
if your wizard needs to change
page order or omit pages dynamically; and
onBindAndValidate()
if you want to override the
built-in binding and validation workflow.
Finally, it is worth pointing out the
setAllowDirtyBack()
and
setAllowDirtyForward()
, which you can call from
getTargetPage()
to allow users to move backwards
and forwards in the wizard even if validation fails for the current
page.
For a full list of methods, see the Javadoc for
AbstractWizardFormController
. There is an
implemented example of this wizard in the jPetStore included in the
Spring distribution:
org.springframework.samples.jpetstore.web.spring.OrderFormController
.
Using a handler mapping you can map incoming web requests to
appropriate handlers. There are some handler mappings you can use out of
the box, for example, the SimpleUrlHandlerMapping
or the BeanNameUrlHandlerMapping
, but let's first
examine the general concept of a
HandlerMapping
.
The functionality a basic
HandlerMapping
provides is the delivering
of a HandlerExecutionChain
, which must contain the
handler that matches the incoming request, and may also contain a list of
handler interceptors that are applied to the request. When a request comes
in, the DispatcherServlet
will hand it over to the
handler mapping to let it inspect the request and come up with an
appropriate HandlerExecutionChain. Then the
DispatcherServlet
will execute the handler and
interceptors in the chain (if any).
The concept of configurable handler mappings that can optionally
contain interceptors (executed before or after the actual handler was
executed, or both) is extremely powerful. A lot of supporting
functionality can be built into custom
HandlerMapping
s. Think of a custom handler
mapping that chooses a handler not only based on the URL of the request
coming in, but also on a specific state of the session associated with the
request.
This section describes two of Spring's most commonly used handler
mappings. They both extend the AbstractHandlerMapping
and share the following properties:
interceptors
: the list of interceptors to
use. HandlerInterceptor
s are discussed
in Section 13.4.3, “Intercepting requests - the
HandlerInterceptor
interface”.
defaultHandler
: the default handler to use,
when this handler mapping does not result in a matching
handler.
order
: based on the value of the order
property (see the org.springframework.core.Ordered
interface), Spring will sort all handler mappings available in the
context and apply the first matching handler.
alwaysUseFullPath
: if this property is set to
true
, Spring will use the full path within the
current servlet context to find an appropriate handler. If this
property is set to false
(the default), the path
within the current servlet mapping will be used. For example, if a
servlet is mapped using /testing/*
and the
alwaysUseFullPath
property is set to true,
/testing/viewPage.html
would be used, whereas if
the property is set to false, /viewPage.html
would
be used.
urlDecode
: the default value for this
property is true
, as of Spring 2.5. If you prefer
to compare encoded paths, switch this flag to
false
. However, note that the
HttpServletRequest
always exposes the
servlet path in decoded form. Be aware that the servlet path will not
match when compared with encoded paths.
lazyInitHandlers
: allows for lazy
initialization of singleton handlers (prototype
handlers are always lazily initialized). Default value is
false
.
(Note: the last three properties are only available to
subclasses of
org.springframework.web.servlet.handler.AbstractUrlHandlerMapping
).
A very simple, but very powerful handler mapping is the
BeanNameUrlHandlerMapping
, which maps incoming
HTTP requests to names of beans, defined in the web application context.
Let's say we want to enable a user to insert an account and we've
already provided an appropriate form controller (see Section 13.3.4, “Command controllers” for more information on command- and
form controllers) and a JSP view (or Velocity template) that renders the
form. When using the BeanNameUrlHandlerMapping
,
we could map the HTTP request with the URL
http://samples.com/editaccount.form
to the
appropriate form Controller
as
follows:
<beans> <bean id="handlerMapping" class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping"/> <bean name="/editaccount.form" class="org.springframework.web.servlet.mvc.SimpleFormController"> <property name="formView" value="account"/> <property name="successView" value="account-created"/> <property name="commandName" value="account"/> <property name="commandClass" value="samples.Account"/> </bean> <beans>
All incoming requests for the URL
/editaccount.form
will now be handled by the form
Controller
in the source listing above.
Of course we have to define a servlet-mapping in
web.xml
as well, to let through all the requests
ending with .form
.
<web-app>
...
<servlet>
<servlet-name>sample</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<!-- maps the sample dispatcher to *.form
-->
<servlet-mapping>
<servlet-name>sample</servlet-name>
<url-pattern>*.form</url-pattern>
</servlet-mapping>
...
</web-app>
![]() | Note |
---|---|
If you want to use the
|
A further - and much more powerful handler mapping - is the
SimpleUrlHandlerMapping
. This mapping is
configurable in the application context and has Ant-style path matching
capabilities (see the Javadoc for the
org.springframework.util.PathMatcher
class). Here
is an example:
<web-app> ... <servlet> <servlet-name>sample</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <!-- maps the sample dispatcher to *.form --> <servlet-mapping> <servlet-name>sample</servlet-name> <url-pattern>*.form</url-pattern> </servlet-mapping> <!-- maps the sample dispatcher to *.html --> <servlet-mapping> <servlet-name>sample</servlet-name> <url-pattern>*.html</url-pattern> </servlet-mapping> ... </web-app>
The above web.xml
configuration snippet enables
all requests ending with .html and .form
to be
handled by the sample dispatcher servlet.
<beans>
<!-- no 'id'
required, HandlerMapping
beans are automatically detected by the DispatcherServlet
-->
<bean class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="mappings">
<value>
/*/account.form=editAccountFormController
/*/editaccount.form=editAccountFormController
/ex/view*.html=helpController
/**/help.html=helpController
</value>
</property>
</bean>
<bean id="helpController"
class="org.springframework.web.servlet.mvc.UrlFilenameViewController"/>
<bean id="editAccountFormController"
class="org.springframework.web.servlet.mvc.SimpleFormController">
<property name="formView" value="account"/>
<property name="successView" value="account-created"/>
<property name="commandName" value="Account"/>
<property name="commandClass" value="samples.Account"/>
</bean>
<beans>
This handler mapping routes requests for
'help.html'
in any directory to the
'helpController'
, which is a
UrlFilenameViewController
(more about controllers
can be found in the section entitled Section 13.3, “Controllers”).
Requests for a resource beginning with 'view'
, and
ending with '.html'
in the directory
'ex'
will be routed to the
'helpController'
. Two further mappings are also
defined for 'editAccountFormController'
.
Spring's handler mapping mechanism has the notion of handler interceptors, that can be extremely useful when you want to apply specific functionality to certain requests, for example, checking for a principal.
Interceptors located in the handler mapping must implement
HandlerInterceptor
from the
org.springframework.web.servlet
package. This
interface defines three methods, one that will be called
before the actual handler will be executed, one
that will be called after the handler is executed,
and one that is called after the complete request has
finished. These three methods should provide enough
flexibility to do all kinds of pre- and post-processing.
The preHandle(..)
method returns a boolean
value. You can use this method to break or continue the processing of
the execution chain. When this method returns true
,
the handler execution chain will continue, when it returns false, the
DispatcherServlet
assumes the interceptor itself
has taken care of requests (and, for example, rendered an appropriate
view) and does not continue executing the other interceptors and the
actual handler in the execution chain.
The following example provides an interceptor that intercepts all requests and reroutes the user to a specific page if the time is not between 9 a.m. and 6 p.m.
<beans> <bean id="handlerMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"> <property name="interceptors"> <list> <ref bean="officeHoursInterceptor"/> </list> </property> <property name="mappings"> <value> /*.form=editAccountFormController /*.view=editAccountFormController </value> </property> </bean> <bean id="officeHoursInterceptor" class="samples.TimeBasedAccessInterceptor"> <property name="openingTime" value="9"/> <property name="closingTime" value="18"/> </bean> <beans>
package samples; public class TimeBasedAccessInterceptor extends HandlerInterceptorAdapter { private int openingTime; private int closingTime; public void setOpeningTime(int openingTime) { this.openingTime = openingTime; } public void setClosingTime(int closingTime) { this.closingTime = closingTime; } public boolean preHandle( HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { Calendar cal = Calendar.getInstance(); int hour = cal.get(HOUR_OF_DAY); if (openingTime <= hour < closingTime) { return true; } else { response.sendRedirect("http://host.com/outsideOfficeHours.html"); return false; } } }
Any request coming in, will be intercepted by the
TimeBasedAccessInterceptor
, and if the current
time is outside office hours, the user will be redirected to a static
html file, saying, for example, he can only access the website during
office hours.
As you can see, Spring has an adapter class (the cunningly named
HandlerInterceptorAdapter
) to make it easier to
extend the HandlerInterceptor
interface.
All MVC frameworks for web applications provide a way to address views. Spring provides view resolvers, which enable you to render models in a browser without tying you to a specific view technology. Out of the box, Spring enables you to use JSPs, Velocity templates and XSLT views, for example. The section entitled Chapter 14, View technologies has details of how to integrate and use a number of disparate view technologies.
The two interfaces which are important to the way Spring handles
views are ViewResolver
and
View
. The
ViewResolver
provides a mapping between
view names and actual views. The View
interface addresses the preparation of the request and hands the request
over to one of the view technologies.
As discussed in the section entitled Section 13.3, “Controllers”, all controllers in the Spring Web MVC
framework return a ModelAndView
instance. Views
in Spring are addressed by a view name and are resolved by a view
resolver. Spring comes with quite a few view resolvers. We'll list most
of them and then provide a couple of examples.
Table 13.4. View resolvers
ViewResolver | Description |
---|---|
AbstractCachingViewResolver | An abstract view resolver which takes care of caching views. Often views need preparation before they can be used, extending this view resolver provides caching of views. |
XmlViewResolver | An implementation of
ViewResolver that accepts a
configuration file written in XML with the same DTD as Spring's
XML bean factories. The default configuration file is
/WEB-INF/views.xml . |
ResourceBundleViewResolver | An implementation of
ViewResolver that uses bean
definitions in a ResourceBundle ,
specified by the bundle basename. The bundle is typically
defined in a properties file, located in the classpath. The
default file name is
views.properties . |
UrlBasedViewResolver | A simple implementation of the
ViewResolver interface that
effects the direct resolution of symbolic view names to URLs,
without an explicit mapping definition. This is appropriate if
your symbolic names match the names of your view resources in a
straightforward manner, without the need for arbitrary
mappings. |
InternalResourceViewResolver | A convenience subclass of
UrlBasedViewResolver that supports
InternalResourceView (i.e. Servlets and
JSPs), and subclasses such as JstlView
and TilesView . The view class for all
views generated by this resolver can be specified via
setViewClass(..) . See the Javadocs for the
UrlBasedViewResolver class for
details. |
VelocityViewResolver /
FreeMarkerViewResolver | A convenience subclass of
UrlBasedViewResolver that supports
VelocityView (i.e. Velocity templates) or
FreeMarkerView respectively and custom
subclasses of them. |
As an example, when using JSP for a view technology you can use
the UrlBasedViewResolver
. This view resolver
translates a view name to a URL and hands the request over to the
RequestDispatcher to render the view.
<bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver"> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean>
When returning test
as a viewname, this view
resolver will hand the request over to the
RequestDispatcher
that will send the request to
/WEB-INF/jsp/test.jsp
.
When mixing different view technologies in a web application, you
can use the ResourceBundleViewResolver
:
<bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"> <property name="basename" value="views"/> <property name="defaultParentView" value="parentView"/> </bean>
The ResourceBundleViewResolver
inspects the
ResourceBundle
identified by the basename, and
for each view it is supposed to resolve, it uses the value of the
property [viewname].class
as the view class and the
value of the property [viewname].url
as the view url.
As you can see, you can identify a parent view, from which all views in
the properties file sort of extend. This way you can specify a default
view class, for example.
A note on caching - subclasses of
AbstractCachingViewResolver
cache view instances
they have resolved. This greatly improves performance when using certain
view technologies. It's possible to turn off the cache, by setting the
cache
property to false
.
Furthermore, if you have the requirement to be able to refresh a certain
view at runtime (for example when a Velocity template has been
modified), you can use the removeFromCache(String viewName,
Locale loc)
method.
Spring supports more than just one view resolver. This allows you
to chain resolvers and, for example, override specific views in certain
circumstances. Chaining view resolvers is pretty straightforward - just
add more than one resolver to your application context and, if
necessary, set the order
property to specify an
order. Remember, the higher the order property, the later the view
resolver will be positioned in the chain.
In the following example, the chain of view resolvers consists of
two resolvers, a InternalResourceViewResolver
(which is always automatically positioned as the last resolver in the
chain) and an XmlViewResolver
for specifying
Excel views (which are not supported by the
InternalResourceViewResolver
):
<bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>
<bean id="excelViewResolver" class="org.springframework.web.servlet.view.XmlViewResolver">
<property name="order" value="1"/>
<property name="location" value="/WEB-INF/views.xml"/>
</bean>
<!-- in views.xml
-->
<beans>
<bean name="report" class="org.springframework.example.ReportExcelView"/>
</beans>
If a specific view resolver does not result in a view, Spring will
inspect the context to see if other view resolvers are configured. If
there are additional view resolvers, it will continue to inspect them.
If not, it will throw an Exception
.
You have to keep something else in mind - the contract of a view
resolver mentions that a view resolver can return
null to indicate the view could not be found. Not all view resolvers do
this however! This is because in some cases, the resolver simply cannot
detect whether or not the view exists. For example, the
InternalResourceViewResolver
uses the
RequestDispatcher
internally, and dispatching is
the only way to figure out if a JSP exists - this can only be done once.
The same holds for the VelocityViewResolver
and
some others. Check the Javadoc for the view resolver to see if you're
dealing with a view resolver that does not report non-existing views. As
a result of this, putting an
InternalResourceViewResolver
in the chain in a
place other than the last, will result in the chain not being fully
inspected, since the InternalResourceViewResolver
will always return a view!
As has been mentioned, a controller normally returns a logical
view name, which a view resolver resolves to a particular view
technology. For view technologies such as JSPs that are actually
processed via the Servlet/JSP engine, this is normally handled via
InternalResourceViewResolver
/
InternalResourceView
which will ultimately end up
issuing an internal forward or include, via the Servlet API's
RequestDispatcher.forward(..)
or
RequestDispatcher.include()
. For other view
technologies, such as Velocity, XSLT, etc., the view itself produces the
content on the response stream.
It is sometimes desirable to issue an HTTP redirect back to the
client, before the view is rendered. This is desirable for example when
one controller has been called with POST
ed data, and
the response is actually a delegation to another controller (for example
on a successful form submission). In this case, a normal internal
forward will mean the other controller will also see the same
POST
data, which is potentially problematic if it can
confuse it with other expected data. Another reason to do a redirect
before displaying the result is that this will eliminate the possibility
of the user doing a double submission of form data. The browser will
have sent the initial POST
, will have seen a redirect
back and done a subsequent GET
because of that, and
thus as far as it is concerned, the current page does not reflect the
result of a POST
, but rather of a
GET
, so there is no way the user can accidentally
re-POST
the same data by doing a refresh. The refresh
would just force a GET
of the result page, not a
resend of the initial POST
data.
One way to force a redirect as the result of a controller
response is for the controller to create and return an instance of
Spring's RedirectView
. In this case,
DispatcherServlet
will not use the normal view
resolution mechanism, but rather as it has been given the (redirect)
view already, will just ask it to do its work.
The RedirectView
simply ends up issuing
an HttpServletResponse.sendRedirect()
call, which
will come back to the client browser as an HTTP redirect. All model
attributes are simply exposed as HTTP query parameters. This does mean
that the model must contain only objects (generally Strings or
convertible to Strings) which can be readily converted to a
string-form HTTP query parameter.
If using RedirectView
and the view is
created by the controller itself, it is preferable for the redirect
URL to be injected into the controller so that it is not baked into
the controller but configured in the context along with the view
names.
While the use of RedirectView
works fine,
if the controller itself is creating the
RedirectView
, there is no getting around the
fact that the controller is aware that a redirection is happening.
This is really suboptimal and couples things too tightly. The
controller should not really care about how the response gets
handled... it should generally think only in terms of view names that
have been injected into it.
The special redirect:
prefix allows this to
be achieved. If a view name is returned which has the prefix
redirect:, then UrlBasedViewResolver
(and all
subclasses) will recognize this as a special indication that a
redirect is needed. The rest of the view name will be treated as the
redirect URL.
The net effect is the same as if the controller had returned a
RedirectView
, but now the controller itself can
deal just in terms of logical view names. A logical view name such as
redirect:/my/response/controller.html
will redirect
relative to the current servlet context, while a name such as
redirect:http://myhost.com/some/arbitrary/path.html
will redirect to an absolute URL. The important thing is that as long
as this redirect view name is injected into the controller like any
other logical view name, the controller is not even aware that
redirection is happening.
It is also possible to use a special forward:
prefix for view names that will ultimately be resolved by
UrlBasedViewResolver
and subclasses. All this
does is create an InternalResourceView
(which
ultimately does a RequestDispatcher.forward()
)
around the rest of the view name, which is considered a URL.
Therefore, there is never any use in using this prefix when using
InternalResourceViewResolver
/
InternalResourceView
anyway (for JSPs for
example), but it's of potential use when you are primarily using
another view technology, but still want to force a forward to happen
to a resource to be handled by the Servlet/JSP engine. (Note that you
may also chain multiple view resolvers, instead.)
As with the redirect:
prefix, if the view
name with the prefix is just injected into the controller, the
controller does not have to be aware that anything special is
happening in terms of handling the response.
Most parts of Spring's architecture support internationalization,
just as the Spring web MVC framework does.
DispatcherServlet
enables you to automatically
resolve messages using the client's locale. This is done with
LocaleResolver
objects.
When a request comes in, the
DispatcherServlet
looks for a locale resolver and
if it finds one it tries to use it to set the locale. Using the
RequestContext.getLocale()
method, you can always
retrieve the locale that was resolved by the locale resolver.
Besides the automatic locale resolution, you can also attach an
interceptor to the handler mapping (see Section 13.4.3, “Intercepting requests - the
HandlerInterceptor
interface” for more information on
handler mapping interceptors), to change the locale under specific
circumstances, based on a parameter in the request, for example.
Locale resolvers and interceptors are all defined in the
org.springframework.web.servlet.i18n
package, and are
configured in your application context in the normal way. Here is a
selection of the locale resolvers included in Spring.
This locale resolver inspects the
accept-language
header in the request that was sent
by the browser of the client. Usually this header field contains the
locale of the client's operating system.
This locale resolver inspects a Cookie
that
might exist on the client, to see if a locale is specified. If so, it
uses that specific locale. Using the properties of this locale resolver,
you can specify the name of the cookie, as well as the maximum age. Find
below an example of defining a
CookieLocaleResolver
.
<bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver">
<property name="cookieName" value="clientlanguage"/>
<!-- in seconds. If set to -1
, the cookie is not persisted (deleted when browser shuts down) -->
<property name="cookieMaxAge" value="100000">
</bean>
Table 13.5. CookieLocaleResolver
properties
Property | Default | Description |
---|---|---|
cookieName | classname + LOCALE | The name of the cookie |
cookieMaxAge | Integer.MAX_INT | The maximum time a cookie will stay persistent on the client. If -1 is specified, the cookie will not be persisted. It will only be available until the client shuts down his or her browser. |
cookiePath | / | Using this parameter, you can limit the visibility of the cookie to a certain part of your site. When cookiePath is specified, the cookie will only be visible to that path, and the paths below it. |
The SessionLocaleResolver
allows you to
retrieve locales from the session that might be associated with the
user's request.
You can build in changing of locales using the
LocaleChangeInterceptor
. This interceptor needs
to be added to one of the handler mappings (see Section 13.4, “Handler mappings”). It will detect a parameter in the
request and change the locale (it calls setLocale()
on the LocaleResolver
that also exists in
the context).
<bean id="localeChangeInterceptor" class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"> <property name="paramName" value="siteLanguage"/> </bean> <bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/> <bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"> <property name="interceptors"> <list> <ref bean="localeChangeInterceptor"/> </list> </property> <property name="mappings"> <value>/**/*.view=someController</value> </property> </bean>
All calls to all *.view
resources containing a
parameter named siteLanguage
will now change the
locale. So a request for the following URL,
http://www.sf.net/home.view?siteLanguage=nl
will
change the site language to Dutch.
The theme support provided by the Spring web MVC framework enables you to further enhance the user experience by allowing the look and feel of your application to be themed. A theme is basically a collection of static resources affecting the visual style of the application, typically style sheets and images.
When you want to use themes in your web application you'll have to
set up a
org.springframework.ui.context.ThemeSource
.
The WebApplicationContext
interface
extends ThemeSource
but delegates its
responsibilities to a dedicated implementation. By default the delegate
will be a
org.springframework.ui.context.support.ResourceBundleThemeSource
that loads properties files from the root of the classpath. If you want
to use a custom ThemeSource
implementation or if you need to configure the basename prefix of the
ResourceBundleThemeSource
, you can register a
bean in the application context with the reserved name "themeSource".
The web application context will automatically detect that bean and
start using it.
When using the ResourceBundleThemeSource
, a
theme is defined in a simple properties file. The properties file lists
the resources that make up the theme. Here is an example:
styleSheet=/themes/cool/style.css background=/themes/cool/img/coolBg.jpg
The keys of the properties are the names used to refer to the
themed elements from view code. For a JSP this would typically be done
using the spring:theme
custom tag, which is very
similar to the spring:message
tag. The following JSP
fragment uses the theme defined above to customize the look and
feel:
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%> <html> <head> <link rel="stylesheet" href="<spring:theme code="styleSheet"/>" type="text/css"/> </head> <body background="<spring:theme code="background"/>"> ... </body> </html>
By default, the ResourceBundleThemeSource
uses an empty basename prefix. As a result the properties files will be
loaded from the root of the classpath, so we'll have to put our
cool.properties
theme definition in a directory at
the root of the classpath, e.g. in /WEB-INF/classes
.
Note that the ResourceBundleThemeSource
uses the
standard Java resource bundle loading mechanism, allowing for full
internationalization of themes. For instance, we could have a
/WEB-INF/classes/cool_nl.properties
that references a
special background image, e.g. with Dutch text on it.
Now that we have our themes defined, the only thing left to do is
decide which theme to use. The DispatcherServlet
will look for a bean named "themeResolver" to find out which
ThemeResolver
implementation to use. A
theme resolver works in much the same way as a
LocaleResolver
. It can detect the theme
that should be used for a particular request and can also alter the
request's theme. The following theme resolvers are provided by
Spring:
Table 13.6. ThemeResolver
implementations
Class | Description |
---|---|
FixedThemeResolver | Selects a fixed theme, set using the "defaultThemeName" property. |
SessionThemeResolver | The theme is maintained in the users HTTP session. It only needs to be set once for each session, but is not persisted between sessions. |
CookieThemeResolver | The selected theme is stored in a cookie on the user-agent's machine. |
Spring also provides a
ThemeChangeInterceptor
, which allows changing the
theme on every request by including a simple request parameter.
Spring has built-in multipart support to handle fileuploads in web
applications. The design for the multipart support is done with
pluggable MultipartResolver
objects,
defined in the org.springframework.web.multipart
package. Out of the box, Spring provides a
MultipartResolver
for use with
Commons FileUpload (http://jakarta.apache.org/commons/fileupload).
How uploading files is supported will be described in the rest of
this chapter.
By default, no multipart handling will be done by Spring, as some
developers will want to handle multiparts themselves. You will have to
enable it yourself by adding a multipart resolver to the web
application's context. After you have done that, each request will be
inspected to see if it contains a multipart. If no multipart is found,
the request will continue as expected. However, if a multipart is found
in the request, the MultipartResolver
that has
been declared in your context will be used. After that, the multipart
attribute in your request will be treated like any other
attribute.
The following example shows how to use the
CommonsMultipartResolver
:
<bean id="multipartResolver"
class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
<!-- one of the properties available; the maximum file size in bytes -->
<property name="maxUploadSize" value="100000"/>
</bean>
This is an example using the
CosMultipartResolver
:
<bean id="multipartResolver" class="org.springframework.web.multipart.cos.CosMultipartResolver">
<!-- one of the properties available; the maximum file size in bytes -->
<property name="maxUploadSize" value="100000"/>
</bean>
Of course you also need to put the appropriate jars in your
classpath for the multipart resolver to work. In the case of the
CommonsMultipartResolver
, you need to use
commons-fileupload.jar
; in the case of the
CosMultipartResolver
, use
cos.jar
.
Now that you have seen how to set Spring up to handle multipart
requests, let's talk about how to actually use it. When the Spring
DispatcherServlet
detects a multi-part request,
it activates the resolver that has been declared in your context and
hands over the request. What the resolver then does is wrap the current
HttpServletRequest
into a
MultipartHttpServletRequest
that has support for
multipart file uploads. Using the
MultipartHttpServletRequest
you can get
information about the multiparts contained by this request and actually
get access to the multipart files themselves in your controllers.
After the MultipartResolver
has finished
doing its job, the request will be processed like any other. To use it,
you create a form with an upload field (see immediately below), then let
Spring bind the file onto your form (backing object). To actually let
the user upload a file, we have to create a (HTML) form:
<html> <head> <title>Upload a file please</title> </head> <body> <h1>Please upload a file</h1> <form method="post" action="upload.form" enctype="multipart/form-data"> <input type="file" name="file"/> <input type="submit"/> </form> </body> </html>
As you can see, we've created a field named after the property of
the bean that holds the byte[]
. Furthermore we've
added the encoding attribute
(enctype="multipart/form-data"
) which is necessary to
let the browser know how to encode the multipart fields (do not forget
this!).
Just as with any other property that's not automagically
convertible to a string or primitive type, to be able to put binary data
in your objects you have to register a custom editor with the
ServletRequestDatabinder
. There are a couple of
editors available for handling files and setting the results on an
object. There's a StringMultipartEditor
capable
of converting files to Strings (using a user-defined character set) and
there is a ByteArrayMultipartEditor
which
converts files to byte arrays. They function just as the
CustomDateEditor
does.
So, to be able to upload files using a (HTML) form, declare the resolver, a url mapping to a controller that will process the bean, and the controller itself.
<beans>
<!-- lets use the Commons-based implementation of the MultipartResolver interface -->
<bean id="multipartResolver"
class="org.springframework.web.multipart.commons.CommonsMultipartResolver"/>
<bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="mappings">
<value>
/upload.form=fileUploadController
</value>
</property>
</bean>
<bean id="fileUploadController" class="examples.FileUploadController">
<property name="commandClass" value="examples.FileUploadBean"/>
<property name="formView" value="fileuploadform"/>
<property name="successView" value="confirmation"/>
</bean>
</beans>
After that, create the controller and the actual class to hold the file property.
public class FileUploadController extends SimpleFormController { protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response, Object command, BindException errors) throws ServletException, IOException { // cast the bean FileUploadBean bean = (FileUploadBean) command; let's see if there's content there byte[] file = bean.getFile(); if (file == null) { // hmm, that's strange, the user did not upload anything } // well, let's do nothing with the bean for now and return return super.onSubmit(request, response, command, errors); } protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) throws ServletException { // to actually be able to convert Multipart instance to byte[] // we have to register a custom editor binder.registerCustomEditor(byte[].class, new ByteArrayMultipartFileEditor()); // now Spring knows how to handle multipart object and convert them } } public class FileUploadBean { private byte[] file; public void setFile(byte[] file) { this.file = file; } public byte[] getFile() { return file; } }
As you can see, the FileUploadBean
has a
property typed byte[]
that holds the file. The
controller registers a custom editor to let Spring know how to actually
convert the multipart objects the resolver has found to properties
specified by the bean. In this example, nothing is done with the
byte[]
property of the bean itself, but in practice
you can do whatever you want (save it in a database, mail it to
somebody, etc).
An equivalent example in which a file is bound straight to a String-typed property on a (form backing) object might look like:
public class FileUploadController extends SimpleFormController { protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response, Object command, BindException errors) throws ServletException, IOException { // cast the bean FileUploadBean bean = (FileUploadBean) command; let's see if there's content there String file = bean.getFile(); if (file == null) { // hmm, that's strange, the user did not upload anything } // well, let's do nothing with the bean for now and return return super.onSubmit(request, response, command, errors); } protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) throws ServletException { // to actually be able to convert Multipart instance to a String // we have to register a custom editor binder.registerCustomEditor(String.class, new StringMultipartFileEditor()); // now Spring knows how to handle multipart object and convert them } } public class FileUploadBean { private String file; public void setFile(String file) { this.file = file; } public String getFile() { return file; } }
Of course, this last example only makes (logical) sense in the context of uploading a plain text file (it wouldn't work so well in the case of uploading an image file).
The third (and final) option is where one binds directly to a
MultipartFile
property declared on the
(form backing) object's class. In this case one does not need to
register any custom PropertyEditor
because there is no type conversion to be performed.
public class FileUploadController extends SimpleFormController { protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response, Object command, BindException errors) throws ServletException, IOException { // cast the bean FileUploadBean bean = (FileUploadBean) command; let's see if there's content there MultipartFile file = bean.getFile(); if (file == null) { // hmm, that's strange, the user did not upload anything } // well, let's do nothing with the bean for now and return return super.onSubmit(request, response, command, errors); } } public class FileUploadBean { private MultipartFile file; public void setFile(MultipartFile file) { this.file = file; } public MultipartFile getFile() { return file; } }
Spring provides HandlerExceptionResolvers
to ease
the pain of unexpected exceptions occurring while your request is being
handled by a controller which matched the request.
HandlerExceptionResolvers
somewhat resemble the
exception mappings you can define in the web application descriptor
web.xml
. However, they provide a more flexible way to
handle exceptions. They provide information about what handler was
executing when the exception was thrown. Furthermore, a programmatic way
of handling exception gives you many more options for how to respond
appropriately before the request is forwarded to another URL (the same end
result as when using the servlet specific exception mappings).
Besides implementing the
HandlerExceptionResolver
interface, which
is only a matter of implementing the resolveException(Exception,
Handler)
method and returning a
ModelAndView
, you may also use the
SimpleMappingExceptionResolver
. This resolver
enables you to take the class name of any exception that might be thrown
and map it to a view name. This is functionally equivalent to the
exception mapping feature from the Servlet API, but it's also possible to
implement more finely grained mappings of exceptions from different
handlers.
For a lot of projects, sticking to established conventions and
having reasonable defaults is just what they (the projects) need... this
theme of convention-over-configuration now has explicit support in Spring
Web MVC. What this means is that if you establish a set of naming
conventions and suchlike, you can substantially cut
down on the amount of configuration that is required to set up handler
mappings, view resolvers, ModelAndView
instances,
etc. This is a great boon with regards to rapid prototyping, and can also
lend a degree of (always good-to-have) consistency across a codebase
should you choose to move forward with it into production.
This convention over configuration support address the three core areas of MVC - namely, the models, views, and controllers.
The ControllerClassNameHandlerMapping
class
is a HandlerMapping
implementation that
uses a convention to determine the mapping between request URLs and the
Controller
instances that are to handle
those requests.
An example; consider the following (simplistic)
Controller
implementation. Take especial
notice of the name of the class.
public class ViewShoppingCartController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { // the implementation is not hugely important for this example... } }
Here is a snippet from the attendent Spring Web MVC configuration file...
<bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/> <bean id="viewShoppingCart" class="x.y.z.ViewShoppingCartController"> <!-- inject dependencies as required... --> </bean>
The ControllerClassNameHandlerMapping
finds
all of the various handler (or
Controller
) beans defined in its
application context and strips 'Controller'
off the
name to define its handler mappings.
Let's look at some more examples so that the central idea becomes immediately familiar.
WelcomeController
maps to the
'/welcome*'
request URL
HomeController
maps to the
'/home*'
request URL
IndexController
maps to the
'/index*'
request URL
RegisterController
maps to the
'/register*'
request URL
DisplayShoppingCartController
maps to
the '/displayshoppingcart*'
request URL
(Notice the casing - all lowercase - in the case of
camel-cased Controller
class
names.)
In the case of MultiActionController
handler classes, the mappings generated are (ever so slightly) more
complex, but hopefully no less understandable. Some examples (all of the
Controller
names in this next bit are
assumed to be MultiActionController
implementations).
AdminController
maps to the
'/admin/*'
request URL
CatalogController
maps to the
'/catalog/*'
request URL
If you follow the pretty standard convention of naming your
Controller
implementations as
xxxController
, then
the ControllerClassNameHandlerMapping
will save
you the tedium of having to firstly define and then having to maintain a
potentially looooong
SimpleUrlHandlerMapping
(or suchlike).
The ControllerClassNameHandlerMapping
class
extends the AbstractHandlerMapping
base class so
you can define HandlerInterceptor
instances and everything else just like you would with many other
HandlerMapping
implementations.
The ModelMap
class is essentially a
glorified Map
that can make adding
objects that are to be displayed in (or on) a
View
adhere to a common naming
convention. Consider the following
Controller
implementation; notice that
objects are added to the ModelAndView
without any
associated name being specified.
public class DisplayShoppingCartController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { List cartItems = // get aList
ofCartItem
objects User user = // get theUser
doing the shopping ModelAndView mav = new ModelAndView("displayShoppingCart"); <-- the logical view name mav.addObject(cartItems); <-- look ma, no name, just the object mav.addObject(user); <-- and again ma! return mav; } }
The ModelAndView
class uses a
ModelMap
class that is a custom
Map
implementation that automatically
generates a key for an object when an object is added to it. The
strategy for determining the name for an added object is, in the case of
a scalar object such as User
, to use the short
class name of the object's class. Find below some examples of the names
that are generated for scalar objects put into a
ModelMap
instance.
An x.y.User
instance added will have
the name 'user'
generated
An x.y.Registration
instance added will
have the name 'registration'
generated
An x.y.Foo
instance added will have the
name 'foo'
generated
A java.util.HashMap
instance added will
have the name 'hashMap'
generated (you'll
probably want to be explicit about the name in this case because
'hashMap'
is less than intuitive).
Adding null
will result in an
IllegalArgumentException
being thrown. If the
object (or objects) that you are adding could potentially be
null
, then you will also want to be explicit
about the name).
The strategy for generating a name after adding a
Set
, List
or array object is to peek into the collection, take the short class
name of the first object in the collection, and use that with
'List'
appended to the name. Some examples will make
the semantics of name generation for collections clearer...
An x.y.User[]
array with one or more
x.y.User
elements added will have the name
'userList'
generated
An x.y.Foo[]
array with one or more
x.y.User
elements added will have the name
'fooList'
generated
A java.util.ArrayList
with one or more
x.y.User
elements added will have the name
'userList'
generated
A java.util.HashSet
with one or more
x.y.Foo
elements added will have the name
'fooList'
generated
An empty
java.util.ArrayList
will not be added at all
(i.e. the addObject(..)
call will
essentially be a no-op).
The RequestToViewNameTranslator
interface is responsible for determining a logical
View
name when no such logical view name
is explicitly supplied. It has just one implementation, the rather
cunningly named
DefaultRequestToViewNameTranslator
class.
The DefaultRequestToViewNameTranslator
maps
request URLs to logical view names in a fashion that is probably best
explained by recourse to an example.
public class RegistrationController implements Controller {
public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
// process the request...
ModelAndView mav = new ModelAndView();
// add data as necessary to the model...
return mav;
// notice that no View
or logical view name has been set
}
}
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd"> <beans> <!-- this bean with the well known name generates view names for us --> <bean id="viewNameTranslator" class="org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator"/> <bean class="x.y.RegistrationController"> <!-- inject dependencies as necessary --> </bean> <!-- maps request URLs to Controller names --> <bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> </beans>
Notice how in the implementation of the
handleRequest(..)
method no
View
or logical view name is ever set on
the ModelAndView
that is returned. It is the
DefaultRequestToViewNameTranslator
that will be
tasked with generating a logical view name from the
URL of the request. In the case of the above
RegistrationController
, which is being used in
conjunction with the
ControllerClassNameHandlerMapping
, a request URL
of 'http://localhost/registration.html'
will result
in a logical view name of 'registration'
being
generated by the
DefaultRequestToViewNameTranslator
. This logical
view name will then be resolved into the
'/WEB-INF/jsp/registration.jsp'
view by the
InternalResourceViewResolver
bean.
![]() | Tip |
---|---|
You don't even need to define a
|
Of course, if you need to change the default settings, then you do
need to configure your own
DefaultRequestToViewNameTranslator
bean
explicitly. Please do consult the quite comprehensive Javadoc for the
DefaultRequestToViewNameTranslator
class for
details of the various properties that can be configured.
There is a current trend to favor annotations over XML files for some types of configuration data. To facilitate this, Spring is now (since 2.5) providing support for configuring the MVC framework components using annotations.
Spring 2.5 introduces an annotation-based programming model for MVC
controllers, using annotations such as
@RequestMapping
,
@RequestParam
,
@ModelAttribute
, etc. This annotation
support is available for both Servlet MVC and Portlet MVC. Controllers
implemented in this style do not have to extend specific base classes or
implement specific interfaces. Furthermore, they do not usually have
direct dependencies on Servlet or Portlet API's, although they can easily
get access to Servlet or Portlet facilities if desired.
![]() | Tip |
---|---|
The Spring distribution ships with the
PetClinic sample, which is a web application that takes
advantage of the annotation support described in this section, in the context
of simple form processing. You can find the PetClinic
application in the For a further sample application that builds on annotation-based Web MVC,
check out imagedb. The focus in that sample is on stateless
multi-action controllers, including the processing of multipart file uploads.
You can find the imagedb application in the
|
The following sections document these annotations and how they are most commonly used in a Servlet environment.
@RequestMapping
will only be processed
if a corresponding HandlerMapping
(for type level annotations)
and/or HandlerAdapter
(for method level annotations) is
present in the dispatcher. This is the case by default in both
DispatcherServlet
and DispatcherPortlet
.
However, if you are defining custom HandlerMappings
or
HandlerAdapters
, then you need to make sure that a
corresponding custom DefaultAnnotationHandlerMapping
and/or AnnotationMethodHandlerAdapter
is defined as well
- provided that you intend to use @RequestMapping
.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping"/>
<bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"/>
// ... (controller bean definitions) ...
</beans>
Defining a DefaultAnnotationHandlerMapping
and/or AnnotationMethodHandlerAdapter
explicitly
also makes sense if you would like to customize the mapping strategy,
e.g. specifying a custom PathMatcher
or
WebBindingInitializer
(see below).
The @Controller
annotation indicates
that a particular class serves the role of a controller.
There is no need to extend any controller base class or reference the
Servlet API. You are of course still able to reference Servlet-specific
features if you need to.
The basic purpose of the @Controller
annotation is to act as a stereotype for the annotated class, indicating
its role. The dispatcher will scan such annotated classes for mapped
methods, detecting @RequestMapping
annotations (see the next section).
Annotated controller beans may be defined explicitly,
using a standard Spring bean definition in the dispatcher's context.
However, the @Controller
stereotype also
allows for autodetection, aligned with Spring 2.5's general support for
detecting component classes in the classpath and auto-registering bean
definitions for them.
To enable autodetection of such annotated controllers, you have to add component scanning to your configuration. This is easily achieved by using the spring-context schema as shown in the following XML snippet:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<context:component-scan base-package="org.springframework.samples.petclinic.web"/>
// ...
</beans>
The @RequestMapping
annotation is used
to map URLs like '/editPet.do' onto an entire class or a particular handler method.
Typically the type-level annotation maps a specific request path (or path pattern)
onto a form controller, with additional method-level annotations 'narrowing' the
primary mapping for a specific HTTP method request method ("GET"/"POST") or
specific HTTP request parameters.
![]() | Tip |
---|---|
In the following discussion, we'll focus on controllers that are based on annotated handler methods. |
The following is an example of a form controller from the PetClinic sample application using this annotation:
@Controller @RequestMapping("/editPet.do") @SessionAttributes("pet") public class EditPetForm { private final Clinic clinic; @Autowired public EditPetForm(Clinic clinic) { this.clinic = clinic; } @ModelAttribute("types") public Collection<PetType> populatePetTypes() { return this.clinic.getPetTypes(); } @RequestMapping(method = RequestMethod.GET) public String setupForm(@RequestParam("petId") int petId, ModelMap model) { Pet pet = this.clinic.loadPet(petId); model.addAttribute("pet", pet); return "petForm"; } @RequestMapping(method = RequestMethod.POST) public String processSubmit( @ModelAttribute("pet") Pet pet, BindingResult result, SessionStatus status) { new PetValidator().validate(pet, result); if (result.hasErrors()) { return "petForm"; } else { this.clinic.storePet(pet); status.setComplete(); return "redirect:owner.do?ownerId=" + pet.getOwner().getId(); } } }
For a traditional multi-action controller the URLs are typically
mapped directly on the methods since the controller responds to multiple
URLs. The following is an example of a multi-action controller from the
PetClinic sample application using
@RequestMapping
:
@Controller public class ClinicController { private final Clinic clinic; @Autowired public ClinicController(Clinic clinic) { this.clinic = clinic; } /** * Custom handler for the welcome view. * Note that this handler relies on the RequestToViewNameTranslator to * determine the logical view name based on the request URL: "/welcome.do" * -> "welcome". */ @RequestMapping("/welcome.do") public void welcomeHandler() { } /** * Custom handler for displaying vets. * Note that this handler returns a plain {@link ModelMap} object instead of * a ModelAndView, thus leveraging convention-based model attribute names. * It relies on the RequestToViewNameTranslator to determine the logical * view name based on the request URL: "/vets.do" -> "vets". * @return a ModelMap with the model attributes for the view */ @RequestMapping("/vets.do") public ModelMap vetsHandler() { return new ModelMap(this.clinic.getVets()); } /** * Custom handler for displaying an owner. * Note that this handler returns a plain {@link ModelMap} object instead of * a ModelAndView, thus leveraging convention-based model attribute names. * It relies on the RequestToViewNameTranslator to determine the logical * view name based on the request URL: "/owner.do" -> "owner". * @param ownerId the ID of the owner to display * @return a ModelMap with the model attributes for the view */ @RequestMapping("/owner.do") public ModelMap ownerHandler(@RequestParam("ownerId") int ownerId) { return new ModelMap(this.clinic.loadOwner(ownerId)); } }
Ant-style path patterns are supported (e.g. "/myPath/*.do"). At the method level, relative paths (e.g. "edit.do") are supported within the primary mapping expressed at the type level.
The handler method names are taken into account for narrowing
if no path was specified explicitly, according to the specified
org.springframework.web.servlet.mvc.multiaction.MethodNameResolver
(by default an
org.springframework.web.servlet.mvc.multiaction.InternalPathMethodNameResolver
).
Note that this only applies in case of ambiguous annotation mappings
that do not specify a path mapping explicitly. In other words,
the method name is only used for narrowing among a set of matching
methods; it does not constitute a primary path mapping itself.
If you have a single default method (without explicit path mapping), then all requests without a more specific mapped method found will be dispatched to it. If you have multiple such default methods, then the method name will be taken into account for choosing between them.
Path mappings can be narrowed through parameter conditions: a sequence of "myParam=myValue" style expressions, with a request only mapped if each such parameter is found to have the given value. "myParam" style expressions are also supported, with such parameters having to be present in the request (allowed to have any value). Finally, "!myParam" style expressions indicate that the specified parameter is not supposed to be present in the request.
Handler methods which are annotated with
@RequestMapping
are allowed to have very flexible
signatures. They may have arguments of the following types, in arbitrary
order (except for validation results, which need to follow right after
the corresponding command object, if desired):
Request and/or response objects (Servlet API). You may choose any
specific request/response type, e.g. ServletRequest
/
HttpServletRequest
.
Session object (Servlet API): of type HttpSession
.
An argument of this type will enforce the presence of a corresponding session.
As a consequence, such an argument will never be null
.
Note that session access may not be thread-safe, in particular
in a Servlet environment: Consider switching the
AnnotationMethodHandlerAdapter
's
"synchronizeOnSession" flag to "true" if multiple requests are allowed
to access a session concurrently.
org.springframework.web.context.request.WebRequest
or org.springframework.web.context.request.NativeWebRequest
.
Allows for generic request parameter access as well as request/session
attribute access, without ties to the native Servlet/Portlet API.
java.util.Locale
for the current request
locale (determined by the most specific locale resolver available,
i.e. the configured LocaleResolver
in a Servlet environment).
java.io.InputStream
/
java.io.Reader
for access to the request's content.
This will be the raw InputStream/Reader as exposed by the Servlet API.
java.io.OutputStream
/
java.io.Writer
for generating the response's content.
This will be the raw OutputStream/Writer as exposed by the Servlet API.
@RequestParam
annotated parameters
for access to specific Servlet request parameters. Parameter values
will be converted to the declared method argument type.
java.util.Map
/
org.springframework.ui.Model
/
org.springframework.ui.ModelMap
for
enriching the implicit model that will be exposed to the web view.
Command/form objects to bind parameters to: as bean
properties or fields, with customizable type conversion, depending
on @InitBinder
methods and/or the
HandlerAdapter configuration - see the
"webBindingInitializer
" property on
AnnotationMethodHandlerAdapter
. Such
command objects along with their validation results will be
exposed as model attributes, by default using the non-qualified
command class name in property notation (e.g. "orderAddress" for
type "mypackage.OrderAddress"). Specify a parameter-level
ModelAttribute
annotation for declaring a
specific model attribute name.
org.springframework.validation.Errors
/
org.springframework.validation.BindingResult
validation results for a preceding command/form object (the
immediate preceding argument).
org.springframework.web.bind.support.SessionStatus
status handle for marking form processing as complete (triggering
the cleanup of session attributes that have been indicated by the
@SessionAttributes
annotation at the
handler type level).
The following return types are supported for handler methods:
A ModelAndView
object, with the model implicitly
enriched with command objects and the results of @ModelAttribute
annotated reference data accessor methods.
A Model
object, with the view name implicitly
determined through a RequestToViewNameTranslator
and the model implicitly enriched with command objects and the results of
@ModelAttribute
annotated reference data accessor methods.
A Map
object for exposing a model, with the view name
implicitly determined through a RequestToViewNameTranslator
and the model implicitly enriched with command objects and the results of
@ModelAttribute
annotated reference data accessor methods.
A View
object, with the model implicitly
determined through command objects and @ModelAttribute
annotated reference data accessor methods. The handler method may also
programmatically enrich the model by declaring a Model
argument (see above).
A String
value which is interpreted as view name,
with the model implicitly determined through command objects and
@ModelAttribute
annotated reference data accessor methods.
The handler method may also programmatically enrich the model by declaring a
Model
argument (see above).
void
if the method handles the response itself
(by writing the response content directly, declaring an argument of type
ServletResponse
/
HttpServletResponse
for that purpose)
or if the view name is supposed to be implicitly determined through a
RequestToViewNameTranslator
(not declaring a response argument in the handler method signature).
Any other return type will be considered as single model attribute
to be exposed to the view, using the attribute name specified through
@ModelAttribute
at the method level (or the default
attribute name based on the return type's class name otherwise). The model
will be implicitly enriched with command objects and the results of
@ModelAttribute
annotated reference data accessor methods.
The @RequestParam
annotation is used to
bind request parameters to a method parameter in your controller.
The following code snippet from the PetClinic sample application shows the usage:
@Controller @RequestMapping("/editPet.do") @SessionAttributes("pet") public class EditPetForm { // ... @RequestMapping(method = RequestMethod.GET) public String setupForm(@RequestParam("petId") int petId, ModelMap model) { Pet pet = this.clinic.loadPet(petId); model.addAttribute("pet", pet); return "petForm"; } // ...
Parameters using this annotation are required by default, but you
can specify that a parameter is optional by setting
@RequestParam
's
required
attribute to false
(e.g.,
@RequestParam(value="id", required="false")
).
@ModelAttribute
has two usage scenarios in
controllers. When placed on a method parameter,
@ModelAttribute
is used to map a model attribute
to the specific, annotated method parameter (see the
processSubmit()
method below). This is how the
controller gets a reference to the object holding the data entered in
the form. In addition, the parameter can be declared as the specific
type of the form backing object rather than as a generic
java.lang.Object
, thus increasing type
safety.
@ModelAttribute
is also used at the method
level to provide reference data for the model (see
the populatePetTypes()
method below). For this usage
the method signature can contain the same types as documented above for
the @RequestMapping
annotation.
Note: @ModelAttribute
annotated methods will be executed before the
chosen @RequestMapping
annotated handler method.
They effectively pre-populate the implicit model with specific attributes,
often loaded from a database. Such an attribute can then already be
accessed through @ModelAttribute
annotated
handler method parameters in the chosen handler method, potentially
with binding and validation applied to it.
The following code snippet shows these two usages of this annotation:
@Controller @RequestMapping("/editPet.do") @SessionAttributes("pet") public class EditPetForm { // ... @ModelAttribute("types") public Collection<PetType> populatePetTypes() { return this.clinic.getPetTypes(); } @RequestMapping(method = RequestMethod.POST) public String processSubmit( @ModelAttribute("pet") Pet pet, BindingResult result, SessionStatus status) { new PetValidator().validate(pet, result); if (result.hasErrors()) { return "petForm"; } else { this.clinic.storePet(pet); status.setComplete(); return "redirect:owner.do?ownerId=" + pet.getOwner().getId(); } } }
The type-level @SessionAttributes
annotation declares session attributes used by a specific handler. This
will typically list the names of model attributes which should be
transparently stored in the session or some conversational storage,
serving as form-backing beans between subsequent requests.
The following code snippet shows the usage of this annotation:
@Controller @RequestMapping("/editPet.do") @SessionAttributes("pet") public class EditPetForm { // ... }
To customize request parameter binding with PropertyEditors, etc.
via Spring's WebDataBinder
, you can either use
@InitBinder
-annotated methods within your
controller or externalize your configuration by providing a custom
WebBindingInitializer
.
Annotating controller methods with
@InitBinder
allows you to configure web
data binding directly within your controller class.
@InitBinder
identifies methods which
initialize the WebDataBinder
which will be used
for populating command and form object arguments of annotated handler
methods.
Such init-binder methods support all arguments that
@RequestMapping
supports, except for
command/form objects and corresponding validation result objects.
Init-binder methods must not have a return value. Thus, they are
usually declared as void
. Typical arguments include
WebDataBinder
in combination with
WebRequest
or
java.util.Locale
, allowing code to register
context-specific editors.
The following example demonstrates the use of
@InitBinder
for configuring a
CustomDateEditor
for all
java.util.Date
form properties.
@Controller public class MyFormController { @InitBinder public void initBinder(WebDataBinder binder) { SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd"); dateFormat.setLenient(false); binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false)); } // ... }
To externalize data binding initialization, you can provide a
custom implementation of the
WebBindingInitializer
interface, which
you then enable by supplying a custom bean configuration for an
AnnotationMethodHandlerAdapter
, thus overriding
the default configuration.
The following example from the PetClinic application shows a
configuration using a custom implementation of the
WebBindingInitializer
interface,
org.springframework.samples.petclinic.web.ClinicBindingInitializer
,
which configures PropertyEditors required by several of the PetClinic
controllers.
<bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"> <property name="cacheSeconds" value="0" /> <property name="webBindingInitializer"> <bean class="org.springframework.samples.petclinic.web.ClinicBindingInitializer" /> </property> </bean>
Find below links and pointers to further resources about Spring Web MVC.
The Spring distribution ships with a Spring Web MVC tutorial
that guides the reader through building a complete Spring Web
MVC-based application using a step-by-step approach. This tutorial is
available in the 'docs'
directory of the Spring
distribution. An online version can also be found on the Spring Framework website.
The book entitled “Expert Spring Web MVC and Web Flow” by Seth Ladd and others (published by Apress) is an excellent hardcopy source of Spring Web MVC goodness.
One of the areas in which Spring excels is in the separation of view technologies from the rest of the MVC framework. For example, deciding to use Velocity or XSLT in place of an existing JSP is primarily a matter of configuration. This chapter covers the major view technologies that work with Spring and touches briefly on how to add new ones. This chapter assumes you are already familiar with Section 13.5, “Views and resolving them” which covers the basics of how views in general are coupled to the MVC framework.
Spring provides a couple of out-of-the-box solutions for JSP and
JSTL views. Using JSP or JSTL is done using a normal view resolver defined
in the WebApplicationContext
. Furthermore,
of course you need to write some JSPs that will actually render the view.
Just as with any other view technology you're integrating with
Spring, for JSPs you'll need a view resolver that will resolve your
views. The most commonly used view resolvers when developing with JSPs
are the InternalResourceViewResolver
and the
ResourceBundleViewResolver
. Both are declared in the
WebApplicationContext
:
<!-- the ResourceBundleViewResolver
-->
<bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver">
<property name="basename" value="views"/>
</bean>
# And a sample properties file is uses (views.properties in WEB-INF/classes):
welcome.class=org.springframework.web.servlet.view.JstlView
welcome.url=/WEB-INF/jsp/welcome.jsp
productList.class=org.springframework.web.servlet.view.JstlView
productList.url=/WEB-INF/jsp/productlist.jsp
As you can see, the ResourceBundleViewResolver
needs
a properties file defining the view names mapped to 1) a class and 2) a URL. With a
ResourceBundleViewResolver
you can mix different types of views using
only one resolver.
<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean>
The InternalResourceBundleViewResolver
can be configured for using
JSPs as described above. As a best practice, we strongly encourage
placing your JSP files in a directory under the 'WEB-INF'
directory, so
there can be no direct access by clients.
When using the Java Standard Tag Library you must use a special view
class, the JstlView
, as JSTL needs some preparation
before things such as the i18N features will work.
Spring provides data binding of request parameters to command objects as described in earlier chapters. To facilitate the development of JSP pages in combination with those data binding features, Spring provides a few tags that make things even easier. All Spring tags have HTML escaping features to enable or disable escaping of characters.
The tag library descriptor (TLD) is included in the
spring.jar
as well in the distribution itself.
Further information about the individual tags can be found in the appendix entitled
Appendix D, spring.tld.
As of version 2.0, Spring provides a comprehensive set of data binding-aware tags for handling form elements when using JSP and Spring Web MVC. Each tag provides support for the set of attributes of its corresponding HTML tag counterpart, making the tags familiar and intuitive to use. The tag-generated HTML is HTML 4.01/XHTML 1.0 compliant.
Unlike other form/input tag libraries, Spring's form tag library is integrated with Spring Web MVC, giving the tags access to the command object and reference data your controller deals with. As you will see in the following examples, the form tags make JSPs easier to develop, read and maintain.
Let's go through the form tags and look at an example of how each tag is used. We have included generated HTML snippets where certain tags require further commentary.
The form tag library comes bundled in
spring.jar
. The library descriptor is called
spring-form.tld
.
To use the tags from this library, add the following directive to the top of your JSP page:
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
... where form
is the tag name prefix you want
to use for the tags from this library.
This tag renders an HTML 'form' tag and exposes a binding path to
inner tags for binding. It puts the command object in the
PageContext
so that the command object can be
accessed by inner tags. All the other tags in this library are
nested tags of the form
tag.
Let's assume we have a domain object called
User
. It is a JavaBean with properties such as
firstName
and lastName
. We will
use it as the form backing object of our form controller which returns
form.jsp
. Below is an example of what
form.jsp
would look like:
<form:form> <table> <tr> <td>First Name:</td> <td><form:input path="firstName" /></td> </tr> <tr> <td>Last Name:</td> <td><form:input path="lastName" /></td> </tr> <tr> <td colspan="2"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form:form>
The firstName
and lastName
values are retrieved from the command object placed in the
PageContext
by the page controller. Keep
reading to see more complex examples of how inner tags are used with the
form
tag.
The generated HTML looks like a standard form:
<form method="POST"> <table> <tr> <td>First Name:</td> <td><input name="firstName" type="text" value="Harry"/></td> </tr> <tr> <td>Last Name:</td> <td><input name="lastName" type="text" value="Potter"/></td> </tr> <tr> <td colspan="2"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form>
The preceding JSP assumes that the variable name of the form
backing object is 'command'
. If you have put the form
backing object into the model under another name (definitely a best
practice), then you can bind the form to the named variable like
so:
<form:form commandName="user">
<table>
<tr>
<td>First Name:</td>
<td><form:input path="firstName" /></td>
</tr>
<tr>
<td>Last Name:</td>
<td><form:input path="lastName" /></td>
</tr>
<tr>
<td colspan="2">
<input type="submit" value="Save Changes" />
</td>
</tr>
</table>
</form:form>
This tag renders an HTML 'input' tag with type 'text' using the
bound value. For an example of this tag, see Section 14.2.4.2, “The form
tag”.
This tag renders an HTML 'input' tag with type 'checkbox'.
Let's assume our User
has preferences such
as newsletter subscription and a list of hobbies. Below is an example of
the Preferences
class:
public class Preferences { private boolean receiveNewsletter; private String[] interests; private String favouriteWord; public boolean isReceiveNewsletter() { return receiveNewsletter; } public void setReceiveNewsletter(boolean receiveNewsletter) { this.receiveNewsletter = receiveNewsletter; } public String[] getInterests() { return interests; } public void setInterests(String[] interests) { this.interests = interests; } public String getFavouriteWord() { return favouriteWord; } public void setFavouriteWord(String favouriteWord) { this.favouriteWord = favouriteWord; } }
The form.jsp
would look like:
<form:form> <table> <tr> <td>Subscribe to newsletter?:</td> <%-- Approach 1: Property is of typejava.lang.Boolean
--%> <td><form:checkbox path="preferences.receiveNewsletter"/></td> </tr> <tr> <td>Interests:</td> <td> <%-- Approach 2: Property is of an array or of typejava.util.Collection
--%> Quidditch: <form:checkbox path="preferences.interests" value="Quidditch"/> Herbology: <form:checkbox path="preferences.interests" value="Herbology"/> Defence Against the Dark Arts: <form:checkbox path="preferences.interests" value="Defence Against the Dark Arts"/> </td> </tr> <tr> <td>Favourite Word:</td> <td> <%-- Approach 3: Property is of typejava.lang.Object
--%> Magic: <form:checkbox path="preferences.favouriteWord" value="Magic"/> </td> </tr> </table> </form:form>
There are 3 approaches to the checkbox
tag which
should meet all your checkbox needs.
Approach One - When the bound value is of type
java.lang.Boolean
, the
input(checkbox)
is marked as 'checked' if the
bound value is true
. The value
attribute corresponds to the resolved value of the
setValue(Object)
value property.
Approach Two - When the bound value is of type
array
or
java.util.Collection
, the
input(checkbox)
is marked as 'checked' if the
configured setValue(Object)
value is present in
the bound Collection
.
Approach Three - For any other bound value type, the
input(checkbox)
is marked as 'checked' if the
configured setValue(Object)
is equal to the bound
value.
Note that regardless of the approach, the same HTML structure is generated. Below is an HTML snippet of some checkboxes:
<tr> <td>Interests:</td> <td> Quidditch: <input name="preferences.interests" type="checkbox" value="Quidditch"/> <input type="hidden" value="1" name="_preferences.interests"/> Herbology: <input name="preferences.interests" type="checkbox" value="Herbology"/> <input type="hidden" value="1" name="_preferences.interests"/> Defence Against the Dark Arts: <input name="preferences.interests" type="checkbox" value="Defence Against the Dark Arts"/> <input type="hidden" value="1" name="_preferences.interests"/> </td> </tr>
What you might not expect to see is the additional hidden field
after each checkbox. When a checkbox in an HTML page is
not checked, its value will not be sent to the server
as part of the HTTP request parameters once the form is submitted, so we
need a workaround for this quirk in HTML in order for Spring form data
binding to work. The checkbox
tag follows the existing
Spring convention of including a hidden parameter prefixed by an
underscore ("_") for each checkbox. By doing this, you are effectively
telling Spring that “
the checkbox was visible in the form and I want my object to
which the form data will be bound to reflect the state of the checkbox
no matter what
”.
This tag renders multiple HTML 'input' tags with type 'checkbox'.
Building on the example from the previous
checkbox
tag section. Sometimes you prefer not to
have to list all the possible hobbies in your JSP page. You would rather
provide a list at runtime of the available options and pass that in to
the tag. That is the purpose of the checkboxes
tag. You pass in an Array
, a
List
or a Map
containing
the available options in the "items" property. Typically the bound
property is a collection so it can hold multiple values selected by the
user. Below is an example of the JSP using this tag:
<form:form>
<table>
<tr>
<td>Interests:</td>
<td>
<%-- Property is of an array or of type java.util.Collection
--%>
<form:checkboxes path="preferences.interests" items="${interestList}"/>
</td>
</tr>
</table>
</form:form>
This example assumes that the "interestList" is a
List
available as a model attribute containing
strings of the values to be selected from. In the case where you use a
Map, the map entry key will be used as the value and the map entry's value
will be used as the label to be displayed. You can also use a custom
object where you can provide the property names for the value using
"itemValue" and the label using "itemLabel".
This tag renders an HTML 'input' tag with type 'radio'.
A typical usage pattern will involve multiple tag instances bound to the same property but with different values.
<tr> <td>Sex:</td> <td>Male: <form:radiobutton path="sex" value="M"/> <br/> Female: <form:radiobutton path="sex" value="F"/> </td> </tr>
This tag renders multiple HTML 'input' tags with type 'radio'.
Just like the checkboxes
tag above, you
might want to pass in the available options as a runtime variable. For
this usage you would use the radiobuttons
tag.
You pass in an Array
, a
List
or a Map
containing
the available options in the "items" property. In the case where you use
a Map, the map entry key will be used as the value and the map entry's
value will be used as the label to be displayed. You can also use a
custom object where you can provide the property names for the value
using "itemValue" and the label using "itemLabel".
<tr> <td>Sex:</td> <td><form:radiobuttons path="sex" items="${sexOptions}"/></td> </tr>
This tag renders an HTML 'input' tag with type 'password' using the bound value.
<tr> <td>Password:</td> <td> <form:password path="password" /> </td> </tr>
Please note that by default, the password value is
not shown. If you do want the password value to be
shown, then set the value of the 'showPassword'
attribute to true, like so.
<tr> <td>Password:</td> <td> <form:password path="password" value="^76525bvHGq" showPassword="true" /> </td> </tr>
This tag renders an HTML 'select' element. It supports data
binding to the selected option as well as the use of nested
option
and options
tags.
Let's assume a User
has a list of
skills.
<tr> <td>Skills:</td> <td><form:select path="skills" items="${skills}"/></td> </tr>
If the User's
skill were in Herbology, the HTML
source of the 'Skills' row would look like:
<tr> <td>Skills:</td> <td><select name="skills" multiple="true"> <option value="Potions">Potions</option> <option value="Herbology" selected="selected">Herbology</option> <option value="Quidditch">Quidditch</option></select> </td> </tr>
This tag renders an HTML 'option'. It sets 'selected' as appropriate based on the bound value.
<tr> <td>House:</td> <td> <form:select path="house"> <form:option value="Gryffindor"/> <form:option value="Hufflepuff"/> <form:option value="Ravenclaw"/> <form:option value="Slytherin"/> </form:select> </td> </tr>
If the User's
house was in Gryffindor, the HTML
source of the 'House' row would look like:
<tr> <td>House:</td> <td> <select name="house"> <option value="Gryffindor" selected="selected">Gryffindor</option> <option value="Hufflepuff">Hufflepuff</option> <option value="Ravenclaw">Ravenclaw</option> <option value="Slytherin">Slytherin</option> </select> </td> </tr>
This tag renders a list of HTML 'option' tags. It sets the 'selected' attribute as appropriate based on the bound value.
<tr> <td>Country:</td> <td> <form:select path="country"> <form:option value="-" label="--Please Select"/> <form:options items="${countryList}" itemValue="code" itemLabel="name"/> </form:select> </td> </tr>
If the User
lived in the UK, the HTML
source of the 'Country' row would look like:
<tr> <td>Country:</td> <td> <select name="country"> <option value="-">--Please Select</option> <option value="AT">Austria</option> <option value="UK" selected="selected">United Kingdom</option> <option value="US">United States</option> </select> </td> </tr>
As the example shows, the combined usage of an
option
tag with the options
tag
generates the same standard HTML, but allows you to explicitly specify a
value in the JSP that is for display only (where it belongs) such as the
default string in the example: "-- Please Select".
This tag renders an HTML 'textarea'.
<tr> <td>Notes:</td> <td><form:textarea path="notes" rows="3" cols="20" /></td> <td><form:errors path="notes" /></td> </tr>
This tag renders an HTML 'input' tag with type 'hidden' using the
bound value. To submit an unbound hidden value, use the HTML
input
tag with type 'hidden'.
<form:hidden path="house" />
If we choose to submit the 'house' value as a hidden one, the HTML would look like:
<input name="house" type="hidden" value="Gryffindor"/>
This tag renders field errors in an HTML 'span' tag. It provides access to the errors created in your controller or those that were created by any validators associated with your controller.
Let's assume we want to display all error messages for the
firstName
and lastName
fields once
we submit the form. We have a validator for instances of the
User
class called
UserValidator
.
public class UserValidator implements Validator { public boolean supports(Class candidate) { return User.class.isAssignableFrom(candidate); } public void validate(Object obj, Errors errors) { ValidationUtils.rejectIfEmptyOrWhitespace(errors, "firstName", "required", "Field is required."); ValidationUtils.rejectIfEmptyOrWhitespace(errors, "lastName", "required", "Field is required."); } }
The form.jsp
would look like:
<form:form> <table> <tr> <td>First Name:</td> <td><form:input path="firstName" /></td> <%-- Show errors for firstName field --%> <td><form:errors path="firstName" /></td> </tr> <tr> <td>Last Name:</td> <td><form:input path="lastName" /></td> <%-- Show errors for lastName field --%> <td><form:errors path="lastName" /></td> </tr> <tr> <td colspan="3"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form:form>
If we submit a form with empty values in the
firstHame
and lastName
fields,
this is what the HTML would look like:
<form method="POST"> <table> <tr> <td>First Name:</td> <td><input name="firstName" type="text" value=""/></td> <%-- Associated errors to firstName field displayed --%> <td><span name="firstName.errors">Field is required.</span></td> </tr> <tr> <td>Last Name:</td> <td><input name="lastName" type="text" value=""/></td> <%-- Associated errors to lastName field displayed --%> <td><span name="lastName.errors">Field is required.</span></td> </tr> <tr> <td colspan="3"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form>
What if we want to display the entire list of errors for a given
page? The example below shows that the errors
tag
also supports some basic wildcarding functionality.
path="*"
- displays all errors
path="lastName*"
- displays all errors
associated with the lastName
field
The example below will display a list of errors at the top of the page, followed by field-specific errors next to the fields:
<form:form> <form:errors path="*" cssClass="errorBox" /> <table> <tr> <td>First Name:</td> <td><form:input path="firstName" /></td> <td><form:errors path="firstName" /></td> </tr> <tr> <td>Last Name:</td> <td><form:input path="lastName" /></td> <td><form:errors path="lastName" /></td> </tr> <tr> <td colspan="3"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form:form>
The HTML would look like:
<form method="POST"> <span name="*.errors" class="errorBox">Field is required.<br/>Field is required.</span> <table> <tr> <td>First Name:</td> <td><input name="firstName" type="text" value=""/></td> <td><span name="firstName.errors">Field is required.</span></td> </tr> <tr> <td>Last Name:</td> <td><input name="lastName" type="text" value=""/></td> <td><span name="lastName.errors">Field is required.</span></td> </tr> <tr> <td colspan="3"> <input type="submit" value="Save Changes" /> </td> </tr> </form>
It is possible to integrate Tiles - just as any other view technology - in web applications using Spring. The following describes in a broad way how to do this.
NOTE: This section focuses on Spring's support
for Tiles 2 (the standalone version of Tiles, requiring Java 5+) in the
org.springframework.web.servlet.view.tiles2
package.
Spring also continues to support Tiles 1.x (a.k.a. "Struts Tiles",
as shipped with Struts 1.1+; compatible with Java 1.4) in the original
org.springframework.web.servlet.view.tiles
package.
To be able to use Tiles you have to have a couple of additional dependencies included in your project. The following is the list of dependencies you need.
Tiles version 2.0.4 or higher
Commons BeanUtils
Commons Digester
Commons Logging
These dependencies are all available in the Spring distribution.
To be able to use Tiles, you have to configure it using files
containing definitions (for basic information on definitions and other
Tiles concepts, please have a look at http://tiles.apache.org). In Spring this is done
using the TilesConfigurer
. Have a look at the
following piece of example ApplicationContext configuration:
<bean id="tilesConfigurer" class="org.springframework.web.servlet.view.tiles2.TilesConfigurer"> <property name="definitions"> <list> <value>/WEB-INF/defs/general.xml</value> <value>/WEB-INF/defs/widgets.xml</value> <value>/WEB-INF/defs/administrator.xml</value> <value>/WEB-INF/defs/customer.xml</value> <value>/WEB-INF/defs/templates.xml</value> </list> </property> </bean>
As you can see, there are five files containing definitions, which
are all located in the 'WEB-INF/defs'
directory.
At initialization of the WebApplicationContext
,
the files will be loaded and the definitions factory will be initialized.
After that has been done, the Tiles includes in the definition files can be used
as views within your Spring web application. To be able to use the views
you have to have a ViewResolver
just as with any
other view technology used with Spring. Below you can find two
possibilities, the UrlBasedViewResolver
and
the ResourceBundleViewResolver
.
The UrlBasedViewResolver
instantiates the given
viewClass
for each view it has to resolve.
<bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.tiles2.TilesView"/> </bean>
The ResourceBundleViewResolver
has to be provided with a
property file containing viewnames and viewclasses the resolver can
use:
<bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"> <property name="basename" value="views"/> </bean>
... welcomeView.class=org.springframework.web.servlet.view.tiles2.TilesView welcomeView.url=welcome (this is the name of a Tiles definition) vetsView.class=org.springframework.web.servlet.view.tiles2.TilesView vetsView.url=vetsView (again, this is the name of a Tiles definition) findOwnersForm.class=org.springframework.web.servlet.view.JstlView findOwnersForm.url=/WEB-INF/jsp/findOwners.jsp ...
As you can see, when using the ResourceBundleViewResolver
,
you can easily mix different view technologies.
Note that the TilesView
class for Tiles 2 supports
JSTL (the JSP Standard Tag Library) out of the box, whereas there is a separate
TilesJstlView
subclass in the Tiles 1.x support.
As an advanced feature, Spring also supports two special Tiles 2
PreparerFactory
implementations. Check out the
Tiles documentation for details on how to use ViewPreparer
references in your Tiles definition files.
Specify SimpleSpringPreparerFactory
to autowire
ViewPreparer instances based on specified preparer classes, applying Spring's
container callbacks as well as applying configured Spring BeanPostProcessors.
If Spring's context-wide annotation-config has been activated, annotations in
ViewPreparer classes will be automatically detected and applied.
Note that this expects preparer classes in the Tiles definition files,
just like the default PreparerFactory
does.
Specify SpringBeanPreparerFactory
to operate on specified
preparer names instead of classes, obtaining the corresponding
Spring bean from the DispatcherServlet's application context. The full bean
creation process will be in the control of the Spring application context in
this case, allowing for the use of explicit dependency injection configuration,
scoped beans etc. Note that you need to define one Spring bean definition per
preparer name (as used in your Tiles definitions).
<bean id="tilesConfigurer" class="org.springframework.web.servlet.view.tiles2.TilesConfigurer">
<property name="definitions">
<list>
<value>/WEB-INF/defs/general.xml</value>
<value>/WEB-INF/defs/widgets.xml</value>
<value>/WEB-INF/defs/administrator.xml</value>
<value>/WEB-INF/defs/customer.xml</value>
<value>/WEB-INF/defs/templates.xml</value>
</list>
</property>
<!-- resolving preparer names as Spring bean definition names -->
<property name="preparerFactoryClass"
value="org.springframework.web.servlet.view.tiles2.SpringBeanPreparerFactory"/>
</bean>
Velocity and FreeMarker are two templating languages that can both be used as view technologies within Spring MVC applications. The languages are quite similar and serve similar needs and so are considered together in this section. For semantic and syntactic differences between the two languages, see the FreeMarker web site.
Your web application will need to include
velocity-1.x.x.jar
or
freemarker-2.x.jar
in order to
work with Velocity or FreeMarker respectively and
commons-collections.jar
needs also to be available for Velocity. Typically they are included in
the WEB-INF/lib
folder where they are guaranteed to
be found by a J2EE server and added to the classpath for your
application. It is of course assumed that you already have the
spring.jar
in your
'WEB-INF/lib'
directory too!
The latest stable Velocity, FreeMarker and Commons
Collections jars are supplied with the Spring framework and can be
copied from the relevant /lib/
sub-directories. If you make use of Spring's 'dateToolAttribute' or
'numberToolAttribute' in your Velocity views, you will also need to include the
velocity-tools-generic-1.x.jar
A suitable configuration is initialized by adding the relevant
configurer bean definition to your '*-servlet.xml'
as shown below:
<!-- This bean sets up the Velocity environment for us based on a root path for templates. Optionally, a properties file can be specified for more control over the Velocity environment, but the defaults are pretty sane for file based template loading. --> <bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer"> <property name="resourceLoaderPath" value="/WEB-INF/velocity/"/> </bean> <!-- View resolvers can also be configured with ResourceBundles or XML files. If you need different view resolving based on Locale, you have to use the resource bundle resolver. --> <bean id="viewResolver" class="org.springframework.web.servlet.view.velocity.VelocityViewResolver"> <property name="cache" value="true"/> <property name="prefix" value=""/> <property name="suffix" value=".vm"/> </bean>
<!-- freemarker config --> <bean id="freemarkerConfig" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer"> <property name="templateLoaderPath" value="/WEB-INF/freemarker/"/> </bean> <!-- View resolvers can also be configured with ResourceBundles or XML files. If you need different view resolving based on Locale, you have to use the resource bundle resolver. --> <bean id="viewResolver" class="org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver"> <property name="cache" value="true"/> <property name="prefix" value=""/> <property name="suffix" value=".ftl"/> </bean>
![]() | Note |
---|---|
For non web-apps add a |
Your templates need to be stored in the directory specified by the
*Configurer
bean shown above. This document does not cover
details of creating templates for the two languages - please see their
relevant websites for information. If you use the view resolvers
highlighted, then the logical view names relate to the template file
names in similar fashion to
InternalResourceViewResolver
for JSP's. So if your
controller returns a ModelAndView object containing a view name of
"welcome" then the resolvers will look for the
/WEB-INF/freemarker/welcome.ftl
or
/WEB-INF/velocity/welcome.vm
template as
appropriate.
The basic configurations highlighted above will be suitable for most application requirements, however additional configuration options are available for when unusual or advanced requirements dictate.
This file is completely optional, but if specified, contains the
values that are passed to the Velocity runtime in order to configure
velocity itself. Only required for advanced configurations, if you
need this file, specify its location on the
VelocityConfigurer
bean definition above.
<bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer"> <property name="configLocation value="/WEB-INF/velocity.properties"/> </bean>
Alternatively, you can specify velocity properties directly in the bean definition for the Velocity config bean by replacing the "configLocation" property with the following inline properties.
<bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer"> <property name="velocityProperties"> <props> <prop key="resource.loader">file</prop> <prop key="file.resource.loader.class"> org.apache.velocity.runtime.resource.loader.FileResourceLoader </prop> <prop key="file.resource.loader.path">${webapp.root}/WEB-INF/velocity</prop> <prop key="file.resource.loader.cache">false</prop> </props> </property> </bean>
Refer to the API
documentation for Spring configuration of Velocity, or the
Velocity documentation for examples and definitions of the
'velocity.properties'
file itself.
FreeMarker 'Settings' and 'SharedVariables' can be passed
directly to the FreeMarker Configuration
object
managed by Spring by setting the appropriate bean properties on the
FreeMarkerConfigurer
bean. The
freemarkerSettings
property requires a
java.util.Properties
object and the
freemarkerVariables
property requires a
java.util.Map
.
<bean id="freemarkerConfig" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer"> <property name="templateLoaderPath" value="/WEB-INF/freemarker/"/> <property name="freemarkerVariables"> <map> <entry key="xml_escape" value-ref="fmXmlEscape"/> </map> </property> </bean> <bean id="fmXmlEscape" class="freemarker.template.utility.XmlEscape"/>
See the FreeMarker documentation for details of settings and
variables as they apply to the Configuration
object.
Spring provides a tag library for use in JSP's that contains
(amongst other things) a <spring:bind/>
tag.
This tag primarily enables forms to display values from form backing
objects and to show the results of failed validations from a
Validator
in the web or business tier. From version
1.1, Spring now has support for the same functionality in both Velocity
and FreeMarker, with additional convenience macros for generating form
input elements themselves.
A standard set of macros are maintained within the
spring.jar
file for both languages, so they are
always available to a suitably configured application.
Some of the macros defined in the Spring libraries are
considered internal (private) but no such scoping exists in the macro
definitions making all macros visible to calling code and user
templates. The following sections concentrate only on the macros you
need to be directly calling from within your templates. If you wish to
view the macro code directly, the files are called spring.vm /
spring.ftl and are in the packages
org.springframework.web.servlet.view.velocity
or
org.springframework.web.servlet.view.freemarker
respectively.
In your html forms (vm / ftl templates) that act as the
'formView' for a Spring form controller, you can use code similar to
the following to bind to field values and display error messages for
each input field in similar fashion to the JSP equivalent. Note that
the name of the command object is "command" by default, but can be
overridden in your MVC configuration by setting the 'commandName' bean
property on your form controller. Example code is shown below for the
personFormV
and personFormF
views configured earlier;
<!-- velocity macros are automatically available --> <html> ... <form action="" method="POST"> Name: #springBind( "command.name" ) <input type="text" name="${status.expression}" value="$!status.value" /><br> #foreach($error in $status.errorMessages) <b>$error</b> <br> #end <br> ... <input type="submit" value="submit"/> </form> ... </html>
<!-- freemarker macros have to be imported into a namespace. We strongly recommend sticking to 'spring' --> <#import "spring.ftl" as spring /> <html> ... <form action="" method="POST"> Name: <@spring.bind "command.name" /> <input type="text" name="${spring.status.expression}" value="${spring.status.value?default("")}" /><br> <#list spring.status.errorMessages as error> <b>${error}</b> <br> </#list> <br> ... <input type="submit" value="submit"/> </form> ... </html>
#springBind
/
<@spring.bind>
requires a 'path' argument
which consists of the name of your command object (it will be
'command' unless you changed it in your FormController properties)
followed by a period and the name of the field on the command object
you wish to bind to. Nested fields can be used too such as
"command.address.street". The bind
macro assumes
the default HTML escaping behavior specified by the ServletContext
parameter defaultHtmlEscape
in web.xml
The optional form of the macro called
#springBindEscaped
/
<@spring.bindEscaped>
takes a second argument
and explicitly specifies whether HTML escaping should be used in the
status error messages or values. Set to true or false as required.
Additional form handling macros simplify the use of HTML escaping and
these macros should be used wherever possible. They are explained in
the next section.
Additional convenience macros for both languages simplify both binding and form generation (including validation error display). It is never necessary to use these macros to generate form input fields, and they can be mixed and matched with simple HTML or calls direct to the spring bind macros highlighted previously.
The following table of available macros show the VTL and FTL definitions and the parameter list that each takes.
Table 14.1. Table of macro definitions
macro | VTL definition | FTL definition |
---|---|---|
message (output a string from a resource bundle based on the code parameter) | #springMessage($code) | <@spring.message
code/> |
messageText (output a string from a resource bundle based on the code parameter, falling back to the value of the default parameter) | #springMessageText($code
$text) | <@spring.messageText code,
text/> |
url (prefix a relative URL with the application's context root) | #springUrl($relativeUrl) | <@spring.url
relativeUrl/> |
formInput (standard input field for gathering user input) | #springFormInput($path
$attributes) | <@spring.formInput path, attributes,
fieldType/> |
formHiddenInput * (hidden input field for submitting non-user input) | #springFormHiddenInput($path
$attributes) | <@spring.formHiddenInput path,
attributes/> |
formPasswordInput * (standard input field for gathering passwords. Note that no value will ever be populated in fields of this type) | #springFormPasswordInput($path
$attributes) | <@spring.formPasswordInput path,
attributes/> |
formTextarea (large text field for gathering long, freeform text input) | #springFormTextarea($path
$attributes) | <@spring.formTextarea path,
attributes/> |
formSingleSelect (drop down box of options allowing a single required value to be selected) | #springFormSingleSelect( $path $options
$attributes) | <@spring.formSingleSelect path, options,
attributes/> |
formMultiSelect (a list box of options allowing the user to select 0 or more values) | #springFormMultiSelect($path $options
$attributes) | <@spring.formMultiSelect path, options,
attributes/> |
formRadioButtons (a set of radio buttons allowing a single selection to be made from the available choices) | #springFormRadioButtons($path $options
$separator $attributes) | <@spring.formRadioButtons path, options
separator, attributes/> |
formCheckboxes (a set of checkboxes allowing 0 or more values to be selected) | #springFormCheckboxes($path $options
$separator $attributes) | <@spring.formCheckboxes path, options,
separator, attributes/> |
showErrors (simplify display of validation errors for the bound field) | #springShowErrors($separator
$classOrStyle) | <@spring.showErrors separator,
classOrStyle/> |
* In FTL (FreeMarker), these two macros are not actually
required as you can use the normal formInput
macro,
specifying 'hidden
' or
'password
' as the value for the
fieldType
parameter.
The parameters to any of the above macros have consistent meanings:
path: the name of the field to bind to (ie "command.name")
options: a Map of all the available values that can be
selected from in the input field. The keys to the map represent
the values that will be POSTed back from the form and bound to the
command object. Map objects stored against the keys are the labels
displayed on the form to the user and may be different from the
corresponding values posted back by the form. Usually such a map
is supplied as reference data by the controller. Any Map
implementation can be used depending on required behavior. For
strictly sorted maps, a SortedMap
such as a
TreeMap
with a suitable Comparator may be used
and for arbitrary Maps that should return values in insertion
order, use a LinkedHashMap
or a
LinkedMap
from commons-collections.
separator: where multiple options are available as discreet elements (radio buttons or checkboxes), the sequence of characters used to separate each one in the list (ie "<br>").
attributes: an additional string of arbitrary tags or text to be included within the HTML tag itself. This string is echoed literally by the macro. For example, in a textarea field you may supply attributes as 'rows="5" cols="60"' or you could pass style information such as 'style="border:1px solid silver"'.
classOrStyle: for the showErrors macro, the name of the CSS class that the span tag wrapping each error will use. If no information is supplied (or the value is empty) then the errors will be wrapped in <b></b> tags.
Examples of the macros are outlined below some in FTL and some in VTL. Where usage differences exist between the two languages, they are explained in the notes.
<!-- the Name field example from above using form macros in VTL --> ... Name: #springFormInput("command.name" "")<br> #springShowErrors("<br>" "")<br>
The formInput macro takes the path parameter (command.name) and an additional attributes parameter which is empty in the example above. The macro, along with all other form generation macros, performs an implicit spring bind on the path parameter. The binding remains valid until a new bind occurs so the showErrors macro doesn't need to pass the path parameter again - it simply operates on whichever field a bind was last created for.
The showErrors macro takes a separator parameter (the characters that will be used to separate multiple errors on a given field) and also accepts a second parameter, this time a class name or style attribute. Note that FreeMarker is able to specify default values for the attributes parameter, unlike Velocity, and the two macro calls above could be expressed as follows in FTL:
<@spring.formInput "command.name"/> <@spring.showErrors "<br>"/>
Output is shown below of the form fragment generating the name field, and displaying a validation error after the form was submitted with no value in the field. Validation occurs through Spring's Validation framework.
The generated HTML looks like this:
Name: <input type="text" name="name" value="" > <br> <b>required</b> <br> <br>
The formTextarea macro works the same way as the formInput macro and accepts the same parameter list. Commonly, the second parameter (attributes) will be used to pass style information or rows and cols attributes for the textarea.
Four selection field macros can be used to generate common UI value selection inputs in your HTML forms.
formSingleSelect
formMultiSelect
formRadioButtons
formCheckboxes
Each of the four macros accepts a Map of options containing the value for the form field, and the label corresponding to that value. The value and the label can be the same.
An example of radio buttons in FTL is below. The form backing object specifies a default value of 'London' for this field and so no validation is necessary. When the form is rendered, the entire list of cities to choose from is supplied as reference data in the model under the name 'cityMap'.
... Town: <@spring.formRadioButtons "command.address.town", cityMap, "" /><br><br>
This renders a line of radio buttons, one for each value in
cityMap
using the separator "". No additional
attributes are supplied (the last parameter to the macro is
missing). The cityMap uses the same String for each key-value pair
in the map. The map's keys are what the form actually submits as
POSTed request parameters, map values are the labels that the user
sees. In the example above, given a list of three well known cities
and a default value in the form backing object, the HTML would
be
Town: <input type="radio" name="address.town" value="London" > London <input type="radio" name="address.town" value="Paris" checked="checked" > Paris <input type="radio" name="address.town" value="New York" > New York
If your application expects to handle cities by internal codes for example, the map of codes would be created with suitable keys like the example below.
protected Map referenceData(HttpServletRequest request) throws Exception { Map cityMap = new LinkedHashMap(); cityMap.put("LDN", "London"); cityMap.put("PRS", "Paris"); cityMap.put("NYC", "New York"); Map m = new HashMap(); m.put("cityMap", cityMap); return m; }
The code would now produce output where the radio values are the relevant codes but the user still sees the more user friendly city names.
Town: <input type="radio" name="address.town" value="LDN" > London <input type="radio" name="address.town" value="PRS" checked="checked" > Paris <input type="radio" name="address.town" value="NYC" > New York
Default usage of the form macros above will result in HTML tags that are HTML 4.01 compliant and that use the default value for HTML escaping defined in your web.xml as used by Spring's bind support. In order to make the tags XHTML compliant or to override the default HTML escaping value, you can specify two variables in your template (or in your model where they will be visible to your templates). The advantage of specifying them in the templates is that they can be changed to different values later in the template processing to provide different behavior for different fields in your form.
To switch to XHTML compliance for your tags, specify a value of 'true' for a model/context variable named xhtmlCompliant:
## for Velocity.. #set($springXhtmlCompliant = true) <#-- for FreeMarker --> <#assign xhtmlCompliant = true in spring>
Any tags generated by the Spring macros will now be XHTML compliant after processing this directive.
In similar fashion, HTML escaping can be specified per field:
<#-- until this point, default HTML escaping is used --> <#assign htmlEscape = true in spring> <#-- next field will use HTML escaping --> <@spring.formInput "command.name" /> <#assign htmlEscape = false in spring> <#-- all future fields will be bound with HTML escaping off -->
XSLT is a transformation language for XML and is popular as a view technology within web applications. XSLT can be a good choice as a view technology if your application naturally deals with XML, or if your model can easily be converted to XML. The following section shows how to produce an XML document as model data and have it transformed with XSLT in a Spring Web MVC application.
This example is a trivial Spring application that creates a list
of words in the Controller
and adds them to the model
map. The map is returned along with the view name of our XSLT view. See the section
entitled Section 13.3, “Controllers” for details of Spring Web MVC's
Controller
interface. The XSLT view will turn the list of
words into a simple XML document ready for transformation.
Configuration is standard for a simple Spring application. The
dispatcher servlet config file contains a reference to a
ViewResolver
, URL mappings and a single controller
bean...
<bean id="homeController"class="xslt.HomeController"/>
... that encapsulates our word generation logic.
The controller logic is encapsulated in a subclass of
AbstractController
, with the handler method being defined like so...
protected ModelAndView handleRequestInternal( HttpServletRequest request, HttpServletResponse response) throws Exception { Map map = new HashMap(); List wordList = new ArrayList(); wordList.add("hello"); wordList.add("world"); map.put("wordList", wordList); return new ModelAndView("home", map); }
So far we've done nothing that's XSLT specific. The model data
has been created in the same way as you would for any other Spring MVC
application. Depending on the configuration of the application now,
that list of words could be rendered by JSP/JSTL by having them added
as request attributes, or they could be handled by Velocity by adding
the object to the VelocityContext
. In
order to have XSLT render them, they of course have to be converted into
an XML document somehow.
There are software packages available that will automatically 'domify'
an object graph, but within Spring, you have complete flexibility to
create the DOM from your model in any way you choose. This prevents
the transformation of XML playing too great a part in the structure of
your model data which is a danger when using tools to manage the
domification process.
In order to create a DOM document from our list of words or any
other model data, we must subclass the (provided)
org.springframework.web.servlet.view.xslt.AbstractXsltView
class. In doing so, we must also typically implement the abstract method
createXsltSource(..)
method. The first parameter passed
to this method is our model map. Here's the complete listing of the
HomePage
class in our trivial word application:
package xslt;
// imports omitted for brevity
public class HomePage extends AbstractXsltView {
protected Source createXsltSource(Map model, String rootName, HttpServletRequest
request, HttpServletResponse response) throws Exception {
Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
Element root = document.createElement(rootName);
List words = (List) model.get("wordList");
for (Iterator it = words.iterator(); it.hasNext();) {
String nextWord = (String) it.next();
Element wordNode = document.createElement("word");
Text textNode = document.createTextNode(nextWord);
wordNode.appendChild(textNode);
root.appendChild(wordNode);
}
return new DOMSource(root);
}
}
A series of parameter name/value pairs can optionally be
defined by your subclass which will be added to the transformation
object. The parameter names must match those defined in your XSLT
template declared with
<xsl:param name="myParam">defaultValue</xsl:param>
.
To specify the parameters, override the
getParameters()
method of the
AbstractXsltView
class and return a
Map
of the name/value pairs. If your parameters
need to derive information from the current request, you can override the
getParameters(HttpServletRequest request)
method instead.
The views.properties file (or equivalent xml definition if you're using an XML based view resolver as we did in the Velocity examples above) looks like this for the one-view application that is 'My First Words':
home.class=xslt.HomePage home.stylesheetLocation=/WEB-INF/xsl/home.xslt home.root=words
Here, you can see how the view is tied in
with the HomePage
class just written which handles the model
domification in the first property '.class'
. The 'stylesheetLocation'
property points to the XSLT file which will handle the XML
transformation into HTML for us and the final property '.root'
is the
name that will be used as the root of the XML document. This gets
passed to the HomePage
class above in the second parameter to the
createXsltSource(..)
method(s).
Finally, we have the XSLT code used for transforming the above
document. As shown in the above 'views.properties'
file, the stylesheet is called
'home.xslt'
and it lives in the war file in the
'WEB-INF/xsl'
directory.
<?xml version="1.0" encoding="utf-8"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:output method="html" omit-xml-declaration="yes"/> <xsl:template match="/"> <html> <head><title>Hello!</title></head> <body> <h1>My First Words</h1> <xsl:apply-templates/> </body> </html> </xsl:template> <xsl:template match="word"> <xsl:value-of select="."/><br/> </xsl:template> </xsl:stylesheet>
A summary of the files discussed and their location in the WAR file is shown in the simplified WAR structure below.
ProjectRoot | +- WebContent | +- WEB-INF | +- classes | | | +- xslt | | | | | +- HomePageController.class | | +- HomePage.class | | | +- views.properties | +- lib | | | +- spring.jar | +- xsl | | | +- home.xslt | +- frontcontroller-servlet.xml
You will also need to ensure that an XML parser and an XSLT engine are available on the classpath. JDK 1.4 provides them by default, and most J2EE containers will also make them available by default, but it's a possible source of errors to be aware of.
Returning an HTML page isn't always the best way for the user to view the model output, and Spring makes it simple to generate a PDF document or an Excel spreadsheet dynamically from the model data. The document is the view and will be streamed from the server with the correct content type to (hopefully) enable the client PC to run their spreadsheet or PDF viewer application in response.
In order to use Excel views, you need to add the 'poi' library to your classpath, and for PDF generation, the iText.jar. Both are included in the main Spring distribution.
Document based views are handled in an almost identical fashion to XSLT views, and the following sections build upon the previous one by demonstrating how the same controller used in the XSLT example is invoked to render the same model as both a PDF document and an Excel spreadsheet (which can also be viewed or manipulated in Open Office).
Firstly, let's amend the views.properties file (or xml equivalent) and add a simple view definition for both document types. The entire file now looks like this with the XSLT view shown from earlier..
home.class=xslt.HomePage home.stylesheetLocation=/WEB-INF/xsl/home.xslt home.root=words xl.class=excel.HomePage pdf.class=pdf.HomePage
If you want to start with a template spreadsheet to add your model data to, specify the location as the 'url' property in the view definition
The controller code we'll use remains exactly the same from the XSLT example earlier other than to change the name of the view to use. Of course, you could be clever and have this selected based on a URL parameter or some other logic - proof that Spring really is very good at decoupling the views from the controllers!
Exactly as we did for the XSLT example, we'll subclass suitable
abstract classes in order to implement custom behavior in generating
our output documents. For Excel, this involves writing a subclass of
org.springframework.web.servlet.view.document.AbstractExcelView
(for Excel files generated by POI)
or org.springframework.web.servlet.view.document.AbstractJExcelView
(for JExcelApi-generated Excel files).
and implementing the buildExcelDocument
Here's the complete listing for our POI Excel view which displays the word list from the model map in consecutive rows of the first column of a new spreadsheet..
package excel; // imports omitted for brevity public class HomePage extends AbstractExcelView { protected void buildExcelDocument( Map model, HSSFWorkbook wb, HttpServletRequest req, HttpServletResponse resp) throws Exception { HSSFSheet sheet; HSSFRow sheetRow; HSSFCell cell; // Go to the first sheet // getSheetAt: only if wb is created from an existing document //sheet = wb.getSheetAt( 0 ); sheet = wb.createSheet("Spring"); sheet.setDefaultColumnWidth((short)12); // write a text at A1 cell = getCell( sheet, 0, 0 ); setText(cell,"Spring-Excel test"); List words = (List ) model.get("wordList"); for (int i=0; i < words.size(); i++) { cell = getCell( sheet, 2+i, 0 ); setText(cell, (String) words.get(i)); } } }
And this a view generating the same Excel file, now using JExcelApi:
package excel; // imports omitted for brevity public class HomePage extends AbstractExcelView { protected void buildExcelDocument(Map model, WritableWorkbook wb, HttpServletRequest request, HttpServletResponse response) throws Exception { WritableSheet sheet = wb.createSheet("Spring"); sheet.addCell(new Label(0, 0, "Spring-Excel test"); List words = (List)model.get("wordList"); for (int i = -; i < words.size(); i++) { sheet.addCell(new Label(2+i, 0, (String)words.get(i)); } } }
Note the differences between the APIs. We've found that the JExcelApi is somewhat more intuitive and furthermore, JExcelApi has a bit better image-handling capabilities. There have been memory problems with large Excel file when using JExcelApi however.
If you now amend the controller such that it returns
xl
as the name of the view (return new
ModelAndView("xl", map);
) and run your application again,
you should find that the Excel spreadsheet is created and downloaded
automatically when you request the same page as before.
The PDF version of the word list is even simpler. This time, the
class extends
org.springframework.web.servlet.view.document.AbstractPdfView
and implements the buildPdfDocument()
method as
follows..
package pdf; // imports omitted for brevity public class PDFPage extends AbstractPdfView { protected void buildPdfDocument( Map model, Document doc, PdfWriter writer, HttpServletRequest req, HttpServletResponse resp) throws Exception { List words = (List) model.get("wordList"); for (int i=0; i<words.size(); i++) doc.add( new Paragraph((String) words.get(i))); } }
Once again, amend the controller to return the
pdf
view with a return new
ModelAndView("pdf", map);
and reload the URL in your
application. This time a PDF document should appear listing each of
the words in the model map.
JasperReports (http://jasperreports.sourceforge.net) is a powerful open-source reporting engine that supports the creation of report designs using an easily understood XML file format. JasperReports is capable of rendering reports output into four different formats: CSV, Excel, HTML and PDF.
Your application will need to include the latest release of JasperReports, which at the time of writing was 0.6.1. JasperReports itself depends on the following projects:
BeanShell
Commons BeanUtils
Commons Collections
Commons Digester
Commons Logging
iText
POI
JasperReports also requires a JAXP compliant XML parser.
To configure JasperReports views in your Spring container configuration
you need to define a ViewResolver
to map view
names to the appropriate view class depending on which format you want your
report rendered in.
Typically, you will use the ResourceBundleViewResolver
to map view names to view classes and files in a properties file.
<bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"> <property name="basename" value="views"/> </bean>
Here we've configured an instance of the ResourceBundleViewResolver
class that will look for view mappings in the resource bundle with base name
views
. (The content of this file is described in the next section.)
The Spring Framework contains five different View
implementations for JasperReports, four of which correspond to one of the four output
formats supported by JasperReports, and one that allows for the format to be determined at runtime:
Table 14.2. JasperReports View
classes
Class Name | Render Format |
---|---|
JasperReportsCsvView | CSV |
JasperReportsHtmlView | HTML |
JasperReportsPdfView | |
JasperReportsXlsView | Microsoft Excel |
JasperReportsMultiFormatView | The view is decided upon at runtime |
Mapping one of these classes to a view name and a report file is a matter of adding the appropriate entries into the resource bundle configured in the previous section as shown here:
simpleReport.class=org.springframework.web.servlet.view.jasperreports.JasperReportsPdfView simpleReport.url=/WEB-INF/reports/DataSourceReport.jasper
Here you can see that the view with name simpleReport
is mapped to the JasperReportsPdfView
class, causing the
output of this report to be rendered in PDF format. The url
property of the view is set to the location of the underlying report file.
JasperReports has two distinct types of report file: the design
file, which has a .jrxml
extension, and the
compiled report file, which has a .jasper
extension. Typically, you use the JasperReports Ant task to compile
your .jrxml
design file into a
.jasper
file before deploying it into your
application. With the Spring Framework you can map either of these files to your
report file and the framework will take care of compiling the
.jrxml
file on the fly for you. You should note
that after a .jrxml
file is compiled by the Spring Framework,
the compiled report is cached for the lifetime of the application. To make
changes to the file you will need to restart your application.
The JasperReportsMultiFormatView
allows for
report format to be specified at runtime. The actual rendering of the
report is delegated to one of the other JasperReports view classes -
the JasperReportsMultiFormatView
class simply adds
a wrapper layer that allows for the exact implementation to be
specified at runtime.
The JasperReportsMultiFormatView
class
introduces two concepts: the format key and the discriminator key. The
JasperReportsMultiFormatView
class uses the mapping
key to lookup the actual view implementation class and uses the format
key to lookup up the mapping key. From a coding perspective you add an
entry to your model with the formay key as the key and the mapping key
as the value, for example:
public ModelAndView handleSimpleReportMulti(HttpServletRequest request, HttpServletResponse response) throws Exception { String uri = request.getRequestURI(); String format = uri.substring(uri.lastIndexOf(".") + 1); Map model = getModel(); model.put("format", format); return new ModelAndView("simpleReportMulti", model); }
In this example, the mapping key is determined from the
extension of the request URI and is added to the model under the
default format key: format
. If you wish to use a
different format key then you can configure this using the
formatKey
property of the
JasperReportsMultiFormatView
class.
By default the following mapping key mappings are configured in
JasperReportsMultiFormatView
:
Table 14.3. JasperReportsMultiFormatView
Default Mapping Key Mappings
Mapping Key | View Class |
---|---|
csv | JasperReportsCsvView |
html | JasperReportsHtmlView |
JasperReportsPdfView | |
xls | JasperReportsXlsView |
So in the example above a request to URI /foo/myReport.pdf
would be mapped to the JasperReportsPdfView
class.
You can override the mapping key to view class mappings using the
formatMappings
property of
JasperReportsMultiFormatView
.
In order to render your report correctly in the format you have
chosen, you must supply Spring with all of the data needed to populate
your report. For JasperReports this means you must pass in all report
parameters along with the report datasource. Report parameters are
simple name/value pairs and can be added be to the
Map
for your model as you would add any name/value
pair.
When adding the datasource to the model you have two approaches to
choose from. The first approach is to add an instance of
JRDataSource
or a Collection
type to the
model Map
under any arbitrary key. Spring will then
locate this object in the model and treat it as the report datasource.
For example, you may populate your model like so:
private Map getModel() { Map model = new HashMap(); Collection beanData = getBeanData(); model.put("myBeanData", beanData); return model; }
The second approach is to add the instance of
JRDataSource
or Collection
under a
specific key and then configure this key using the
reportDataKey
property of the view class. In both
cases Spring will instances of Collection
in a
JRBeanCollectionDataSource
instance. For example:
private Map getModel() { Map model = new HashMap(); Collection beanData = getBeanData(); Collection someData = getSomeData(); model.put("myBeanData", beanData); model.put("someData", someData); return model; }
Here you can see that two Collection
instances are being added to the model. To ensure that the correct one
is used, we simply modify our view configuration as appropriate:
simpleReport.class=org.springframework.web.servlet.view.jasperreports.JasperReportsPdfView simpleReport.url=/WEB-INF/reports/DataSourceReport.jasper simpleReport.reportDataKey=myBeanData
Be aware that when using the first approach, Spring will use the
first instance of JRDataSource
or
Collection
that it encounters. If you need to place
multiple instances of JRDataSource
or
Collection
into the model then you need to use the
second approach.
JasperReports provides support for embedded sub-reports within your master report files. There are a wide variety of mechanisms for including sub-reports in your report files. The easiest way is to hard code the report path and the SQL query for the sub report into your design files. The drawback of this approach is obvious - the values are hard-coded into your report files reducing reusability and making it harder to modify and update report designs. To overcome this you can configure sub-reports declaratively and you can include additional data for these sub-reports directly from your controllers.
To control which sub-report files are included in a master report using Spring, your report file must be configured to accept sub-reports from an external source. To do this you declare a parameter in your report file like so:
<parameter name="ProductsSubReport" class="net.sf.jasperreports.engine.JasperReport"/>
Then, you define your sub-report to use this sub-report parameter:
<subreport> <reportElement isPrintRepeatedValues="false" x="5" y="25" width="325" height="20" isRemoveLineWhenBlank="true" backcolor="#ffcc99"/> <subreportParameter name="City"> <subreportParameterExpression><![CDATA[$F{city}]]></subreportParameterExpression> </subreportParameter> <dataSourceExpression><![CDATA[$P{SubReportData}]]></dataSourceExpression> <subreportExpression class="net.sf.jasperreports.engine.JasperReport"> <![CDATA[$P{ProductsSubReport}]]></subreportExpression> </subreport>
This defines a master report file that
expects the sub-report to be passed in as an instance of
net.sf.jasperreports.engine.JasperReports
under the
parameter ProductsSubReport
. When configuring your
Jasper view class, you can instruct Spring to load a report file and
pass into the JasperReports engine as a sub-report using the
subReportUrls
property:
<property name="subReportUrls"> <map> <entry key="ProductsSubReport" value="/WEB-INF/reports/subReportChild.jrxml"/> </map> </property>
Here, the key of the Map
corresponds to the name of the sub-report parameter in th report
design file, and the entry is the URL of the report file. Spring will
load this report file, compiling it if necessary, and will pass into
the JasperReports engine under the given key.
This step is entirely optional when using Spring configure your
sub-reports. If you wish, you can still configure the data source for
your sub-reports using static queries. However, if you want Spring to
convert data returned in your ModelAndView
into
instances of JRDataSource
then you need to specify
which of the parameters in your ModelAndView
Spring
should convert. To do this configure the list of parameter names using
the subReportDataKeys
property of the your chosen
view class:
<property name="subReportDataKeys" value="SubReportData"/>
Here, the key you supply MUST
correspond to both the key used in your ModelAndView
and the key used in your report design file.
If you have special requirements for exporter configuration -
perhaps you want a specific page size for your PDF report, then you can
configure these exporter parameters declaratively in your Spring
configuration file using the exporterParameters
property of the view class. The exporterParameters
property is typed as Map
and in your configuration
the key of an entry should be the fully-qualified name of a static field
that contains the exporter parameter definition and the value of an
entry should be the value you want to assign to the parameter. An
example of this is shown below:
<bean id="htmlReport" class="org.springframework.web.servlet.view.jasperreports.JasperReportsHtmlView"> <property name="url" value="/WEB-INF/reports/simpleReport.jrxml"/> <property name="exporterParameters"> <map> <entry key="net.sf.jasperreports.engine.export.JRHtmlExporterParameter.HTML_FOOTER"> <value>Footer by Spring! </td><td width="50%">&nbsp; </td></tr> </table></body></html> </value> </entry> </map> </property> </bean>
Here you can see that the JasperReportsHtmlView
is
being configured with an exporter parameter for
net.sf.jasperreports.engine.export.JRHtmlExporterParameter.HTML_FOOTER
which will output a footer in the resulting HTML.
This chapter details Spring's integration with third party web frameworks such as JSF, Struts, WebWork, and Tapestry.
One of the core value propositions of the Spring Framework is that of enabling choice. In a general sense, Spring does not force one to use or buy into any particular architecture, technology, or methodology (although it certainly recommends some over others). This freedom to pick and choose the architecture, technology, or methodology that is most relevant to a developer and his or her development team is arguably most evident in the web area, where Spring provides its own web framework (Spring MVC), while at the same time providing integration with a number of popular third party web frameworks. This allows one to continue to leverage any and all of the skills one may have acquired in a particular web framework such as Struts, while at the same time being able to enjoy the benefits afforded by Spring in other areas such as data access, declarative transaction management, and flexible configuration and application assembly.
Having dispensed with the woolly sales patter (c.f. the previous paragraph), the remainder of this chapter will concentrate upon the meaty details of integrating your favourite web framework with Spring. One thing that is often commented upon by developers coming to Java from other languages is the seeming super-abundance of web frameworks available in Java... there are indeed a great number of web frameworks in the Java space; in fact there are far too many to cover with any semblance of detail in a single chapter. This chapter thus picks four of the more popular web frameworks in Java, starting with the Spring configuration that is common to all of the supported web frameworks, and then detailing the specific integration options for each supported web framework.
Please note that this chapter does not attempt to explain how to use any of the supported web frameworks. For example, if you want to use Struts for the presentation layer of your web application, the assumption is that you are already familiar with Struts. If you need further details about any of the supported web frameworks themselves, please do consult the section entitled Section 15.7, “Further Resources” at the end of this chapter.
Before diving into the integration specifics of each supported web framework, let us first take a look at the Spring configuration that not specific to any one web framework. (This section is equally applicable to Spring's own web framework, Spring MVC.)
One of the concepts (for want of a better word) espoused by (Spring's) lightweight
application model is that of a layered architecture. Remember that in a 'classic'
layered architecture, the web layer is but one of many layers... it serves as one
of the entry points into a server side application, and it delegates to service
objects (facades) defined in a service layer to satisfy business specific (and
presentation-technology agnostic) use cases. In Spring, these service objects,
any other business-specific objects, data access objects, etc. exist in a
distinct 'business context', which contains no web or
presentation layer objects (presentation objects such as Spring MVC controllers
are typically configured in a distinct 'presentation context'). This section
details how one configures a Spring container (a
WebApplicationContext
) that contains all of the
'business beans' in one's application.
Onto specifics... all that one need do is to declare a
ContextLoaderListener
in the standard J2EE servlet web.xml
file of one's web application,
and add a contextConfigLocation
<context-param/> section
(in the same file) that defines which set of Spring XML cpnfiguration files to load.
Find below the <listener/> configuration:
<listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener>
![]() | Note |
---|---|
Listeners were added to the Servlet API in version 2.3; listener startup order was
finally clarified in Servlet 2.4. If you have a Servlet 2.3 container, you can use the
|
Find below the <context-param/> configuration:
<context-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/applicationContext*.xml</param-value> </context-param>
If you don't specify the contextConfigLocation
context parameter, the ContextLoaderListener
will look
for a file called /WEB-INF/applicationContext.xml
to load.
Once the context files are loaded, Spring creates a
WebApplicationContext
object based on the bean definitions and stores it in the
ServletContext of one's web application.
All Java web frameworks are built on top of the Servlet API, and so one can
use the following code snippet to get access to this 'business context'
ApplicationContext created by the
ContextLoaderListener
.
WebApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(servletContext);
The WebApplicationContextUtils
class is for convenience, so you don't have to remember the name of the
ServletContext attribute. Its getWebApplicationContext()
method will return null
if an object doesn't exist under the
WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE
key. Rather
than risk getting NullPointerExceptions
in your application, it's
better to use the getRequiredWebApplicationContext()
method. This
method throws an exception when the ApplicationContext is missing.
Once you have a reference to the WebApplicationContext
,
you can retrieve beans by their name or type. Most developers retrieve beans
by name, then cast them to one of their implemented interfaces.
Fortunately, most of the frameworks in this section have simpler ways of looking up beans. Not only do they make it easy to get beans from a Spring container, but they also allow you to use dependency injection on their controllers. Each web framework section has more detail on its specific integration strategies.
JavaServer Faces (JSF) is the JCP's standard component-based, event-driven web user interface framework. As of Java EE 5, it is an official part of the Java EE umbrella.
For a popular JSF runtime as well as for popular JSF component libraries, check out the Apache MyFaces project. The MyFaces project also provides common JSF extensions such as MyFaces Orchestra: a Spring-based JSF extension that provides rich conversation scope support.
![]() | Note |
---|---|
Spring Web Flow 2.0 provides rich JSF support through its newly established Spring Faces module, both for JSF-centric usage (as described in this section) and for Spring-centric usage (using JSF views within a Spring MVC dispatcher). Check out the Spring Web Flow website for details! |
The key element in Spring's JSF integration is the JSF 1.1
VariableResolver
mechanism. On JSF 1.2,
Spring supports the ELResolver
mechanism
as a next-generation version of JSF EL integration.
The easiest way to integrate one's Spring middle-tier with one's
JSF web layer is to use the
DelegatingVariableResolver
class. To configure
this variable resolver in one's application, one will need to edit one's
faces-context.xml file. After the opening
<faces-config/>
element, add an <application/>
element and a <variable-resolver/>
element within it.
The value of the variable resolver should reference Spring's
DelegatingVariableResolver
; for example:
<faces-config> <application> <variable-resolver>org.springframework.web.jsf.DelegatingVariableResolver</variable-resolver> <locale-config> <default-locale>en</default-locale> <supported-locale>en</supported-locale> <supported-locale>es</supported-locale> </locale-config> <message-bundle>messages</message-bundle> </application> </faces-config>
The DelegatingVariableResolver
will first delegate value
lookups to the default resolver of the underlying JSF implementation, and
then to Spring's 'business context' WebApplicationContext
.
This allows one to easily inject dependencies into one's JSF-managed beans.
Managed beans are defined in one's faces-config.xml
file. Find below an example where #{userManager}
is a bean
that is retrieved from the Spring 'business context'.
<managed-bean> <managed-bean-name>userList</managed-bean-name> <managed-bean-class>com.whatever.jsf.UserList</managed-bean-class> <managed-bean-scope>request</managed-bean-scope> <managed-property> <property-name>userManager</property-name> <value>#{userManager}</value> </managed-property> </managed-bean>
SpringBeanVariableResolver
is a variant of
DelegatingVariableResolver
. It delegates to the
Spring's 'business context' WebApplicationContext
first, then to the default resolver of the
underlying JSF implementation. This is useful in particular when
using request/session-scoped beans with special Spring resolution rules,
e.g. Spring FactoryBean
implementations.
Configuration-wise, simply define SpringBeanVariableResolver
in your faces-context.xml file:
<faces-config> <application> <variable-resolver>org.springframework.web.jsf.SpringBeanVariableResolver</variable-resolver> ... </application> </faces-config>
SpringBeanFacesELResolver
is a JSF 1.2 compliant
ELResolver
implementation, integrating with
the standard Unified EL as used by JSF 1.2 and JSP 2.1. Like
SpringBeanVariableResolver
, it delegates to the
Spring's 'business context' WebApplicationContext
first, then to the default resolver of the
underlying JSF implementation.
Configuration-wise, simply define SpringBeanFacesELResolver
in your JSF 1.2 faces-context.xml file:
<faces-config> <application> <el-resolver>org.springframework.web.jsf.el.SpringBeanFacesELResolver</el-resolver> ... </application> </faces-config>
A custom VariableResolver
works well when mapping
one's properties to beans in faces-config.xml, but at times
one may need to grab a bean explicitly. The
FacesContextUtils
class makes this easy. It is
similar to WebApplicationContextUtils
, except that it
takes a FacesContext
parameter rather than a
ServletContext parameter.
ApplicationContext ctx = FacesContextUtils.getWebApplicationContext(FacesContext.getCurrentInstance());
Struts is the de facto web framework for Java applications, mainly because it was one of the first to be released (June 2001). Invented by Craig McClanahan, Struts is an open source project hosted by the Apache Software Foundation. At the time, it greatly simplified the JSP/Servlet programming paradigm and won over many developers who were using proprietary frameworks. It simplified the programming model, it was open source (and thus free as in beer), and it had a large community, which allowed the project to grow and become popular among Java web developers.
![]() | Note |
---|---|
The following section discusses Struts 1 a.k.a. "Struts Classic". Struts 2 is effectively a different product - a successor of WebWork 2.2 (as discussed in Section 15.5, “WebWork 2.x”), carrying the Struts brand now. Check out the Struts 2 Spring Plugin for the built-in Spring integration shipped with Struts 2. In general, Struts 2 is closer to WebWork 2.2 than to Struts 1 in terms of its Spring integration implications. |
To integrate your Struts 1.x application with Spring, you have two options:
Configure Spring to manage your Actions as beans, using the
ContextLoaderPlugin
, and set their
dependencies in a Spring context file.
Subclass Spring's ActionSupport
classes and grab your Spring-managed beans explicitly using
a getWebApplicationContext() method.
The ContextLoaderPlugin
is a Struts 1.1+ plug-in that loads a Spring context file for the Struts
ActionServlet
. This context refers to the root
WebApplicationContext
(loaded by the
ContextLoaderListener
) as its parent. The default
name of the context file is the name of the mapped servlet, plus
-servlet.xml. If ActionServlet
is defined in web.xml as
<servlet-name>action</servlet-name>
, the
default is /WEB-INF/action-servlet.xml.
To configure this plug-in, add the following XML to the plug-ins section near the bottom of your struts-config.xml file:
<plug-in className="org.springframework.web.struts.ContextLoaderPlugIn"/>
The location of the context configuration files can be customized using the
'contextConfigLocation
' property.
<plug-in className="org.springframework.web.struts.ContextLoaderPlugIn"> <set-property property="contextConfigLocation" value="/WEB-INF/action-servlet.xml,/WEB-INF/applicationContext.xml"/> </plug-in>
It is possible to use this plugin to load all your context files, which can be
useful when using testing tools like StrutsTestCase. StrutsTestCase's
MockStrutsTestCase
won't initialize Listeners on startup
so putting all your context files in the plugin is a workaround. (A
bug has been filed for this issue, but has been closed as 'Wont Fix').
After configuring this plug-in in struts-config.xml, you can
configure your Action
to be managed by Spring. Spring (1.1.3+)
provides two ways to do this:
Override Struts' default RequestProcessor
with Spring's DelegatingRequestProcessor
.
Use the DelegatingActionProxy
class
in the type
attribute of your
<action-mapping>
.
Both of these methods allow you to manage your Actions and their dependencies in the action-servlet.xml file. The bridge between the Action in struts-config.xml and action-servlet.xml is built with the action-mapping's "path" and the bean's "name". If you have the following in your struts-config.xml file:
<action path="/users" .../>
You must define that Action's bean with the "/users" name in action-servlet.xml:
<bean name="/users" .../>
To configure the
DelegatingRequestProcessor
in your
struts-config.xml file, override the "processorClass"
property in the <controller> element. These lines follow the
<action-mapping> element.
<controller> <set-property property="processorClass" value="org.springframework.web.struts.DelegatingRequestProcessor"/> </controller>
After adding this setting, your Action will automatically be looked up in Spring's context file, no matter what the type. In fact, you don't even need to specify a type. Both of the following snippets will work:
<action path="/user" type="com.whatever.struts.UserAction"/> <action path="/user"/>
If you're using Struts' modules feature,
your bean names must contain the module prefix. For example, an action
defined as <action path="/user"/>
with module
prefix "admin" requires a bean name with
<bean name="/admin/user"/>
.
![]() | Note |
---|---|
If you are using Tiles in your Struts application, you must configure your
<controller> with the
|
If you have a custom RequestProcessor
and
can't use the DelegatingRequestProcessor
or
DelegatingTilesRequestProcessor
approaches, you can
use the
DelegatingActionProxy
as the type in your
action-mapping.
<action path="/user" type="org.springframework.web.struts.DelegatingActionProxy" name="userForm" scope="request" validate="false" parameter="method"> <forward name="list" path="/userList.jsp"/> <forward name="edit" path="/userForm.jsp"/> </action>
The bean definition in action-servlet.xml
remains the same, whether you use a custom RequestProcessor
or the DelegatingActionProxy
.
If you define your Action
in a context file, the
full feature set of Spring's bean container will be available for it:
dependency injection as well as the option to instantiate a new
Action
instance for each request. To activate the latter,
add scope="prototype" to your Action's bean definition.
<bean name="/user" scope="prototype" autowire="byName" class="org.example.web.UserAction"/>
As previously mentioned, you can retrieve the
WebApplicationContext
from the ServletContext
using the WebApplicationContextUtils
class. An
easier way is to extend Spring's Action
classes for
Struts. For example, instead of subclassing Struts'
Action
class, you can subclass Spring's
ActionSupport
class.
The ActionSupport
class provides additional
convenience methods, like getWebApplicationContext().
Below is an example of how you might use this in an Action:
public class UserAction extends DispatchActionSupport { public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { if (log.isDebugEnabled()) { log.debug("entering 'delete' method..."); } WebApplicationContext ctx = getWebApplicationContext(); UserManager mgr = (UserManager) ctx.getBean("userManager"); // talk to manager for business logic return mapping.findForward("success"); } }
Spring includes subclasses for all of the standard Struts Actions - the Spring versions merely have Support appended to the name:
The recommended strategy is to use the approach that best suits
your project. Subclassing makes your code more readable, and you know
exactly how your dependencies are resolved. However, using the
ContextLoaderPlugin
allow you to easily add new
dependencies in your context XML file. Either way, Spring provides some
nice options for integrating the two frameworks.
From the WebWork homepage...
“ WebWork is a Java web-application development framework. It is built specifically with developer productivity and code simplicity in mind, providing robust support for building reusable UI templates, such as form controls, UI themes, internationalization, dynamic form parameter mapping to JavaBeans, robust client and server side validation, and much more. ”WebWork is (in the opinion of this author) a very clean, elegant web framework. Its architecture and key concepts are not only very easy to understand, it has a rich tag library, nicely decoupled validation, and it is (again, in the opinion of this author) quite easy to be productive in next to no time at all (the documentation and tutorials are pretty good too).
One of the key enablers in WebWork's technology stack is an IoC container to manage Webwork Actions, handle the "wiring" of business objects, etc. Previous to WebWork version 2.2, WebWork used it's own proprietary IoC container (and provided integration points so that one could integrate an IoC container such as Springs into the mix). However, as of WebWork version 2.2, the default IoC container that is used within WebWork is Spring. This is obviously great news if one is a Spring developer, because it means that one is immediately familiar with the basics of IoC configuration, idioms and suchlike within WebWork.
Now in the interests of adhering to the DRY (Dont Repeat Yourself) principle, it would be foolish to writeup the Spring-WebWork integration in light of the fact that the WebWork team have already written such a writeup. Please do consult the Spring-WebWork integration page on the WebWork wiki for the full lowdown.
Note that the Spring-WebWork integration code was developed (and continues to be maintained and improved) by the WebWork developers themselves, so in the first instance please do refer to the WebWork site and forums if you are having issues with the integration. Do feel free to post comments and queries regarding the Spring-WebWork integration on the Spring support forums too.
From the Tapestry homepage...
“ Tapestry is an open-source framework for creating dynamic, robust, highly scalable web applications in Java. Tapestry complements and builds upon the standard Java Servlet API, and so it works in any servlet container or application server. ”While Spring has its own powerful web layer, there are a number of unique advantages to building a J2EE application using a combination of Tapestry for the web user interface and the Spring container for the lower layers. This section of the web integration chapter attempts to detail a few best practices for combining these two frameworks.
A typical layered J2EE application built with Tapestry
and Spring will consist of a top user interface (UI) layer built with Tapestry,
and a number of lower layers, all wired together by one or more Spring containers.
Tapestry's own reference documentation contains the following snippet of best
practice advice. (Text that the author of this Spring section has added is
contained within []
brackets.)
The key question then is... how does one supply Tapestry pages with collaborating services? The answer, ideally, is that one would want to dependency inject those services directly into one's Tapestry pages. In Tapestry, one can effect this dependency injection by a variety of means... This section is only going to enumerate the dependency injection means afforded by Spring. The real beauty of the rest of this Spring-Tapestry integration is that the elegant and flexible design of Tapestry itself makes doing this dependency injection of Spring-managed beans a cinch. (Another nice thing is that this Spring-Tapestry integration code was written - and continues to be maintained - by the Tapestry creator Howard M. Lewis Ship, so hats off to him for what is really some silky smooth integration).
Assume we have the following simple Spring container definition (in the ubiquitous XML format):
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd"> <beans> <!-- the DataSource --> <bean id="dataSource" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="java:DefaultDS"/> </bean> <bean id="hibSessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"> <property name="dataSource" ref="dataSource"/> </bean> <bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager"/> <bean id="mapper" class="com.whatever.dataaccess.mapper.hibernate.MapperImpl"> <property name="sessionFactory" ref="hibSessionFactory"/> </bean> <!-- (transactional) AuthenticationService --> <bean id="authenticationService" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean"> <property name="transactionManager" ref="transactionManager"/> <property name="target"> <bean class="com.whatever.services.service.user.AuthenticationServiceImpl"> <property name="mapper" ref="mapper"/> </bean> </property> <property name="proxyInterfacesOnly" value="true"/> <property name="transactionAttributes"> <value> *=PROPAGATION_REQUIRED </value> </property> </bean> <!-- (transactional) UserService --> <bean id="userService" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean"> <property name="transactionManager" ref="transactionManager"/> <property name="target"> <bean class="com.whatever.services.service.user.UserServiceImpl"> <property name="mapper" ref="mapper"/> </bean> </property> <property name="proxyInterfacesOnly" value="true"/> <property name="transactionAttributes"> <value> *=PROPAGATION_REQUIRED </value> </property> </bean> </beans>
Inside the Tapestry application, the above bean definitions need to
be loaded into a Spring container,
and any relevant Tapestry pages need to be supplied (injected) with the
authenticationService
and
userService
beans, which implement the
AuthenticationService
and
UserService
interfaces, respectively.
At this point, the application context is available to a web
application by calling Spring's static utility function
WebApplicationContextUtils.getApplicationContext(servletContext)
,
where servletContext is the standard ServletContext
from the J2EE Servlet specification. As such, one simple mechanism for
a page to get an instance of the UserService
,
for example, would be with code such as:
WebApplicationContext appContext = WebApplicationContextUtils.getApplicationContext(
getRequestCycle().getRequestContext().getServlet().getServletContext());
UserService userService = (UserService) appContext.getBean("userService");
... some code which uses UserService
This mechanism does work... having said that, it can be made a lot less verbose by encapsulating most of the functionality in a method in the base class for the page or component. However, in some respects it goes against the IoC principle; ideally you would like the page to not have to ask the context for a specific bean by name, and in fact, the page would ideally not know about the context at all.
Luckily, there is a mechanism to allow this. We rely upon the fact that Tapestry already has a mechanism to declaratively add properties to a page, and it is in fact the preferred approach to manage all properties on a page in this declarative fashion, so that Tapestry can properly manage their lifecycle as part of the page and component lifecycle.
![]() | Note |
---|---|
This next section is applicable to Tapestry 3.x. If you are using Tapestry version 4.x, please consult the section entitled Section 15.6.1.4, “Dependency Injecting Spring Beans into Tapestry pages - Tapestry 4.x style”. |
First we need to make the ApplicationContext
available to the Tapestry page or Component without having to have the
ServletContext; this is because at the stage in the
page's/component's lifecycle when we need to access the
ApplicationContext, the
ServletContext won't be easily available to the
page, so we can't use
WebApplicationContextUtils.getApplicationContext(servletContext)
directly. One way is by defining a custom version of the Tapestry
IEngine
which exposes this for us:
package com.whatever.web.xportal; import ... public class MyEngine extends org.apache.tapestry.engine.BaseEngine { public static final String APPLICATION_CONTEXT_KEY = "appContext"; /** * @see org.apache.tapestry.engine.AbstractEngine#setupForRequest(org.apache.tapestry.request.RequestContext) */ protected void setupForRequest(RequestContext context) { super.setupForRequest(context); // insert ApplicationContext in global, if not there Map global = (Map) getGlobal(); ApplicationContext ac = (ApplicationContext) global.get(APPLICATION_CONTEXT_KEY); if (ac == null) { ac = WebApplicationContextUtils.getWebApplicationContext( context.getServlet().getServletContext() ); global.put(APPLICATION_CONTEXT_KEY, ac); } } }
This engine class places the Spring Application Context as an attribute called "appContext" in this Tapestry app's 'Global' object. Make sure to register the fact that this special IEngine instance should be used for this Tapestry application, with an entry in the Tapestry application definition file. For example:
file: xportal.application:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE application PUBLIC
"-//Apache Software Foundation//Tapestry Specification 3.0//EN"
"http://jakarta.apache.org/tapestry/dtd/Tapestry_3_0.dtd">
<application
name="Whatever xPortal"
engine-class="com.whatever.web.xportal.MyEngine">
</application>
Now in our page or component definition file (*.page or *.jwc),
we simply add property-specification elements to grab the beans we
need out of the ApplicationContext
,
and create page or component properties for them. For example:
<property-specification name="userService" type="com.whatever.services.service.user.UserService"> global.appContext.getBean("userService") </property-specification> <property-specification name="authenticationService" type="com.whatever.services.service.user.AuthenticationService"> global.appContext.getBean("authenticationService") </property-specification>
The OGNL expression inside the property-specification specifies the initial value for the property, as a bean obtained from the context. The entire page definition might look like this:
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE page-specification PUBLIC "-//Apache Software Foundation//Tapestry Specification 3.0//EN" "http://jakarta.apache.org/tapestry/dtd/Tapestry_3_0.dtd"> <page-specification class="com.whatever.web.xportal.pages.Login"> <property-specification name="username" type="java.lang.String"/> <property-specification name="password" type="java.lang.String"/> <property-specification name="error" type="java.lang.String"/> <property-specification name="callback" type="org.apache.tapestry.callback.ICallback" persistent="yes"/> <property-specification name="userService" type="com.whatever.services.service.user.UserService"> global.appContext.getBean("userService") </property-specification> <property-specification name="authenticationService" type="com.whatever.services.service.user.AuthenticationService"> global.appContext.getBean("authenticationService") </property-specification> <bean name="delegate" class="com.whatever.web.xportal.PortalValidationDelegate"/> <bean name="validator" class="org.apache.tapestry.valid.StringValidator" lifecycle="page"> <set-property name="required" expression="true"/> <set-property name="clientScriptingEnabled" expression="true"/> </bean> <component id="inputUsername" type="ValidField"> <static-binding name="displayName" value="Username"/> <binding name="value" expression="username"/> <binding name="validator" expression="beans.validator"/> </component> <component id="inputPassword" type="ValidField"> <binding name="value" expression="password"/> <binding name="validator" expression="beans.validator"/> <static-binding name="displayName" value="Password"/> <binding name="hidden" expression="true"/> </component> </page-specification>
Now in the Java class definition for the page or component itself, all we need to do is add an abstract getter method for the properties we have defined (in order to be able to access the properties).
// our UserService implementation; will come from page definition public abstract UserService getUserService(); // our AuthenticationService implementation; will come from page definition public abstract AuthenticationService getAuthenticationService();
For the sake of completeness, the entire Java class, for a login page in this example, might look like this:
package com.whatever.web.xportal.pages; /** * Allows the user to login, by providing username and password. * After successfully logging in, a cookie is placed on the client browser * that provides the default username for future logins (the cookie * persists for a week). */ public abstract class Login extends BasePage implements ErrorProperty, PageRenderListener { /** the key under which the authenticated user object is stored in the visit as */ public static final String USER_KEY = "user"; /** The name of the cookie that identifies a user **/ private static final String COOKIE_NAME = Login.class.getName() + ".username"; private final static int ONE_WEEK = 7 * 24 * 60 * 60; public abstract String getUsername(); public abstract void setUsername(String username); public abstract String getPassword(); public abstract void setPassword(String password); public abstract ICallback getCallback(); public abstract void setCallback(ICallback value); public abstract UserService getUserService(); public abstract AuthenticationService getAuthenticationService(); protected IValidationDelegate getValidationDelegate() { return (IValidationDelegate) getBeans().getBean("delegate"); } protected void setErrorField(String componentId, String message) { IFormComponent field = (IFormComponent) getComponent(componentId); IValidationDelegate delegate = getValidationDelegate(); delegate.setFormComponent(field); delegate.record(new ValidatorException(message)); } /** * Attempts to login. * <p> * If the user name is not known, or the password is invalid, then an error * message is displayed. **/ public void attemptLogin(IRequestCycle cycle) { String password = getPassword(); // Do a little extra work to clear out the password. setPassword(null); IValidationDelegate delegate = getValidationDelegate(); delegate.setFormComponent((IFormComponent) getComponent("inputPassword")); delegate.recordFieldInputValue(null); // An error, from a validation field, may already have occurred. if (delegate.getHasErrors()) { return; } try { User user = getAuthenticationService().login(getUsername(), getPassword()); loginUser(user, cycle); } catch (FailedLoginException ex) { this.setError("Login failed: " + ex.getMessage()); return; } } /** * Sets up the {@link User} as the logged in user, creates * a cookie for their username (for subsequent logins), * and redirects to the appropriate page, or * a specified page). **/ public void loginUser(User user, IRequestCycle cycle) { String username = user.getUsername(); // Get the visit object; this will likely force the // creation of the visit object and an HttpSession Map visit = (Map) getVisit(); visit.put(USER_KEY, user); // After logging in, go to the MyLibrary page, unless otherwise specified ICallback callback = getCallback(); if (callback == null) { cycle.activate("Home"); } else { callback.performCallback(cycle); } IEngine engine = getEngine(); Cookie cookie = new Cookie(COOKIE_NAME, username); cookie.setPath(engine.getServletPath()); cookie.setMaxAge(ONE_WEEK); // Record the user's username in a cookie cycle.getRequestContext().addCookie(cookie); engine.forgetPage(getPageName()); } public void pageBeginRender(PageEvent event) { if (getUsername() == null) { setUsername(getRequestCycle().getRequestContext().getCookieValue(COOKIE_NAME)); } } }
Effecting the dependency injection of Spring-managed beans into Tapestry
pages in Tapestry version 4.x is so much simpler.
All that is needed is a single
add-on library,
and some (small) amount of (essentially boilerplate) configuration.
Simply package and deploy this library with the (any of the) other
libraries required by your web application (typically in
WEB-INF/lib
).
You will then need to create and expose the Spring container using the
method detailed previously.
You can then inject Spring-managed beans into Tapestry very easily; if
we are using Java 5, consider the Login
page from above:
we simply need to annotate the appropriate getter methods
in order to dependency inject the Spring-managed userService
and authenticationService
objects (lots of the class
definition has been elided for clarity)...
package com.whatever.web.xportal.pages; public abstract class Login extends BasePage implements ErrorProperty, PageRenderListener { @InjectObject("spring:userService") public abstract UserService getUserService(); @InjectObject("spring:authenticationService") public abstract AuthenticationService getAuthenticationService(); }
We are almost done... all that remains is the HiveMind configuration that exposes the
Spring container stored in the ServletContext
as a
HiveMind service; for example:
<?xml version="1.0"?> <module id="com.javaforge.tapestry.spring" version="0.1.1"> <service-point id="SpringApplicationInitializer" interface="org.apache.tapestry.services.ApplicationInitializer" visibility="private"> <invoke-factory> <construct class="com.javaforge.tapestry.spring.SpringApplicationInitializer"> <set-object property="beanFactoryHolder" value="service:hivemind.lib.DefaultSpringBeanFactoryHolder" /> </construct> </invoke-factory> </service-point> <!-- Hook the Spring setup into the overall application initialization. --> <contribution configuration-id="tapestry.init.ApplicationInitializers"> <command id="spring-context" object="service:SpringApplicationInitializer" /> </contribution> </module>
If you are using Java 5 (and thus have access to annotations), then that really is it.
If you are not using Java 5, then one obviously doesn't annotate one's
Tapestry page classes with annotations; instead, one simply uses
good old fashioned XML to declare the dependency injection; for example,
inside the .page
or .jwc
file
for the Login
page (or component):
<inject property="userService" object="spring:userService"/> <inject property="authenticationService" object="spring:authenticationService"/>
In this example, we've managed to allow service beans defined in a Spring container to be provided to the Tapestry page in a declarative fashion. The page class does not know where the service implementations are coming from, and in fact it is easy to slip in another implementation, for example, during testing. This inversion of control is one of the prime goals and benefits of the Spring Framework, and we have managed to extend it all the way up the J2EE stack in this Tapestry application.
In addition to supporting conventional (servlet-based) Web development, Spring also supports JSR-168 Portlet development. As much as possible, the Portlet MVC framework is a mirror image of the Web MVC framework, and also uses the same underlying view abstractions and integration technology. So, be sure to review the chapters entitled Chapter 13, Web MVC framework and Chapter 14, View technologies before continuing with this chapter.
![]() | Note |
---|---|
Bear in mind that while the concepts of Spring MVC are the same in Spring Portlet MVC, there are some notable differences created by the unique workflow of JSR-168 portlets. |
The main way in which portlet workflow differs from servlet workflow is that the request to the portlet can have two distinct phases: the action phase and the render phase. The action phase is executed only once and is where any 'backend' changes or actions occur, such as making changes in a database. The render phase then produces what is displayed to the user each time the display is refreshed. The critical point here is that for a single overall request, the action phase is executed only once, but the render phase may be executed multiple times. This provides (and requires) a clean separation between the activities that modify the persistent state of your system and the activities that generate what is displayed to the user.
The dual phases of portlet requests are one of the real strengths
of the JSR-168 specification. For example, dynamic search results can be
updated routinely on the display without the user explicitly rerunning
the search. Most other portlet MVC frameworks attempt to completely
hide the two phases from the developer and make it look as much like
traditional servlet development as possible - we think this
approach removes one of the main benefits of using portlets. So, the
separation of the two phases is preserved throughout the Spring Portlet
MVC framework. The primary manifestation of this approach is that where
the servlet version of the MVC classes will have one method that deals
with the request, the portlet version of the MVC classes will have two
methods that deal with the request: one for the action phase and one for
the render phase. For example, where the servlet version of
AbstractController
has the
handleRequestInternal(..)
method, the portlet
version of AbstractController
has
handleActionRequestInternal(..)
and
handleRenderRequestInternal(..)
methods.
The framework is designed around a
DispatcherPortlet
that dispatches requests to
handlers, with configurable handler mappings and view resolution, just
as the DispatcherServlet
in the web framework
does. File upload is also supported in the same way.
Locale resolution and theme resolution are not supported in
Portlet MVC - these areas are in the purview of the
portal/portlet container and are not appropriate at the Spring level.
However, all mechanisms in Spring that depend on the locale (such as
internationalization of messages) will still function properly because
DispatcherPortlet
exposes the current locale in
the same way as DispatcherServlet
.
The default handler is still a very simple
Controller
interface, offering just two
methods:
void handleActionRequest(request,response)
ModelAndView handleRenderRequest(request,response)
The framework also includes most of the same controller
implementation hierarchy, such as AbstractController
,
SimpleFormController
, and so on. Data binding,
command object usage, model handling, and view resolution are all the
same as in the servlet framework.
All the view rendering capabilities of the servlet framework are
used directly via a special bridge servlet named
ViewRendererServlet
. By using this servlet, the
portlet request is converted into a servlet request and the view can be
rendered using the entire normal servlet infrastructure. This means all
the existing renderers, such as JSP, Velocity, etc., can still be used
within the portlet.
Spring Portlet MVC supports beans whose lifecycle is scoped to the
current HTTP request or HTTP Session
(both
normal and global). This is not a specific feature of Spring Portlet MVC
itself, but rather of the WebApplicationContext
container(s) that Spring Portlet MVC uses. These bean scopes are described
in detail in the section entitled Section 3.4.4, “The other scopes”
![]() | Note |
---|---|
The Spring distribution ships with a complete Spring Portlet MVC
sample application that demonstrates all of the features and functionality
of the Spring Portlet MVC framework. This 'petportal' application can be found
in the |
Portlet MVC is a request-driven web MVC framework, designed around
a portlet that dispatches requests to controllers and offers other
functionality facilitating the development of portlet applications.
Spring's DispatcherPortlet
however, does more
than just that. It is completely integrated with the Spring
ApplicationContext
and allows you to use
every other feature Spring has.
Like ordinary portlets, the
DispatcherPortlet
is declared in the
portlet.xml
of your web application:
<portlet> <portlet-name>sample</portlet-name> <portlet-class>org.springframework.web.portlet.DispatcherPortlet</portlet-class> <supports> <mime-type>text/html</mime-type> <portlet-mode>view</portlet-mode> </supports> <portlet-info> <title>Sample Portlet</title> </portlet-info> </portlet>
The DispatcherPortlet
now needs to be
configured.
In the Portlet MVC framework, each
DispatcherPortlet
has its own
WebApplicationContext
, which inherits all
the beans already defined in the Root
WebApplicationContext
. These inherited
beans can be overridden in the portlet-specific scope, and new scope-
specific beans can be defined local to a given portlet instance.
The framework will, on initialization of a
DispatcherPortlet
, look for a file named
[portlet-name]-portlet.xml
in the WEB-INF
directory of your web application and create the beans defined there
(overriding the definitions of any beans defined with the same name in
the global scope).
The config location used by the
DispatcherPortlet
can be modified through a
portlet initialization parameter (see below for details).
The Spring DispatcherPortlet
has a few
special beans it uses, in order to be able to process requests and
render the appropriate views. These beans are included in the Spring
framework and can be configured in the
WebApplicationContext
, just as any other
bean would be configured. Each of those beans is described in more
detail below. Right now, we'll just mention them, just to let you know
they exist and to enable us to go on talking about the
DispatcherPortlet
. For most of the beans,
defaults are provided so you don't have to worry about configuring
them.
Table 16.1. Special beans in the WebApplicationContext
Expression | Explanation |
---|---|
handler mapping(s) | (Section 16.5, “Handler mappings”) a list of pre- and post-processors and controllers that will be executed if they match certain criteria (for instance a matching portlet mode specified with the controller) |
controller(s) | (Section 16.4, “Controllers”) the beans providing the actual functionality (or at least, access to the functionality) as part of the MVC triad |
view resolver | (Section 16.6, “Views and resolving them”) capable of resolving view names to view definitions |
multipart resolver | (Section 16.7, “Multipart (file upload) support”) offers functionality to process file uploads from HTML forms |
handler exception resolver | (Section 16.8, “Handling exceptions”) offers functionality to map exceptions to views or implement other more complex exception handling code |
When a DispatcherPortlet
is setup for use
and a request comes in for that specific
DispatcherPortlet
, it starts processing the
request. The list below describes the complete process a request goes
through if handled by a DispatcherPortlet
:
The locale returned by
PortletRequest.getLocale()
is bound to the
request to let elements in the process resolve the locale to use
when processing the request (rendering the view, preparing data,
etc.).
If a multipart resolver is specified and this is an
ActionRequest
, the request is
inspected for multiparts and if they are found, it is wrapped in a
MultipartActionRequest
for further
processing by other elements in the process. (See Section 16.7, “Multipart (file upload) support” for further information about
multipart handling).
An appropriate handler is searched for. If a handler is found, the execution chain associated with the handler (pre- processors, post-processors, controllers) will be executed in order to prepare a model.
If a model is returned, the view is rendered, using
the view resolver that has been configured with the
WebApplicationContext
. If no model is
returned (which could be due to a pre- or post-processor
intercepting the request, for example, for security reasons), no
view is rendered, since the request could already have been
fulfilled.
Exceptions that might be thrown during processing of the request
get picked up by any of the handler exception resolvers that are
declared in the WebApplicationContext
.
Using these exception resolvers you can define custom behavior in case
such exceptions get thrown.
You can customize Spring's DispatcherPortlet
by adding context parameters in the portlet.xml
file or
portlet init-parameters. The possibilities are listed below.
Table 16.2. DispatcherPortlet
initialization parameters
Parameter | Explanation |
---|---|
contextClass | Class that implements
WebApplicationContext ,
which will be used to instantiate the context used by
this portlet. If this parameter isn't specified, the
XmlPortletApplicationContext will
be used. |
contextConfigLocation | String which is passed to the context instance
(specified by contextClass ) to
indicate where context(s) can be found. The String is
potentially split up into multiple Strings (using a
comma as a delimiter) to support multiple contexts (in
case of multiple context locations, of beans that are
defined twice, the latest takes precedence). |
namespace | The namespace of the
WebApplicationContext .
Defaults to [portlet-name]-
portlet . |
viewRendererUrl | The URL at which
DispatcherPortlet can access an
instance of ViewRendererServlet
(see Section 16.3, “The ViewRendererServlet ”). |
The rendering process in Portlet MVC is a bit more complex than in
Web MVC. In order to reuse all the view technologies
from Spring Web MVC), we must convert the
PortletRequest
/
PortletResponse
to
HttpServletRequest
/
HttpServletResponse
and then call the
render
method of the
View
. To do this,
DispatcherPortlet
uses a special servlet that
exists for just this purpose: the
ViewRendererServlet
.
In order for DispatcherPortlet
rendering to
work, you must declare an instance of the
ViewRendererServlet
in the
web.xml
file for your web application as
follows:
<servlet> <servlet-name>ViewRendererServlet</servlet-name> <servlet-class>org.springframework.web.servlet.ViewRendererServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>ViewRendererServlet</servlet-name> <url-pattern>/WEB-INF/servlet/view</url-pattern> </servlet-mapping>
To perform the actual rendering, DispatcherPortlet
does the following:
Binds the
WebApplicationContext
to the request
as an attribute under the same
WEB_APPLICATION_CONTEXT_ATTRIBUTE
key that
DispatcherServlet
uses.
Binds the Model
and
View
objects to the request to make
them available to the
ViewRendererServlet
.
Constructs a
PortletRequestDispatcher
and performs
an include
using the /WEB-
INF/servlet/view
URL that is mapped to the
ViewRendererServlet
.
The ViewRendererServlet
is then able to
call the render
method on the
View
with the appropriate
arguments.
The actual URL for the ViewRendererServlet
can be changed using DispatcherPortlet
’s
viewRendererUrl
configuration parameter.
The controllers in Portlet MVC are very similar to the Web MVC Controllers and porting code from one to the other should be simple.
The basis for the Portlet MVC controller architecture is the
org.springframework.web.portlet.mvc.Controller
interface, which is listed below.
public interface Controller { /** * Process the render request and return a ModelAndView object which the * DispatcherPortlet will render. */ ModelAndView handleRenderRequest(RenderRequest request, RenderResponse response) throws Exception; /** * Process the action request. There is nothing to return. */ void handleActionRequest(ActionRequest request, ActionResponse response) throws Exception; }
As you can see, the Portlet
Controller
interface requires two methods
that handle the two phases of a portlet request: the action request and
the render request. The action phase should be capable of handling an
action request and the render phase should be capable of handling a
render request and returning an appropriate model and view. While the
Controller
interface is quite abstract,
Spring Portlet MVC offers a lot of controllers that already contain a
lot of the functionality you might need – most of these are very similar
to controllers from Spring Web MVC. The
Controller
interface just defines the
most common functionality required of every controller - handling an
action request, handling a render request, and returning a model and a
view.
Of course, just a Controller
interface isn't enough. To provide a basic infrastructure, all of
Spring Portlet MVC's Controller
s
inherit from AbstractController
, a class
offering access to Spring's
ApplicationContext
and control over
caching.
Table 16.3. Features offered by the AbstractController
Parameter | Explanation |
---|---|
requireSession | Indicates whether or not this
Controller requires a
session to do its work. This feature is offered to
all controllers. If a session is not present when
such a controller receives a request, the user is
informed using a
SessionRequiredException . |
synchronizeSession | Use this if you want handling by this
controller to be synchronized on the user's session.
To be more specific, the extending controller will
override the handleRenderRequestInternal(..) and
handleActionRequestInternal(..) methods, which will be
synchronized on the user’s session if you specify
this variable. |
renderWhenMinimized | If you want your controller to actually render the view when the portlet is in a minimized state, set this to true. By default, this is set to false so that portlets that are in a minimized state don’t display any content. |
cacheSeconds | When you want a controller to override the
default cache expiration defined for the portlet,
specify a positive integer here. By default it is
set to -1 , which does not change
the default caching. Setting it to 0
will ensure the result is never cached. |
The requireSession
and
cacheSeconds
properties are declared on the
PortletContentGenerator
class, which is the
superclass of AbstractController
) but are
included here for completeness.
When using the AbstractController
as a
baseclass for your controllers (which is not recommended since there
are a lot of other controllers that might already do the job for
you) you only have to override either the
handleActionRequestInternal(ActionRequest,
ActionResponse)
method or the
handleRenderRequestInternal(RenderRequest,
RenderResponse)
method (or both), implement your logic,
and return a ModelAndView
object (in the case
of handleRenderRequestInternal
).
The default implementations of both
handleActionRequestInternal(..)
and
handleRenderRequestInternal(..)
throw a
PortletException
. This is consistent with
the behavior of GenericPortlet
from the JSR-
168 Specification API. So you only need to override the method that
your controller is intended to handle.
Here is short example consisting of a class and a declaration in the web application context.
package samples; import javax.portlet.RenderRequest; import javax.portlet.RenderResponse; import org.springframework.web.portlet.mvc.AbstractController; import org.springframework.web.portlet.ModelAndView; public class SampleController extends AbstractController { public ModelAndView handleRenderRequestInternal(RenderRequest request, RenderResponse response) { ModelAndView mav = new ModelAndView("foo"); mav.addObject("message", "Hello World!"); return mav; } } <bean id="sampleController" class="samples.SampleController"> <property name="cacheSeconds" value="120"/> </bean>
The class above and the declaration in the web application context is all you need besides setting up a handler mapping (see Section 16.5, “Handler mappings”) to get this very simple controller working.
Although you can extend AbstractController
,
Spring Portlet MVC provides a number of concrete implementations which offer
functionality that is commonly used in simple MVC applications.
The ParameterizableViewController
is
basically the same as the example above, except for the fact that
you can specify the view name that it will return in the web
application context (no need to hard-code the view name).
The PortletModeNameViewController
uses
the current mode of the portlet as the view name. So, if your
portlet is in View mode (i.e. PortletMode.VIEW
)
then it uses "view" as the view name.
Spring Portlet MVC has the exact same hierarchy of
command controllers as Spring Web MVC. They
provide a way to interact with data objects and dynamically bind
parameters from the PortletRequest
to
the data object specified. Your data objects don't have to
implement a framework-specific interface, so you can directly
manipulate your persistent objects if you desire. Let's examine what
command controllers are available, to get an overview of what you can do
with them:
AbstractCommandController
- a command controller you can use to create your own command
controller, capable of binding request parameters to a data
object you specify. This class does not offer form
functionality, it does however offer validation features and
lets you specify in the controller itself what to do with the
command object that has been filled with the parameters from the
request.
AbstractFormController
-
an abstract controller offering form submission support. Using
this controller you can model forms and populate them using a
command object you retrieve in the controller. After a user has
filled the form, AbstractFormController
binds the fields, validates, and hands the object back to the
controller to take appropriate action. Supported features are:
invalid form submission (resubmission), validation, and normal
form workflow. You implement methods to determine which views
are used for form presentation and success. Use this controller
if you need forms, but don't want to specify what views you're
going to show the user in the application
context.
SimpleFormController
- a
concrete AbstractFormController
that
provides even more support when creating a form with a
corresponding command object. The
SimpleFormController
lets you specify a
command object, a viewname for the form, a viewname for the page you
want to show the user when form submission has succeeded, and
more.
AbstractWizardFormController
–
a concrete AbstractFormController
that
provides a wizard-style interface for editing the contents of a
command object across multiple display pages. Supports multiple
user actions: finish, cancel, or page change, all of which are
easily specified in request parameters from the
view.
These command controllers are quite powerful, but they do require a detailed understanding of how they operate in order to use them efficiently. Carefully review the Javadocs for this entire hierarchy and then look at some sample implementations before you start using them.
Instead of developing new controllers, it is possible to use
existing portlets and map requests to them from a
DispatcherPortlet
. Using the
PortletWrappingController
, you can
instantiate an existing Portlet
as a
Controller
as follows:
<bean id="myPortlet" class="org.springframework.web.portlet.mvc.PortletWrappingController"> <property name="portletClass" value="sample.MyPortlet"/> <property name="portletName" value="my-portlet"/> <property name="initParameters"> <value>config=/WEB-INF/my-portlet-config.xml</value> </property> </bean>
This can be very valuable since you can then use interceptors
to pre-process and post-process requests going to these portlets.
Since JSR-168 does not support any kind of filter mechanism, this is
quite handy. For example, this can be used to wrap the Hibernate
OpenSessionInViewInterceptor
around a MyFaces
JSF Portlet.
Using a handler mapping you can map incoming portlet requests to
appropriate handlers. There are some handler mappings you can use out
of the box, for example, the
PortletModeHandlerMapping
, but let's first
examine the general concept of a
HandlerMapping
.
Note: We are intentionally using the term “Handler” here instead
of “Controller”. DispatcherPortlet
is designed
to be used with other ways to process requests than just Spring Portlet
MVC’s own Controllers. A Handler is any Object that can handle portlet
requests. Controllers are an example of Handlers, and they are of
course the default. To use some other framework with
DispatcherPortlet
, a corresponding implementation
of HandlerAdapter
is all that is needed.
The functionality a basic
HandlerMapping
provides is the delivering
of a HandlerExecutionChain
, which must contain
the handler that matches the incoming request, and may also contain a
list of handler interceptors that are applied to the request. When a
request comes in, the DispatcherPortlet
will hand
it over to the handler mapping to let it inspect the request and come up
with an appropriate HandlerExecutionChain
. Then
the DispatcherPortlet
will execute the handler
and interceptors in the chain (if any). These concepts are all exactly
the same as in Spring Web MVC.
The concept of configurable handler mappings that can optionally
contain interceptors (executed before or after the actual handler was
executed, or both) is extremely powerful. A lot of supporting
functionality can be built into a custom
HandlerMapping
. Think of a custom handler
mapping that chooses a handler not only based on the portlet mode of the
request coming in, but also on a specific state of the session
associated with the request.
In Spring Web MVC, handler mappings are commonly based on URLs. Since there is really no such thing as a URL within a Portlet, we must use other mechanisms to control mappings. The two most common are the portlet mode and a request parameter, but anything available to the portlet request can be used in a custom handler mapping.
The rest of this section describes three of Spring Portlet MVC's
most commonly used handler mappings. They all extend
AbstractHandlerMapping
and share the following
properties:
interceptors
: The list of
interceptors to use.
HandlerInterceptor
s are discussed in
Section 16.5.4, “Adding HandlerInterceptor
s”.
defaultHandler
: The default
handler to use, when this handler mapping does not result in a
matching handler.
order
: Based on the value of the
order property (see the
org.springframework.core.Ordered
interface), Spring will sort all handler mappings available in the
context and apply the first matching handler.
lazyInitHandlers
: Allows for lazy
initialization of singleton handlers (prototype handlers are always
lazily initialized). Default value is false. This property is
directly implemented in the three concrete
Handlers.
This is a simple handler mapping that maps incoming requests based on the current mode of the portlet (e.g. ‘view’, ‘edit’, ‘help’). An example:
<bean class="org.springframework.web.portlet.handler.PortletModeHandlerMapping"> <property name="portletModeMap"> <map> <entry key="view" value-ref="viewHandler"/> <entry key="edit" value-ref="editHandler"/> <entry key="help" value-ref="helpHandler"/> </map> </property> </bean>
If we need to navigate around to multiple controllers without changing portlet mode, the simplest way to do this is with a request parameter that is used as the key to control the mapping.
ParameterHandlerMapping
uses the value
of a specific request parameter to control the mapping. The default
name of the parameter is 'action'
, but can be changed
using the 'parameterName'
property.
The bean configuration for this mapping will look something like this:
<bean class="org.springframework.web.portlet.handler.ParameterHandlerMapping”> <property name="parameterMap"> <map> <entry key="add" value-ref="addItemHandler"/> <entry key="edit" value-ref="editItemHandler"/> <entry key="delete" value-ref="deleteItemHandler"/> </map> </property> </bean>
The most powerful built-in handler mapping,
PortletModeParameterHandlerMapping
combines
the capabilities of the two previous ones to allow different
navigation within each portlet mode.
Again the default name of the parameter is "action", but can
be changed using the parameterName
property.
By default, the same parameter value may not be used in two
different portlet modes. This is so that if the portal itself
changes the portlet mode, the request will no longer be valid in the
mapping. This behavior can be changed by setting the
allowDupParameters
property to true. However,
this is not recommended.
The bean configuration for this mapping will look something like this:
<bean class="org.springframework.web.portlet.handler.PortletModeParameterHandlerMapping"> <property name="portletModeParameterMap"> <map> <entry key="view"> <!-- 'view' portlet mode --> <map> <entry key="add" value-ref="addItemHandler"/> <entry key="edit" value-ref="editItemHandler"/> <entry key="delete" value-ref="deleteItemHandler"/> </map> </entry> <entry key="edit"> <!-- 'edit' portlet mode --> <map> <entry key="prefs" value-ref="prefsHandler"/> <entry key="resetPrefs" value-ref="resetPrefsHandler"/> </map> </entry> </map> </property> </bean>
This mapping can be chained ahead of a
PortletModeHandlerMapping
, which can then provide
defaults for each mode and an overall default as well.
Spring's handler mapping mechanism has a notion of handler interceptors, which can be extremely useful when you want to apply specific functionality to certain requests, for example, checking for a principal. Again Spring Portlet MVC implements these concepts in the same way as Web MVC.
Interceptors located in the handler mapping must implement
HandlerInterceptor
from the
org.springframework.web.portlet
package. Just
like the servlet version, this interface defines three methods: one
that will be called before the actual handler will be executed
(preHandle
), one that will be called after the
handler is executed (postHandle
), and one that is
called after the complete request has finished
(afterCompletion
). These three methods should
provide enough flexibility to do all kinds of pre- and post-
processing.
The preHandle
method returns a boolean
value. You can use this method to break or continue the processing
of the execution chain. When this method returns
true
, the handler execution chain will continue.
When it returns false
, the
DispatcherPortlet
assumes the interceptor
itself has taken care of requests (and, for example, rendered an
appropriate view) and does not continue executing the other
interceptors and the actual handler in the execution chain.
The postHandle
method is only called on a
RenderRequest
. The
preHandle
and afterCompletion
methods are called on both an
ActionRequest
and a
RenderRequest
. If you need to
execute logic in these methods for just one type of request, be sure
to check what kind of request it is before processing it.
As with the servlet package, the portlet package has a
concrete implementation of
HandlerInterceptor
called
HandlerInterceptorAdapter
. This class has
empty versions of all the methods so that you can inherit from this
class and implement just one or two methods when that is all you
need.
The portlet package also has a concrete interceptor named
ParameterMappingInterceptor
that is meant to
be used directly with ParameterHandlerMapping
and PortletModeParameterHandlerMapping
. This
interceptor will cause the parameter that is being used to control
the mapping to be forwarded from an
ActionRequest
to the subsequent
RenderRequest
. This will help ensure
that the RenderRequest
is mapped to
the same Handler as the
ActionRequest
. This is done in the
preHandle
method of the interceptor, so you can
still modify the parameter value in your handler to change where the
RenderRequest
will be mapped.
Be aware that this interceptor is calling
setRenderParameter
on the
ActionResponse
, which means that you
cannot call sendRedirect
in your handler when
using this interceptor. If you need to do external redirects then
you will either need to forward the mapping parameter manually or
write a different interceptor to handle this for you.
As mentioned previously, Spring Portlet MVC directly reuses all
the view technologies from Spring Web MVC. This includes not only the
various View
implementations themselves,
but also the ViewResolver
implementations.
For more information, refer to the sections entitled
Chapter 14, View technologies and Section 13.5, “Views and resolving them” respectively.
A few items on using the existing View
and
ViewResolver
implementations are worth mentioning:
Most portals expect the result of rendering a portlet to be an HTML fragment. So, things like JSP/JSTL, Velocity, FreeMarker, and XSLT all make sense. But it is unlikely that views that return other document types will make any sense in a portlet context.
There is no such thing as an HTTP redirect from
within a portlet (the sendRedirect(..)
method of
ActionResponse
cannot
be used to stay within the portal). So, RedirectView
and use of the 'redirect:'
prefix will
not work correctly from within Portlet MVC.
It may be possible to use the 'forward:'
prefix from
within Portlet MVC. However, remember that since you are in a
portlet, you have no idea what the current URL looks like. This
means you cannot use a relative URL to access other resources in
your web application and that you will have to use an absolute
URL.
Also, for JSP development, the new Spring Taglib and the new Spring Form Taglib both work in portlet views in exactly the same way that they work in servlet views.
Spring Portlet MVC has built-in multipart support to handle file
uploads in portlet applications, just like Web MVC does. The design for
the multipart support is done with pluggable
PortletMultipartResolver
objects, defined
in the org.springframework.web.portlet.multipart
package. Spring provides a PortletMultipartResolver
for use with
Commons FileUpload.
How uploading files is supported will be described in the rest of this section.
By default, no multipart handling will be done by Spring Portlet
MVC, as some developers will want to handle multiparts themselves. You
will have to enable it yourself by adding a multipart resolver to the
web application's context. After you have done that,
DispatcherPortlet
will inspect each request to
see if it contains a multipart. If no multipart is found, the request
will continue as expected. However, if a multipart is found in the
request, the PortletMultipartResolver
that has been declared in your context will be used. After that, the
multipart attribute in your request will be treated like any other
attribute.
![]() | Note |
---|---|
Any configured |
The following example shows how to use the
CommonsPortletMultipartResolver
:
<bean id="portletMultipartResolver"
class="org.springframework.web.portlet.multipart.CommonsPortletMultipartResolver">
<!-- one of the properties available; the maximum file size in bytes -->
<property name="maxUploadSize" value="100000"/>
</bean>
Of course you also need to put the appropriate jars in your
classpath for the multipart resolver to work. In the case of the
CommonsMultipartResolver
, you need to use
commons-fileupload.jar
. Be sure to use at least
version 1.1 of Commons FileUpload as previous versions do not
support JSR-168 Portlet applications.
Now that you have seen how to set Portlet MVC up to handle
multipart requests, let's talk about how to actually use it. When
DispatcherPortlet
detects a multipart
request, it activates the resolver that has been declared in your
context and hands over the request. What the resolver then does is
wrap the current ActionRequest
into a
MultipartActionRequest
that has
support for multipart file uploads. Using the
MultipartActionRequest
you can get
information about the multiparts contained by this request and
actually get access to the multipart files themselves in your
controllers.
Note that you can only receive multipart file uploads as part
of an ActionRequest
, not as part of a
RenderRequest
.
After the
PortletMultipartResolver
has finished
doing its job, the request will be processed like any other. To use
it, you create a form with an upload field (see immediately below),
then let Spring bind the file onto your form (backing object). To
actually let the user upload a file, we have to create a (JSP/HTML)
form:
<h1>Please upload a file</h1> <form method="post" action="<portlet:actionURL/>" enctype="multipart/form-data"> <input type="file" name="file"/> <input type="submit"/> </form>
As you can see, we've created a field named “file” after the
property of the bean that holds the byte[]
.
Furthermore we've added the encoding attribute
(enctype="multipart/form-data"
), which is
necessary to let the browser know how to encode the multipart fields
(do not forget this!).
Just as with any other property that's not automagically
convertible to a string or primitive type, to be able to put binary
data in your objects you have to register a custom editor with the
PortletRequestDataBinder
. There are a couple
of editors available for handling files and setting the results on
an object. There's a
StringMultipartFileEditor
capable of
converting files to Strings (using a user-defined character set) and
there is a ByteArrayMultipartFileEditor
which
converts files to byte arrays. They function just as the
CustomDateEditor
does.
So, to be able to upload files using a form, declare the resolver, a mapping to a controller that will process the bean, and the controller itself.
<bean id="portletMultipartResolver" class="org.springframework.web.portlet.multipart.CommonsPortletMultipartResolver"/> <bean class="org.springframework.web.portlet.handler.PortletModeHandlerMapping"> <property name="portletModeMap"> <map> <entry key="view" value-ref="fileUploadController"/> </map> </property> </bean> <bean id="fileUploadController" class="examples.FileUploadController"> <property name="commandClass" value="examples.FileUploadBean"/> <property name="formView" value="fileuploadform"/> <property name="successView" value="confirmation"/> </bean>
After that, create the controller and the actual class to hold the file property.
public class FileUploadController extends SimpleFormController { public void onSubmitAction(ActionRequest request, ActionResponse response, Object command, BindException errors) throws Exception { // cast the bean FileUploadBean bean = (FileUploadBean) command; // let's see if there's content there byte[] file = bean.getFile(); if (file == null) { // hmm, that's strange, the user did not upload anything } // do something with the file here } protected void initBinder( PortletRequest request, PortletRequestDataBinder binder) throws Exception { // to actually be able to convert Multipart instance to byte[] // we have to register a custom editor binder.registerCustomEditor(byte[].class, new ByteArrayMultipartFileEditor()); // now Spring knows how to handle multipart object and convert } } public class FileUploadBean { private byte[] file; public void setFile(byte[] file) { this.file = file; } public byte[] getFile() { return file; } }
As you can see, the FileUploadBean
has
a property typed byte[]
that holds the file. The
controller registers a custom editor to let Spring know how to
actually convert the multipart objects the resolver has found to
properties specified by the bean. In this example, nothing is done
with the byte[]
property of the bean itself, but
in practice you can do whatever you want (save it in a database,
mail it to somebody, etc).
An equivalent example in which a file is bound straight to a String-typed property on a (form backing) object might look like this:
public class FileUploadController extends SimpleFormController { public void onSubmitAction(ActionRequest request, ActionResponse response, Object command, BindException errors) throws Exception { // cast the bean FileUploadBean bean = (FileUploadBean) command; // let's see if there's content there String file = bean.getFile(); if (file == null) { // hmm, that's strange, the user did not upload anything } // do something with the file here } protected void initBinder( PortletRequest request, PortletRequestDataBinder binder) throws Exception { // to actually be able to convert Multipart instance to a String // we have to register a custom editor binder.registerCustomEditor(String.class, new StringMultipartFileEditor()); // now Spring knows how to handle multipart objects and convert } } public class FileUploadBean { private String file; public void setFile(String file) { this.file = file; } public String getFile() { return file; } }
Of course, this last example only makes (logical) sense in the context of uploading a plain text file (it wouldn't work so well in the case of uploading an image file).
The third (and final) option is where one binds directly to a
MultipartFile
property declared on
the (form backing) object's class. In this case one does not need to
register any custom property editor because there is no type
conversion to be performed.
public class FileUploadController extends SimpleFormController { public void onSubmitAction(ActionRequest request, ActionResponse response, Object command, BindException errors) throws Exception { // cast the bean FileUploadBean bean = (FileUploadBean) command; // let's see if there's content there MultipartFile file = bean.getFile(); if (file == null) { // hmm, that's strange, the user did not upload anything } // do something with the file here } } public class FileUploadBean { private MultipartFile file; public void setFile(MultipartFile file) { this.file = file; } public MultipartFile getFile() { return file; } }
Just like Web MVC, Portlet MVC provides
HandlerExceptionResolver
s to ease the
pain of unexpected exceptions occurring while your request is being
processed by a handler that matched the request. Portlet MVC also
provides the same concrete
SimpleMappingExceptionResolver
that enables you
to take the class name of any exception that might be thrown and map it
to a view name.
Spring 2.5 introduces an annotation-based programming model for MVC
controllers, using annotations such as
@RequestMapping
,
@RequestParam
,
@ModelAttribute
, etc. This annotation
support is available for both Servlet MVC and Portlet MVC. Controllers
implemented in this style do not have to extend specific base classes or
implement specific interfaces. Furthermore, they do not usually have
direct dependencies on Servlet or Portlet API's, although they can easily
get access to Servlet or Portlet facilities if desired.
![]() | Tip |
---|---|
The Spring distribution ships with the
PetPortal sample, which is a portal application that takes
advantage of the annotation support described in this section, in the context
of simple form processing. You can find the PetPortal
application in the |
The following sections document these annotations and how they are most commonly used in a Portlet environment.
@RequestMapping
will only be processed
if a corresponding HandlerMapping
(for type level annotations)
and/or HandlerAdapter
(for method level annotations) is
present in the dispatcher. This is the case by default in both
DispatcherServlet
and DispatcherPortlet
.
However, if you are defining custom HandlerMappings
or
HandlerAdapters
, then you need to make sure that a
corresponding custom DefaultAnnotationHandlerMapping
and/or AnnotationMethodHandlerAdapter
is defined as well
- provided that you intend to use @RequestMapping
.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean class="org.springframework.web.portlet.mvc.annotation.DefaultAnnotationHandlerMapping"/>
<bean class="org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter"/>
// ... (controller bean definitions) ...
</beans>
Defining a DefaultAnnotationHandlerMapping
and/or AnnotationMethodHandlerAdapter
explicitly
also makes sense if you would like to customize the mapping strategy, e.g.
specifying a custom WebBindingInitializer
(see below).
The @Controller
annotation indicates
that a particular class serves the role of a controller.
There is no need to extend any controller base class or reference the
Portlet API. You are of course still able to reference Portlet-specific
features if you need to.
The basic purpose of the @Controller
annotation is to act as a stereotype for the annotated class, indicating
its role. The dispatcher will scan such annotated classes for mapped
methods, detecting @RequestMapping
annotations (see the next section).
Annotated controller beans may be defined explicitly,
using a standard Spring bean definition in the dispatcher's context.
However, the @Controller
stereotype also
allows for autodetection, aligned with Spring 2.5's general support for
detecting component classes in the classpath and auto-registering bean
definitions for them.
To enable autodetection of such annotated controllers, you have to add component scanning to your configuration. This is easily achieved by using the spring-context schema as shown in the following XML snippet:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<context:component-scan base-package="org.springframework.samples.petportal.portlet"/>
// ...
</beans>
The @RequestMapping
annotation is used
to map portlet modes like 'VIEW'/'EDIT' onto an entire class or a particular
handler method. Typically the type-level annotation maps a specific mode
(or mode plus parameter condition) onto a form controller, with additional
method-level annotations 'narrowing' the primary mapping for specific
portlet request parameters.
![]() | Tip |
---|---|
In the following discussion, we'll focus on controllers that are based on annotated handler methods. |
The following is an example of a form controller from the PetPortal sample application using this annotation:
@Controller @RequestMapping("EDIT") @SessionAttributes("site") public class PetSitesEditController { private Properties petSites; public void setPetSites(Properties petSites) { this.petSites = petSites; } @ModelAttribute("petSites") public Properties getPetSites() { return this.petSites; } @RequestMapping // default (action=list) public String showPetSites() { return "petSitesEdit"; } @RequestMapping(params = "action=add") // render phase public String showSiteForm(Model model) { // Used for the initial form as well as for redisplaying with errors. if (!model.containsAttribute("site")) { model.addAttribute("site", new PetSite()); } return "petSitesAdd"; } @RequestMapping(params = "action=add") // action phase public void populateSite( @ModelAttribute("site") PetSite petSite, BindingResult result, SessionStatus status, ActionResponse response) { new PetSiteValidator().validate(petSite, result); if (!result.hasErrors()) { this.petSites.put(petSite.getName(), petSite.getUrl()); status.setComplete(); response.setRenderParameter("action", "list"); } } @RequestMapping(params = "action=delete") public void removeSite(@RequestParam("site") String site, ActionResponse response) { this.petSites.remove(site); response.setRenderParameter("action", "list"); } }
Handler methods which are annotated with
@RequestMapping
are allowed to have very flexible
signatures. They may have arguments of the following types, in arbitrary
order (except for validation results, which need to follow right after
the corresponding command object, if desired):
Request and/or response objects (Portlet API). You may choose any specific request/response type, e.g. PortletRequest / ActionRequest / RenderRequest. An explicitly declared action/render argument is also used for mapping specific request types onto a handler method (in case of no other information given that differentiates between action and render requests).
Session object (Portlet API): of type PortletSession. An argument
of this type will enforce the presence of a corresponding session.
As a consequence, such an argument will never be null
.
org.springframework.web.context.request.WebRequest
or org.springframework.web.context.request.NativeWebRequest
.
Allows for generic request parameter access as well as request/session
attribute access, without ties to the native Servlet/Portlet API.
java.util.Locale
for the current request
locale (the portal locale in a Portlet environment).
java.io.InputStream
/
java.io.Reader
for access to the request's content.
This will be the raw InputStream/Reader as exposed by the Portlet API.
java.io.OutputStream
/
java.io.Writer
for generating the response's content.
This will be the raw OutputStream/Writer as exposed by the Portlet API.
@RequestParam
annotated parameters
for access to specific Portlet request parameters. Parameter values
will be converted to the declared method argument type.
java.util.Map
/
org.springframework.ui.Model
/
org.springframework.ui.ModelMap
for
enriching the implicit model that will be exposed to the web view.
Command/form objects to bind parameters to: as bean
properties or fields, with customizable type conversion, depending
on @InitBinder
methods and/or the
HandlerAdapter configuration - see the
"webBindingInitializer
" property on
AnnotationMethodHandlerAdapter
. Such
command objects along with their validation results will be
exposed as model attributes, by default using the non-qualified
command class name in property notation (e.g. "orderAddress" for
type "mypackage.OrderAddress"). Specify a parameter-level
ModelAttribute
annotation for declaring a
specific model attribute name.
org.springframework.validation.Errors
/
org.springframework.validation.BindingResult
validation results for a preceding command/form object (the
immediate preceding argument).
org.springframework.web.bind.support.SessionStatus
status handle for marking form processing as complete (triggering
the cleanup of session attributes that have been indicated by the
@SessionAttributes
annotation at the
handler type level).
The following return types are supported for handler methods:
A ModelAndView
object, with the model implicitly
enriched with command objects and the results of @ModelAttribute
annotated reference data accessor methods.
A Model
object, with the view name implicitly
determined through a RequestToViewNameTranslator
and the model implicitly enriched with command objects and the results of
@ModelAttribute
annotated reference data accessor methods.
A Map
object for exposing a model, with the view name
implicitly determined through a RequestToViewNameTranslator
and the model implicitly enriched with command objects and the results of
@ModelAttribute
annotated reference data accessor methods.
A View
object, with the model implicitly
determined through command objects and @ModelAttribute
annotated reference data accessor methods. The handler method may also
programmatically enrich the model by declaring a Model
argument (see above).
A String
value which is interpreted as view name,
with the model implicitly determined through command objects and
@ModelAttribute
annotated reference data accessor methods.
The handler method may also programmatically enrich the model by declaring a
Model
argument (see above).
void
if the method handles the response itself
(e.g. by writing the response content directly).
Any other return type will be considered as single model attribute
to be exposed to the view, using the attribute name specified through
@ModelAttribute
at the method level (or the default
attribute name based on the return type's class name otherwise). The model
will be implicitly enriched with command objects and the results of
@ModelAttribute
annotated reference data accessor methods.
The @RequestParam
annotation is used to
bind request parameters to a method parameter in your controller.
The following code snippet from the PetPortal sample application shows the usage:
@Controller @RequestMapping("EDIT") @SessionAttributes("site") public class PetSitesEditController { // ... public void removeSite(@RequestParam("site") String site, ActionResponse response) { this.petSites.remove(site); response.setRenderParameter("action", "list"); } // ... }
Parameters using this annotation are required by default, but you
can specify that a parameter is optional by setting
@RequestParam
's
required
attribute to false
(e.g.,
@RequestParam(value="id", required="false")
).
@ModelAttribute
has two usage scenarios in
controllers. When placed on a method parameter,
@ModelAttribute
is used to map a model attribute
to the specific, annotated method parameter (see the
processSubmit()
method below). This is how the
controller gets a reference to the object holding the data entered in
the form. In addition, the parameter can be declared as the specific
type of the form backing object rather than as a generic
java.lang.Object
, thus increasing type
safety.
@ModelAttribute
is also used at the method
level to provide reference data for the model (see
the populatePetTypes()
method below). For this usage
the method signature can contain the same types as documented above for
the @RequestMapping
annotation.
Note: @ModelAttribute
annotated methods will be executed before the
chosen @RequestMapping
annotated handler method.
They effectively pre-populate the implicit model with specific attributes,
often loaded from a database. Such an attribute can then already be
accessed through @ModelAttribute
annotated
handler method parameters in the chosen handler method, potentially
with binding and validation applied to it.
The following code snippet shows these two usages of this annotation:
@Controller @RequestMapping("EDIT") @SessionAttributes("site") public class PetSitesEditController { // ... @ModelAttribute("petSites") public Properties getPetSites() { return this.petSites; } @RequestMapping(params = "action=add") // action phase public void populateSite( @ModelAttribute("site") PetSite petSite, BindingResult result, SessionStatus status, ActionResponse response) { new PetSiteValidator().validate(petSite, result); if (!result.hasErrors()) { this.petSites.put(petSite.getName(), petSite.getUrl()); status.setComplete(); response.setRenderParameter("action", "list"); } } }
The type-level @SessionAttributes
annotation declares session attributes used by a specific handler. This
will typically list the names of model attributes which should be
transparently stored in the session or some conversational storage,
serving as form-backing beans between subsequent requests.
The following code snippet shows the usage of this annotation:
@Controller @RequestMapping("EDIT") @SessionAttributes("site") public class PetSitesEditController { // ... }
To customize request parameter binding with PropertyEditors, etc.
via Spring's WebDataBinder
, you can either use
@InitBinder
-annotated methods within your
controller or externalize your configuration by providing a custom
WebBindingInitializer
.
Annotating controller methods with
@InitBinder
allows you to configure web
data binding directly within your controller class.
@InitBinder
identifies methods which
initialize the WebDataBinder
which will be used
for populating command and form object arguments of annotated handler
methods.
Such init-binder methods support all arguments that
@RequestMapping
supports, except for
command/form objects and corresponding validation result objects.
Init-binder methods must not have a return value. Thus, they are
usually declared as void
. Typical arguments include
WebDataBinder
in combination with
WebRequest
or
java.util.Locale
, allowing code to register
context-specific editors.
The following example demonstrates the use of
@InitBinder
for configuring a
CustomDateEditor
for all
java.util.Date
form properties.
@Controller public class MyFormController { @InitBinder public void initBinder(WebDataBinder binder) { SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd"); dateFormat.setLenient(false); binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false)); } // ... }
To externalize data binding initialization, you can provide a
custom implementation of the
WebBindingInitializer
interface, which
you then enable by supplying a custom bean configuration for an
AnnotationMethodHandlerAdapter
, thus overriding
the default configuration.
The process of deploying a Spring Portlet MVC application is no different than deploying any JSR-168 Portlet application. However, this area is confusing enough in general that it is worth talking about here briefly.
Generally, the portal/portlet container runs in one webapp in your
servlet container and your portlets run in another webapp in your
servlet container. In order for the portlet container webapp to make
calls into your portlet webapp it must make cross-context calls to a
well-known servlet that provides access to the portlet services defined
in your portlet.xml
file.
The JSR-168 specification does not specify exactly how this should happen, so each portlet container has its own mechanism for this, which usually involves some kind of “deployment process” that makes changes to the portlet webapp itself and then registers the portlets within the portlet container.
At a minimum, the web.xml
file in your portlet
webapp is modified to inject the well-known servlet that the portlet
container will call. In some cases a single servlet will service all
portlets in the webapp, in other cases there will be an instance of the
servlet for each portlet.
Some portlet containers will also inject libraries and/or configuration files into the webapp as well. The portlet container must also make its implementation of the Portlet JSP Tag Library available to your webapp.
The bottom line is that it is important to understand the deployment needs of your target portal and make sure they are met (usually by following the automated deployment process it provides). Be sure to carefully review the documentation from your portal for this process.
Once you have deployed your portlet, review the resulting
web.xml
file for sanity. Some older portals have
been known to corrupt the definition of the
ViewRendererServlet
, thus breaking the rendering
of your portlets.
This part of the reference documentation covers the Spring Framework's integration with a number of J2EE (and related) technologies.
Spring features integration classes for remoting support using various technologies. The remoting support eases the development of remote-enabled services, implemented by your usual (Spring) POJOs. Currently, Spring supports four remoting technologies:
Remote Method Invocation (RMI). Through the use
of the RmiProxyFactoryBean
and the
RmiServiceExporter
Spring supports both traditional
RMI (with java.rmi.Remote
interfaces and
java.rmi.RemoteException
) and
transparent remoting via RMI invokers (with any Java interface).
Spring's HTTP invoker. Spring provides a special
remoting strategy which allows for Java serialization via HTTP,
supporting any Java interface (just like the RMI invoker). The corresponding
support classes are HttpInvokerProxyFactoryBean
and
HttpInvokerServiceExporter
.
Hessian. By using Spring's
HessianProxyFactoryBean
and the
HessianServiceExporter
you can transparently
expose your services using the lightweight binary HTTP-based protocol
provided by Caucho.
Burlap. Burlap is Caucho's XML-based
alternative to Hessian. Spring provides support classes such
as BurlapProxyFactoryBean
and
BurlapServiceExporter
.
JAX-RPC. Spring provides remoting support for web services via JAX-RPC (J2EE 1.4's web service API).
JAX-WS. Spring provides remoting support for web services via JAX-WS (the successor of JAX-RPC, as introduced in Java EE 5 and Java 6).
JMS. Remoting using JMS as the underlying protocol
is supported via the JmsInvokerServiceExporter
and
JmsInvokerProxyFactoryBean
classes.
While discussing the remoting capabilities of Spring, we'll use the following domain model and corresponding services:
public class Account implements Serializable{ private String name; public String getName(); public void setName(String name) { this.name = name; } }
public interface AccountService { public void insertAccount(Account account); public List getAccounts(String name); }
public interface RemoteAccountService extends Remote { public void insertAccount(Account account) throws RemoteException; public List getAccounts(String name) throws RemoteException; }
// the implementation doing nothing at the moment public class AccountServiceImpl implements AccountService { public void insertAccount(Account acc) { // do something... } public List getAccounts(String name) { // do something... } }
We will start exposing the service to a remote client by using RMI and talk a bit about the drawbacks of using RMI. We'll then continue to show an example using Hessian as the protocol.
Using Spring's support for RMI, you can transparently expose your services through the RMI infrastructure. After having this set up, you basically have a configuration similar to remote EJBs, except for the fact that there is no standard support for security context propagation or remote transaction propagation. Spring does provide hooks for such additional invocation context when using the RMI invoker, so you can for example plug in security frameworks or custom security credentials here.
Using the RmiServiceExporter
, we can expose the interface
of our AccountService object as RMI object. The interface can be accessed by using
RmiProxyFactoryBean
, or via plain RMI in case of a traditional
RMI service. The RmiServiceExporter
explicitly supports the
exposing of any non-RMI services via RMI invokers.
Of course, we first have to set up our service in the Spring container:
<bean id="accountService" class="example.AccountServiceImpl">
<!-- any additional properties, maybe a DAO? -->
</bean>
Next we'll have to expose our service using the RmiServiceExporter
:
<bean class="org.springframework.remoting.rmi.RmiServiceExporter">
<!-- does not necessarily have to be the same name as the bean to be exported -->
<property name="serviceName" value="AccountService"/>
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
<!-- defaults to 1099
-->
<property name="registryPort" value="1199"/>
</bean>
As you can see, we're overriding the port for the RMI registry. Often,
your application server also maintains an RMI registry and it is wise
to not interfere with that one. Furthermore, the service name is used to bind the
service under. So right now, the service will be bound at
'rmi://HOST:1199/AccountService'
. We'll use the URL later on to
link in the service at the client side.
![]() | Note |
---|---|
The |
Our client is a simple object using the AccountService
to manage accounts:
public class SimpleObject { private AccountService accountService; public void setAccountService(AccountService accountService) { this.accountService = accountService; } }
To link in the service on the client, we'll create a separate Spring container, containing the simple object and the service linking configuration bits:
<bean class="example.SimpleObject"> <property name="accountService" ref="accountService"/> </bean> <bean id="accountService" class="org.springframework.remoting.rmi.RmiProxyFactoryBean"> <property name="serviceUrl" value="rmi://HOST:1199/AccountService"/> <property name="serviceInterface" value="example.AccountService"/> </bean>
That's all we need to do to support the remote account service on the client.
Spring will transparently create an invoker and remotely enable the account
service through the RmiServiceExporter
. At the client
we're linking it in using the RmiProxyFactoryBean
.
Hessian offers a binary HTTP-based remoting protocol. It is developed by Caucho and more information about Hessian itself can be found at http://www.caucho.com.
Hessian communicates via HTTP and does so using a custom servlet.
Using Spring's DispatcherServlet
principles, as known
from Spring Web MVC usage, you can easily wire up such a servlet exposing
your services. First we'll have to create a new servlet in your application
(this an excerpt from 'web.xml'
):
<servlet> <servlet-name>remoting</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>remoting</servlet-name> <url-pattern>/remoting/*</url-pattern> </servlet-mapping>
You're probably familiar with Spring's DispatcherServlet
principles and if so, you know that now you'll have to create a Spring container
configuration resource named 'remoting-servlet.xml'
(after
the name of your servlet) in the 'WEB-INF'
directory. The application context will be used in the next section.
Alternatively, consider the use of Spring's simpler
HttpRequestHandlerServlet
.
This allows you to embed the remote exporter definitions in your root application
context (by default in 'WEB-INF/applicationContext.xml'
),
with individual servlet definitions pointing to specific exporter beans.
Each servlet name needs to match the bean name of its target exporter in this case.
In the newly created application context called remoting-servlet.xml
,
we'll create a HessianServiceExporter
exporting your services:
<bean id="accountService" class="example.AccountServiceImpl">
<!-- any additional properties, maybe a DAO? -->
</bean>
<bean name="/AccountService" class="org.springframework.remoting.caucho.HessianServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>
Now we're ready to link in the service at the client. No explicit handler mapping
is specified, mapping request URLs onto services, so BeanNameUrlHandlerMapping
will be used: Hence, the service will be exported at the URL indicated through
its bean name within the containing DispatcherServlet
's
mapping (as defined above): 'http://HOST:8080/remoting/AccountService'
.
Alternatively, create a HessianServiceExporter
in your
root application context (e.g. in 'WEB-INF/applicationContext.xml'
):
<bean name="accountExporter" class="org.springframework.remoting.caucho.HessianServiceExporter"> <property name="service" ref="accountService"/> <property name="serviceInterface" value="example.AccountService"/> </bean>
In the latter case, define a corresponding servlet for this exporter
in 'web.xml'
, with the same end result: The exporter
getting mapped to the request path /remoting/AccountService
.
Note that the servlet name needs to match the bean name of the target exporter.
<servlet> <servlet-name>accountExporter</servlet-name> <servlet-class>org.springframework.web.context.support.HttpRequestHandlerServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>accountExporter</servlet-name> <url-pattern>/remoting/AccountService</url-pattern> </servlet-mapping>
Using the we can link in the service
at the client. The same principles apply as with the RMI example. We'll create
a separate bean factory or application context and mention the following beans
where the
SimpleObject
is using the
AccountService
to manage accounts:
<bean class="example.SimpleObject"> <property name="accountService" ref="accountService"/> </bean> <bean id="accountService" class="org.springframework.remoting.caucho.HessianProxyFactoryBean"> <property name="serviceUrl" value="http://remotehost:8080/remoting/AccountService"/> <property name="serviceInterface" value="example.AccountService"/> </bean>
We won't discuss Burlap, the XML-based equivalent of Hessian, in detail here,
since it is configured and set up in exactly the same way as the Hessian
variant explained above. Just replace the word Hessian
with Burlap
and you're all set to go.
One of the advantages of Hessian and Burlap is that we can easily apply HTTP basic
authentication, because both protocols are HTTP-based. Your normal HTTP server security
mechanism can easily be applied through using the web.xml
security
features, for example. Usually, you don't use per-user security credentials here, but
rather shared credentials defined at the Hessian/BurlapProxyFactoryBean
level
(similar to a JDBC DataSource
).
<bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping"> <property name="interceptors" ref="authorizationInterceptor"/> </bean> <bean id="authorizationInterceptor" class="org.springframework.web.servlet.handler.UserRoleAuthorizationInterceptor"> <property name="authorizedRoles" value="administrator,operator"/> </bean>
This an example where we explicitly mention the BeanNameUrlHandlerMapping
and set an interceptor allowing only administrators and operators to call
the beans mentioned in this application context.
![]() | Note |
---|---|
Of course, this example doesn't show a flexible kind of security infrastructure. For more options as far as security is concerned, have a look at the Acegi Security System for Spring, to be found at http://acegisecurity.sourceforge.net. |
As opposed to Burlap and Hessian, which are both lightweight protocols using their own slim serialization mechanisms, Spring Http invokers use the standard Java serialization mechanism to expose services through HTTP. This has a huge advantage if your arguments and return types are complex types that cannot be serialized using the serialization mechanisms Hessian and Burlap use (refer to the next section for more considerations when choosing a remoting technology).
Under the hood, Spring uses either the standard facilities provided by J2SE to
perform HTTP calls or Commons HttpClient
. Use the latter if you need more advanced
and easy-to-use functionality. Refer to
jakarta.apache.org/commons/httpclient
for more info.
Setting up the HTTP invoker infrastructure for a service objects much resembles
the way you would do using Hessian or Burlap. Just as Hessian support provides
the HessianServiceExporter
, Spring's HttpInvoker support provides
the org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter
.
To expose the AccountService
(mentioned above) within a
Spring Web MVC DispatcherServlet
, the following configuration
needs to be in place in the dispatcher's application context:
<bean name="/AccountService" class="org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter"> <property name="service" ref="accountService"/> <property name="serviceInterface" value="example.AccountService"/> </bean>
Such an exporter definition will be exposed through the
DispatcherServlet
's standard mapping facilities,
as explained in the section on Hessian.
Alternatively, create an HttpInvokerServiceExporter
in your
root application context (e.g. in 'WEB-INF/applicationContext.xml'
):
<bean name="accountExporter" class="org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter"> <property name="service" ref="accountService"/> <property name="serviceInterface" value="example.AccountService"/> </bean>
In addition, define a corresponding servlet for this exporter in
'web.xml'
, with the servlet name matching the bean
name of the target exporter:
<servlet> <servlet-name>accountExporter</servlet-name> <servlet-class>org.springframework.web.context.support.HttpRequestHandlerServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>accountExporter</servlet-name> <url-pattern>/remoting/AccountService</url-pattern> </servlet-mapping>
Again, linking in the service from the client much resembles the way you would do it when using Hessian or Burlap. Using a proxy, Spring will be able to translate your calls to HTTP POST requests to the URL pointing to the exported service.
<bean id="httpInvokerProxy" class="org.springframework.remoting.httpinvoker.HttpInvokerProxyFactoryBean"> <property name="serviceUrl" value="http://remotehost:8080/remoting/AccountService"/> <property name="serviceInterface" value="example.AccountService"/> </bean>
As mentioned before, you can choose what HTTP client you want to use.
By default, the HttpInvokerProxy
uses the J2SE HTTP functionality, but
you can also use the Commons HttpClient
by setting the
httpInvokerRequestExecutor
property:
<property name="httpInvokerRequestExecutor"> <bean class="org.springframework.remoting.httpinvoker.CommonsHttpInvokerRequestExecutor"/> </property>
Spring provides full support for standard Java web services APIs:
Exposing web services using JAX-RPC
Accessing web services using JAX-RPC
Exposing web services using JAX-WS
Accessing web services using JAX-WS
![]() | Note |
---|---|
Why two standard Java web services APIs? JAX-RPC 1.1 is the standard web service API in J2EE 1.4. As its name indicates, it focuses on on RPC bindings, which became less and less popular in the past couple of years. As a consequence, it has been superseded by JAX-WS 2.0 in Java EE 5, being more flexible in terms of bindings but also being heavily annotation-based. JAX-WS 2.1 is also included in Java 6 (or more specifically, in Sun's JDK 1.6.0_04 and above; previous Sun JDK 1.6.0 releases included JAX-WS 2.0), integrated with the JDK's built-in HTTP server. Spring can work with both standard Java web services APIs. The choice is effectively dependent on the runtime platform: On JDK 1.4 / J2EE 1.4, the only option is JAX-RPC. On Java EE 5 / Java 6, the obvious choice is JAX-WS. On J2EE 1.4 environments that run on Java 5, you might have the option to plug in a JAX-WS provider; check your J2EE server's documentation. |
In addition to stock support for JAX-RPC and JAX-WS in Spring Core, the Spring portfolio also features Spring Web Services, a solution for contract-first, document-driven web services - highly recommended for building modern, future-proof web services. Last but not least, XFire also allows you to export Spring-managed beans as a web service, through built-in Spring support.
Spring provides a convenience base class for JAX-RPC servlet endpoint implementations -
ServletEndpointSupport
. To expose our
AccountService
we extend Spring's
ServletEndpointSupport
class and implement our business
logic here, usually delegating the call to the business layer.
/**
* JAX-RPC compliant RemoteAccountService implementation that simply delegates
* to the AccountService implementation in the root web application context.
*
* This wrapper class is necessary because JAX-RPC requires working with dedicated
* endpoint classes. If an existing service needs to be exported, a wrapper that
* extends ServletEndpointSupport for simple application context access is
* the simplest JAX-RPC compliant way.
*
* This is the class registered with the server-side JAX-RPC implementation.
* In the case of Axis, this happens in "server-config.wsdd" respectively via
* deployment calls. The web service engine manages the lifecycle of instances
* of this class: A Spring application context can just be accessed here.
*/import org.springframework.remoting.jaxrpc.ServletEndpointSupport;
public class AccountServiceEndpoint extends ServletEndpointSupport implements RemoteAccountService {
private AccountService biz;
protected void onInit() {
this.biz = (AccountService) getWebApplicationContext().getBean("accountService");
}
public void insertAccount(Account acc) throws RemoteException {
biz.insertAccount(acc);
}
public Account[] getAccounts(String name) throws RemoteException {
return biz.getAccounts(name);
}
}
Our AccountServletEndpoint
needs to run in the same web
application as the Spring context to allow for access to Spring's facilities. In case of
Axis, copy the AxisServlet
definition into your
'web.xml'
, and set up the endpoint in
'server-config.wsdd'
(or use the deploy tool). See the sample
application JPetStore where the OrderService
is exposed as
a web service using Axis.
Spring provides two factory beans to create JAX-RPC web service proxies,
namely LocalJaxRpcServiceFactoryBean
and
JaxRpcPortProxyFactoryBean
. The former can only return a JAX-RPC
service class for us to work with. The latter is the full-fledged version that can return
a proxy that implements our business service interface. In this example we use the latter
to create a proxy for the AccountService
endpoint we exposed
in the previous section. You will see that Spring has great support for web services
requiring little coding efforts - most of the setup is done in the Spring configuration
file as usual:
<bean id="accountWebService" class="org.springframework.remoting.jaxrpc.JaxRpcPortProxyFactoryBean"> <property name="serviceInterface" value="example.RemoteAccountService"/> <property name="wsdlDocumentUrl" value="http://localhost:8080/account/services/accountService?WSDL"/> <property name="namespaceUri" value="http://localhost:8080/account/services/accountService"/> <property name="serviceName" value="AccountService"/> <property name="portName" value="AccountPort"/> </bean>
Where serviceInterface
is our remote business interface the clients will use.
wsdlDocumentUrl
is the URL for the WSDL file. Spring needs this a startup time to create the JAX-RPC Service.
namespaceUri
corresponds to the targetNamespace in the .wsdl file.
serviceName
corresponds to the service name in the .wsdl file.
portName
corresponds to the port name in the .wsdl file.
Accessing the web service is now very easy as we have a bean factory for it that will expose it
as RemoteAccountService
interface. We can wire this up in Spring:
<bean id="client" class="example.AccountClientImpl"> ... <property name="service" ref="accountWebService"/> </bean>
From the client code we can access the web service just as if it
was a normal class, except that it throws RemoteException
.
public class AccountClientImpl {
private RemoteAccountService service;
public void setService(RemoteAccountService service) {
this.service = service;
}
public void foo() {
try {
service.insertAccount(...);
}
catch (RemoteException ex) {
// ouch
}
}
}
We can get rid of the checked RemoteException
since
Spring supports automatic conversion to its corresponding unchecked
RemoteException
. This requires that we provide a non-RMI
interface also. Our configuration is now:
<bean id="accountWebService" class="org.springframework.remoting.jaxrpc.JaxRpcPortProxyFactoryBean"> <property name="serviceInterface" value="example.AccountService"/> <property name="portInterface" value="example.RemoteAccountService"/> </bean>
Where serviceInterface
is changed to our non RMI interface. Our RMI
interface is now defined using the property portInterface
. Our client
code can now avoid handling java.rmi.RemoteException
:
public class AccountClientImpl { private AccountService service; public void setService(AccountService service) { this.service = service; } public void foo() { service.insertAccount(...); } }
Note that you can also drop the "portInterface" part and specify a plain
business interface as "serviceInterface". In this case,
JaxRpcPortProxyFactoryBean
will automatically switch
to the JAX-RPC "Dynamic Invocation Interface", performing dynamic invocations
without a fixed port stub. The advantage is that you don't even need to have
an RMI-compliant Java port interface around (e.g. in case of a non-Java target
web service); all you need is a matching business interface. Check out
JaxRpcPortProxyFactoryBean
's javadoc for details
on the runtime implications.
To transfer complex objects over the wire such as Account
we must
register bean mappings on the client side.
![]() | Note |
---|---|
On the server side using Axis registering bean mappings is usually done in
the |
We will use Axis to register bean mappings on the client side. To do this we need to register the bean mappings programmatically:
public class AxisPortProxyFactoryBean extends JaxRpcPortProxyFactoryBean { protected void postProcessJaxRpcService(Service service) { TypeMappingRegistry registry = service.getTypeMappingRegistry(); TypeMapping mapping = registry.createTypeMapping(); registerBeanMapping(mapping, Account.class, "Account"); registry.register("http://schemas.xmlsoap.org/soap/encoding/", mapping); } protected void registerBeanMapping(TypeMapping mapping, Class type, String name) { QName qName = new QName("http://localhost:8080/account/services/accountService", name); mapping.register(type, qName, new BeanSerializerFactory(type, qName), new BeanDeserializerFactory(type, qName)); } }
In this section we will register our own
javax.rpc.xml.handler.Handler
to the web service proxy
where we can do custom code before the SOAP message is sent over the wire.
The Handler
is a callback interface. There is a convenience
base class provided in jaxrpc.jar
, namely
javax.rpc.xml.handler.GenericHandler
that we will extend:
public class AccountHandler extends GenericHandler { public QName[] getHeaders() { return null; } public boolean handleRequest(MessageContext context) { SOAPMessageContext smc = (SOAPMessageContext) context; SOAPMessage msg = smc.getMessage(); try { SOAPEnvelope envelope = msg.getSOAPPart().getEnvelope(); SOAPHeader header = envelope.getHeader(); ... } catch (SOAPException ex) { throw new JAXRPCException(ex); } return true; } }
What we need to do now is to register our AccountHandler to JAX-RPC Service so it would
invoke handleRequest(..)
before the message is sent over the wire.
Spring has at this time of writing no declarative support for registering handlers, so we must
use the programmatic approach. However Spring has made it very easy for us to do this as we can
override the postProcessJaxRpcService(..)
method that is designed for
this:
public class AccountHandlerJaxRpcPortProxyFactoryBean extends JaxRpcPortProxyFactoryBean { protected void postProcessJaxRpcService(Service service) { QName port = new QName(this.getNamespaceUri(), this.getPortName()); List list = service.getHandlerRegistry().getHandlerChain(port); list.add(new HandlerInfo(AccountHandler.class, null, null)); logger.info("Registered JAX-RPC AccountHandler on port " + port); } }
The last thing we must remember to do is to change the Spring configuration to use our factory bean:
<bean id="accountWebService" class="example.AccountHandlerJaxRpcPortProxyFactoryBean"> ... </bean>
Spring provides a convenient base class for JAX-WS servlet endpoint implementations -
SpringBeanAutowiringSupport
. To expose our
AccountService
we extend Spring's
SpringBeanAutowiringSupport
class and implement our business
logic here, usually delegating the call to the business layer.
We'll simply use Spring 2.5's @Autowired
annotation for expressing such dependencies on Spring-managed beans.
/**
* JAX-WS compliant AccountService implementation that simply delegates
* to the AccountService implementation in the root web application context.
*
* This wrapper class is necessary because JAX-WS requires working with dedicated
* endpoint classes. If an existing service needs to be exported, a wrapper that
* extends SpringBeanAutowiringSupport for simple Spring bean autowiring (through
* the @Autowired annotation) is the simplest JAX-WS compliant way.
*
* This is the class registered with the server-side JAX-WS implementation.
* In the case of a Java EE 5 server, this would simply be defined as a servlet
* in web.xml, with the server detecting that this is a JAX-WS endpoint and reacting
* accordingly. The servlet name usually needs to match the specified WS service name.
*
* The web service engine manages the lifecycle of instances of this class.
* Spring bean references will just be wired in here.
*/import org.springframework.web.context.support.SpringBeanAutowiringSupport;
@WebService(serviceName="AccountService")
public class AccountServiceEndpoint extends SpringBeanAutowiringSupport {
@Autowired
private AccountService biz;
@WebMethod
public void insertAccount(Account acc) {
biz.insertAccount(acc);
}
@WebMethod
public Account[] getAccounts(String name) {
return biz.getAccounts(name);
}
}
Our AccountServletEndpoint
needs to run in the same web
application as the Spring context to allow for access to Spring's facilities. This is
the case by default in Java EE 5 environments, using the standard contract for JAX-WS
servlet endpoint deployment. See Java EE 5 web service tutorials for details.
The built-in JAX-WS provider that comes with Sun's JDK 1.6 supports exposure
of web services using the built-in HTTP server that's included in JDK 1.6 as well.
Spring's SimpleJaxWsServiceExporter
detects all
@WebService
annotated beans in the Spring application context,
exporting them through the default JAX-WS server (the JDK 1.6 HTTP server).
In this scenario, the endpoint instances are defined and managed as Spring beans
themselves; they will be registered with the JAX-WS engine but their lifecycle
will be up to the Spring application context. This means that Spring functionality
like explicit dependency injection may be applied to the endpoint instances.
Of course, annotation-driven injection through @Autowired
will work as well.
<bean class="org.springframework.remoting.jaxws.SimpleJaxWsServiceExporter"> <property name="baseAddress" value="http://localhost:9999/"/> </bean> <bean id="accountServiceEndpoint" class="example.AccountServiceEndpoint"> ... </bean> ...
The AccountServiceEndpoint
may derive from
Spring's SpringBeanAutowiringSupport
but doesn't
have to since the endpoint is a fully Spring-managed bean here.
This means that the endpoint implementation may look like as follows,
without any superclass declared - and Spring's @Autowired
configuration annotation still being honored:
@WebService(serviceName="AccountService") public class AccountServiceEndpoint { @Autowired private AccountService biz; @WebMethod public void insertAccount(Account acc) { biz.insertAccount(acc); } @WebMethod public Account[] getAccounts(String name) { return biz.getAccounts(name); } }
Sun's JAX-WS RI, developed as part of the GlassFish project, ships Spring support as part of its JAX-WS Commons project. This allows for defining JAX-WS endpoints as Spring-managed beans, similar to the standalone mode discussed in the previous section - but this time in a Servlet environment. Note that this is not portable in a Java EE 5 environment; it is mainly intended for non-EE environments such as Tomcat, embedding the JAX-WS RI as part of the web application.
The difference to the standard style of exporting servlet-based endpoints is
that the lifecycle of the endpoint instances themselves will be managed by Spring here,
and that there will be only one JAX-WS servlet defined in web.xml
.
With the standard Java EE 5 style (as illustrated above), you'll have one servlet
definition per service endpoint, with each endpoint typically delegating to Spring
beans (through the use of @Autowired
, as shown above).
Check out https://jax-ws-commons.dev.java.net/spring/ for the details on setup and usage style.
Analogous to the JAX-RPC support, Spring provides two factory beans
to create JAX-WS web service proxies, namely LocalJaxWsServiceFactoryBean
and
JaxWsPortProxyFactoryBean
. The former can only return a JAX-WS
service class for us to work with. The latter is the full-fledged version that can return
a proxy that implements our business service interface. In this example we use the latter
to create a proxy for the AccountService
endpoint (again):
<bean id="accountWebService" class="org.springframework.remoting.jaxws.JaxWsPortProxyFactoryBean"> <property name="serviceInterface" value="example.AccountService"/> <property name="wsdlDocumentUrl" value="http://localhost:8080/account/services/accountService?WSDL"/> <property name="namespaceUri" value="http://localhost:8080/account/services/accountService"/> <property name="serviceName" value="AccountService"/> <property name="portName" value="AccountPort"/> </bean>
Where serviceInterface
is our business interface the clients will use.
wsdlDocumentUrl
is the URL for the WSDL file. Spring needs this a startup time to create the JAX-WS Service.
namespaceUri
corresponds to the targetNamespace in the .wsdl file.
serviceName
corresponds to the service name in the .wsdl file.
portName
corresponds to the port name in the .wsdl file.
Accessing the web service is now very easy as we have a bean factory for it that will expose it
as AccountService
interface. We can wire this up in Spring:
<bean id="client" class="example.AccountClientImpl"> ... <property name="service" ref="accountWebService"/> </bean>
From the client code we can access the web service just as if it was a normal class:
public class AccountClientImpl { private AccountService service; public void setService(AccountService service) { this.service = service; } public void foo() { service.insertAccount(...); } }
NOTE: The above is slightly simplified in that JAX-WS
requires endpoint interfaces and implementation classes to be annotated with
@WebService
, @SOAPBinding
etc annotations.
This means that you cannot (easily) use plain Java interfaces and implementation
classes as JAX-WS endpoint artifacts; you need to annotate them accordingly first.
Check the JAX-WS documentation for details on those requirements.
XFire is a lightweight SOAP library, hosted by Codehaus. Exposing XFire is done using a
XFire context that shipping with XFire itself in combination with a RemoteExporter-style bean
you have to add to your WebApplicationContext
. As with all
methods that allow you to expose service, you have to create a
DispatcherServlet
with a corresponding
WebApplicationContext
containing the services you will be
exposing:
<servlet> <servlet-name>xfire</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> </servlet>
You also have to link in the XFire configuration. This is done by adding a context
file to the contextConfigLocations
context parameter picked up by the
ContextLoaderListener
(or ContextLoaderServlet
for that matter).
<context-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:org/codehaus/xfire/spring/xfire.xml</param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener>
After you added a servlet mapping (mapping /*
to the XFire servlet
declared above) you only have to add one extra bean to expose the service using XFire.
Add for example the following configuration in your 'xfire-servlet.xml'
file:
<beans>
<bean name="/Echo" class="org.codehaus.xfire.spring.remoting.XFireExporter">
<property name="serviceInterface" value="org.codehaus.xfire.spring.Echo"/>
<property name="serviceBean">
<bean class="org.codehaus.xfire.spring.EchoImpl"/>
</property>
<!-- the XFire bean is defined in the xfire.xml
file -->
<property name="xfire" ref="xfire"/>
</bean>
</beans>
XFire handles the rest. It introspects your service interface and generates a WSDL from it. Parts of this documentation have been taken from the XFire site; for more detailed information on XFire Spring integration, navigate to http://docs.codehaus.org/display/XFIRE/Spring.
It is also possible to expose services transparently using JMS as the underlying
communication protocol. The JMS remoting support in the Spring Framework is pretty basic -
it sends and receives on the same thread
and in the
same non-transactional Session
, and as
such throughput will be very implementation dependent.
The following interface is used on both the server and the client side.
package com.foo; public interface CheckingAccountService { public void cancelAccount(Long accountId); }
The following simple implementation of the above interface is used on the server-side.
package com.foo; public class SimpleCheckingAccountService implements CheckingAccountService { public void cancelAccount(Long accountId) { System.out.println("Cancelling account [" + accountId + "]"); } }
This configuration file contains the JMS-infrastructure beans that are shared on both the client and server.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"> <bean id="connectionFactory" class="org.apache.activemq.ActiveMQConnectionFactory"> <property name="brokerURL" value="tcp://ep-t43:61616"/> </bean> <bean id="queue" class="org.apache.activemq.command.ActiveMQQueue"> <constructor-arg value="mmm"/> </bean> </beans>
On the server, you just need to expose the service object using the
JmsInvokerServiceExporter
.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"> <bean id="checkingAccountService" class="org.springframework.jms.remoting.JmsInvokerServiceExporter"> <property name="serviceInterface" value="com.foo.CheckingAccountService"/> <property name="service"> <bean class="com.foo.SimpleCheckingAccountService"/> </property> </bean> <bean class="org.springframework.jms.listener.SimpleMessageListenerContainer"> <property name="connectionFactory" ref="connectionFactory"/> <property name="destination" ref="queue"/> <property name="concurrentConsumers" value="3"/> <property name="messageListener" ref="checkingAccountService"/> </bean> </beans>
package com.foo; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Server { public static void main(String[] args) throws Exception { new ClassPathXmlApplicationContext(new String[]{"com/foo/server.xml", "com/foo/jms.xml"}); } }
The client merely needs to create a client-side proxy that will implement the agreed
upon interface (CheckingAccountService
). The resulting
object created off the back of the following bean definition can be injected into other
client side objects, and the proxy will take care of forwarding the call to the
server-side object via JMS.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"> <bean id="checkingAccountService" class="org.springframework.jms.remoting.JmsInvokerProxyFactoryBean"> <property name="serviceInterface" value="com.foo.CheckingAccountService"/> <property name="connectionFactory" ref="connectionFactory"/> <property name="queue" ref="queue"/> </bean> </beans>
package com.foo; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Client { public static void main(String[] args) throws Exception { ApplicationContext ctx = new ClassPathXmlApplicationContext( new String[] {"com/foo/client.xml", "com/foo/jms.xml"}); CheckingAccountService service = (CheckingAccountService) ctx.getBean("checkingAccountService"); service.cancelAccount(new Long(10)); } }
You may also wish to investigate the support provided by the Lingo project, which (to quote the homepage blurb) “... is a lightweight POJO based remoting and messaging library based on the Spring Framework's remoting libraries which extends it to support JMS.”
The main reason why auto-detection of implemented interfaces does not occur for
remote interfaces is to avoid opening too many doors to remote callers. The target
object might implement internal callback interfaces like InitializingBean
or
DisposableBean
which one would not want to expose to callers.
Offering a proxy with all interfaces implemented by the target usually does not matter in the local case. But when exporting a remote service, you should expose a specific service interface, with specific operations intended for remote usage. Besides internal callback interfaces, the target might implement multiple business interfaces, with just one of them intended for remote exposure. For these reasons, we require such a service interface to be specified.
This is a trade-off between configuration convenience and the risk of accidental exposure of internal methods. Always specifying a service interface is not too much effort, and puts you on the safe side regarding controlled exposure of specific methods.
Each and every technology presented here has its drawbacks. You should carefully consider you needs, the services your exposing and the objects you'll be sending over the wire when choosing a technology.
When using RMI, it's not possible to access the objects through the HTTP protocol, unless you're tunneling the RMI traffic. RMI is a fairly heavy-weight protocol in that it support full-object serialization which is important when using a complex data model that needs serialization over the wire. However, RMI-JRMP is tied to Java clients: It is a Java-to-Java remoting solution.
Spring's HTTP invoker is a good choice if you need HTTP-based remoting but also rely on Java serialization. It shares the basic infrastructure with RMI invokers, just using HTTP as transport. Note that HTTP invokers are not only limited to Java-to-Java remoting but also to Spring on both the client and server side. (The latter also applies to Spring's RMI invoker for non-RMI interfaces.)
Hessian and/or Burlap might provide significant value when operating in a heterogeneous environment, because they explicitly allow for non-Java clients. However, non-Java support is still limited. Known issues include the serialization of Hibernate objects in combination with lazily-initialized collections. If you have such a data model, consider using RMI or HTTP invokers instead of Hessian.
JMS can be useful for providing clusters of services and allowing the JMS broker to take care of load balancing, discovery and auto-failover. By default: Java serialization is used when using JMS remoting but the JMS provider could use a different mechanism for the wire formatting, such as XStream to allow servers to be implemented in other technologies.
Last but not least, EJB has an advantage over RMI in that it supports standard role-based authentication and authorization and remote transaction propagation. It is possible to get RMI invokers or HTTP invokers to support security context propagation as well, although this is not provided by core Spring: There are just appropriate hooks for plugging in third-party or custom solutions here.
As a lightweight container, Spring is often considered an EJB replacement. We do believe that for many if not most applications and use cases, Spring as a container, combined with its rich supporting functionality in the area of transactions, ORM and JDBC access, is a better choice than implementing equivalent functionality via an EJB container and EJBs.
However, it is important to note that using Spring does not prevent you from using EJBs. In fact, Spring makes it much easier to access EJBs and implement EJBs and functionality within them. Additionally, using Spring to access services provided by EJBs allows the implementation of those services to later transparently be switched between local EJB, remote EJB, or POJO (plain old Java object) variants, without the client code having to be changed.
In this chapter, we look at how Spring can help you access and implement EJBs. Spring provides particular value when accessing stateless session beans (SLSBs), so we'll begin by discussing this.
To invoke a method on a local or remote stateless session bean, client code must normally perform a JNDI lookup to obtain the (local or remote) EJB Home object, then use a 'create' method call on that object to obtain the actual (local or remote) EJB object. One or more methods are then invoked on the EJB.
To avoid repeated low-level code, many EJB applications use the Service Locator and Business Delegate patterns. These are better than spraying JNDI lookups throughout client code, but their usual implementations have significant disadvantages. For example:
Typically code using EJBs depends on Service Locator or Business Delegate singletons, making it hard to test.
In the case of the Service Locator pattern used without a Business Delegate, application code still ends up having to invoke the create() method on an EJB home, and deal with the resulting exceptions. Thus it remains tied to the EJB API and the complexity of the EJB programming model.
Implementing the Business Delegate pattern typically results in significant code duplication, where we have to write numerous methods that simply call the same method on the EJB.
The Spring approach is to allow the creation and use of proxy objects, normally configured inside a Spring container, which act as codeless business delegates. You do not need to write another Service Locator, another JNDI lookup, or duplicate methods in a hand-coded Business Delegate unless you are actually adding real value in such code.
Assume that we have a web controller that needs to use a local
EJB. We’ll follow best practice and use the EJB Business Methods
Interface pattern, so that the EJB’s local interface extends a non
EJB-specific business methods interface. Let’s call this business
methods interface MyComponent
.
public interface MyComponent { ... }
One of the main reasons to use the Business Methods Interface pattern
is to ensure that synchronization between method signatures in local
interface and bean implementation class is automatic. Another reason is
that it later makes it much easier for us to switch to a POJO (plain old
Java object) implementation of the service if it makes sense to do so.
Of course we’ll also need to implement the local home interface and
provide an implementation class that implements SessionBean
and the MyComponent
business methods interface. Now the
only Java coding we’ll need to do to hook up our web tier controller to the
EJB implementation is to expose a setter method of type MyComponent
on the controller. This will save the reference as an instance variable in the
controller:
private MyComponent myComponent; public void setMyComponent(MyComponent myComponent) { this.myComponent = myComponent; }
We can subsequently use this instance variable in any business
method in the controller. Now assuming we are obtaining our controller
object out of a Spring container, we can (in the same context) configure a
LocalStatelessSessionProxyFactoryBean
instance, which
will be the EJB proxy object. The configuration of the proxy, and setting of
the myComponent
property of the controller is done
with a configuration entry such as:
<bean id="myComponent" class="org.springframework.ejb.access.LocalStatelessSessionProxyFactoryBean"> <property name="jndiName" value="ejb/myBean"/> <property name="businessInterface" value="com.mycom.MyComponent"/> </bean> <bean id="myController" class="com.mycom.myController"> <property name="myComponent" ref="myComponent"/> </bean>
There’s a lot of work happening behind the scenes, courtesy of
the Spring AOP framework, although you aren’t forced to work with AOP
concepts to enjoy the results. The myComponent
bean
definition creates a proxy for the EJB, which implements the business
method interface. The EJB local home is cached on startup, so there’s
only a single JNDI lookup. Each time the EJB is invoked, the proxy
invokes the classname
method on the local EJB and
invokes the corresponding business method on the EJB.
The myController
bean definition sets the
myComponent
property of the controller class to the
EJB proxy.
Alternatively (and preferably in case of many such proxy definitions),
consider using the <jee:local-slsb>
configuration element in Spring's "jee" namespace:
<jee:local-slsb id="myComponent" jndi-name="ejb/myBean" business-interface="com.mycom.MyComponent"/> <bean id="myController" class="com.mycom.myController"> <property name="myComponent" ref="myComponent"/> </bean>
This EJB access mechanism delivers huge simplification of
application code: the web tier code (or other EJB client code) has no
dependence on the use of EJB. If we want to replace this EJB reference
with a POJO or a mock object or other test stub, we could simply change
the myComponent
bean definition without changing a
line of Java code. Additionally, we haven’t had to write a single line of
JNDI lookup or other EJB plumbing code as part of our application.
Benchmarks and experience in real applications indicate that the performance overhead of this approach (which involves reflective invocation of the target EJB) is minimal, and is typically undetectable in typical use. Remember that we don’t want to make fine-grained calls to EJBs anyway, as there’s a cost associated with the EJB infrastructure in the application server.
There is one caveat with regards to the JNDI lookup. In a bean
container, this class is normally best used as a singleton (there simply
is no reason to make it a prototype). However, if that bean container
pre-instantiates singletons (as do the various XML
ApplicationContext
variants)
you may have a problem if the bean container is loaded before the EJB
container loads the target EJB. That is because the JNDI lookup will be
performed in the init()
method of this class and then
cached, but the EJB will not have been bound at the target location yet.
The solution is to not pre-instantiate this factory object, but allow it
to be created on first use. In the XML containers, this is controlled via
the lazy-init
attribute.
Although this will not be of interest to the majority of Spring
users, those doing programmatic AOP work with EJBs may want to look at
LocalSlsbInvokerInterceptor
.
Accessing remote EJBs is essentially identical to accessing local
EJBs, except that the
SimpleRemoteStatelessSessionProxyFactoryBean
or
<jee:remote-slsb>
configuration element is used.
Of course, with or without Spring, remote invocation semantics apply; a
call to a method on an object in another VM in another computer does
sometimes have to be treated differently in terms of usage scenarios and
failure handling.
Spring's EJB client support adds one more advantage over the
non-Spring approach. Normally it is problematic for EJB client code to
be easily switched back and forth between calling EJBs locally or
remotely. This is because the remote interface methods must declare that
they throw RemoteException
, and client code must deal
with this, while the local interface methods don't. Client code
written for local EJBs which needs to be moved to remote EJBs
typically has to be modified to add handling for the remote exceptions,
and client code written for remote EJBs which needs to be moved to local
EJBs, can either stay the same but do a lot of unnecessary handling of
remote exceptions, or needs to be modified to remove that code. With the
Spring remote EJB proxy, you can instead not declare any thrown
RemoteException
in your Business Method Interface and
implementing EJB code, have a remote interface which is identical except
that it does throw RemoteException
, and rely on the
proxy to dynamically treat the two interfaces as if they were the same.
That is, client code does not have to deal with the checked
RemoteException
class. Any actual
RemoteException
that is thrown during the EJB
invocation will be re-thrown as the non-checked
RemoteAccessException
class, which is a subclass of
RuntimeException
. The target service can then be
switched at will between a local EJB or remote EJB (or even plain Java
object) implementation, without the client code knowing or caring. Of
course, this is optional; there is nothing stopping you from declaring
RemoteExceptions
in your business interface.
Accessing EJB 2.x Session Beans and EJB 3 Session Beans via Spring
is largely transparent. Spring's EJB accessors, including the
<jee:local-slsb>
and <jee:remote-slsb>
facilities, transparently adapt to the actual component at runtime.
They handle a home interface if found (EJB 2.x style), or perform straight
component invocations if no home interface is available (EJB 3 style).
Note: For EJB 3 Session Beans, you could effectively use a
JndiObjectFactoryBean
/ <jee:jndi-lookup>
as well, since fully usable component references are exposed for plain
JNDI lookups there. Defining explicit <jee:local-slsb>
/ <jee:remote-slsb>
lookups simply provides
consistent and more explicit EJB access configuration.
Spring provides convenience classes to help you implement EJBs. These are designed to encourage the good practice of putting business logic behind EJBs in POJOs, leaving EJBs responsible for transaction demarcation and (optionally) remoting.
To implement a Stateless or Stateful session bean, or a Message Driven
bean, you need only derive your implementation class from
AbstractStatelessSessionBean
,
AbstractStatefulSessionBean
, and
AbstractMessageDrivenBean
/AbstractJmsMessageDrivenBean
,
respectively.
Consider an example Stateless Session bean which actually delegates the implementation to a plain java service object. We have the business interface:
public interface MyComponent { public void myMethod(...); ... }
We also have the plain Java implementation object:
public class MyComponentImpl implements MyComponent { public String myMethod(...) { ... } ... }
And finally the Stateless Session Bean itself:
public class MyFacadeEJB extends AbstractStatelessSessionBean implements MyFacadeLocal { private MyComponent myComp; /** * Obtain our POJO service object from the BeanFactory/ApplicationContext * @see org.springframework.ejb.support.AbstractStatelessSessionBean#onEjbCreate() */ protected void onEjbCreate() throws CreateException { myComp = (MyComponent) getBeanFactory().getBean( ServicesConstants.CONTEXT_MYCOMP_ID); } // for business method, delegate to POJO service impl. public String myFacadeMethod(...) { return myComp.myMethod(...); } ... }
The Spring EJB support base classes will by default create and load
a Spring IoC container as part of their lifecycle, which is then available
to the EJB (for example, as used in the code above to obtain the POJO
service object). The loading is done via a strategy object which is a subclass of
BeanFactoryLocator
. The actual implementation of
BeanFactoryLocator
used by default is
ContextJndiBeanFactoryLocator
, which creates the
ApplicationContext from a resource locations specified as a JNDI
environment variable (in the case of the EJB classes, at
java:comp/env/ejb/BeanFactoryPath
). If there is a need
to change the BeanFactory/ApplicationContext loading strategy, the default
BeanFactoryLocator
implementation used may be overridden
by calling the setBeanFactoryLocator()
method, either
in setSessionContext()
, or in the actual constructor of
the EJB. Please see the Javadocs for more details.
As described in the Javadocs, Stateful Session beans expecting to be
passivated and reactivated as part of their lifecycle, and which use a
non-serializable container instance (which is the normal case) will have
to manually call unloadBeanFactory()
and
loadBeanFactory
from ejbPassivate
and ejbActivate
, respectively, to unload and reload the
BeanFactory on passivation and activation, since it can not be saved by
the EJB container.
The default behavior of the ContextJndiBeanFactoryLocator
classes which is to load an ApplicationContext
for the
use of the EJB is adequate for some situations. However, it is problematic when
the ApplicationContext
is loading a number
of beans, or the initialization of those beans is time consuming or memory
intensive (such as a Hibernate SessionFactory
initialization, for
example), since every EJB will have their own copy. In this case, the user
may want to override the default ContextJndiBeanFactoryLocator
usage and use another BeanFactoryLocator
variant, such as the
ContextSingletonBeanFactoryLocator
which can load and use a
shared container to be used by multiple EJBs or other clients. Doing this is relatively
simple, by adding code similar to this to the EJB:
/** * Override default BeanFactoryLocator implementation * @see javax.ejb.SessionBean#setSessionContext(javax.ejb.SessionContext) */ public void setSessionContext(SessionContext sessionContext) { super.setSessionContext(sessionContext); setBeanFactoryLocator(ContextSingletonBeanFactoryLocator.getInstance()); setBeanFactoryLocatorKey(ServicesConstants.PRIMARY_CONTEXT_ID); }
You would then need to create a bean definition file named beanRefContext.xml
.
This file defines all bean factories (usually in the form of application contexts) that may be used
in the EJB. In many cases, this file will only contain a single bean definition such as this (where
businessApplicationContext.xml
contains the bean definitions for all business
service POJOs):
<beans> <bean id="businessBeanFactory" class="org.springframework.context.support.ClassPathXmlApplicationContext"> <constructor-arg value="businessApplicationContext.xml" /> </bean> </beans>
In the above example, the ServicesConstants.PRIMARY_CONTEXT_ID
constant
would be defined as follows:
public static final String ServicesConstants.PRIMARY_CONTEXT_ID = "businessBeanFactory";
Please see the respective Javadocs for the BeanFactoryLocator
and
ContextSingletonBeanFactoryLocator
classes for more information on
their usage.
For EJB 3 Session Beans and Message-Driven Beans, Spring provides a convenient
interceptor that resolves Spring 2.5's @Autowired
annotation
in the EJB component class:
org.springframework.ejb.interceptor.SpringBeanAutowiringInterceptor
.
This interceptor can be applied through an @Interceptors
annotation
in the EJB component class, or through an interceptor-binding
XML element in the EJB deployment descriptor.
@Stateless @Interceptors(SpringBeanAutowiringInterceptor.class) public class MyFacadeEJB implements MyFacadeLocal { // automatically injected with a matching Spring bean @Autowired private MyComponent myComp; // for business method, delegate to POJO service impl. public String myFacadeMethod(...) { return myComp.myMethod(...); } ... }
SpringBeanAutowiringInterceptor
by default obtains target
beans from a ContextSingletonBeanFactoryLocator
, with the
context defined in a bean definition file named beanRefContext.xml
.
By default, a single context definition is expected, which is obtained by type rather
than by name. However, if you need to choose between multiple context definitions,
a specific locator key is required. The locator key (i.e. the name of the context
definition in beanRefContext.xml
) can be explicitly specified
either through overriding the getBeanFactoryLocatorKey
method
in a custom SpringBeanAutowiringInterceptor
subclass.
Alternatively, consider overriding SpringBeanAutowiringInterceptor
's
getBeanFactory
method, e.g. obtaining a shared
ApplicationContext
from a custom holder class.
Spring provides a JMS integration framework that simplifies the use of the JMS API and shields the user from differences between the JMS 1.0.2 and 1.1 APIs.
JMS can be roughly divided into two areas of functionality, namely the
production and consumption of messages. The JmsTemplate
class is used for message production and synchronous message reception. For
asynchronous reception similar to J2EE's message-driven bean style, Spring
provides a number of message listener containers that are used to create
Message-Driven POJOs (MDPs).
The package org.springframework.jms.core
provides
the core functionality for using JMS. It contains JMS template classes
that simplifies the use of the JMS by handling the creation and release of
resources, much like the JdbcTemplate
does for
JDBC. The design principle common to Spring template classes is to provide
helper methods to perform common operations and for more sophisticated
usage, delegate the essence of the processing task to user implemented
callback interfaces. The JMS template follows the same design. The classes
offer various convenience methods for the sending of messages, consuming a
message synchronously, and exposing the JMS session and message producer
to the user.
The package org.springframework.jms.support
provides JMSException translation functionality. The translation converts
the checked JMSException
hierarchy to a mirrored
hierarchy of unchecked exceptions. If there are any provider specific
subclasses of the checked javax.jms.JMSException
,
this exception is wrapped in the unchecked
UncategorizedJmsException
.
The package org.springframework.jms.support.converter
provides a
MessageConverter
abstraction to convert between Java objects
and JMS messages.
The package org.springframework.jms.support.destination
provides
various strategies for managing JMS destinations, such as providing a
service locator for destinations stored in JNDI.
Finally, the package
org.springframework.jms.connection
provides an
implementation of the ConnectionFactory
suitable
for use in standalone applications. It also contains an implementation of
Spring's PlatformTransactionManager
for
JMS (the cunningly named JmsTransactionManager
).
This allows for seamless integration of JMS as a transactional resource into
Spring's transaction management mechanisms.
There are two variants of the functionality offered by the
JmsTemplate
: the JmsTemplate
uses the JMS 1.1 API, and the subclass JmsTemplate102
uses the JMS 1.0.2 API.
Code that uses the JmsTemplate
only needs to
implement callback interfaces giving them a clearly defined contract. The
MessageCreator
callback interface creates a message
given a Session
provided by the calling code
in JmsTemplate
. In order to allow for more complex
usage of the JMS API, the callback SessionCallback
provides the user with the JMS session and the callback
ProducerCallback
exposes a
Session
and
MessageProducer
pair.
The JMS API exposes two types of send methods, one that takes
delivery mode, priority, and time-to-live as Quality of Service (QOS)
parameters and one that takes no QOS parameters which uses default values.
Since there are many send methods in JmsTemplate
,
the setting of the QOS parameters have been exposed as bean properties to
avoid duplication in the number of send methods. Similarly, the timeout
value for synchronous receive calls is set using the property
setReceiveTimeout
.
Some JMS providers allow the setting of default QOS values
administratively through the configuration of the ConnectionFactory. This
has the effect that a call to MessageProducer
's
send method send(Destination destination, Message
message)
will use different QOS default values than those
specified in the JMS specification. In order to provide consistent
management of QOS values, the JmsTemplate
must
therefore be specifically enabled to use its own QOS values by setting
the boolean property isExplicitQosEnabled
to true
.
![]() | Note |
---|---|
Instances of the |
The JmsTemplate
requires a reference to a
ConnectionFactory
. The
ConnectionFactory
is part of the JMS
specification and serves as the entry point for working with JMS. It is
used by the client application as a factory to create connections with
the JMS provider and encapsulates various configuration parameters, many
of which are vendor specific such as SSL configuration options.
When using JMS inside an EJB, the vendor provides implementations
of the JMS interfaces so that they can participate in declarative
transaction management and perform pooling of connections and session.
In order to use this implementation, J2EE containers typically require
that you declare a JMS connection factory as a
resource-ref inside the EJB or servlet deployment
descriptors. To ensure the use of these features with the
JmsTemplate
inside an EJB, the client application
should ensure that it references the managed implementation of the
ConnectionFactory
.
Spring provides an implementation of the
ConnectionFactory
interface,
SingleConnectionFactory
, that will return the
same Connection
on all
createConnection
calls and ignore calls to
close.
This is useful for testing and
standalone environments so that the same connection can be used for
multiple JmsTemplate
calls that may span any
number of transactions. SingleConnectionFactory
takes a reference to a standard ConnectionFactory
that would typically come from JNDI.
Destinations, like ConnectionFactories, are JMS administered
objects that can be stored and retrieved in JNDI. When configuring a
Spring application context you can use the JNDI factory class
JndiObjectFactoryBean
to perform dependency
injection on your object's references to JMS destinations. However,
often this strategy is cumbersome if there are a large number of
destinations in the application or if there are advanced destination
management features unique to the JMS provider. Examples of such
advanced destination management would be the creation of dynamic
destinations or support for a hierarchical namespace of destinations.
The JmsTemplate
delegates the resolution of a
destination name to a JMS destination object to an implementation of the
interface DestinationResolver
.
DynamicDestinationResolver
is the default
implementation used by JmsTemplate
and
accommodates resolving dynamic destinations. A
JndiDestinationResolver
is also provided that
acts as a service locator for destinations contained in JNDI and
optionally falls back to the behavior contained in
DynamicDestinationResolver
.
Quite often the destinations used in a JMS application are only
known at runtime and therefore cannot be administratively created when
the application is deployed. This is often because there is shared
application logic between interacting system components that create
destinations at runtime according to a well-known naming convention.
Even though the creation of dynamic destinations are not part of the JMS
specification, most vendors have provided this functionality. Dynamic
destinations are created with a name defined by the user which
differentiates them from temporary destinations and are often not
registered in JNDI. The API used to create dynamic destinations varies
from provider to provider since the properties associated with the
destination are vendor specific. However, a simple implementation choice
that is sometimes made by vendors is to disregard the warnings in the
JMS specification and to use the TopicSession
method createTopic(String topicName)
or the
QueueSession
method
createQueue(String queueName)
to create a new
destination with default destination properties. Depending on the vendor
implementation, DynamicDestinationResolver
may
then also create a physical destination instead of only resolving
one.
The boolean property pubSubDomain is used to
configure the JmsTemplate
with knowledge of what
JMS domain is being used. By default the value of this property is
false, indicating that the point-to-point domain, Queues, will be used.
In the 1.0.2 implementation the value of this property determines if the
JmsTemplate
's send operations will send a message
to a Queue
or to a Topic
.
This flag has no effect on send operations for
the 1.1 implementation. However, in both implementations, this property
determines the behavior of dynamic destination resolution via
implementations of the DestinationResolver
interface.
You can also configure the JmsTemplate
with
a default destination via the property
defaultDestination. The default destination will be
used with send and receive operations that do not refer to a specific
destination.
One of the most common uses of JMS messages in the EJB world is to drive message-driven beans (MDBs). Spring offers a solution to create message-driven POJOs (MDPs) in a way that does not tie a user to an EJB container. (See the section entitled Section 19.4.2, “Asynchronous Reception - Message-Driven POJOs” for detailed coverage of Spring's MDP support.)
A message listener container is used to receive messages from a JMS message queue and drive the MessageListener that is injected into it. The listener container is responsible for all threading of message reception and dispatches into the listener for processing. A message listener container is the intermediary between an MDP and a messaging provider, and takes care of registering to receive messages, participating in transactions, resource acquisition and release, exception conversion and suchlike. This allows you as an application developer to write the (possibly complex) business logic associated with receiving a message (and possibly responding to it), and delegates boilerplate JMS infrastructure concerns to the framework.
There are three standard JMS message listener containers packaged with Spring, each with its specialised feature set.
This message listener container is the simplest of the three standard flavors. It simply creates a fixed number of JMS sessions at startup and uses them throughout the lifespan of the container. This container doesn't allow for dynamic adaption to runtime demands or participate in externally managed transactions. However, it does have the fewest requirements on the JMS provider: This listener container only requires simple JMS API compliance.
This message listener container is the one used in most cases.
In contrast to SimpleMessageListenerContainer
,
this container variant does allow for dynamic adaption to runtime
demands and is able to participate in externally managed transactions.
Each received message is registered with an XA transaction
(when configured with a JtaTransactionManager
);
processing can take advantage of XA transation semantics.
This listener container strikes a good balance between low
requirements on the JMS provider and good functionality including
transaction participation.
This listener container leverages the JMS ServerSessionPool SPI
to allow for dynamic management of JMS sessions. The use of this variety
of message listener container enables the provider to perform dynamic
runtime tuning but, at the expense of requiring the JMS provider to support
the ServerSessionPool SPI. If there is no need for provider-driven runtime
tuning, look at the DefaultMessageListenerContainer
or the SimpleMessageListenerContainer
instead.
Spring provides a JmsTransactionManager
that manages transactions for a single JMS
ConnectionFactory
. This allows JMS applications
to leverage the managed transaction features of Spring as described in
Chapter 9, Transaction management. The JmsTransactionManager
performs local resource transactions, binding a JMS Connection/Session
pair from the specified ConnectionFactory
to the
thread. JmsTemplate
automatically detects such
transactional resources and operates on them accordingly.
In a J2EE environment, the ConnectionFactory
will pool Connections and Sessions, so those resources are efficiently
reused across transactions. In a standalone environment, using Spring's
SingleConnectionFactory
will result in a shared
JMS Connection
, with each transaction having its
own independent Session
. Alternatively, consider
the use of a provider-specific pooling adapter such as ActiveMQ's
PooledConnectionFactory
class.
JmsTemplate
can also be used with the
JtaTransactionManager
and an XA-capable JMS
ConnectionFactory
for performing distributed
transactions. Note that this requires the use of a JTA transaction
manager as well as a properly XA-configured ConnectionFactory!
(Check your J2EE server's / JMS provider's documentation.)
Reusing code across a managed and unmanaged transactional
environment can be confusing when using the JMS API to create a
Session
from a Connection
.
This is because the JMS API has only one factory method to create a
Session
and it requires values for the
transaction and acknowledgement modes. In a managed environment, setting
these values is the responsibility of the environment's transactional
infrastructure, so these values are ignored by the vendor's wrapper to
the JMS Connection. When using the JmsTemplate
in
an unmanaged environment you can specify these values through the use of
the properties sessionTransacted
and
sessionAcknowledgeMode
. When using a
PlatformTransactionManager
with
JmsTemplate
, the template will always be given a
transactional JMS Session
.
The JmsTemplate
contains many convenience
methods to send a message. There are send methods that specify the
destination using a javax.jms.Destination
object
and those that specify the destination using a string for use in a JNDI
lookup. The send method that takes no destination argument uses the
default destination. Here is an example that sends a message to a queue
using the 1.0.2 implementation.
import javax.jms.ConnectionFactory; import javax.jms.JMSException; import javax.jms.Message; import javax.jms.Queue; import javax.jms.Session; import org.springframework.jms.core.MessageCreator; import org.springframework.jms.core.JmsTemplate; import org.springframework.jms.core.JmsTemplate102; public class JmsQueueSender { private JmsTemplate jmsTemplate; private Queue queue; public void setConnectionFactory(ConnectionFactory cf) { this.jmsTemplate = new JmsTemplate102(cf, false); } public void setQueue(Queue queue) { this.queue = queue; } public void simpleSend() { this.jmsTemplate.send(this.queue, new MessageCreator() { public Message createMessage(Session session) throws JMSException { return session.createTextMessage("hello queue world"); } }); } }
This example uses the MessageCreator
callback to create a text message from the supplied
Session
object and the
JmsTemplate
is constructed by passing a reference
to a ConnectionFactory
and a boolean specifying
the messaging domain. A zero argument constructor and
connectionFactory / queue bean
properties are provided and can be used for constructing the instance
(using a BeanFactory or plain Java code). Alternatively, consider
deriving from Spring's JmsGatewaySupport
convenience base class, which provides pre-built bean properties for JMS
configuration.
When configuring the JMS 1.0.2 support in an application context, it is important to remember setting the value of the boolean property pubSubDomain property in order to indicate if you want to send to Queues or Topics.
The method send(String destinationName, MessageCreator
creator)
lets you send to a message using the string name
of the destination. If these names are registered in JNDI, you should
set the destinationResolver property of the
template to an instance of
JndiDestinationResolver
.
If you created the JmsTemplate
and
specified a default destination, the send(MessageCreator c)
sends a message to that destination.
In order to facilitate the sending of domain model objects, the
JmsTemplate
has various send methods that take a
Java object as an argument for a message's data content. The overloaded
methods convertAndSend
and
receiveAndConvert
in
JmsTemplate
delegate the conversion process to an
instance of the MessageConverter
interface. This
interface defines a simple contract to convert between Java objects and
JMS messages. The default implementation
SimpleMessageConverter
supports conversion
between String
and
TextMessage
, byte[]
and
BytesMesssage
, and
java.util.Map
and
MapMessage
. By using the converter, you and your
application code can focus on the business object that is being sent or
received via JMS and not be concerned with the details of how it is
represented as a JMS message.
The sandbox currently includes a
MapMessageConverter
which uses reflection to
convert between a JavaBean and a MapMessage
.
Other popular implementations choices you might implement yourself are
Converters that use an existing XML marshalling package, such as JAXB,
Castor, XMLBeans, or XStream, to create a
TextMessage
representing the object.
To accommodate the setting of a message's properties, headers, and
body that can not be generically encapsulated inside a converter class,
the MessagePostProcessor
interface gives you access
to the message after it has been converted, but before it is sent. The
example below demonstrates how to modify a message header and a property after
a java.util.Map
is converted to a message.
public void sendWithConversion() { Map map = new HashMap(); map.put("Name", "Mark"); map.put("Age", new Integer(47)); jmsTemplate.convertAndSend("testQueue", map, new MessagePostProcessor() { public Message postProcessMessage(Message message) throws JMSException { message.setIntProperty("AccountID", 1234); message.setJMSCorrelationID("123-00001"); return message; } }); }
This results in a message of the form:
MapMessage={ Header={ ... standard headers ... CorrelationID={123-00001} } Properties={ AccountID={Integer:1234} } Fields={ Name={String:Mark} Age={Integer:47} } }
While the send operations cover many common usage scenarios, there
are cases when you want to perform multiple operations on a JMS
Session
or
MessageProducer
. The
SessionCallback
and
ProducerCallback
expose the JMS
Session
and
Session
/ MessageProducer
pair respectfully. The execute()
methods on
JmsTemplate
execute these callback
methods.
While JMS is typically associated with asynchronous processing, it
is possible to consume messages synchronously. The overloaded
receive(..)
methods provide this functionality.
During a synchronous receive, the calling thread blocks until a message
becomes available. This can be a dangerous operation since the calling
thread can potentially be blocked indefinitely. The property
receiveTimeout specifies how long the receiver
should wait before giving up waiting for a message.
In a fashion similar to a Message-Driven Bean (MDB) in the EJB world,
the Message-Driven POJO (MDP) acts as a receiver for JMS messages. The one
restriction (but see also below for the discussion of the
MessageListenerAdapter
class) on an MDP is that it
must implement the javax.jms.MessageListener
interface. Please also be aware that in the case where your POJO will be
receiving messages on multiple threads, it is important to ensure that your
implementation is thread-safe.
Below is a simple implementation of an MDP:
import javax.jms.JMSException; import javax.jms.Message; import javax.jms.MessageListener; import javax.jms.TextMessage; public class ExampleListener implements MessageListener { public void onMessage(Message message) { if (message instanceof TextMessage) { try { System.out.println(((TextMessage) message).getText()); } catch (JMSException ex) { throw new RuntimeException(ex); } } else { throw new IllegalArgumentException("Message must be of type TextMessage"); } } }
Once you've implemented your MessageListener
,
it's time to create a message listener container.
Find below an example of how to define and configure one of the message listener
containers that ships with Spring (in this case the
DefaultMessageListenerContainer
).
<!-- this is the Message Driven POJO (MDP) --> <bean id="messageListener" class="jmsexample.ExampleListener" /> <!-- and this is the message listener container --> <bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer"> <property name="connectionFactory" ref="connectionFactory"/> <property name="destination" ref="destination"/> <property name="messageListener" ref="messageListener" /> </bean>
Please refer to the Spring Javadoc of the various message listener containers for a full description of the features supported by each implementation.
The SessionAwareMessageListener
interface
is a Spring-specific interface that provides a similar contract the JMS
MessageListener
interface, but also provides
the message handling method with access to the JMS Session
from which the Message
was received.
package org.springframework.jms.listener;
public interface SessionAwareMessageListener {
void onMessage(Message message, Session session) throws JMSException;
}
You can choose to have your MDPs implement this interface (in preference to the
standard JMS MessageListener
interface) if you
want your MDPs to be able to respond to any received messages (using the
Session
supplied in the
onMessage(Message, Session)
method). All of the message listener
container implementations that ship wth Spring have support for MDPs that implement either
the MessageListener
or
SessionAwareMessageListener
interface. Classes
that implement the SessionAwareMessageListener
come
with the caveat that they are then tied to Spring through the interface. The choice of whether
or not to use it is left entirely up to you as an application developer or architect.
Please note that the 'onMessage(..)'
method of the
SessionAwareMessageListener
interface throws
JMSException
. In contrast to the standard JMS
MessageListener
interface, when using the
SessionAwareMessageListener
interface, it is the responsibility
of the client code to handle any exceptions thrown.
The MessageListenerAdapter
class is the final component in
Spring's asynchronous messaging support: in a nutshell, it allows you to
expose almost any class as a MDP (there are of course some constraints).
![]() | Note |
---|---|
If you are using the JMS 1.0.2 API, you will want to use the
|
Consider the following interface definition. Notice that although the interface extends
neither the MessageListener
nor
SessionAwareMessageListener
interfaces, it can still
be used as a MDP via the use of the MessageListenerAdapter
class.
Notice also how the various message handling methods are strongly typed according to
the contents of the various Message
types that they can receive and handle.
public interface MessageDelegate { void handleMessage(String message); void handleMessage(Map message); void handleMessage(byte[] message); void handleMessage(Serializable message); }
public class DefaultMessageDelegate implements MessageDelegate {
// implementation elided for clarity...
}
In particular, note how the above implementation of the MessageDelegate
interface (the above DefaultMessageDelegate
class) has
no JMS dependencies at all. It truly is a POJO that we will
make into an MDP via the following configuration.
<!-- this is the Message Driven POJO (MDP) --> <bean id="messageListener" class="org.springframework.jms.listener.adapter.MessageListenerAdapter"> <constructor-arg> <bean class="jmsexample.DefaultMessageDelegate"/> </constructor-arg> </bean> <!-- and this is the message listener container... --> <bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer"> <property name="connectionFactory" ref="connectionFactory"/> <property name="destination" ref="destination"/> <property name="messageListener" ref="messageListener" /> </bean>
Below is an example of another MDP that can only handle the receiving of
JMS TextMessage
messages. Notice how the message handling
method is actually called 'receive'
(the name of the message handling
method in a MessageListenerAdapter
defaults to
'handleMessage'
), but it is configurable (as you will see below).
Notice also how the 'receive(..)'
method is strongly typed to
receive and respond only to JMS TextMessage
messages.
public interface TextMessageDelegate { void receive(TextMessage message); }
public class DefaultTextMessageDelegate implements TextMessageDelegate {
// implementation elided for clarity...
}
The configuration of the attendant MessageListenerAdapter
would
look like this:
<bean id="messageListener" class="org.springframework.jms.listener.adapter.MessageListenerAdapter">
<constructor-arg>
<bean class="jmsexample.DefaultTextMessageDelegate"/>
</constructor-arg>
<property name="defaultListenerMethod" value="receive"/>
<!-- we don't want automatic message context extraction -->
<property name="messageConverter">
<null/>
</property>
</bean>
Please note that if the above 'messageListener'
receives a
JMS Message
of a type other than
TextMessage
, an IllegalStateException
will be thrown (and subsequently swallowed).
Another of the capabilities of the MessageListenerAdapter
class is the ability to automatically send back a response Message
if a handler method returns a non-void value.
Consider the interface and class:
public interface ResponsiveTextMessageDelegate {
// notice the return type...
String receive(TextMessage message);
}
public class DefaultResponsiveTextMessageDelegate implements ResponsiveTextMessageDelegate {
// implementation elided for clarity...
}
If the above DefaultResponsiveTextMessageDelegate
is used in
conjunction with a MessageListenerAdapter
then any non-null
value that is returned from the execution of the 'receive(..)'
method will (in the default configuration) be converted into a
TextMessage
. The resulting TextMessage
will then be sent to the Destination
(if one exists)
defined in the JMS Reply-To property of the original Message
, or the
default Destination
set on the
MessageListenerAdapter
(if one has been configured); if no
Destination
is found then an
InvalidDestinationException
will be thrown (and please note
that this exception will not be swallowed and
will propagate up the call stack).
Invoking a message listener within a transaction only requires reconfiguration of the listener container.
Local resource transactions can simply be activated through the
sessionTransacted
flag on the listener container
definition. Each message listener invocation will then operate within
an active JMS transaction, with message reception rolled back in case
of listener execution failure. Sending a response message
(via SessionAwareMessageListener
)
will be part of the same local transaction, but any other resource
operations (such as database access) will operate independently.
This usually requires duplicate message detection in the listener
implementation, covering the case where database processing has
committed but message processing failed to commit.
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="destination"/>
<property name="messageListener" ref="messageListener"/>
<property name="sessionTransacted" value="true"/>
</bean>
For participating in an externally managed transaction,
you will need to configure a transaction manager and use a listener
container which supports externally managed transactions: typically
DefaultMessageListenerContainer
.
To configure a message listener container for XA transaction
participation, you'll want to configure a JtaTransactionManager
(which, by default, delegates to the J2EE server's transaction subsystem).
Note that the underlying JMS ConnectionFactory needs to be XA-capable
and properly registered with your JTA transaction coordinator!
(Check your J2EE server's configuration of JNDI resources.)
This allows message recepton as well as e.g. database access to be
part of the same transaction (with unified commit semantics,
at the expense of XA transaction log overhead).
<bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager"/>
Then you just need to add it to our earlier container configuration. The container will take care of the rest.
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="destination"/>
<property name="messageListener" ref="messageListener"/>
<property name="transactionManager" ref="transactionManager"/>
</bean>
Beginning with version 2.5, Spring also provides support for a JCA-based
MessageListener
container. The
JmsMessageEndpointManager
will attempt to automatically
determine the ActivationSpec
class name from the
provider's ResourceAdapter
class name. Therefore,
it is typically possible to just provide Spring's generic
JmsActivationSpecConfig
as shown in the following example.
<bean class="org.springframework.jms.listener.endpoint.JmsMessageEndpointManager"> <property name="resourceAdapter" ref="resourceAdapter"/> <property name="activationSpecConfig"> <bean class="org.springframework.jms.listener.endpoint.JmsActivationSpecConfig"> <property name="destinationName" value="myQueue"/> </bean> </property> <property name="messageListener" ref="myMessageListener"/> </bean>
Alternatively, you may set up a JmsMessageEndpointManager
with a given ActivationSpec
object. The
ActivationSpec
object may also come
from a JNDI lookup (using <jee:jndi-lookup>
).
<bean class="org.springframework.jms.listener.endpoint.JmsMessageEndpointManager"> <property name="resourceAdapter" ref="resourceAdapter"/> <property name="activationSpec"> <bean class="org.apache.activemq.ra.ActiveMQActivationSpec"> <property name="destination" value="myQueue"/> <property name="destinationType" value="javax.jms.Queue"/> </bean> </property> <property name="messageListener" ref="myMessageListener"/> </bean>
Using Spring's ResourceAdapterFactoryBean
,
the target ResourceAdapter
may be
configured locally as depicted in the following example.
<bean id="resourceAdapter" class="org.springframework.jca.support.ResourceAdapterFactoryBean"> <property name="resourceAdapter"> <bean class="org.apache.activemq.ra.ActiveMQResourceAdapter"> <property name="serverUrl" value="tcp://localhost:61616"/> </bean> </property> <property name="workManager"> <bean class="org.springframework.jca.work.SimpleTaskWorkManager"/> </property> </bean>
The specified WorkManager
may also point to an environment-specific thread pool - typically
through SimpleTaskWorkManager's
"asyncTaskExecutor" property. Consider defining a shared thread
pool for all your ResourceAdapter
instances if you happen to use multiple adapters.
In some environments (e.g. WebLogic 9 or above), the entire
ResourceAdapter
object may be obtained
from JNDI instead (using <jee:jndi-lookup>
).
The Spring-based message listeners can then interact with the server-hosted
ResourceAdapter
, also using the server's
built-in WorkManager
.
Please consult the JavaDoc for JmsMessageEndpointManager
,
JmsActivationSpecConfig
, and
ResourceAdapterFactoryBean
for more details.
Spring also provides a generic JCA message endpoint manager which is not tied to JMS:
org.springframework.jca.endpoint.GenericMessageEndpointManager
.
This component allows for using any message listener type (e.g. a CCI MessageListener)
and any provided-specific ActivationSpec object. Check out your JCA provider's
documentation to find out about the actual capabilities of your connector,
and consult GenericMessageEndpointManager
's JavaDoc
for the Spring-specific configuration details.
![]() | Note |
---|---|
JCA-based message endpoint management is very analogous to EJB 2.1 Message-Driven Beans; it uses the same underlying resource provider contract. Like with EJB 2.1 MDBs, any message listener interface supported by your JCA provider can be used in the Spring context as well. Spring nevertheless provides explicit 'convenience' support for JMS, simply because JMS is the most common endpoint API used with the JCA endpoint management contract. |
Spring 2.5 introduces an XML namespace for simplifying JMS configuration. To use the JMS namespace elements you will need to reference the JMS schema:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jms="http://www.springframework.org/schema/jms"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/jms http://www.springframework.org/schema/jms/spring-jms-2.5.xsd">
<!-- <bean/>
definitions here -->
</beans>
The namespace consists of two top-level elements: <listener-container/>
and <jca-listener-container/>
both of which may contain one or more
<listener/>
child elements. Here is an example of a basic configuration
for two listeners.
<jms:listener-container> <jms:listener destination="queue.orders" ref="orderService" method="placeOrder"/> <jms:listener destination="queue.confirmations" ref="confirmationLogger" method="log"/> </jms:listener-container>
The example above is equivalent to creating two distinct listener container bean
definitions and two distinct MessageListenerAdapter
bean
definitions as demonstrated in the section entitled
Section 19.4.4, “The MessageListenerAdapter
”. In addition to the
attributes shown above, the listener
element may contain several
optional ones. The following table describes all available attributes:
Table 19.1. Attributes of the JMS <listener>
element
Attribute | Description |
---|---|
id |
A bean name for the hosting listener container. If not specified, a bean name will be automatically generated. |
destination (required) |
The destination name for this listener, resolved through the
|
ref (required) |
The bean name of the handler object. |
method |
The name of the handler method to invoke. If the
|
response-destination |
The name of the default response destination to send response messages to. This will be applied in case of a request message that does not carry a "JMSReplyTo" field. The type of this destination will be determined by the listener-container's "destination-type" attribute. Note: This only applies to a listener method with a return value, for which each result object will be converted into a response message. |
subscription |
The name of the durable subscription, if any. |
selector |
An optional message selector for this listener. |
The <listener-container/>
element also accepts several optional
attributes. This allows for customization of the various strategies (for example,
taskExecutor and destinationResolver) as well as
basic JMS settings and resource references. Using these attributes, it is possible to define
highly-customized listener containers while still benefiting from the convenience of the
namespace.
<jms:listener-container connection-factory="myConnectionFactory" task-executor="myTaskExecutor" destination-resolver="myDestinationResolver" transaction-manager="myTransactionManager" concurrency="10"> <jms:listener destination="queue.orders" ref="orderService" method="placeOrder"/> <jms:listener destination="queue.confirmations" ref="confirmationLogger" method="log"/> </jms:listener-container>
The following table describes all available attributes. Consult the class-level
Javadoc of the AbstractMessageListenerContainer
and its
concrete subclasses for more detail on the individual properties. The Javadoc also
provides a discussion of transaction choices and message redelivery scenarios.
Table 19.2. Attributes of the JMS <listener-container>
element
Attribute | Description |
---|---|
container-type |
The type of this listener container. Available options are:
|
connection-factory |
A reference to the JMS
|
task-executor |
A reference to the Spring |
destination-resolver |
A reference to the |
message-converter |
A reference to the |
destination-type |
The JMS destination type for this listener: |
client-id |
The JMS client id for this listener container. Needs to be specified when using durable subscriptions. |
cache |
The cache level for JMS resources: |
acknowledge |
The native JMS acknowledge mode: |
transaction-manager |
A reference to an external
|
concurrency |
The number of concurrent sessions/consumers to start for each listener. Can either be a simple number indicating the maximum number (e.g. "5") or a range indicating the lower as well as the upper limit (e.g. "3-5"). Note that a specified minimum is just a hint and might be ignored at runtime. Default is 1; keep concurrency limited to 1 in case of a topic listener or if queue ordering is important; consider raising it for general queues. |
prefetch |
The maximum number of messages to load into a single session. Note that raising this number might lead to starvation of concurrent consumers! |
Configuring a JCA-based listener container with the "jms" schema support is very similar.
<jms:jca-listener-container resource-adapter="myResourceAdapter" destination-resolver="myDestinationResolver" transaction-manager="myTransactionManager" concurrency="10"> <jms:listener destination="queue.orders" ref="myMessageListener"/> </jms:jca-listener-container>
The available configuration options for the JCA variant are described in the following table:
Table 19.3. Attributes of the JMS <jca-listener-container/>
element
Attribute | Description |
---|---|
resource-adapter |
A reference to the JCA
|
activation-spec-factory |
A reference to the |
destination-resolver |
A reference to the |
message-converter |
A reference to the |
destination-type |
The JMS destination type for this listener: |
client-id |
The JMS client id for this listener container. Needs to be specified when using durable subscriptions. |
acknowledge |
The native JMS acknowledge mode: |
transaction-manager |
A reference to a Spring |
concurrency |
The number of concurrent sessions/consumers to start for each listener. Can either be a simple number indicating the maximum number (e.g. "5") or a range indicating the lower as well as the upper limit (e.g. "3-5"). Note that a specified minimum is just a hint and will typically be ignored at runtime when using a JCA listener container. Default is 1. |
prefetch |
The maximum number of messages to load into a single session. Note that raising this number might lead to starvation of concurrent consumers! |
The JMX support in Spring provides you with the features to easily and transparently integrate your Spring application into a JMX infrastructure.
Specifically, Spring's JMX support provides four core features:
The automatic registration of any Spring bean as a JMX MBean
A flexible mechanism for controlling the management interface of your beans
The declarative exposure of MBeans over remote, JSR-160 connectors
The simple proxying of both local and remote MBean resources
These features are designed to work without coupling your application components to either Spring or JMX interfaces and classes. Indeed, for the most part your application classes need not be aware of either Spring or JMX in order to take advantage of the Spring JMX features.
The core class in Spring's JMX framework is the
MBeanExporter
. This class is responsible for taking
your Spring beans and registering them with a JMX
MBeanServer
. For example, consider the following
class:
package org.springframework.jmx; public class JmxTestBean implements IJmxTestBean { private String name; private int age; private boolean isSuperman; public int getAge() { return age; } public void setAge(int age) { this.age = age; } public void setName(String name) { this.name = name; } public String getName() { return name; } public int add(int x, int y) { return x + y; } public void dontExposeMe() { throw new RuntimeException(); } }
To expose the properties and methods of this bean as attributes and
operations of an MBean you simply configure an instance of the
MBeanExporter
class in your configuration file and
pass in the bean as shown below:
<beans> <!-- this bean must not be lazily initialized if the exporting is to happen --> <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter" lazy-init="false"> <property name="beans"> <map> <entry key="bean:name=testBean1" value-ref="testBean"/> </map> </property> </bean> <bean id="testBean" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="TEST"/> <property name="age" value="100"/> </bean> </beans>
The pertinent bean definition from the above configuration snippet
is the exporter
bean. The beans
property tells the MBeanExporter
exactly which of
your beans must be exported to the JMX MBeanServer
.
In the default configuration, the key of each entry in the
beans
Map
is used as the
ObjectName
for the bean referenced by the
corresponding entry value. This behavior can be changed as described in
the section entitled Section 20.4, “Controlling the ObjectName
s for your beans”.
With this configuration the testBean
bean is
exposed as an MBean under the ObjectName
bean:name=testBean1
. By default, all
public properties of the bean are exposed as
attributes and all public methods (bar those
inherited from the Object
class) are exposed as
operations.
The above configuration assumes that the application is running in
an environment that has one (and only one)
MBeanServer
already running. In this case, Spring
will attempt to locate the running MBeanServer
and register your beans with that server (if any). This behavior is
useful when your application is running inside a container such as
Tomcat or IBM WebSphere that has it's own
MBeanServer
.
However, this approach is of no use in a standalone environment,
or when running inside a container that does not provide an
MBeanServer
. To address this you can create an
MBeanServer
instance declaratively by adding an
instance of the
org.springframework.jmx.support.MBeanServerFactoryBean
class to your configuration. You can also ensure that a specific
MBeanServer
is used by setting the value of the
MBeanExporter
's server
property to the MBeanServer
value returned by an
MBeanServerFactoryBean
; for example:
<beans>
<bean id="mbeanServer" class="org.springframework.jmx.support.MBeanServerFactoryBean"/>
<!--
this bean needs to be eagerly pre-instantiated in order for the exporting to occur;
this means that it must not be marked as lazily initialized
-->
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="server" ref="mbeanServer"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>
Here an instance of MBeanServer
is created
by the MBeanServerFactoryBean
and is supplied to
the MBeanExporter
via the server property. When
you supply your own MBeanServer
instance, the
MBeanExporter
will not attempt to locate a
running MBeanServer
and will use the supplied
MBeanServer
instance. For this to work correctly,
you must (of course) have a JMX implementation on your classpath.
If no server is specified, the MBeanExporter
tries to automatically detect a running MBeanServer
.
This works in most environment where only one
MBeanServer
instance is used, however when multiple
instances exist, the exporter might pick the wrong server. In such
cases, one should use the MBeanServer
agentId
to indicate which instance to be used:
<beans>
<bean id="mbeanServer" class="org.springframework.jmx.support.MBeanServerFactoryBean">
<!-- indicate to first look for a server -->
<property name="locateExistingServerIfPossible" value="true"/>
<!-- search for the MBeanServer
instance with the given agentId -->
<property name="agentId" value="<MBeanServer instance agentId>"/>
</bean>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="server" ref="mbeanServer"/>
...
</bean>
</beans>
For platforms/cases where the existing MBeanServer
has a dynamic (or unknown) agentId
which is retrieved through lookup
methods, one should use factory-method:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="server">
<!-- Custom MBeanServerLocator
-->
<bean class="platform.package.MBeanServerLocator" factory-method="locateMBeanServer"/>
</property>
<!-- other beans here -->
</bean>
</beans>
If you configure a bean with the
MBeanExporter
that is also configured for lazy
initialization, then the MBeanExporter
will
not break this contract and will avoid
instantiating the bean. Instead, it will register a proxy with
the MBeanServer
and will defer obtaining the bean
from the container until the first invocation on the proxy occurs.
Any beans that are exported through the
MBeanExporter
and are already valid MBeans are
registered as-is with the MBeanServer
without
further intervention from Spring. MBeans can be automatically detected
by the MBeanExporter
by setting the
autodetect
property to true
:
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="autodetect" value="true"/> </bean> <bean name="spring:mbean=true" class="org.springframework.jmx.export.TestDynamicMBean"/>
Here, the bean called spring:mbean=true
is
already a valid JMX MBean and will be automatically registered by
Spring. By default, beans that are autodetected for JMX registration
have their bean name used as the ObjectName
. This
behavior can be overridden as detailed in the section entitled
Section 20.4, “Controlling the ObjectName
s for your beans”.
Consider the scenario where a Spring
MBeanExporter
attempts to register an
MBean
with an MBeanServer
using the ObjectName
'bean:name=testBean1'
. If an
MBean
instance has already been registered under
that same ObjectName
, the default behavior is to
fail (and throw an
InstanceAlreadyExistsException
).
It is possible to control the behavior of exactly what happens
when an MBean
is registered with an
MBeanServer
. Spring's JMX support allows for
three different registration behaviors to control the registration
behavior when the registration process finds that an
MBean
has already been registered under the same
ObjectName
; these registration behaviors are
summarized on the following table:
Table 20.1. Registration Behaviors
Registration behavior | Explanation |
---|---|
| This is the default registration behavior. If an
|
| If an This is useful in settings where multiple applications
want to share a common |
| If an |
The above values are defined as constants on the
MBeanRegistrationSupport
class (the
MBeanExporter
class derives from this
superclass). If you want to change the default registration behavior,
you simply need to set the value of the
registrationBehaviorName
property on your
MBeanExporter
definition to one of those
values.
The following example illustrates how to effect a change from the
default registration behavior to the
REGISTRATION_REPLACE_EXISTING
behavior:
<beans> <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="beans"> <map> <entry key="bean:name=testBean1" value-ref="testBean"/> </map> </property> <property name="registrationBehaviorName" value="REGISTRATION_REPLACE_EXISTING"/> </bean> <bean id="testBean" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="TEST"/> <property name="age" value="100"/> </bean> </beans>
In the previous example, you had little control over the management interface of your bean; all of the public properties and methods of each exported bean was exposed as JMX attributes and operations respectively. To exercise finer-grained control over exactly which properties and methods of your exported beans are actually exposed as JMX attributes and operations, Spring JMX provides a comprehensive and extensible mechanism for controlling the management interfaces of your beans.
Behind the scenes, the MBeanExporter
delegates to an implementation of the
org.springframework.jmx.export.assembler.MBeanInfoAssembler
interface which is responsible for defining the management interface of
each bean that is being exposed. The default implementation,
org.springframework.jmx.export.assembler.SimpleReflectiveMBeanInfoAssembler
,
simply defines a management interface that exposes all public properties
and methods (as you saw in the previous examples). Spring provides two
additional implementations of the
MBeanInfoAssembler
interface that allow
you to control the generated management interface using either
source-level metadata or any arbitrary interface.
Using the MetadataMBeanInfoAssembler
you
can define the management interfaces for your beans using source level
metadata. The reading of metadata is encapsulated by the
org.springframework.jmx.export.metadata.JmxAttributeSource
interface. Out of the box, Spring JMX provides support for two
implementations of this interface:
org.springframework.jmx.export.metadata.AttributesJmxAttributeSource
for Commons Attributes and
org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource
for JDK 5.0 annotations. The
MetadataMBeanInfoAssembler
must be configured with an implementation instance
of the JmxAttributeSource
interface for it to
function correctly (there is no default). For the
following example, we will use the Commons Attributes metadata
approach.
To mark a bean for export to JMX, you should annotate the bean
class with the ManagedResource
attribute. In the
case of the Commons Attributes metadata approach this class can be found
in the org.springframework.jmx.metadata
package. Each
method you wish to expose as an operation must be marked with the
ManagedOperation
attribute and each property you
wish to expose must be marked with the
ManagedAttribute
attribute. When marking
properties you can omit either the annotation of the getter or the
setter to create a write-only or read-only attribute
respectively.
The example below shows the JmxTestBean
class that you saw earlier marked with Commons Attributes
metadata:
package org.springframework.jmx; /** * @@org.springframework.jmx.export.metadata.ManagedResource * (description="My Managed Bean", objectName="spring:bean=test", * log=true, logFile="jmx.log", currencyTimeLimit=15, persistPolicy="OnUpdate", * persistPeriod=200, persistLocation="foo", persistName="bar") */ public class JmxTestBean implements IJmxTestBean { private String name; private int age; /** * @@org.springframework.jmx.export.metadata.ManagedAttribute * (description="The Age Attribute", currencyTimeLimit=15) */ public int getAge() { return age; } public void setAge(int age) { this.age = age; } /** * @@org.springframework.jmx.export.metadata.ManagedAttribute * (description="The Name Attribute", currencyTimeLimit=20, * defaultValue="bar", persistPolicy="OnUpdate") */ public void setName(String name) { this.name = name; } /** * @@org.springframework.jmx.export.metadata.ManagedAttribute * (defaultValue="foo", persistPeriod=300) */ public String getName() { return name; } /** * @@org.springframework.jmx.export.metadata.ManagedOperation * (description="Add Two Numbers Together") */ public int add(int x, int y) { return x + y; } public void dontExposeMe() { throw new RuntimeException(); } }
Here you can see that the JmxTestBean
class
is marked with the ManagedResource
attribute and
that this ManagedResource
attribute is configured
with a set of properties. These properties can be used to configure
various aspects of the MBean that is generated by the
MBeanExporter
, and are explained in greater
detail later in section entitled Section 20.3.4, “Source-Level Metadata Types”.
You will also notice that both the age
and
name
properties are annotated with the
ManagedAttribute
attribute, but in the case of
the age
property, only the getter is marked. This
will cause both of these properties to be included in the management
interface as attributes, but the age
attribute will
be read-only.
Finally, you will notice that the add(int, int)
method is marked with the ManagedOperation
attribute whereas the dontExposeMe()
method is not.
This will cause the management interface to contain only one operation,
add(int, int)
, when using the
MetadataMBeanInfoAssembler
.
The code below shows how you configure the
MBeanExporter
to use the
MetadataMBeanInfoAssembler
:
<beans> <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="beans"> <map> <entry key="bean:name=testBean1" value-ref="testBean"/> </map> </property> <property name="assembler" ref="assembler"/> </bean> <bean id="testBean" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="TEST"/> <property name="age" value="100"/> </bean> <bean id="attributeSource" class="org.springframework.jmx.export.metadata.AttributesJmxAttributeSource"> <property name="attributes"> <bean class="org.springframework.metadata.commons.CommonsAttributes"/> </property> </bean> <bean id="assembler" class="org.springframework.jmx.export.assembler.MetadataMBeanInfoAssembler"> <property name="attributeSource" ref="attributeSource"/> </bean> </beans>
Here you can see that an
MetadataMBeanInfoAssembler
bean has been
configured with an instance of the
AttributesJmxAttributeSource
class and passed to
the MBeanExporter
through the assembler property.
This is all that is required to take advantage of metadata-driven
management interfaces for your Spring-exposed MBeans.
To enable the use of JDK 5.0 annotations for management interface
definition, Spring provides a set of annotations that mirror the Commons
Attribute attribute classes and an implementation of the
JmxAttributeSource
strategy interface,
the AnnotationsJmxAttributeSource
class, that
allows the MBeanInfoAssembler
to read
them.
The example below shows a bean where the management interface is defined by the presence of JDK 5.0 annotation types:
package org.springframework.jmx; import org.springframework.jmx.export.annotation.ManagedResource; import org.springframework.jmx.export.annotation.ManagedOperation; import org.springframework.jmx.export.annotation.ManagedAttribute; @ManagedResource(objectName="bean:name=testBean4", description="My Managed Bean", log=true, logFile="jmx.log", currencyTimeLimit=15, persistPolicy="OnUpdate", persistPeriod=200, persistLocation="foo", persistName="bar") public class AnnotationTestBean implements IJmxTestBean { private String name; private int age; @ManagedAttribute(description="The Age Attribute", currencyTimeLimit=15) public int getAge() { return age; } public void setAge(int age) { this.age = age; } @ManagedAttribute(description="The Name Attribute", currencyTimeLimit=20, defaultValue="bar", persistPolicy="OnUpdate") public void setName(String name) { this.name = name; } @ManagedAttribute(defaultValue="foo", persistPeriod=300) public String getName() { return name; } @ManagedOperation(description="Add two numbers") @ManagedOperationParameters({ @ManagedOperationParameter(name = "x", description = "The first number"), @ManagedOperationParameter(name = "y", description = "The second number")}) public int add(int x, int y) { return x + y; } public void dontExposeMe() { throw new RuntimeException(); } }
As you can see little has changed, other than the basic syntax of the metadata definitions. Behind the scenes this approach is a little slower at startup because the JDK 5.0 annotations are converted into the classes used by Commons Attributes. However, this is only a one-off cost and JDK 5.0 annotations give you the added (and valuable) benefit of compile-time checking.
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="assembler" ref="assembler"/>
<property name="namingStrategy" ref="namingStrategy"/>
<property name="autodetect" value="true"/>
</bean>
<bean id="jmxAttributeSource"
class="org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource"/>
<!-- will create management interface using annotation metadata -->
<bean id="assembler"
class="org.springframework.jmx.export.assembler.MetadataMBeanInfoAssembler">
<property name="attributeSource" ref="jmxAttributeSource"/>
</bean>
<!-- will pick up the ObjectName
from the annotation -->
<bean id="namingStrategy"
class="org.springframework.jmx.export.naming.MetadataNamingStrategy">
<property name="attributeSource" ref="jmxAttributeSource"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.AnnotationTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>
The following source level metadata types are available for use in Spring JMX:
Table 20.2. Source-Level Metadata Types
Purpose | Commons Attributes Attribute | JDK 5.0 Annotation | Attribute / Annotation Type |
---|---|---|---|
Mark all instances of a Class as
JMX managed resources | ManagedResource | @ManagedResource | Class |
Mark a method as a JMX operation | ManagedOperation | @ManagedOperation | Method |
Mark a getter or setter as one half of a JMX attribute | ManagedAttribute | @ManagedAttribute | Method (only getters and setters) |
Define descriptions for operation parameters | ManagedOperationParameter | @ManagedOperationParameter and
@ManagedOperationParameters | Method |
The following configuration parameters are available for use on these source-level metadata types:
Table 20.3. Source-Level Metadata Parameters
Parameter | Description | Applies to |
---|---|---|
ObjectName | Used by MetadataNamingStrategy
to determine the ObjectName of a
managed resource | ManagedResource |
description | Sets the friendly description of the resource, attribute or operation | ManagedResource ,
ManagedAttribute ,
ManagedOperation ,
ManagedOperationParameter |
currencyTimeLimit | Sets the value of the
currencyTimeLimit descriptor field | ManagedResource ,
ManagedAttribute |
defaultValue | Sets the value of the defaultValue
descriptor field | ManagedAttribute |
log | Sets the value of the log descriptor
field | ManagedResource |
logFile | Sets the value of the logFile
descriptor field | ManagedResource |
persistPolicy | Sets the value of the persistPolicy
descriptor field | ManagedResource |
persistPeriod | Sets the value of the persistPeriod
descriptor field | ManagedResource |
persistLocation | Sets the value of the
persistLocation descriptor field | ManagedResource |
persistName | Sets the value of the persistName
descriptor field | ManagedResource |
name | Sets the display name of an operation parameter | ManagedOperationParameter |
index | Sets the index of an operation parameter | ManagedOperationParameter |
To simplify configuration even further, Spring introduces the
AutodetectCapableMBeanInfoAssembler
interface
which extends the MBeanInfoAssembler
interface to add support for autodetection of MBean resources. If you
configure the MBeanExporter
with an instance of
AutodetectCapableMBeanInfoAssembler
then it is
allowed to "vote" on the inclusion of beans for exposure to JMX.
Out of the box, the only implementation of the
AutodetectCapableMBeanInfo
interface is the
MetadataMBeanInfoAssembler
which will vote to
include any bean which is marked with the
ManagedResource
attribute. The default approach
in this case is to use the bean name as the
ObjectName
which results in a configuration like
this:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<!-- notice how no 'beans'
are explicitly configured here -->
<property name="autodetect" value="true"/>
<property name="assembler" ref="assembler"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
<!-- (for Commons Attributes-based metadata) -->
<bean id="attributeSource"
class="org.springframework.jmx.export.metadata.AttributesJmxAttributeSource">
<property name="attributes">
<bean class="org.springframework.metadata.commons.CommonsAttributes"/>
</property>
</bean>
<!-- (for Java 5+ annotations-based metadata) -->
<!--
<bean id="attributeSource"
class="org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource"/>
-->
<bean id="assembler" class="org.springframework.jmx.export.assembler.MetadataMBeanInfoAssembler">
<property name="attributeSource" ref="attributeSource"/>
</bean>
</beans>
Notice that in this configuration no beans are passed to the
MBeanExporter
; however, the
JmxTestBean
will still be registered since it is
marked with the ManagedResource
attribute and the
MetadataMBeanInfoAssembler
detects this and votes
to include it. The only problem with this approach is that the name of
the JmxTestBean
now has business meaning. You can
address this issue by changing the default behavior for
ObjectName
creation as defined in the section
entitled Section 20.4, “Controlling the ObjectName
s for your beans”.
In addition to the
MetadataMBeanInfoAssembler
, Spring also includes
the InterfaceBasedMBeanInfoAssembler
which allows
you to constrain the methods and properties that are exposed based on
the set of methods defined in a collection of interfaces.
Although the standard mechanism for exposing MBeans is to use
interfaces and a simple naming scheme, the
InterfaceBasedMBeanInfoAssembler
extends this
functionality by removing the need for naming conventions, allowing you
to use more than one interface and removing the need for your beans to
implement the MBean interfaces.
Consider this interface that is used to define a management
interface for the JmxTestBean
class that you saw
earlier:
public interface IJmxTestBean { public int add(int x, int y); public long myOperation(); public int getAge(); public void setAge(int age); public void setName(String name); public String getName(); }
This interface defines the methods and properties that will be exposed as operations and attributes on the JMX MBean. The code below shows how to configure Spring JMX to use this interface as the definition for the management interface:
<beans> <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="beans"> <map> <entry key="bean:name=testBean5" value-ref="testBean"/> </map> </property> <property name="assembler"> <bean class="org.springframework.jmx.export.assembler.InterfaceBasedMBeanInfoAssembler"> <property name="managedInterfaces"> <value>org.springframework.jmx.IJmxTestBean</value> </property> </bean> </property> </bean> <bean id="testBean" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="TEST"/> <property name="age" value="100"/> </bean> </beans>
Here you can see that the
InterfaceBasedMBeanInfoAssembler
is configured to
use the IJmxTestBean
interface when
constructing the management interface for any bean. It is important to
understand that beans processed by the
InterfaceBasedMBeanInfoAssembler
are
not required to implement the interface used to
generate the JMX management interface.
In the case above, the IJmxTestBean
interface is used to construct all management interfaces for all beans.
In many cases this is not the desired behavior and you may want to use
different interfaces for different beans. In this case, you can pass
InterfaceBasedMBeanInfoAssembler
a
Properties
instance via the
interfaceMappings
property, where the key of each
entry is the bean name and the value of each entry is a comma-separated
list of interface names to use for that bean.
If no management interface is specified through either the
managedInterfaces
or
interfaceMappings
properties, then the
InterfaceBasedMBeanInfoAssembler
will reflect on
the bean and use all of the interfaces implemented by that bean to
create the management interface.
The MethodNameBasedMBeanInfoAssembler
allows you to specify a list of method names that will be exposed to JMX
as attributes and operations. The code below shows a sample
configuration for this:
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="beans"> <map> <entry key="bean:name=testBean5" value-ref="testBean"/> </map> </property> <property name="assembler"> <bean class="org.springframework.jmx.export.assembler.MethodNameBasedMBeanInfoAssembler"> <property name="managedMethods"> <value>add,myOperation,getName,setName,getAge</value> </property> </bean> </property> </bean>
Here you can see that the methods add
and
myOperation
will be exposed as JMX operations and
getName()
, setName(String)
and
getAge()
will be exposed as the appropriate half of a
JMX attribute. In the code above, the method mappings apply to beans
that are exposed to JMX. To control method exposure on a bean-by-bean
basis, use the methodMappings
property of
MethodNameMBeanInfoAssembler
to map bean names to
lists of method names.
Behind the scenes, the MBeanExporter
delegates to an implementation of the
ObjectNamingStrategy
to obtain
ObjectName
s for each of the beans it is
registering. The default implementation,
KeyNamingStrategy
, will, by default, use the key of
the beans
Map
as the
ObjectName
. In addition, the
KeyNamingStrategy
can map the key of the
beans
Map
to an entry in a
Properties
file (or files) to resolve the
ObjectName
. In addition to the
KeyNamingStrategy
, Spring provides two additional
ObjectNamingStrategy
implementations: the
IdentityNamingStrategy
that builds an
ObjectName
based on the JVM identity of the bean
and the MetadataNamingStrategy
that uses source
level metadata to obtain the ObjectName
.
You can configure your own
KeyNamingStrategy
instance and configure it to
read ObjectName
s from a
Properties
instance rather than use bean key. The
KeyNamingStrategy
will attempt to locate an entry
in the Properties
with a key corresponding to the
bean key. If no entry is found or if the
Properties
instance is null
then the bean key itself is used.
The code below shows a sample configuration for the
KeyNamingStrategy
:
<beans> <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="beans"> <map> <entry key="testBean" value-ref="testBean"/> </map> </property> <property name="namingStrategy" ref="namingStrategy"/> </bean> <bean id="testBean" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="TEST"/> <property name="age" value="100"/> </bean> <bean id="namingStrategy" class="org.springframework.jmx.export.naming.KeyNamingStrategy"> <property name="mappings"> <props> <prop key="testBean">bean:name=testBean1</prop> </props> </property> <property name="mappingLocations"> <value>names1.properties,names2.properties</value> </property> </bean </beans>
Here an instance of KeyNamingStrategy
is
configured with a Properties
instance that is
merged from the Properties
instance defined by
the mapping property and the properties files located in the paths
defined by the mappings property. In this configuration, the
testBean
bean will be given the
ObjectName
bean:name=testBean1
since this is the entry in the Properties
instance that has a key corresponding to the bean key.
If no entry in the Properties
instance can
be found then the bean key name is used as the
ObjectName
.
The MetadataNamingStrategy
uses
the objectName
property of the
ManagedResource
attribute on each bean to create
the ObjectName
. The code below shows the
configuration for the
MetadataNamingStrategy
:
<beans> <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="beans"> <map> <entry key="testBean" value-ref="testBean"/> </map> </property> <property name="namingStrategy" ref="namingStrategy"/> </bean> <bean id="testBean" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="TEST"/> <property name="age" value="100"/> </bean> <bean id="namingStrategy" class="org.springframework.jmx.export.naming.MetadataNamingStrategy"> <property name="attributeSource" ref="attributeSource"/> </bean> <bean id="attributeSource" class="org.springframework.jmx.export.metadata.AttributesJmxAttributeSource"/> </beans>
If no objectName
has been provided for
the ManagedResource
attribute, then an
ObjectName
will be created with the
following format:
[fully-qualified-package-name]:type=[short-classname],name=[bean-name].
For example, the generated ObjectName
for the
following bean would be: com.foo:type=MyClass,name=myBean.
<bean id="myBean" class="com.foo.MyClass"/>
If you are using at least Java 5, then a convenience subclass of
MBeanExporter
is available:
AnnotationMBeanExporter
.
When defining an instance of this subclass, the namingStrategy
,
assembler
, and attributeSource
configuration is no longer needed, since it will always use standard Java
annotation-based metadata (autodetection is always enabled as well). In fact,
an even simpler syntax is supported with the inclusion of Spring's
'context
' namespace in Spring 2.5. Rather than defining an
MBeanExporter
bean, provide this single element:
<context:mbean-export/>
You can provide a reference to a particular MBean server if
necessary, and the defaultDomain
attribute
(a property of AnnotationMBeanExporter
)
accepts an alternate value for the generated MBean
ObjectNames
' domains. This would be used
in place of the fully qualified package name as described in the
previous section on
MetadataNamingStrategy
.
<context:mbean-export server="myMBeanServer" default-domain="myDomain"/>.
For remote access, Spring JMX module offers two
FactoryBean
implementations inside the
org.springframework.jmx.support
package for creating
both server- and client-side connectors.
To have Spring JMX create, start and expose a JSR-160
JMXConnectorServer
use the following
configuration:
<bean id="serverConnector" class="org.springframework.jmx.support.ConnectorServerFactoryBean"/>
By default ConnectorServerFactoryBean
creates a
JMXConnectorServer
bound to
"service:jmx:jmxmp://localhost:9875"
. The
serverConnector
bean thus exposes the local
MBeanServer
to clients through the JMXMP protocol
on localhost, port 9875. Note that the JMXMP protocol is marked as
optional by the JSR 160 specification: currently, the main open-source
JMX implementation, MX4J, and the one provided with J2SE 5.0 do
not support JMXMP.
To specify another URL and register the
JMXConnectorServer
itself with the
MBeanServer
use the serviceUrl
and ObjectName
properties respectively:
<bean id="serverConnector" class="org.springframework.jmx.support.ConnectorServerFactoryBean"> <property name="objectName" value="connector:name=rmi"/> <property name="serviceUrl" value="service:jmx:rmi://localhost/jndi/rmi://localhost:1099/myconnector"/> </bean>
If the ObjectName
property is set Spring
will automatically register your connector with the
MBeanServer
under that
ObjectName
. The example below shows the full set
of parameters which you can pass to the
ConnectorServerFactoryBean
when creating a
JMXConnector:
<bean id="serverConnector" class="org.springframework.jmx.support.ConnectorServerFactoryBean"> <property name="objectName" value="connector:name=iiop"/> <property name="serviceUrl" value="service:jmx:iiop://localhost/jndi/iiop://localhost:900/myconnector"/> <property name="threaded" value="true"/> <property name="daemon" value="true"/> <property name="environment"> <map> <entry key="someKey" value="someValue"/> </map> </property> </bean>
Note that when using a RMI-based connector you need the lookup service (tnameserv or rmiregistry) to be started in order for the name registration to complete. If you are using Spring to export remote services for you via RMI, then Spring will already have constructed an RMI registry. If not, you can easily start a registry using the following snippet of configuration:
<bean id="registry" class="org.springframework.remoting.rmi.RmiRegistryFactoryBean"> <property name="port" value="1099"/> </bean>
To create an MBeanServerConnection
to a
remote JSR-160 enabled MBeanServer
use the
MBeanServerConnectionFactoryBean
as shown
below:
<bean id="clientConnector" class="org.springframework.jmx.support.MBeanServerConnectionFactoryBean"> <property name="serviceUrl" value="service:jmx:rmi://localhost:9875"/> </bean>
JSR-160 permits extensions to the way in which communication is done between the client and the server. The examples above are using the mandatory RMI-based implementation required by the JSR-160 specification (IIOP and JRMP) and the (optional) JMXMP. By using other providers or JMX implementations (such as MX4J) you can take advantage of protocols like SOAP, Hessian, Burlap over simple HTTP or SSL and others:
<bean id="serverConnector" class="org.springframework.jmx.support.ConnectorServerFactoryBean"> <property name="objectName" value="connector:name=burlap"/> <property name="serviceUrl" value="service:jmx:burlap://localhost:9874"/> </bean>
In the case of the above example, MX4J 3.0.0 was used; see the official MX4J documentation for more information.
Spring JMX allows you to create proxies that re-route calls to
MBeans registered in a local or remote MBeanServer
.
These proxies provide you with a standard Java interface through which you
can interact with your MBeans. The code below shows how to configure a
proxy for an MBean running in a local
MBeanServer
:
<bean id="proxy" class="org.springframework.jmx.access.MBeanProxyFactoryBean"> <property name="objectName" value="bean:name=testBean"/> <property name="proxyInterface" value="org.springframework.jmx.IJmxTestBean"/> </bean>
Here you can see that a proxy is created for the MBean registered
under the ObjectName
:
bean:name=testBean
. The set of interfaces that the
proxy will implement is controlled by the
proxyInterfaces
property and the rules for mapping
methods and properties on these interfaces to operations and attributes on
the MBean are the same rules used by the
InterfaceBasedMBeanInfoAssembler
.
The MBeanProxyFactoryBean
can create a proxy
to any MBean that is accessible via an
MBeanServerConnection
. By default, the local
MBeanServer
is located and used, but you can
override this and provide an MBeanServerConnection
pointing to a remote MBeanServer
to cater for
proxies pointing to remote MBeans:
<bean id="clientConnector" class="org.springframework.jmx.support.MBeanServerConnectionFactoryBean"> <property name="serviceUrl" value="service:jmx:rmi://remotehost:9875"/> </bean> <bean id="proxy" class="org.springframework.jmx.access.MBeanProxyFactoryBean"> <property name="objectName" value="bean:name=testBean"/> <property name="proxyInterface" value="org.springframework.jmx.IJmxTestBean"/> <property name="server" ref="clientConnector"/> </bean>
Here you can see that we create an
MBeanServerConnection
pointing to a remote machine
using the MBeanServerConnectionFactoryBean
. This
MBeanServerConnection
is then passed to the
MBeanProxyFactoryBean
via the
server
property. The proxy that is created will forward
all invocations to the MBeanServer
via this
MBeanServerConnection
.
Spring's JMX offering includes comprehensive support for JMX notifications.
Spring's JMX support makes it very easy to register any number of
NotificationListeners
with any number of MBeans
(this includes MBeans exported by Spring's
MBeanExporter
and MBeans registered via some
other mechanism). By way of an example, consider the scenario where one
would like to be informed (via a Notification
)
each and every time an attribute of a target MBean changes.
package com.example; import javax.management.AttributeChangeNotification; import javax.management.Notification; import javax.management.NotificationFilter; import javax.management.NotificationListener; public class ConsoleLoggingNotificationListener implements NotificationListener, NotificationFilter { public void handleNotification(Notification notification, Object handback) { System.out.println(notification); System.out.println(handback); } public boolean isNotificationEnabled(Notification notification) { return AttributeChangeNotification.class.isAssignableFrom(notification.getClass()); } }
<beans> <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="beans"> <map> <entry key="bean:name=testBean1" value-ref="testBean"/> </map> </property> <property name="notificationListenerMappings"> <map> <entry key="bean:name=testBean1"> <bean class="com.example.ConsoleLoggingNotificationListener"/> </entry> </map> </property> </bean> <bean id="testBean" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="TEST"/> <property name="age" value="100"/> </bean> </beans>
With the above configuration in place, every time a JMX
Notification
is broadcast from the target MBean
(bean:name=testBean1
), the
ConsoleLoggingNotificationListener
bean that was
registered as a listener via the
notificationListenerMappings
property will be
notified. The ConsoleLoggingNotificationListener
bean can then take whatever action it deems appropriate in response to
the Notification
.
You can also use straight bean names as the link between exported beans and listeners:
<beans> <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="beans"> <map> <entry key="bean:name=testBean1" value-ref="testBean"/> </map> </property> <property name="notificationListenerMappings"> <map> <entry key="testBean"> <bean class="com.example.ConsoleLoggingNotificationListener"/> </entry> </map> </property> </bean> <bean id="testBean" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="TEST"/> <property name="age" value="100"/> </bean> </beans>
If one wants to register a single NotificationListener
instance for all of the beans that the enclosing MBeanExporter
is exporting, one can use the special wildcard '*'
(sans quotes)
as the key for an entry in the notificationListenerMappings
property map; for example:
<property name="notificationListenerMappings"> <map> <entry key="*"> <bean class="com.example.ConsoleLoggingNotificationListener"/> </entry> </map> </property>
If one needs to do the inverse (that is, register a number of distinct
listeners against an MBean), then one has to use the
notificationListeners
list property instead (and in
preference to the notificationListenerMappings
property). This time, instead of configuring simply a
NotificationListener
for a single MBean, one
configures NotificationListenerBean
instances...
a NotificationListenerBean
encapsulates a
NotificationListener
and the
ObjectName
(or
ObjectNames
) that it is to be registered against
in an MBeanServer
. The
NotificationListenerBean
also encapsulates a
number of other properties such as a
NotificationFilter
and an arbitrary handback
object that can be used in advanced JMX notification scenarios.
The configuration when using
NotificationListenerBean
instances is not wildly
different to what was presented previously:
<beans> <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="beans"> <map> <entry key="bean:name=testBean1" value-ref="testBean"/> </map> </property> <property name="notificationListeners"> <list> <bean class="org.springframework.jmx.export.NotificationListenerBean"> <constructor-arg> <bean class="com.example.ConsoleLoggingNotificationListener"/> </constructor-arg> <property name="mappedObjectNames"> <list> <value>bean:name=testBean1</value> </list> </property> </bean> </list> </property> </bean> <bean id="testBean" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="TEST"/> <property name="age" value="100"/> </bean> </beans>
The above example is equivalent to the first notification example.
Lets assume then that we want to be given a handback object every time a
Notification
is raised, and that additionally we
want to filter out extraneous Notifications
by
supplying a NotificationFilter
. (For a full
discussion of just what a handback object is, and indeed what a
NotificationFilter
is, please do consult that
section of the JMX specification (1.2) entitled 'The JMX
Notification Model'
.)
<beans> <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter"> <property name="beans"> <map> <entry key="bean:name=testBean1" value-ref="testBean1"/> <entry key="bean:name=testBean2" value-ref="testBean2"/> </map> </property> <property name="notificationListeners"> <list> <bean class="org.springframework.jmx.export.NotificationListenerBean"> <constructor-arg ref="customerNotificationListener"/> <property name="mappedObjectNames"> <list> <!-- handles notifications from two distinct MBeans --> <value>bean:name=testBean1</value> <value>bean:name=testBean2</value> </list> </property> <property name="handback"> <bean class="java.lang.String"> <constructor-arg value="This could be anything..."/> </bean> </property> <property name="notificationFilter" ref="customerNotificationListener"/> </bean> </list> </property> </bean> <!-- implements both theNotificationListener
andNotificationFilter
interfaces --> <bean id="customerNotificationListener" class="com.example.ConsoleLoggingNotificationListener"/> <bean id="testBean1" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="TEST"/> <property name="age" value="100"/> </bean> <bean id="testBean2" class="org.springframework.jmx.JmxTestBean"> <property name="name" value="ANOTHER TEST"/> <property name="age" value="200"/> </bean> </beans>
Spring provides support not just for registering to receive
Notifications
, but also for publishing
Notifications
.
![]() | Note |
---|---|
Please note that this section is really only relevant to Spring
managed beans that have been exposed as MBeans via an
|
The key interface in Spring's JMX notification publication support
is the NotificationPublisher
interface (defined
in the org.springframework.jmx.export.notification
package). Any bean that is going to be exported as an MBean via an
MBeanExporter
instance can implement the related
NotificationPublisherAware
interface to gain
access to a NotificationPublisher
instance. The
NotificationPublisherAware
interface simply
supplies an instance of a NotificationPublisher
to the implementing bean via a simple setter method, which the bean can
then use to publish Notifications
.
As stated in the Javadoc for the
NotificationPublisher
class, managed beans that
are publishing events via the
NotificationPublisher
mechanism are
not responsible for the state management of any
notification listeners and the like ... Spring's JMX support will take
care of handling all the JMX infrastructure issues. All one need do as
an application developer is implement the
NotificationPublisherAware
interface and start
publishing events using the supplied
NotificationPublisher
instance. Note that the
NotificationPublisher
will be set
after the managed bean has been registered with an
MBeanServer
.
Using a NotificationPublisher
instance is
quite straightforward... one simply creates a JMX
Notification
instance (or an instance of an
appropriate Notification
subclass), populates
the notification with the data pertinent to the event that is to be
published, and one then invokes the
sendNotification(Notification)
on the
NotificationPublisher
instance, passing in the
Notification
.
Find below a simple example... in this scenario, exported
instances of the JmxTestBean
are going to publish
a NotificationEvent
every time the
add(int, int)
operation is invoked.
package org.springframework.jmx;
import org.springframework.jmx.export.notification.NotificationPublisherAware;
import org.springframework.jmx.export.notification.NotificationPublisher;
import javax.management.Notification;
public class JmxTestBean implements IJmxTestBean, NotificationPublisherAware {
private String name;
private int age;
private boolean isSuperman;
private NotificationPublisher publisher;
// other getters and setters omitted for clarity
public int add(int x, int y) {
int answer = x + y;
this.publisher.sendNotification(new Notification("add", this, 0));
return answer;
}
public void dontExposeMe() {
throw new RuntimeException();
}
public void setNotificationPublisher(NotificationPublisher notificationPublisher) {
this.publisher = notificationPublisher;
}
}
The NotificationPublisher
interface and the
machinery to get it all working is one of the nicer features of Spring's JMX support.
It does however come with the price tag of coupling your classes to both Spring and JMX; as
always, the advice here is to be pragmatic... if you need the functionality offered by the
NotificationPublisher
and you can accept the coupling to both Spring
and JMX, then do so.
This section contains links to further resources about JMX.
The JMX homepage at Sun
The JMX specification (JSR-000003)
The JMX Remote API specification (JSR-000160)
The MX4J homepage (an Open Source implementation of various JMX specs)
Getting Started with JMX - an introductory article from Sun.
J2EE provides a specification to standardize access to enterprise information systems (EIS): the JCA (Java Connector Architecture). This specification is divided into several different parts:
SPI (Service provider interfaces) that the connector provider must implement. These interfaces constitute a resource adapter which can be deployed on a J2EE application server. In such a scenario, the server manages connection pooling, transaction and security (managed mode). The application server is also responsible for managing the configuration, which is held outside the client application. A connector can be used without an application server as well; in this case, the application must configure it directly (non-managed mode).
CCI (Common Client Interface) that an application can use to interact with the connector and thus communicate with an EIS. An API for local transaction demarcation is provided as well.
The aim of the Spring CCI support is to provide classes to access a CCI connector in typical Spring style, leveraging the Spring Framework's general resource and transaction management facilities.
![]() | Note |
---|---|
The client side of connectors doesn't alway use CCI. Some connectors expose their own APIs, only providing JCA resource adapter to use the system contracts of a J2EE container (connection pooling, global transactions, security). Spring does not offer special support for such connector-specific APIs. |
The base resource to use JCA CCI is the
ConnectionFactory
interface. The connector used
must provide an implementation of this interface.
To use your connector, you can deploy it on your application
server and fetch the ConnectionFactory
from the
server's JNDI environment (managed mode). The connector must be
packaged as a RAR file (resource adapter archive) and contain a
ra.xml
file to describe its deployment
characteristics. The actual name of the resource is specified when
you deploy it. To access it within Spring, simply use Spring's
JndiObjectFactoryBean
to fetch the factory
by its JNDI name.
Another way to use a connector is to embed it in your application
(non-managed mode), not using an application server to deploy and
configure it. Spring offers the possibility to configure a connector
as a bean, through a provided FactoryBean
(LocalConnectionFactoryBean
). In this manner,
you only need the connector library in the classpath (no RAR file and
no ra.xml
descriptor needed). The library must
be extracted from the connector's RAR file, if necessary.
Once you have got access to your ConnectionFactory
instance, you can inject it into your components. These components can
either be coded against the plain CCI API or leverage Spring's support
classes for CCI access (e.g. CciTemplate
).
![]() | Note |
---|---|
When you use a connector in non-managed mode, you can't use global transactions because the resource is never enlisted / delisted in the current global transaction of the current thread. The resource is simply not aware of any global J2EE transactions that might be running. |
In order to make connections to the EIS, you need to obtain a
ConnectionFactory
from the application server if
you are in a managed mode, or directly from Spring if you are in a
non-managed mode.
In a managed mode, you access a ConnectionFactory
from JNDI; its properties will be configured in the application server.
<bean id="eciConnectionFactory" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="eis/cicseci"/> </bean>
In non-managed mode, you must configure the ConnectionFactory
you want to use in the configuration of Spring as a JavaBean. The
LocalConnectionFactoryBean
class offers this
setup style, passing in the ManagedConnectionFactory
implementation of your connector, exposing the application-level
CCI ConnectionFactory
.
<bean id="eciManagedConnectionFactory" class="com.ibm.connector2.cics.ECIManagedConnectionFactory"> <property name="serverName" value="TXSERIES"/> <property name="connectionURL" value="tcp://localhost/"/> <property name="portNumber" value="2006"/> </bean> <bean id="eciConnectionFactory" class="org.springframework.jca.support.LocalConnectionFactoryBean"> <property name="managedConnectionFactory" ref="eciManagedConnectionFactory"/> </bean>
![]() | Note |
---|---|
You can't directly instantiate a specific
|
JCA CCI allow the developer to configure the connections to the
EIS using the ConnectionSpec
implementation of your
connector. In order to configure its properties, you need to wrap the
target connection factory with a dedicated adapter,
ConnectionSpecConnectionFactoryAdapter
. So, the
dedicated ConnectionSpec
can be configured with the
property connectionSpec
(as an inner bean).
This property is not mandatory because the CCI
ConnectionFactory
interface defines two different
methods to obtain a CCI connection. Some of the
ConnectionSpec
properties can often be configured
in the application server (in managed mode) or on the corresponding local
ManagedConnectionFactory
implementation.
public interface ConnectionFactory implements Serializable, Referenceable { ... Connection getConnection() throws ResourceException; Connection getConnection(ConnectionSpec connectionSpec) throws ResourceException; ... }
Spring provides a ConnectionSpecConnectionFactoryAdapter
that allows for specifying a ConnectionSpec
instance
to use for all operations on a given factory. If the adapter's
connectionSpec
property is specified, the adapter
uses the getConnection
variant without argument,
else the one with the ConnectionSpec
argument.
<bean id="managedConnectionFactory" class="com.sun.connector.cciblackbox.CciLocalTxManagedConnectionFactory"> <property name="connectionURL" value="jdbc:hsqldb:hsql://localhost:9001"/> <property name="driverName" value="org.hsqldb.jdbcDriver"/> </bean> <bean id="targetConnectionFactory" class="org.springframework.jca.support.LocalConnectionFactoryBean"> <property name="managedConnectionFactory" ref="managedConnectionFactory"/> </bean> <bean id="connectionFactory" class="org.springframework.jca.cci.connection.ConnectionSpecConnectionFactoryAdapter"> <property name="targetConnectionFactory" ref="targetConnectionFactory"/> <property name="connectionSpec"> <bean class="com.sun.connector.cciblackbox.CciConnectionSpec"> <property name="user" value="sa"/> <property name="password" value=""/> </bean> </property> </bean>
If you want to use a single CCI connection, Spring provides a further
ConnectionFactory
adapter to manage this. The
SingleConnectionFactory
adapter class will open a single
connection lazily and close it when this bean is destroyed at application
shutdown. This class will expose special Connection
proxies that behave accordingly, all sharing the same underlying physical
connection.
<bean id="eciManagedConnectionFactory" class="com.ibm.connector2.cics.ECIManagedConnectionFactory"> <property name="serverName" value="TEST"/> <property name="connectionURL" value="tcp://localhost/"/> <property name="portNumber" value="2006"/> </bean> <bean id="targetEciConnectionFactory" class="org.springframework.jca.support.LocalConnectionFactoryBean"> <property name="managedConnectionFactory" ref="eciManagedConnectionFactory"/> </bean> <bean id="eciConnectionFactory" class="org.springframework.jca.cci.connection.SingleConnectionFactory"> <property name="targetConnectionFactory" ref="targetEciConnectionFactory"/> </bean>
![]() | Note |
---|---|
This |
One of the aims of the JCA CCI support is to provide convenient
facilities for manipulating CCI records. The developer can specify the
strategy to create records and extract datas from records, for use
with Spring's CciTemplate
. The following interfaces will configure the
strategy to use input and output records if you don't want to work
with records directly in your application.
In order to create an input Record
, the
developer can use a dedicated implementation of the
RecordCreator
interface.
public interface RecordCreator { Record createRecord(RecordFactory recordFactory) throws ResourceException, DataAccessException; }
As you can see, the createRecord(..)
method
receives a RecordFactory
instance as parameter,
which corresponds to the RecordFactory
of the
ConnectionFactory
used. This reference can be
used to create IndexedRecord
or
MappedRecord
instances. The following sample
shows how to use the RecordCreator
interface
and indexed/mapped records.
public class MyRecordCreator implements RecordCreator { public Record createRecord(RecordFactory recordFactory) throws ResourceException { IndexedRecord input = recordFactory.createIndexedRecord("input"); input.add(new Integer(id)); return input; } }
An output Record
can be used to receive
data back from the EIS. Hence, a specific implementation of the
RecordExtractor
interface can be passed to
Spring's CciTemplate
for extracting data from the output
Record
.
public interface RecordExtractor { Object extractData(Record record) throws ResourceException, SQLException, DataAccessException; }
The following sample shows how to use the RecordExtractor
interface.
public class MyRecordExtractor implements RecordExtractor { public Object extractData(Record record) throws ResourceException { CommAreaRecord commAreaRecord = (CommAreaRecord) record; String str = new String(commAreaRecord.toByteArray()); String field1 = string.substring(0,6); String field2 = string.substring(6,1); return new OutputObject(Long.parseLong(field1), field2); } }
The CciTemplate
is the central class of the core CCI support package
(org.springframework.jca.cci.core
). It simplifies
the use of CCI since it handles the creation and release of resources.
This helps to avoid common errors like forgetting to always close the
connection. It cares for the lifecycle of connection and interaction
objects, letting application code focus on generating input records
from application data and extracting application data from output
records.
The JCA CCI specification defines two distinct methods to call
operations on an EIS. The CCI Interaction
interface provides two execute method signatures:
public interface javax.resource.cci.Interaction { ... boolean execute(InteractionSpec spec, Record input, Record output) throws ResourceException; Record execute(InteractionSpec spec, Record input) throws ResourceException; ... }
Depending on the template method called, CciTemplate
will know which execute
method to call on the interaction.
In any case, a correctly initialized InteractionSpec
instance is mandatory.
CciTemplate.execute(..)
can be used in two ways:
With direct Record
arguments. In this case,
you simply need to pass the CCI input record in, and the returned object
be the corresponding CCI output record.
With application objects, using record mapping. In this case,
you need to provide corresponding RecordCreator
and RecordExtractor
instances.
With the first approach, the following methods of the template
will be used. These methods directly correspond to those on the
Interaction
interface.
public class CciTemplate implements CciOperations { public Record execute(InteractionSpec spec, Record inputRecord) throws DataAccessException { ... } public void execute(InteractionSpec spec, Record inputRecord, Record outputRecord) throws DataAccessException { ... } }
With the second approach, we need to specify the record creation
and record extraction strategies as arguments. The interfaces used
are those describe in the previous section on record conversion.
The corresponding CciTemplate
methods are the
following:
public class CciTemplate implements CciOperations { public Record execute(InteractionSpec spec, RecordCreator inputCreator) throws DataAccessException { ... } public Object execute(InteractionSpec spec, Record inputRecord, RecordExtractor outputExtractor) throws DataAccessException { ... } public Object execute(InteractionSpec spec, RecordCreator creator, RecordExtractor extractor) throws DataAccessException { ... } }
Unless the outputRecordCreator
property is
set on the template (see the following section), every method will call
the corresponding execute
method of the CCI
Interaction
with two parameters:
InteractionSpec
and input Record
,
receiving an output Record
as return value.
CciTemplate
also provides methods to create
IndexRecord
and MappedRecord
outside a RecordCreator
implementation, through
its createIndexRecord(..)
and
createMappedRecord(..)
methods. This can be used
within DAO implementations to create Record
instances to pass into corresponding
CciTemplate.execute(..)
methods.
public class CciTemplate implements CciOperations { public IndexedRecord createIndexedRecord(String name) throws DataAccessException { ... } public MappedRecord createMappedRecord(String name) throws DataAccessException { ... } }
Spring's CCI support provides a abstract class for DAOs,
supporting injection of a ConnectionFactory
or a CciTemplate
instances. The name of the
class is CciDaoSupport
: It provides simple
setConnectionFactory
and
setCciTemplate
methods. Internally, this
class will create a CciTemplate
instance
for a passed-in ConnectionFactory
, exposing
it to concrete data access implementations in subclasses.
public abstract class CciDaoSupport { public void setConnectionFactory(ConnectionFactory connectionFactory) { ... } public ConnectionFactory getConnectionFactory() { ... } public void setCciTemplate(CciTemplate cciTemplate) { ... } public CciTemplate getCciTemplate() { ... } }
If the connector used only supports the
Interaction.execute(..)
method with input and output
records as parameters (that is, it requires the desired output record
to be passed in instead of returning an appropriate output record),
you can set the outputRecordCreator
property of the
CciTemplate
to automatically generate an output
record to be filled by the JCA connector when the response is received.
This record will be then returned to the caller of the template.
This property simply holds an implementation of the
RecordCreator
interface, used for that purpose.
The RecordCreator
interface has already been
discussed in the section entitled Section 21.3.1, “Record conversion”.
The outputRecordCreator
property must be directly specified on the CciTemplate
.
This could be done in the application code like so:
cciTemplate.setOutputRecordCreator(new EciOutputRecordCreator());
Or (recommended) in the Spring configuration, if the CciTemplate
is configured as a dedicated bean instance:
<bean id="eciOutputRecordCreator" class="eci.EciOutputRecordCreator"/> <bean id="cciTemplate" class="org.springframework.jca.cci.core.CciTemplate"> <property name="connectionFactory" ref="eciConnectionFactory"/> <property name="outputRecordCreator" ref="eciOutputRecordCreator"/> </bean>
![]() | Note |
---|---|
As the |
The following table summarizes the mechanisms of the
CciTemplate
class and the corresponding methods
called on the CCI Interaction
interface:
Table 21.1. Usage of Interaction
execute methods
CciTemplate method signature | CciTemplate outputRecordCreator property | execute method called on the CCI Interaction |
---|---|---|
Record execute(InteractionSpec, Record) | not set | Record execute(InteractionSpec, Record) |
Record execute(InteractionSpec, Record) | set | boolean execute(InteractionSpec, Record, Record) |
void execute(InteractionSpec, Record, Record) | not set | void execute(InteractionSpec, Record, Record) |
void execute(InteractionSpec, Record, Record) | set | void execute(InteractionSpec, Record, Record) |
Record execute(InteractionSpec, RecordCreator) | not set | Record execute(InteractionSpec, Record) |
Record execute(InteractionSpec, RecordCreator) | set | void execute(InteractionSpec, Record, Record) |
Record execute(InteractionSpec, Record, RecordExtractor) | not set | Record execute(InteractionSpec, Record) |
Record execute(InteractionSpec, Record, RecordExtractor) | set | void execute(InteractionSpec, Record, Record) |
Record execute(InteractionSpec, RecordCreator, RecordExtractor) | not set | Record execute(InteractionSpec, Record) |
Record execute(InteractionSpec, RecordCreator, RecordExtractor) | set | void execute(InteractionSpec, Record, Record) |
CciTemplate
also offers the possibility to
work directly with CCI connections and interactions, in the same manner
as JdbcTemplate
and JmsTemplate
.
This is useful when you want to perform multiple operations on a CCI
connection or interaction, for example.
The interface ConnectionCallback
provides a
CCI Connection
as argument, in order to perform
custom operations on it, plus the CCI ConnectionFactory
which the Connection
was created with. The latter
can be useful for example to get an associated RecordFactory
instance and create indexed/mapped records, for example.
public interface ConnectionCallback { Object doInConnection(Connection connection, ConnectionFactory connectionFactory) throws ResourceException, SQLException, DataAccessException; }
The interface InteractionCallback
provides
the CCI Interaction
, in order to perform custom
operations on it, plus the corresponding CCI ConnectionFactory
.
public interface InteractionCallback { Object doInInteraction(Interaction interaction, ConnectionFactory connectionFactory) throws ResourceException, SQLException, DataAccessException; }
![]() | Note |
---|---|
|
In this section, the usage of the CciTemplate
will be shown to acces to a CICS with ECI mode, with the IBM CICS ECI
connector.
Firstly, some initializations on the CCI
InteractionSpec
must be done to specify which CICS
program to access and how to interact with it.
ECIInteractionSpec interactionSpec = new ECIInteractionSpec(); interactionSpec.setFunctionName("MYPROG"); interactionSpec.setInteractionVerb(ECIInteractionSpec.SYNC_SEND_RECEIVE);
Then the program can use CCI via Spring's template and specify
mappings between custom objects and CCI Records
.
public class MyDaoImpl extends CciDaoSupport implements MyDao { public OutputObject getData(InputObject input) { ECIInteractionSpec interactionSpec = ...; OutputObject output = (ObjectOutput) getCciTemplate().execute(interactionSpec, new RecordCreator() { public Record createRecord(RecordFactory recordFactory) throws ResourceException { return new CommAreaRecord(input.toString().getBytes()); } }, new RecordExtractor() { public Object extractData(Record record) throws ResourceException { CommAreaRecord commAreaRecord = (CommAreaRecord)record; String str = new String(commAreaRecord.toByteArray()); String field1 = string.substring(0,6); String field2 = string.substring(6,1); return new OutputObject(Long.parseLong(field1), field2); } }); return output; } }
As discussed previously, callbacks can be used to work directly on CCI connections or interactions.
public class MyDaoImpl extends CciDaoSupport implements MyDao {
public OutputObject getData(InputObject input) {
ObjectOutput output = (ObjectOutput) getCciTemplate().execute(
new ConnectionCallback() {
public Object doInConnection(Connection connection, ConnectionFactory factory)
throws ResourceException {
// do something...
}
});
}
return output;
}
}
![]() | Note |
---|---|
With a |
For a more specific callback, you can implement an
InteractionCallback
. The passed-in
Interaction
will be managed and closed by the
CciTemplate
in this case.
public class MyDaoImpl extends CciDaoSupport implements MyDao { public String getData(String input) { ECIInteractionSpec interactionSpec = ...; String output = (String) getCciTemplate().execute(interactionSpec, new InteractionCallback() { public Object doInInteraction(Interaction interaction, ConnectionFactory factory) throws ResourceException { Record input = new CommAreaRecord(inputString.getBytes()); Record output = new CommAreaRecord(); interaction.execute(holder.getInteractionSpec(), input, output); return new String(output.toByteArray()); } }); return output; } }
For the examples above, the corresponding configuration of the involved Spring beans could look like this in non-managed mode:
<bean id="managedConnectionFactory" class="com.ibm.connector2.cics.ECIManagedConnectionFactory"> <property name="serverName" value="TXSERIES"/> <property name="connectionURL" value="local:"/> <property name="userName" value="CICSUSER"/> <property name="password" value="CICS"/> </bean> <bean id="connectionFactory" class="org.springframework.jca.support.LocalConnectionFactoryBean"> <property name="managedConnectionFactory" ref="managedConnectionFactory"/> </bean> <bean id="component" class="mypackage.MyDaoImpl"> <property name="connectionFactory" ref="connectionFactory"/> </bean>
In managed mode (that is, in a J2EE environment), the configuration could look as follows:
<bean id="connectionFactory" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="eis/cicseci"/> </bean> <bean id="component" class="MyDaoImpl"> <property name="connectionFactory" ref="connectionFactory"/> </bean>
The org.springframework.jca.cci.object
package
contains support classes that allow you to access the EIS in a different
style: through reusable operation objects, analogous to Spring's JDBC
operation objects (see JDBC chapter). This will usually encapsulate the
CCI API: an application-level input object will be passed to the operation
object, so it can construct the input record and then convert the received
record data to an application-level output object and return it.
Note: This approach is internally based on the
CciTemplate
class and the RecordCreator
/ RecordExtractor
interfaces, reusing the machinery of
Spring's core CCI support.
MappingRecordOperation
essentially performs the
same work as CciTemplate
, but represents a specific,
pre-configured operation as an object. It provides two template methods
to specify how to convert an input object to a input record, and how to
convert an output record to an output object (record mapping):
createInputRecord(..)
to specify how to
convert an input object to an input Record
extractOutputData(..)
to specify how to
extract an output object from an output Record
Here are the signatures of these methods:
public abstract class MappingRecordOperation extends EisOperation { ... protected abstract Record createInputRecord(RecordFactory recordFactory, Object inputObject) throws ResourceException, DataAccessException { ... } protected abstract Object extractOutputData(Record outputRecord) throws ResourceException, SQLException, DataAccessException { ... } ... }
Thereafter, in order to execute an EIS operation, you need to use a single execute method, passing in an application-level input object and receiving an application-level output object as result:
public abstract class MappingRecordOperation extends EisOperation { ... public Object execute(Object inputObject) throws DataAccessException { ... }
As you can see, contrary to the CciTemplate
class,
this execute(..)
method does not have an
InteractionSpec
as argument. Instead, the
InteractionSpec
is global to the operation.
The following constructor must be used to instantiate an operation
object with a specific InteractionSpec
:
InteractionSpec spec = ...; MyMappingRecordOperation eisOperation = new MyMappingRecordOperation(getConnectionFactory(), spec); ...
Some connectors use records based on a COMMAREA which represents
an array of bytes containing parameters to send to the EIS and data
returned by it. Spring provides a special operation class for working
directly on COMMAREA rather than on records. The
MappingCommAreaOperation
class extends the
MappingRecordOperation
class to provide such special
COMMAREA support. It implicitly uses the CommAreaRecord
class as input and output record type, and provides two new methods to
convert an input object into an input COMMAREA and the output COMMAREA
into an output object.
public abstract class MappingCommAreaOperation extends MappingRecordOperation { ... protected abstract byte[] objectToBytes(Object inObject) throws IOException, DataAccessException; protected abstract Object bytesToObject(byte[] bytes) throws IOException, DataAccessException; ... }
As every MappingRecordOperation
subclass is
based on CciTemplate internally, the same way to automatically generate
output records as with CciTemplate
is available.
Every operation object provides a corresponding
setOutputRecordCreator(..)
method. For further information,
see the section entitled Section 21.3.4, “Automatic output record generation”.
The operation object approach uses records in the same manner
as the CciTemplate
class.
Table 21.2. Usage of Interaction execute methods
MappingRecordOperation method
signature | MappingRecordOperation
outputRecordCreator property | execute method called on the CCI
Interaction |
---|---|---|
Object execute(Object) | not set | Record execute(InteractionSpec, Record) |
Object execute(Object) | set | boolean execute(InteractionSpec, Record, Record) |
In this section, the usage of the
MappingRecordOperation
will be shown to access a
database with the Blackbox CCI connector.
![]() | Note |
---|---|
The original version of this connector is provided by the J2EE SDK (version 1.3), available from Sun. |
Firstly, some initializations on the CCI
InteractionSpec
must be done to specify which SQL
request to execute. In this sample, we directly define the way to
convert the parameters of the request to a CCI record and the way to
convert the CCI result record to an instance of the
Person
class.
public class PersonMappingOperation extends MappingRecordOperation { public PersonMappingOperation(ConnectionFactory connectionFactory) { setConnectionFactory(connectionFactory); CciInteractionSpec interactionSpec = new CciConnectionSpec(); interactionSpec.setSql("select * from person where person_id=?"); setInteractionSpec(interactionSpec); } protected Record createInputRecord(RecordFactory recordFactory, Object inputObject) throws ResourceException { Integer id = (Integer) inputObject; IndexedRecord input = recordFactory.createIndexedRecord("input"); input.add(new Integer(id)); return input; } protected Object extractOutputData(Record outputRecord) throws ResourceException, SQLException { ResultSet rs = (ResultSet) outputRecord; Person person = null; if (rs.next()) { Person person = new Person(); person.setId(rs.getInt("person_id")); person.setLastName(rs.getString("person_last_name")); person.setFirstName(rs.getString("person_first_name")); } return person; } }
Then the application can execute the operation object, with the person identifier as argument. Note that operation object could be set up as shared instance, as it is thread-safe.
public class MyDaoImpl extends CciDaoSupport implements MyDao { public Person getPerson(int id) { PersonMappingOperation query = new PersonMappingOperation(getConnectionFactory()); Person person = (Person) query.execute(new Integer(id)); return person; } }
The corresponding configuration of Spring beans could look as follows in non-managed mode:
<bean id="managedConnectionFactory" class="com.sun.connector.cciblackbox.CciLocalTxManagedConnectionFactory"> <property name="connectionURL" value="jdbc:hsqldb:hsql://localhost:9001"/> <property name="driverName" value="org.hsqldb.jdbcDriver"/> </bean> <bean id="targetConnectionFactory" class="org.springframework.jca.support.LocalConnectionFactoryBean"> <property name="managedConnectionFactory" ref="managedConnectionFactory"/> </bean> <bean id="connectionFactory" class="org.springframework.jca.cci.connection.ConnectionSpecConnectionFactoryAdapter"> <property name="targetConnectionFactory" ref="targetConnectionFactory"/> <property name="connectionSpec"> <bean class="com.sun.connector.cciblackbox.CciConnectionSpec"> <property name="user" value="sa"/> <property name="password" value=""/> </bean> </property> </bean> <bean id="component" class="MyDaoImpl"> <property name="connectionFactory" ref="connectionFactory"/> </bean>
In managed mode (that is, in a J2EE environment), the configuration could look as follows:
<bean id="targetConnectionFactory" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="eis/blackbox"/> </bean> <bean id="connectionFactory" class="org.springframework.jca.cci.connection.ConnectionSpecConnectionFactoryAdapter"> <property name="targetConnectionFactory" ref="targetConnectionFactory"/> <property name="connectionSpec"> <bean class="com.sun.connector.cciblackbox.CciConnectionSpec"> <property name="user" value="sa"/> <property name="password" value=""/> </bean> </property> </bean> <bean id="component" class="MyDaoImpl"> <property name="connectionFactory" ref="connectionFactory"/> </bean>
In this section, the usage of the
MappingCommAreaOperation
will be shown: accessing
a CICS with ECI mode with the IBM CICS ECI connector.
Firstly, the CCI InteractionSpec
needs to be
initialized to specify which CICS program to access and how to interact
with it.
public abstract class EciMappingOperation extends MappingCommAreaOperation { public EciMappingOperation(ConnectionFactory connectionFactory, String programName) { setConnectionFactory(connectionFactory); ECIInteractionSpec interactionSpec = new ECIInteractionSpec(), interactionSpec.setFunctionName(programName); interactionSpec.setInteractionVerb(ECIInteractionSpec.SYNC_SEND_RECEIVE); interactionSpec.setCommareaLength(30); setInteractionSpec(interactionSpec); setOutputRecordCreator(new EciOutputRecordCreator()); } private static class EciOutputRecordCreator implements RecordCreator { public Record createRecord(RecordFactory recordFactory) throws ResourceException { return new CommAreaRecord(); } } }
The abstract EciMappingOperation
class can
then be subclassed to specify mappings between custom objects and
Records
.
public class MyDaoImpl extends CciDaoSupport implements MyDao { public OutputObject getData(Integer id) { EciMappingOperation query = new EciMappingOperation(getConnectionFactory(), "MYPROG") { protected abstract byte[] objectToBytes(Object inObject) throws IOException { Integer id = (Integer) inObject; return String.valueOf(id); } protected abstract Object bytesToObject(byte[] bytes) throws IOException; String str = new String(bytes); String field1 = str.substring(0,6); String field2 = str.substring(6,1); String field3 = str.substring(7,1); return new OutputObject(field1, field2, field3); } }); return (OutputObject) query.execute(new Integer(id)); } }
The corresponding configuration of Spring beans could look as follows in non-managed mode:
<bean id="managedConnectionFactory" class="com.ibm.connector2.cics.ECIManagedConnectionFactory"> <property name="serverName" value="TXSERIES"/> <property name="connectionURL" value="local:"/> <property name="userName" value="CICSUSER"/> <property name="password" value="CICS"/> </bean> <bean id="connectionFactory" class="org.springframework.jca.support.LocalConnectionFactoryBean"> <property name="managedConnectionFactory" ref="managedConnectionFactory"/> </bean> <bean id="component" class="MyDaoImpl"> <property name="connectionFactory" ref="connectionFactory"/> </bean>
In managed mode (that is, in a J2EE environment), the configuration could look as follows:
<bean id="connectionFactory" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="eis/cicseci"/> </bean> <bean id="component" class="MyDaoImpl"> <property name="connectionFactory" ref="connectionFactory"/> </bean>
JCA specifies several levels of transaction support for resource adapters.
The kind of transactions that your resource adapter supports is specified
in its ra.xml
file. There are essentially three options:
none (for example with CICS EPI connector), local transactions (for
example with a CICS ECI connector), global transactions (for example with an
IMS connector).
<connector> <resourceadapter> <!-- <transaction-support>NoTransaction</transaction-support> --> <!-- <transaction-support>LocalTransaction</transaction-support> --> <transaction-support>XATransaction</transaction-support> <resourceadapter> <connector>
For global transactions, you can use Spring's generic transaction
infrastructure to demarcate transactions, with JtaTransactionManager
as
backend (delegating to the J2EE server's distributed transaction coordinator
underneath).
For local transactions on a single CCI ConnectionFactory
,
Spring provides a specific transaction management strategy for CCI, analogous
to the DataSourceTransactionManager
for JDBC. The CCI API
defines a local transaction object and corresponding local transaction
demarcation methods. Spring's CciLocalTransactionManager
executes such local CCI transactions, fully compliant with Spring's generic
PlatformTransactionManager
abstraction.
<bean id="eciConnectionFactory" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="eis/cicseci"/> </bean> <bean id="eciTransactionManager" class="org.springframework.jca.cci.connection.CciLocalTransactionManager"> <property name="connectionFactory" ref="eciConnectionFactory"/> </bean>
Both transaction strategies can be used with any of Spring's
transaction demarcation facilities, be it declarative or programmatic.
This is a consequence of Spring's generic
PlatformTransactionManager
abstraction, which
decouples transaction demarcation from the actual execution strategy.
Simply switch between JtaTransactionManager
and
CciLocalTransactionManager
as needed, keeping
your transaction demarcation as-is.
For more information on Spring's transaction facilities, see the chapter entitled Chapter 9, Transaction management.
The Spring Framework provides a helpful utility library for sending email that shields the user from the specifics of the underlying mailing system and is responsible for low level resource handling on behalf of the client.
The org.springframework.mail
package is the root level package
for the Spring Framework's email support. The central interface for sending
emails is the MailSender
interface; a simple value object
encapsulating the properties of a simple mail such as from and
to (plus many others) is the SimpleMailMessage
class.
This package also contains a hierarchy of checked exceptions which provide
a higher level of abstraction over the lower level mail system exceptions
with the root exception being MailException
. Please
refer to the Javadocs for more information on the rich mail exception hierarchy.
The org.springframework.mail.javamail.JavaMailSender
interface adds specialized JavaMail features such as MIME
message support to the MailSender
interface
(from which it inherits). JavaMailSender
also provides a
callback interface for preparation of JavaMail MIME messages, called
org.springframework.mail.javamail.MimeMessagePreparator
Let's assume there is a business interface called OrderManager
:
public interface OrderManager { void placeOrder(Order order); }
Let us also assume that there is a requirement stating that an email message with an order number needs to be generated and sent to a customer placing the relevant order.
import org.springframework.mail.MailException; import org.springframework.mail.MailSender; import org.springframework.mail.SimpleMailMessage; public class SimpleOrderManager implements OrderManager { private MailSender mailSender; private SimpleMailMessage templateMessage; public void setMailSender(MailSender mailSender) { this.mailSender = mailSender; } public void setTemplateMessage(SimpleMailMessage templateMessage) { this.templateMessage = templateMessage; } public void placeOrder(Order order) { // Do the business calculations... // Call the collaborators to persist the order... // Create a thread safe "copy" of the template message and customize it SimpleMailMessage msg = new SimpleMailMessage(this.templateMessage); msg.setTo(order.getCustomer().getEmailAddress()); msg.setText( "Dear " + order.getCustomer().getFirstName() + order.getCustomer().getLastName() + ", thank you for placing order. Your order number is " + order.getOrderNumber()); try{ this.mailSender.send(msg); } catch(MailException ex) { // simply log it and go on... System.err.println(ex.getMessage()); } } }
Find below the bean definitions for the above code:
<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
<property name="host" value="mail.mycompany.com"/>
</bean>
<!-- this is a template message that we can pre-load with default state -->
<bean id="templateMessage" class="org.springframework.mail.SimpleMailMessage">
<property name="from" value="customerservice@mycompany.com"/>
<property name="subject" value="Your order"/>
</bean>
<bean id="orderManager" class="com.mycompany.businessapp.support.SimpleOrderManager">
<property name="mailSender" ref="mailSender"/>
<property name="templateMessage" ref="templateMessage"/>
</bean>
Here is another implementation of OrderManager
using
the MimeMessagePreparator
callback interface. Please note
in this case that the mailSender
property is of type
JavaMailSender
so that we are able to use the JavaMail
MimeMessage
class:
import javax.mail.Message; import javax.mail.MessagingException; import javax.mail.internet.InternetAddress; import javax.mail.internet.MimeMessage; import javax.mail.internet.MimeMessage; import org.springframework.mail.MailException; import org.springframework.mail.javamail.JavaMailSender; import org.springframework.mail.javamail.MimeMessagePreparator; public class SimpleOrderManager implements OrderManager { private JavaMailSender mailSender; public void setMailSender(JavaMailSender mailSender) { this.mailSender = mailSender; } public void placeOrder(final Order order) { // Do the business calculations... // Call the collaborators to persist the order... MimeMessagePreparator preparator = new MimeMessagePreparator() { public void prepare(MimeMessage mimeMessage) throws Exception { mimeMessage.setRecipient(Message.RecipientType.TO, new InternetAddress(order.getCustomer().getEmailAddress())); mimeMessage.setFrom(new InternetAddress("mail@mycompany.com")); mimeMessage.setText( "Dear " + order.getCustomer().getFirstName() + " " + order.getCustomer().getLastName() + ", thank you for placing order. Your order number is " + order.getOrderNumber()); } }; try { this.mailSender.send(preparator); } catch (MailException ex) { // simply log it and go on... System.err.println(ex.getMessage()); } } }
![]() | Note |
---|---|
The mail code is a crosscutting concern and could well be a candidate
for refactoring into a custom Spring AOP aspect,
which then could be executed at appropriate joinpoints on the
|
The Spring Framework's mail support ships with two
MailSender
implementations. The standard JavaMail
implementation and the implementation on top of Jason Hunter's
MailMessage
class that is included in
the com.oreilly.servlet
package. Please refer to the relevant Javadocs for more information.
A class that comes in pretty handy when dealing with JavaMail messages is
the org.springframework.mail.javamail.MimeMessageHelper
class,
which shields you from having to use the verbose JavaMail API. Using
the MimeMessageHelper
it is pretty easy to
create a MimeMessage
:
// of course you would use DI in any real-world cases
JavaMailSenderImpl sender = new JavaMailSenderImpl();
sender.setHost("mail.host.com");
MimeMessage message = sender.createMimeMessage();
MimeMessageHelper helper = new MimeMessageHelper(message);
helper.setTo("test@host.com");
helper.setText("Thank you for ordering!");
sender.send(message);
Multipart email messages allow for both attachments and inline resources. Examples of inline resources would be be images or a stylesheet you want to use in your message, but that you don't want displayed as an attachment.
The following example shows you how to use the
MimeMessageHelper
to send an email along with a
single JPEG image attachment.
JavaMailSenderImpl sender = new JavaMailSenderImpl(); sender.setHost("mail.host.com"); MimeMessage message = sender.createMimeMessage(); // use the true flag to indicate you need a multipart message MimeMessageHelper helper = new MimeMessageHelper(message, true); helper.setTo("test@host.com"); helper.setText("Check out this image!"); // let's attach the infamous windows Sample file (this time copied to c:/) FileSystemResource file = new FileSystemResource(new File("c:/Sample.jpg")); helper.addAttachment("CoolImage.jpg", file); sender.send(message);
The following example shows you how to use the
MimeMessageHelper
to send an email along with an
inline image.
JavaMailSenderImpl sender = new JavaMailSenderImpl(); sender.setHost("mail.host.com"); MimeMessage message = sender.createMimeMessage(); // use the true flag to indicate you need a multipart message MimeMessageHelper helper = new MimeMessageHelper(message, true); helper.setTo("test@host.com"); // use the true flag to indicate the text included is HTML helper.setText("<html><body><img src='cid:identifier1234'></body></html>", true); // let's include the infamous windows Sample file (this time copied to c:/) FileSystemResource res = new FileSystemResource(new File("c:/Sample.jpg")); helper.addInline("identifier1234", res); sender.send(message);
![]() | Warning |
---|---|
Inline resources are added to the mime message using the
specified |
The code in the previous examples explicitly has been creating the
content of the email message, using methods calls such as
message.setText(..)
. This is fine for
simple cases, and it is okay in the context of the aforementioned
examples, where the intent was to show you the very basics of the API.
In your typical enterprise application though, you are not going to create the content of your emails using the above approach for a number of reasons.
Creating HTML-based email content in Java code is tedious and error prone
There is no clear separation between display logic and business logic
Changing the display structure of the email content requires writing Java code, recompiling, redeploying...
Typically the approach taken to address these issues is to use a template library such as FreeMarker or Velocity to define the display structure of email content. This leaves your code tasked only with creating the data that is to be rendered in the email template and sending the email. It is definitely a best practice for when the content of your emails becomes even moderately complex, and with the Spring Framework's support classes for FreeMarker and Velocity becomes quite easy to do. Find below an example of using the Velocity template library to create email content.
To use Velocity to create your email template(s), you will need to have the Velocity libraries available on your classpath. You will also need to create one or more Velocity templates for the email content that your application needs. Find below the Velocity template that this example will be using... as you can see it is HTML-based, and since it is plain text it can be created using your favorite HTML editor without recourse to having to know Java.
# in the com/foo/package
<html>
<body>
<h3>Hi ${user.userName}, welcome to the Chipping Sodbury On-the-Hill message boards!</h3>
<div>
Your email address is <a href="mailto:${user.emailAddress}">${user.emailAddress}</a>.
</div>
</body>
</html>
Find below some simple code and Spring XML configuration that makes use of the above Velocity template to create email content and send email(s).
package com.foo; import org.apache.velocity.app.VelocityEngine; import org.springframework.mail.javamail.JavaMailSender; import org.springframework.mail.javamail.MimeMessageHelper; import org.springframework.mail.javamail.MimeMessagePreparator; import org.springframework.ui.velocity.VelocityEngineUtils; import javax.mail.internet.MimeMessage; import java.util.HashMap; import java.util.Map; public class SimpleRegistrationService implements RegistrationService { private JavaMailSender mailSender; private VelocityEngine velocityEngine; public void setMailSender(JavaMailSender mailSender) { this.mailSender = mailSender; } public void setVelocityEngine(VelocityEngine velocityEngine) { this.velocityEngine = velocityEngine; } public void register(User user) { // Do the registration logic... sendConfirmationEmail(user); } private void sendConfirmationEmail(final User user) { MimeMessagePreparator preparator = new MimeMessagePreparator() { public void prepare(MimeMessage mimeMessage) throws Exception { MimeMessageHelper message = new MimeMessageHelper(mimeMessage); message.setTo(user.getEmailAddress()); message.setFrom("webmaster@csonth.gov.uk"); // could be parameterized... Map model = new HashMap(); model.put("user", user); String text = VelocityEngineUtils.mergeTemplateIntoString( velocityEngine, "com/dns/registration-confirmation.vm", model); message.setText(text, true); } }; this.mailSender.send(preparator); } }
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"> <bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl"> <property name="host" value="mail.csonth.gov.uk"/> </bean> <bean id="registrationService" class="com.foo.SimpleRegistrationService"> <property name="mailSender" ref="mailSender"/> <property name="velocityEngine" ref="velocityEngine"/> </bean> <bean id="velocityEngine" class="org.springframework.ui.velocity.VelocityEngineFactoryBean"> <property name="velocityProperties"> <value> resource.loader=class class.resource.loader.class=org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader </value> </property> </bean> </beans>
The Spring Framework features integration classes for scheduling support. Currently, Spring
supports the Timer
, part of the JDK since 1.3, and the
Quartz Scheduler (http://www.opensymphony.com/quartz/). Both schedulers
are set up using a FactoryBean
with optional references
to Timer
or Trigger
instances, respectively.
Furthermore, a convenience class for both the Quartz Scheduler and the Timer
is
available that allows you to invoke a method of an existing target object
(analogous to the normal MethodInvokingFactoryBean
operation).
Spring also features classes for thread pooling that abstract
away differences between Java SE 1.4, Java SE 5 and Java EE environments.
Quartz uses Trigger
, Job
and
JobDetail
objects to realize scheduling of all kinds of jobs.
For the basic concepts behind Quartz, have a look at
http://www.opensymphony.com/quartz. For convenience purposes,
Spring offers a couple of classes that simplify the usage of Quartz within
Spring-based applications.
JobDetail
objects contain all information needed to
run a job. The Spring Framework provides a JobDetailBean
that makes the JobDetail
more of an actual JavaBean
with sensible defaults. Let's have a look at an example:
<bean name="exampleJob" class="org.springframework.scheduling.quartz.JobDetailBean"> <property name="jobClass" value="example.ExampleJob" /> <property name="jobDataAsMap"> <map> <entry key="timeout" value="5" /> </map> </property> </bean>
The job detail bean has all information it needs to run the job (ExampleJob
).
The timeout is specified in the job data map. The job data map is
available through the JobExecutionContext
(passed to you at execution time), but the JobDetailBean
also maps the properties from the job data map to properties of the actual job.
So in this case, if the ExampleJob
contains a property
named timeout
, the JobDetailBean
will
automatically apply it:
package example;
public class ExampleJob extends QuartzJobBean {
private int timeout;
/**
* Setter called after the ExampleJob is instantiated
* with the value from the JobDetailBean (5)
*/
public void setTimeout(int timeout) {
this.timeout = timeout;
}
protected void executeInternal(JobExecutionContext ctx) throws JobExecutionException {
// do the actual work
}
}
All additional settings from the job detail bean are of course available to you as well.
Note: Using the name
and group
properties,
you can modify the name and the group of the job, respectively. By default, the name of
the job matches the bean name of the job detail bean (in the example above, this is
exampleJob
).
Often you just need to invoke a method on a specific object. Using the
MethodInvokingJobDetailFactoryBean
you can do exactly this:
<bean id="jobDetail" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean"> <property name="targetObject" ref="exampleBusinessObject" /> <property name="targetMethod" value="doIt" /> </bean>
The above example will result in the doIt
method being called on the
exampleBusinessObject
method (see below):
public class ExampleBusinessObject { // properties and collaborators public void doIt() { // do the actual work } }
<bean id="exampleBusinessObject" class="examples.ExampleBusinessObject"/>
Using the MethodInvokingJobDetailFactoryBean
, you don't need to
create one-line jobs that just invoke a method, and you only need to create the actual
business object and wire up the detail object.
By default, Quartz Jobs are stateless, resulting in the possibility of jobs interfering
with each other. If you specify two triggers for the same JobDetail
,
it might be possible that before the first job has finished, the second one will start.
If JobDetail
classes implement the
Stateful
interface, this won't happen. The second job
will not start before the first one has finished. To make jobs resulting from the
MethodInvokingJobDetailFactoryBean
non-concurrent, set the
concurrent
flag to false
.
<bean id="jobDetail" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean"> <property name="targetObject" ref="exampleBusinessObject" /> <property name="targetMethod" value="doIt" /> <property name="concurrent" value="false" /> </bean>
![]() | Note |
---|---|
By default, jobs will run in a concurrent fashion. |
We've created job details and jobs. We've also reviewed the convenience bean
that allows to you invoke a method on a specific object. Of course, we still need
to schedule the jobs themselves. This is done using triggers and a
SchedulerFactoryBean
. Several triggers are available
within Quartz. Spring offers two subclassed triggers with convenient defaults:
CronTriggerBean
and SimpleTriggerBean
.
Triggers need to be scheduled. Spring offers a SchedulerFactoryBean
that exposes triggers to be set as properties. SchedulerFactoryBean
schedules the actual jobs with those triggers.
Find below a couple of examples:
<bean id="simpleTrigger" class="org.springframework.scheduling.quartz.SimpleTriggerBean"> <!-- see the example of method invoking job above --> <property name="jobDetail" ref="jobDetail" /> <!-- 10 seconds --> <property name="startDelay" value="10000" /> <!-- repeat every 50 seconds --> <property name="repeatInterval" value="50000" /> </bean> <bean id="cronTrigger" class="org.springframework.scheduling.quartz.CronTriggerBean"> <property name="jobDetail" ref="exampleJob" /> <!-- run every morning at 6 AM --> <property name="cronExpression" value="0 0 6 * * ?" /> </bean>
Now we've set up two triggers, one running every 50 seconds with a starting delay of
10 seconds and one every morning at 6 AM. To finalize everything, we need to set up the
SchedulerFactoryBean
:
<bean class="org.springframework.scheduling.quartz.SchedulerFactoryBean"> <property name="triggers"> <list> <ref bean="cronTrigger" /> <ref bean="simpleTrigger" /> </list> </property> </bean>
More properties are available for the SchedulerFactoryBean
for you
to set, such as the calendars used by the job details, properties to customize Quartz with,
etc. Have a look at the
SchedulerFactoryBean Javadoc
for more information.
The other way to schedule jobs in Spring is to use JDK
Timer
objects. You can create custom timers or
use the timer that invokes methods. Wiring timers is done using the
TimerFactoryBean
.
Using the TimerTask
you can create customer
timer tasks, similar to Quartz jobs:
public class CheckEmailAddresses extends TimerTask {
private List emailAddresses;
public void setEmailAddresses(List emailAddresses) {
this.emailAddresses = emailAddresses;
}
public void run() {
// iterate over all email addresses and archive them
}
}
Wiring it up is simple:
<bean id="checkEmail" class="examples.CheckEmailAddress"> <property name="emailAddresses"> <list> <value>test@springframework.org</value> <value>foo@bar.com</value> <value>john@doe.net</value> </list> </property> </bean> <bean id="scheduledTask" class="org.springframework.scheduling.timer.ScheduledTimerTask"> <!-- wait 10 seconds before starting repeated execution --> <property name="delay" value="10000" /> <!-- run every 50 seconds --> <property name="period" value="50000" /> <property name="timerTask" ref="checkEmail" /> </bean>
Note that letting the task only run once can be done by changing the
period
property to 0 (or a negative value).
Similar to the Quartz support, the Timer
support also features
a component that allows you to periodically invoke a method:
<bean id="doIt" class="org.springframework.scheduling.timer.MethodInvokingTimerTaskFactoryBean"> <property name="targetObject" ref="exampleBusinessObject" /> <property name="targetMethod" value="doIt" /> </bean>
The above example will result in the doIt
method being called on the
exampleBusinessObject
(see below):
public class BusinessObject { // properties and collaborators public void doIt() { // do the actual work } }
Changing the timerTask
reference of the
ScheduledTimerTask
example to the bean doIt
will result in the doIt
method being executed on a fixed schedule.
The TimerFactoryBean
is similar to the Quartz
SchedulerFactoryBean
in that it serves the same
purpose: setting up the actual scheduling. The TimerFactoryBean
sets up an actual Timer
and schedules the tasks it has
references to. You can specify whether or not daemon threads should be used.
<bean id="timerFactory" class="org.springframework.scheduling.timer.TimerFactoryBean">
<property name="scheduledTimerTasks">
<list>
<!-- see the example above -->
<ref bean="scheduledTask" />
</list>
</property>
</bean>
Spring 2.0 introduces a new abstraction for dealing with executors. Executors are the Java 5 name for the concept of thread pools. The "executor" naming is due to the fact that there is no guarantee that the underlying implementation is actually a pool; an executor may be single-threaded or even synchronous. Spring's abstraction hides implementation details between Java SE 1.4, Java SE 5 and Java EE environments.
Spring's TaskExecutor
interface is
identical to the java.util.concurrent.Executor
interface. In fact, its primary reason for existence is to abstract away
the need for Java 5 when using thread pools. The interface has a single
method execute(Runnable task)
that accepts a task
for execution based on the semantics and configuration of the thread pool.
The TaskExecutor
was originally
created to give other Spring components an abstraction for thread pooling where
needed. Components such as the ApplicationEventMulticaster
,
JMS's AbstractMessageListenerContainer
,
and Quartz integration all use the TaskExecutor
abstraction to pool threads. However, if your beans need thread pooling behavior,
it is possible to use this abstraction for your own needs.
There are a number of pre-built implementations of
TaskExecutor
included with the
Spring distribution. In all likelihood, you shouldn't ever
need to implement your own.
SimpleAsyncTaskExecutor
This implementation does not reuse any threads, rather it starts up a new thread for each invocation. However, it does support a concurrency limit which will block any invocations that are over the limit until a slot has been freed up. If you're looking for true pooling, keep scrolling further down the page.
This implementation doesn't execute invocations asynchronously. Instead, each invocation takes place in the calling thread. It is primarily used in situations where mutlithreading isn't necessary such as simple test cases.
This implementation is a wrapper for a Java 5
java.util.concurrent.Executor
.
There is an alternative,
ThreadPoolTaskExecutor
,
that exposes the Executor
configuration parameters as bean properties. It
is rare to need to use the ConcurrentTaskExecutor
but if the
ThreadPoolTaskExecutor
isn't robust enough for your needs, the
ConcurrentTaskExecutor
is an alternative.
This implementation is actually a subclass of
Quartz's SimpleThreadPool
which listens to Spring's lifecycle callbacks.
This is typically used when you have a
threadpool that may need to be shared by both
Quartz and non-Quartz components.
This implementation can only be used in a Java 5
environment but is also the most commonly used
one in that environment. It exposes bean properties for
configuring a
java.util.concurrent.ThreadPoolExecutor
and wraps it in a TaskExecutor
.
If you need something advanced such as a
ScheduledThreadPoolExecutor
,
it is recommended that you use a
ConcurrentTaskExecutor
instead.
TimerTaskExecutor
This implementation uses a single
TimerTask
as its backing implementation. It's different
from the
SyncTaskExecutor
in that the method invocations are executed in a
separate thread, although they are synchronous
in that thread.
WorkManagerTaskExecutor
This implementation uses the CommonJ WorkManager
as its backing implementation and is the central
convenience class for setting up a CommonJ
WorkManager reference in a Spring context.
Similar to the
SimpleThreadPoolTaskExecutor
,
this class implements the WorkManager
interface and therefore can be used directly as
a WorkManager as well.
Spring's TaskExecutor
implementations
are used as simple JavaBeans. In the example below, we define
a bean that uses the ThreadPoolTaskExecutor
to asynchronously print out a set of messages.
import org.springframework.core.task.TaskExecutor; public class TaskExecutorExample { private class MessagePrinterTask implements Runnable { private String message; public MessagePrinterTask(String message) { this.message = message; } public void run() { System.out.println(message); } } private TaskExecutor taskExecutor; public TaskExecutorExample(TaskExecutor taskExecutor) { this.taskExecutor = taskExecutor; } public void printMessages() { for(int i = 0; i < 25; i++) { taskExecutor.execute(new MessagePrinterTask("Message" + i)); } } }
As you can see, rather than retrieving a thread from the
pool and executing yourself, you add your Runnable
to the queue and the TaskExecutor
uses it's internal rules to decide when the task gets executed.
To configure the rules that the TaskExecutor
will use, simple bean properties have been exposed.
<bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor"> <property name="corePoolSize" value="5" /> <property name="maxPoolSize" value="10" /> <property name="queueCapacity" value="25" /> </bean> <bean id="taskExecutorExample" class="TaskExecutorExample"> <constructor-arg ref="taskExecutor" /> </bean>
Spring 2.0 introduces comprehensive support for using classes and objects that have been defined using a dynamic language (such as JRuby) with Spring. This support allows you to write any number of classes in a supported dynamic language, and have the Spring container transparently instantiate, configure and dependency inject the resulting objects.
The dynamic languages currently supported are:
JRuby 0.9 / 1.0
Groovy 1.0 / 1.5
BeanShell 2.0
Fully working examples of where this dynamic language support can be immediately useful are described in the section entitled Section 24.4, “Scenarios”.
Note: Only the specific versions as listed above are supported in Spring 2.5. In particular, JRuby 1.1 (which introduced many incompatible API changes) is not supported at this point of time.
This bulk of this chapter is concerned with describing the dynamic language support in detail. Before diving into all of the ins and outs of the dynamic language support, let's look at a quick example of a bean defined in a dynamic language. The dynamic language for this first bean is Groovy (the basis of this example was taken from the Spring test suite, so if you want to see equivalent examples in any of the other supported languages, take a look at the source code).
Find below the Messenger
interface that the
Groovy bean is going to be implementing, and note that this interface is defined
in plain Java. Dependent objects that are injected with a reference to the
Messenger
won't know that the underlying
implementation is a Groovy script.
package org.springframework.scripting; public interface Messenger { String getMessage(); }
Here is the definition of a class that has a dependency on the
Messenger
interface.
package org.springframework.scripting; public class DefaultBookingService implements BookingService { private Messenger messenger; public void setMessenger(Messenger messenger) { this.messenger = messenger; } public void processBooking() { // use the injected Messenger object... } }
Here is an implementation of the Messenger
interface
in Groovy.
// from the file 'Messenger.groovy' package org.springframework.scripting.groovy; // import the Messenger interface (written in Java) that is to be implemented import org.springframework.scripting.Messenger // define the implementation in Groovy class GroovyMessenger implements Messenger { String message }
Finally, here are the bean definitions that will effect the injection of the
Groovy-defined Messenger
implementation into
an instance of the DefaultBookingService
class.
![]() | Note |
---|---|
To use the custom dynamic language tags to define dynamic-language-backed beans,
you need to have the XML Schema preamble at the top of your Spring XML
configuration file. You also need to be using a Spring
For more information on schema-based configuration, see Appendix A, XML Schema-based configuration. |
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:lang="http://www.springframework.org/schema/lang" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang-2.5.xsd"> <!-- this is the bean definition for the Groovy-backedMessenger
implementation --> <lang:groovy id="messenger" script-source="classpath:Messenger.groovy"> <lang:property name="message" value="I Can Do The Frug" /> </lang:groovy> <!-- an otherwise normal bean that will be injected by the Groovy-backedMessenger
--> <bean id="bookingService" class="x.y.DefaultBookingService"> <property name="messenger" ref="messenger" /> </bean> </beans>
The bookingService
bean (a
DefaultBookingService
) can now use its private
messenger
member variable as normal because the
Messenger
instance that was injected
into it is a Messenger
instance. There is nothing special going on here, just plain Java and
plain Groovy.
Hopefully the above XML snippet is self-explanatory, but don't worry unduly if it isn't. Keep reading for the in-depth detail on the whys and wherefores of the above configuration.
This section describes exactly how you define Spring managed beans in any of the supported dynamic languages.
Please note that this chapter does not attempt to explain the syntax and idioms of the supported dynamic languages. For example, if you want to use Groovy to write certain of the classes in your application, then the assumption is that you already know Groovy. If you need further details about the dynamic languages themselves, please consult the section entitled Section 24.6, “Further Resources” at the end of this chapter.
The steps involved in using dynamic-language-backed beans are as follows:
Write the test for the dynamic language source code (naturally)
Then write the dynamic language source code itself :)
Define your dynamic-language-backed beans using the appropriate
<lang:language/>
element in the XML
configuration (you can of course define such beans programmatically
using the Spring API - although you will have to consult the source
code for directions on how to do this as this type of advanced
configuration is not covered in this chapter). Note this is an iterative
step. You will need at least one bean definition per dynamic
language source file (although the same dynamic language source
file can of course be referenced by multiple bean definitions).
The first two steps (testing and writing your dynamic language source files) are beyond the scope of this chapter. Refer to the language specification and / or reference manual for your chosen dynamic language and crack on with developing your dynamic language source files. You will first want to read the rest of this chapter though, as Spring's dynamic language support does make some (small) assumptions about the contents of your dynamic language source files.
The final step involves defining dynamic-language-backed bean definitions,
one for each bean that you want to configure (this is no different to
normal Java bean configuration). However, instead of specifying the
fully qualified classname of the class that is to be instantiated and
configured by the container, you use the <lang:language/>
element to define the dynamic language-backed bean.
Each of the supported languages has a corresponding
<lang:language/>
element:
<lang:jruby/>
(JRuby)
<lang:groovy/>
(Groovy)
<lang:bsh/>
(BeanShell)
The exact attributes and child elements that are available for configuration depends on exactly which language the bean has been defined in (the language-specific sections below provide the full lowdown on this).
One of the (if not the) most compelling value adds of the dynamic language support in Spring is the 'refreshable bean' feature.
A refreshable bean is a dynamic-language-backed bean that with a small amount of configuration, a dynamic-language-backed bean can monitor changes in its underlying source file resource, and then reload itself when the dynamic language source file is changed (for example when a developer edits and saves changes to the file on the filesystem).
This allows a developer to deploy any number of dynamic language source files as part of an application, configure the Spring container to create beans backed by dynamic language source files (using the mechanisms described in this chapter), and then later, as requirements change or some other external factor comes into play, simply edit a dynamic language source file and have any change they make reflected in the bean that is backed by the changed dynamic language source file. There is no need to shut down a running application (or redeploy in the case of a web application). The dynamic-language-backed bean so amended will pick up the new state and logic from the changed dynamic language source file.
![]() | Note |
---|---|
Please note that this feature is off by default. |
Let's take a look at an example to see just how easy it is to start using
refreshable beans. To turn on the refreshable beans
feature, you simply have to specify exactly one
additional attribute on the <lang:language/>
element
of your bean definition. So if we stick with
the example from earlier
in this chapter, here's what we would change in the Spring XML configuration
to effect refreshable beans:
<beans> <!-- this bean is now 'refreshable' due to the presence of the 'refresh-check-delay' attribute --> <lang:groovy id="messenger" refresh-check-delay="5000" <!-- switches refreshing on with 5 seconds between checks --> script-source="classpath:Messenger.groovy"> <lang:property name="message" value="I Can Do The Frug" /> </lang:groovy> <bean id="bookingService" class="x.y.DefaultBookingService"> <property name="messenger" ref="messenger" /> </bean> </beans>
That really is all you have to do. The 'refresh-check-delay'
attribute defined on the 'messenger'
bean definition
is the number of milliseconds after which the bean will be refreshed with
any changes made to the underlying dynamic language source file.
You can turn off the refresh behavior by assigning a negative value
to the 'refresh-check-delay'
attribute.
Remember that, by default, the refresh behavior is disabled. If you don't
want the refresh behavior, then simply don't define the attribute.
If we then run the following application we can exercise the refreshable feature;
please do excuse the 'jumping-through-hoops-to-pause-the-execution'
shenanigans in this next slice of code. The System.in.read()
call is only there so that the execution of the program pauses while I (the author)
go off and edit the underlying dynamic language source file so that the refresh will
trigger on the dynamic-language-backed bean when the program resumes execution.
import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import org.springframework.scripting.Messenger; public final class Boot { public static void main(final String[] args) throws Exception { ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml"); Messenger messenger = (Messenger) ctx.getBean("messenger"); System.out.println(messenger.getMessage()); // pause execution while I go off and make changes to the source file... System.in.read(); System.out.println(messenger.getMessage()); } }
Let's assume then, for the purposes of this example, that all
calls to the getMessage()
method of
Messenger
implementations have to be
changed such that the message is surrounded by quotes.
Below are the changes that I (the author) make to the
Messenger.groovy
source file when the execution of
the program is paused.
package org.springframework.scripting class GroovyMessenger implements Messenger { private String message = "Bingo" public String getMessage() { // change the implementation to surround the message in quotes return "'" + this.message + "'" } public void setMessage(String message) { this.message = message } }
When the program executes, the output before the input pause will be
I Can Do The Frug
. After the change
to the source file is made and saved, and the program resumes execution,
the result of calling the getMessage()
method on the
dynamic-language-backed Messenger
implementation
will be 'I Can Do The Frug'
(notice
the inclusion of the additional quotes).
It is important to understand that changes to a script will
not trigger a refresh if the changes occur
within the window of the 'refresh-check-delay'
value.
It is equally important to understand that changes to the script are
not actually 'picked up' until a method is called
on the dynamic-language-backed bean. It is only when a method is called on a
dynamic-language-backed bean that it checks to see if its underlying script
source has changed. Any exceptions relating to refreshing the script
(such as encountering a compilation error, or finding that the script
file has been deleted) will result in a fatal
exception being propagated to the calling code.
The refreshable bean behavior described above does
not apply to dynamic language source files
defined using the <lang:inline-script/>
element
notation (see the section entitled Section 24.3.1.3, “Inline dynamic language source files”).
Additionally, it only applies to beans where
changes to the underlying source file can actually be detected;
for example, by code that checks the last modified date of a
dynamic language source file that exists on the filesystem.
The dynamic language support can also cater for dynamic language
source files that are embedded directly in Spring bean definitions.
More specifically, the <lang:inline-script/>
element allows you to define dynamic language source immediately
inside a Spring configuration file. An example will perhaps make the
inline script feature crystal clear:
<lang:groovy id="messenger"> <lang:inline-script> package org.springframework.scripting.groovy; import org.springframework.scripting.Messenger class GroovyMessenger implements Messenger { String message } </lang:inline-script> <lang:property name="message" value="I Can Do The Frug" /> </lang:groovy>
If we put to one side the issues surrounding whether it is good practice
to define dynamic language source inside a Spring configuration file, the
<lang:inline-script/>
element can be useful in
some scenarios. For instance, we might want to quickly add a Spring
Validator
implementation to a Spring MVC
Controller
. This is but a moment's work
using inline source. (See the section entitled
Section 24.4.2, “Scripted Validators” for such an example.)
Find below an example of defining the source for a JRuby-based bean
directly in a Spring XML configuration file using the
inline:
notation. (Notice the use of the <
characters to denote a '<'
character. In such a case
surrounding the inline source in a <![CDATA[]]>
region might be better.)
<lang:jruby id="messenger" script-interfaces="org.springframework.scripting.Messenger"> <lang:inline-script> require 'java' include_class 'org.springframework.scripting.Messenger' class RubyMessenger < Messenger def setMessage(message) @@message = message end def getMessage @@message end end </lang:inline-script> <lang:property name="message" value="Hello World!" /> </lang:jruby>
There is one very important thing to be aware of with regard to Spring's dynamic language support. Namely, it is not (currently) possible to supply constructor arguments to dynamic-language-backed beans (and hence constructor-injection is not available for dynamic-language-backed beans). In the interests of making this special handling of constructors and properties 100% clear, the following mixture of code and configuration will not work.
// from the file 'Messenger.groovy' package org.springframework.scripting.groovy; import org.springframework.scripting.Messenger class GroovyMessenger implements Messenger { GroovyMessenger() {} // this constructor is not available for Constructor Injection GroovyMessenger(String message) { this.message = message; } String message String anotherMessage }
<lang:groovy id="badMessenger"
script-source="classpath:Messenger.groovy">
<!-- this next constructor argument will *not* be injected into the GroovyMessenger
-->
<!-- in fact, this isn't even allowed according to the schema -->
<constructor-arg value="This will *not* work" />
<!-- only property values are injected into the dynamic-language-backed object -->
<lang:property name="anotherMessage" value="Passed straight through to the dynamic-language-backed object" />
</lang>
In practice this limitation is not as significant as it first appears since setter injection is the injection style favored by the overwhelming majority of developers anyway (let's leave the discussion as to whether that is a good thing to another day).
From the JRuby homepage...
“ JRuby is an 100% pure-Java implementation of the Ruby programming language. ”In keeping with the Spring philosophy of offering choice, Spring's dynamic language support also supports beans defined in the JRuby language. The JRuby language is based on the quite intuitive Ruby language, and has support for inline regular expressions, blocks (closures), and a whole host of other features that do make solutions for some domain problems a whole lot easier to develop.
The implementation of the JRuby dynamic language support in Spring is
interesting in that what happens is this: Spring creates a JDK dynamic
proxy implementing all of the interfaces that are specified in the
'script-interfaces'
attribute value of the
<lang:ruby>
element (this is why
you must supply at least one interface in the value
of the attribute, and (accordingly) program to interfaces when using
JRuby-backed beans).
Let us look at a fully working example of using a JRuby-based bean. Here is
the JRuby implementation of the Messenger
interface that was defined earlier in this chapter (for your convenience it
is repeated below).
package org.springframework.scripting; public interface Messenger { String getMessage(); }
require 'java' class RubyMessenger include org.springframework.scripting.Messenger def setMessage(message) @@message = message end def getMessage @@message end end # this last line is not essential (but see below) RubyMessenger.new
And here is the Spring XML that defines an instance of the
RubyMessenger
JRuby bean.
<lang:jruby id="messageService" script-interfaces="org.springframework.scripting.Messenger" script-source="classpath:RubyMessenger.rb"> <lang:property name="message" value="Hello World!" /> </lang:jruby>
Take note of the last line of that JRuby source ('RubyMessenger.new'
).
When using JRuby in the context of Spring's dynamic language support, you are encouraged
to instantiate and return a new instance of the JRuby class that you want to use as a
dynamic-language-backed bean as the result of the execution of your JRuby source. You
can achieve this by simply instantiating a new instance of your JRuby class on the last
line of the source file like so:
require 'java' include_class 'org.springframework.scripting.Messenger' # class definition same as above... # instantiate and return a new instance of the RubyMessenger class RubyMessenger.new
If you forget to do this, it is not the end of the world; this will however result in
Spring having to trawl (reflectively) through the type representation of your JRuby class
looking for a class to instantiate. In the grand scheme of things this will be so fast
that you'll never notice it, but it is something that can be avoided by simply
having a line such as the one above as the last line of your JRuby script. If you don't
supply such a line, or if Spring cannot find a JRuby class in your script to instantiate
then an opaque ScriptCompilationException
will be thrown immediately after the source is executed by the JRuby
interpreter. The key text that identifies this as the root cause of an
exception can be found immediately below (so if your Spring container
throws the following exception when creating your dynamic-language-backed bean
and the following text is there in the corresponding stacktrace, this will hopefully
allow you to identify and then easily rectify the issue):
org.springframework.scripting.ScriptCompilationException: Compilation of JRuby script returned ''
To rectify this, simply instantiate a new instance of whichever class you want to expose as a JRuby-dynamic-language-backed bean (as shown above). Please also note that you can actually define as many classes and objects as you want in your JRuby script; what is important is that the source file as a whole must return an object (for Spring to configure).
See the section entitled Section 24.4, “Scenarios” for some scenarios where you might want to use JRuby-based beans.
From the Groovy homepage...
“ Groovy is an agile dynamic language for the Java 2 Platform that has many of the features that people like so much in languages like Python, Ruby and Smalltalk, making them available to Java developers using a Java-like syntax. ”If you have read this chapter straight from the top, you will already have seen an example of a Groovy-dynamic-language-backed bean. Let's look at another example (again using an example from the Spring test suite).
package org.springframework.scripting; public interface Calculator { int add(int x, int y); }
Here is an implementation of the Calculator
interface in Groovy.
// from the file 'calculator.groovy'
package org.springframework.scripting.groovy
class GroovyCalculator implements Calculator {
int add(int x, int y) {
x + y
}
}
<-- from the file 'beans.xml' -->
<beans>
<lang:groovy id="calculator" script-source="classpath:calculator.groovy"/>
</beans>
Lastly, here is a small application to exercise the above configuration.
package org.springframework.scripting; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Main { public static void Main(String[] args) { ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml"); Calculator calc = (Calculator) ctx.getBean("calculator"); System.out.println(calc.add(2, 8)); } }
The resulting output from running the above program will be
(unsurprisingly) 10
.
(Exciting example, huh? Remember that the intent is to illustrate the
concept. Please consult the dynamic language showcase project for a
more complex example, or indeed the section entitled
Section 24.4, “Scenarios” later in this chapter).
It is important that you do not define more than one class per Groovy source file. While this is perfectly legal in Groovy, it is (arguably) a bad practice: in the interests of a consistent approach, you should (in the opinion of this author) respect the standard Java conventions of one (public) class per source file.
The GroovyObjectCustomizer
interface is a callback that allows you to hook additional
creation logic into the process of creating a Groovy-backed bean.
For example, implementations of this interface could invoke
any required initialization method(s), or set some default property
values, or specify a custom MetaClass
.
public interface GroovyObjectCustomizer { void customize(GroovyObject goo); }
The Spring Framework will instantiate an instance of your Groovy-backed
bean, and will then pass the created GroovyObject
to the specified GroovyObjectCustomizer
if one has been defined. You can do whatever you like with the supplied
GroovyObject
reference: it is expected
that the setting of a custom MetaClass
is what most
folks will want to do with this callback, and you can see an example
of doing that below.
public final class SimpleMethodTracingCustomizer implements GroovyObjectCustomizer { public void customize(GroovyObject goo) { DelegatingMetaClass metaClass = new DelegatingMetaClass(goo.getMetaClass()) { public Object invokeMethod(Object object, String methodName, Object[] arguments) { System.out.println("Invoking '" + methodName + "'."); return super.invokeMethod(object, methodName, arguments); } }; metaClass.initialize(); goo.setMetaClass(metaClass); } }
A full discussion of meta-programming in Groovy is beyond the scope of the
Spring reference manual. Consult the relevant section of the Groovy
reference manual, or do a search online: there are plenty of articles
concerning this topic.
Actually making use of a GroovyObjectCustomizer
is easy if you are using the Spring 2.0 namespace support.
<!-- define theGroovyObjectCustomizer
just like any other bean --> <bean id="tracingCustomizer" class="example.SimpleMethodTracingCustomizer" /> <!-- ... and plug it into the desired Groovy bean via the 'customizer-ref
' attribute --> <lang:groovy id="calculator" script-source="classpath:org/springframework/scripting/groovy/Calculator.groovy" customizer-ref="tracingCustomizer" />
If you are not using the Spring 2.0 namespace support, you can still
use the GroovyObjectCustomizer
functionality.
<bean id="calculator" class="org.springframework.scripting.groovy.GroovyScriptFactory">
<constructor-arg value="classpath:org/springframework/scripting/groovy/Calculator.groovy"/>
<!-- define the GroovyObjectCustomizer
(as an inner bean) -->
<constructor-arg>
<bean id="tracingCustomizer" class="example.SimpleMethodTracingCustomizer" />
</constructor-arg>
</bean>
<bean class="org.springframework.scripting.support.ScriptFactoryPostProcessor"/>
From the BeanShell homepage...
“ BeanShell is a small, free, embeddable Java source interpreter with dynamic language features, written in Java. BeanShell dynamically executes standard Java syntax and extends it with common scripting conveniences such as loose types, commands, and method closures like those in Perl and JavaScript. ”
In contrast to Groovy, BeanShell-backed bean definitions require some (small)
additional configuration. The implementation of the BeanShell dynamic language
support in Spring is interesting in that what happens is this: Spring creates
a JDK dynamic proxy implementing all of the interfaces that are specified in the
'script-interfaces'
attribute value of the
<lang:bsh>
element (this is why
you must supply at least one interface in the value
of the attribute, and (accordingly) program to interfaces when using
BeanShell-backed beans). This means that every method call on a BeanShell-backed
object is going through the JDK dynamic proxy invocation mechanism.
Let's look at a fully working example of using a BeanShell-based bean
that implements the Messenger
interface
that was defined earlier in this chapter (repeated below for your
convenience).
package org.springframework.scripting; public interface Messenger { String getMessage(); }
Here is the BeanShell 'implementation' (the term is used loosely here) of the
Messenger
interface.
String message; String getMessage() { return message; } void setMessage(String aMessage) { message = aMessage; }
And here is the Spring XML that defines an 'instance' of the above 'class' (again, the term is used very loosely here).
<lang:bsh id="messageService" script-source="classpath:BshMessenger.bsh" script-interfaces="org.springframework.scripting.Messenger"> <lang:property name="message" value="Hello World!" /> </lang:bsh>
See the section entitled Section 24.4, “Scenarios” for some scenarios where you might want to use BeanShell-based beans.
The possible scenarios where defining Spring managed beans in a scripting language would be beneficial are, of course, many and varied. This section describes two possible use cases for the dynamic language support in Spring.
One group of classes that may benefit from using dynamic-language-backed beans is that of Spring MVC controllers. In pure Spring MVC applications, the navigational flow through a web application is to a large extent determined by code encapsulated within your Spring MVC controllers. As the navigational flow and other presentation layer logic of a web application needs to be updated to respond to support issues or changing business requirements, it may well be easier to effect any such required changes by editing one or more dynamic language source files and seeing those changes being immediately reflected in the state of a running application.
Remember that in the lightweight architectural model espoused by projects such as Spring, you are typically aiming to have a really thin presentation layer, with all the meaty business logic of an application being contained in the domain and service layer classes. Developing Spring MVC controllers as dynamic-language-backed beans allows you to change presentation layer logic by simply editing and saving text files; any changes to such dynamic language source files will (depending on the configuration) automatically be reflected in the beans that are backed by dynamic language source files.
![]() | Note |
---|---|
In order to effect this automatic 'pickup' of any changes to dynamic-language-backed beans, you will have had to enable the 'refreshable beans' functionality. See the section entitle Section 24.3.1.2, “Refreshable beans” for a full treatment of this feature. |
Find below an example of an
org.springframework.web.servlet.mvc.Controller
implemented using the Groovy dynamic language.
// from the file '/WEB-INF/groovy/FortuneController.groovy' package org.springframework.showcase.fortune.web import org.springframework.showcase.fortune.service.FortuneService import org.springframework.showcase.fortune.domain.Fortune import org.springframework.web.servlet.ModelAndView import org.springframework.web.servlet.mvc.Controller import javax.servlet.http.HttpServletRequest import javax.servlet.http.HttpServletResponse class FortuneController implements Controller { @Property FortuneService fortuneService ModelAndView handleRequest( HttpServletRequest request, HttpServletResponse httpServletResponse) { return new ModelAndView("tell", "fortune", this.fortuneService.tellFortune()) } }
<lang:groovy id="fortune" refresh-check-delay="3000" script-source="/WEB-INF/groovy/FortuneController.groovy"> <lang:property name="fortuneService" ref="fortuneService"/> </lang:groovy>
Another area of application development with Spring that may benefit from the flexibility afforded by dynamic-language-backed beans is that of validation. It may be easier to express complex validation logic using a loosely typed dynamic language (that may also have support for inline regular expressions) as opposed to regular Java.
Again, developing validators as dynamic-language-backed beans allows you to change validation logic by simply editing and saving a simple text file; any such changes will (depending on the configuration) automatically be reflected in the execution of a running application and would not require the restart of an application.
![]() | Note |
---|---|
Please note that in order to effect the automatic 'pickup' of any changes to dynamic-language-backed beans, you will have had to enable the 'refreshable beans' feature. See the section entitled Section 24.3.1.2, “Refreshable beans” for a full and detailed treatment of this feature. |
Find below an example of a Spring
org.springframework.validation.Validator
implemented using the Groovy dynamic language. (See the section entitled
Section 5.2, “Validation using Spring's Validator
interface” for a discussion of the
Validator
interface.)
import org.springframework.validation.Validator import org.springframework.validation.Errors import org.springframework.beans.TestBean class TestBeanValidator implements Validator { boolean supports(Class clazz) { return TestBean.class.isAssignableFrom(clazz) } void validate(Object bean, Errors errors) { if(bean.name?.trim()?.size() > 0) { return } errors.reject("whitespace", "Cannot be composed wholly of whitespace.") } }
This last section contains some bits and bobs related to the dynamic language support.
It is possible to use the Spring AOP framework to advise scripted beans. The Spring AOP framework actually is unaware that a bean that is being advised might be a scripted bean, so all of the AOP use cases and functionality that you may be using or aim to use will work with scripted beans. There is just one (small) thing that you need to be aware of when advising scripted beans... you cannot use class-based proxies, you must use interface-based proxies.
You are of course not just limited to advising scripted beans... you can also write aspects themselves in a supported dynamic language and use such beans to advise other Spring beans. This really would be an advanced use of the dynamic language support though.
In case it is not immediately obvious, scripted beans can of course be scoped
just like any other bean. The scope
attribute on the
various <lang:language/>
elements allows you to
control the scope of the underlying scripted bean, just as it does with a
regular bean. (The default scope is
singleton, just as it
is with 'regular' beans.)
Find below an example of using the scope
attribute
to define a Groovy bean scoped as a
prototype.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:lang="http://www.springframework.org/schema/lang"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang-2.5.xsd">
<lang:groovy id="messenger" script-source="classpath:Messenger.groovy" scope="prototype">
<lang:property name="message" value="I Can Do The RoboCop" />
</lang:groovy>
<bean id="bookingService" class="x.y.DefaultBookingService">
<property name="messenger" ref="messenger" />
</bean>
</beans>
See the section entitled Section 3.4, “Bean scopes” in Chapter 3, The IoC container for a fuller discussion of the scoping support in the Spring Framework.
Find below links to further resources about the various dynamic languages described in this chapter.
Some of the more active members of the Spring community have also added support for a number of additional dynamic languages above and beyond the ones covered in this chapter. While it is possible that such third party contributions may be added to the list of languages supported by the main Spring distribution, your best bet for seeing if your favourite scripting language is supported is the Spring Modules project.
Source-level metadata is the addition of attributes or annotations to program elements - usually, classes and/or methods.
For example, we might add metadata to a class as follows:
/** * Normal comments here * @@org.springframework.transaction.interceptor.DefaultTransactionAttribute() */ public class PetStoreImpl implements PetStoreFacade, OrderService {
We could add metadata to a method as follows:
/** * Normal comments here * @@org.springframework.transaction.interceptor.RuleBasedTransactionAttribute() * @@org.springframework.transaction.interceptor.RollbackRuleAttribute(Exception.class) * @@org.springframework.transaction.interceptor.NoRollbackRuleAttribute("ServletException") */ public void echoException(Exception ex) throws Exception { .... }
Both of these examples use Jakarta Commons Attributes syntax.
Source-level metadata was introduced to the mainstream by XDoclet (in the Java world) and by the release of Microsoft's .NET platform, which uses source-level attributes to control transactions, pooling and other behavior.
The value in this approach has been recognized in the J2EE community. For example, it's much less verbose than the traditional XML deployment descriptors used exclusively by EJB. While it is desirable to externalize some things from program source code, some important enterprise settings - notably transaction characteristics - arguably belong in program source. Contrary to the assumptions of the EJB spec, it seldom makes sense to modify the transactional characteristics of a method (although parameters like transaction timeouts might change!).
Although metadata attributes are typically used mainly by framework infrastructure to describe the services application classes require, it should also be possible for metadata attributes to be queried at runtime. This is a key distinction from solutions such as XDoclet, which view metadata primarily as a way of generating code such as EJB artefacts.
There are a number of solutions in this space, including:
Standard Java Annotations: the standard Java metadata implementation (developed as JSR-175 and available in Java 5). Spring has specific Java 5 annotations for transactional demarcation, JMX, and aspects (to be precise they are AspectJ annotations). However, since Spring supports Java 1.4 as well, a solution for said JVM versions is needed too. Spring metadata support provides such a solution.
XDoclet: well-established solution, primarily intended for code generation.
Various open source attribute implementations, for Java 1.4, of which Commons Attributes is the most complete implementation. All these require a special pre- or post-compilation step.
In keeping with its provision of abstractions over important
concepts, Spring provides a facade to metadata implementations, in the
form of the org.springframework.metadata.Attributes
interface. Such a facade adds value for several reasons:
Even though Java 5 provides metadata support at language level, there will still be value in providing such an abstraction:
Java 5 metadata is static. It is associated with a class at compile time, and cannot be changed in a deployed environment (annotation state can actually be changed at runtime using reflection, but doing so would really be a bad practice). There is a need for hierarchical metadata, providing the ability to override certain attribute values in deployment - for example, in an XML file.
Java 5 metadata is returned through the Java reflection API. This makes it impossible to mock during test time. Spring provides a simple interface to allow this.
There will be a need for metadata support in 1.3 and 1.4 applications for at least two years. Spring aims to provide working solutions now; forcing the use of Java 5 is not an option in such an important area.
Current metadata APIs, such as Commons Attributes (used by Spring 1.0-1.2) are hard to test. Spring provides a simple metadata interface that is much easier to mock.
The Spring Attributes
interface looks like this:
public interface Attributes { Collection getAttributes(Class targetClass); Collection getAttributes(Class targetClass, Class filter); Collection getAttributes(Method targetMethod); Collection getAttributes(Method targetMethod, Class filter); Collection getAttributes(Field targetField); Collection getAttributes(Field targetField, Class filter); }
This is a lowest common denominator interface. JSR-175 offers more capabilities than this, such as attributes on method arguments.
Note that this interface offers Object
attributes, like .NET. This distinguishes it from attribute systems such
as that of Nanning Aspects, which offer only String
attributes. There is a significant advantage in supporting
Object
attributes, namely that it enables
attributes to participate in class hierarchies and allows such
attributes to react intelligently to their configuration parameters.
With most attribute providers, attribute classes are configured via constructor arguments or JavaBean properties. Commons Attributes supports both.
As with all Spring abstraction APIs, Attributes
is an interface. This makes it easy to mock attribute implementations for unit tests.
The Spring Framework ships with a number of custom Java 5+ annotations.
The @Required
annotation in the
org.springframework.beans.factory.annotation
package can be used to mark a property as
being 'required-to-be-set' (i.e. an
annotated (setter) method of a class must be configured to be
dependency injected with a value), else an
Exception
will be thrown by the container
at runtime.
The best way to illustrate the usage of this annotation is to show an example:
public class SimpleMovieLister { // theSimpleMovieLister
has a dependency on theMovieFinder
private MovieFinder movieFinder; // a setter method so that the Spring container can 'inject' aMovieFinder
@Required public void setMovieFinder(MovieFinder movieFinder) { this.movieFinder = movieFinder; } // business logic that actually 'uses' the injectedMovieFinder
is omitted... }
Hopefully the above class definition reads easy on the eye.
Any and all BeanDefinitions
for the
SimpleMovieLister
class must be provided
with a value.
Let's look at an example of some XML configuration that will not pass validation.
<bean id="movieLister" class="x.y.SimpleMovieLister">
<!-- whoops, no MovieFinder is set (and this property is @Required
) -->
</bean>
At runtime the following message will be generated by the Spring container (the rest of the stack trace has been truncated).
Exception in thread "main" java.lang.IllegalArgumentException: Property 'movieFinder' is required for bean 'movieLister'.
There is one last little (small, tiny) piece of Spring configuration
that is required to actually 'switch on' this
behavior. Simply annotating the 'setter' properties
of your classes is not enough to get this behavior. You need
to enable a component that is aware of the @Required
annotation and that can process it appropriately.
This component is the RequiredAnnotationBeanPostProcessor
class.
This is a special BeanPostProcessor
implementation that is @Required
-aware
and actually provides the 'blow up if this required property
has not been set' logic. It is very easy
to configure; simply drop the following bean definition into your Spring
XML configuration.
<bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor"/>
Finally, one can configure an instance of the
RequiredAnnotationBeanPostProcessor
class to look
for another Annotation
type.
This is great if you already have your own
@Required
-style annotation. Simply plug it into
the definition of a RequiredAnnotationBeanPostProcessor
and
you are good to go.
By way of an example, let's suppose you (or your organization / team) have
defined an attribute called @ Mandatory
.
You can make a RequiredAnnotationBeanPostProcessor
instance @Mandatory
-aware like so:
<bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor"> <property name="requiredAnnotationType" value="your.company.package.Mandatory"/> </bean>
Here is the source code for the @Mandatory
annotation. You will need to ensure that your custom annotation type
is itself annotated with appropriate annotations for it's target
and runtime retention policy.
package your.company.package; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD) public @interface Mandatory { }
Annotations are also used in a number of other places throughout Spring. Rather than being described here, these annotations are described in that section or chapter of the reference documentation to which they are most relevant.
Presently Spring supports only Jakarta Commons Attributes out of the
box, although it is easy to provide implementations of the
org.springframework.metadata.Attributes
interface for
other metadata providers.
Commons Attributes 2.2 (http://jakarta.apache.org/commons/attributes/) is a capable attributes solution. It supports attribute configuration via constructor arguments and JavaBean properties, which offers better self-documentation in attribute definitions. (Support for JavaBean properties was added at the request of the Spring team.)
We've already seen two examples of Commons Attributes attributes definitions. In general, we will need to express:
The name of the attribute class. This can be a fully qualified name (FQN), as shown above. If the relevant attribute class has already been imported, the FQN isn't required. It's also possible to specify "attribute packages" in attribute compiler configuration.
Any necessary parameterization. This is done via constructor arguments or JavaBean properties.
Bean properties look as follows:
/** * @@MyAttribute(myBooleanJavaBeanProperty=true) */
It's possible to combine constructor arguments and JavaBean properties (as in Spring IoC).
Because, unlike Java 1.5 attributes, Commons Attributes is not integrated with the Java language, it is necessary to run a special attribute compilation step as part of the build process.
To run Commons Attributes as part of the build process, you will need to do the following:
1. Copy the necessary library jars to
$ANT_HOME/lib
. Four Jars are required, and all are
distributed with Spring:
the Commons Attributes compiler jar and API jar
xJavadoc.jar from XDoclet
commons-collections.jar from Jakarta Commons
2. Import the Commons Attributes ant tasks into your project build script, as follows:
<taskdef resource="org/apache/commons/attributes/anttasks.properties"/>
3. Next, define an attribute compilation task, which will use the
Commons Attributes attribute-compiler task to "compile" the attributes in
the source. This process results in the generation of additional sources,
to a location specified by the destdir
attribute. Here we show the use of
a temporary directory for storing the generated files:
<target name="compileAttributes"> <attribute-compiler destdir="${commons.attributes.tempdir}"> <fileset dir="${src.dir}" includes="**/*.java"/> </attribute-compiler> </target>
The compile target that runs javac over the sources should depend on this attribute compilation task, and must also compile the generated sources, which we output to our destination temporary directory. If there are syntax errors in your attribute definitions, they will normally be caught by the attribute compiler. However, if the attribute definitions are syntactically plausible, but specify invalid types or class names, the compilation of the generated attribute classes may fail. In this case, you can look at the generated classes to establish the cause of the problem.
Commons Attributes also provides Maven support. Please refer to Commons Attributes documentation for further information.
While this attribute compilation process may look complex, in fact it's a one-off cost. Once set up, attribute compilation is incremental, so it doesn't usually noticeably slow the build process. And once the compilation process is set up, you may find that use of attributes as described in this chapter can save you a lot of time in other areas.
If you require attribute indexing support (only currently required by Spring for attribute-targeted web controllers, discussed below), you will need an additional step, which must be performed on a jar file of your compiled classes. In this additional step, Commons Attributes will create an index of all the attributes defined on your sources, for efficient lookup at runtime. The step looks like this:
<attribute-indexer jarFile="myCompiledSources.jar"> <classpath refid="master-classpath"/> </attribute-indexer>
See the /attributes
directory of the Spring JPetStore sample
application for an example of this build process. You can take the build
script it contains and modify it for your own projects.
If your unit tests depend on attributes, try to express the dependency on the Spring Attributes abstraction, rather than Commons Attributes. Not only is this more portable - for example, your tests will still work if you switch to Java 1.5 attributes in future - it simplifies testing. Also, Commons Attributes is a static API, while Spring provides a metadata interface that you can easily mock.
The most important uses of metadata attributes are in conjunction with Spring AOP. This provides a .NET-like programming model, where declarative services are automatically provided to application objects that declare metadata attributes. Such metadata attributes can be supported out of the box by the framework, as in the case of declarative transaction management, or can be custom.
This builds on the Spring AOP autoproxy functionality. Configuration might look like this:
<bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/> <bean class="org.springframework.transaction.interceptor.TransactionAttributeSourceAdvisor"> <property name="transactionInterceptor" ref="txInterceptor" /> </bean> <bean id="txInterceptor" class="org.springframework.transaction.interceptor.TransactionInterceptor"> <property name="transactionManager" ref="transactionManager" /> <property name="transactionAttributeSource"> <bean class="org.springframework.transaction.interceptor.AttributesTransactionAttributeSource"> <property name="attributes" ref="attributes" /> </bean> </property> </bean> <bean id="attributes" class="org.springframework.metadata.commons.CommonsAttributes" />
The basic concepts here should be familiar from the discussion of autoproxying in the AOP chapter.
The most important bean definitions are the auto-proxy creator and the advisor. Note that the actual bean names are not important; what matters is their class.
The bean definition of class
org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator
will automatically advise ("auto-proxy") all bean instances in the
current factory based on matching advisor implementations. This class
knows nothing about attributes, but relies on advisors' pointcuts
matching. The pointcuts, however, do know about attributes.
Thus we simply need an AOP advisor that will provide declarative transaction management based on attributes.
It is possible to add arbitrary custom advisor implementations as well, and they will also be evaluated and applied automatically. (You can use advisors whose pointcuts match on criteria besides attributes in the same autoproxy configuration, if necessary.)
Finally, the attributes
bean is the Commons
Attributes Attributes implementation. Replace it with another
implementation of the
org.springframework.metadata.Attributes
interface to source attributes from a different source.
The most common use of source-level attributes is to provide declarative transaction management. Once the bean definitions shown above are in place, you can define any number of application objects requiring declarative transactions. Only those classes or methods with transaction attributes will be given transaction advice. You need to do nothing except define the required transaction attributes.
Please note that you can specify transaction attributes at either class or method level. Class-level attributes, if specified, will be "inherited" by all methods whereas method attributes will wholly override any class-level attributes.
This appendix details the XML Schema-based configuration introduced in Spring 2.0.
The central motivation for moving to XML Schema based configuration files was
to make Spring XML configuration easier. The 'classic'
<bean/>
-based approach is good, but its generic-nature comes
with a price in terms of configuration overhead.
From the Spring IoC containers point-of-view, everything is a bean. That's great news for the Spring IoC container, because if everything is a bean then everything can be treated in the exact same fashion. The same, however, is not true from a developer's point-of-view. The objects defined in a Spring XML configuration file are not all generic, vanilla beans. Usually, each bean requires some degree of specific configuration.
Spring 2.0's new XML Schema-based configuration addresses this issue.
The <bean/>
element is still present, and if you
wanted to, you could continue to write the exact same
style of Spring XML configuration using only <bean/>
elements. The new XML Schema-based configuration does, however, make
Spring XML configuration files substantially clearer to read. In addition, it allows
you to express the intent of a bean definition.
The key thing to remember is that the new custom tags work best for infrastructure or integration beans: for example, AOP, collections, transactions, integration with 3rd-party frameworks such as Mule, etc., while the existing bean tags are best suited to application-specific beans, such as DAOs, service layer objects, validators, etc.
The examples included below will hopefully convince you that the inclusion of XML Schema support in Spring 2.0 was a good idea. The reception in the community has been encouraging; also, please note the fact that this new configuration mechanism is totally customisable and extensible. This means you can write your own domain-specific configuration tags that would better represent your application's domain; the process involved in doing so is covered in the appendix entitled Appendix B, Extensible XML authoring.
To switch over from the DTD-style to the new XML Schema-style, you need to make the following change.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN"
"http://www.springframework.org/dtd/spring-beans-2.0.dtd">
<beans>
<!-- <bean/>
definitions here -->
</beans>
The equivalent file in the XML Schema-style would be...
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<!-- <bean/>
definitions here -->
</beans>
![]() | Note |
---|---|
The |
The above Spring XML configuration fragment is boilerplate that you can copy and paste
(!) and then plug <bean/>
definitions into like you have always
done. However, the entire point of switching over is to
take advantage of the new Spring 2.0 XML tags since they make configuration easier. The
section entitled Section A.2.2, “The util
schema” demonstrates how you can
start immediately by using some of the more common utility tags.
The rest of this chapter is devoted to showing examples of the new Spring XML Schema based configuration, with at least one example for every new tag. The format follows a before and after style, with a before snippet of XML showing the old (but still 100% legal and supported) style, followed immediately by an after example showing the equivalent in the new XML Schema-based style.
First up is coverage of the util
tags. As the name
implies, the util
tags deal with common, utility
configuration issues, such as configuring collections, referencing constants,
and suchlike.
To use the tags in the util
schema, you need to have
the following preamble at the top of your Spring XML configuration file;
the emboldened text in the snippet below references the correct schema so that
the tags in the util
namespace are available to you.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.5.xsd">
<!-- <bean/>
definitions here -->
</beans>
Before...
<bean id="..." class="..."> <property name="isolation"> <bean id="java.sql.Connection.TRANSACTION_SERIALIZABLE" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean" /> </property> </bean>
The above configuration uses a Spring FactoryBean
implementation, the FieldRetrievingFactoryBean
, to
set the value of the 'isolation'
property on a bean
to the value of the 'java.sql.Connection.TRANSACTION_SERIALIZABLE'
constant. This is all well and good, but it is a tad verbose and (unneccessarily)
exposes Spring's internal plumbing to the end user.
The following XML Schema-based version is more concise and clearly expresses the developer's intent ('inject this constant value'), and it just reads better.
<bean id="..." class="..."> <property name="isolation"> <util:constant static-field="java.sql.Connection.TRANSACTION_SERIALIZABLE"/> </property> </bean>
FieldRetrievingFactoryBean
is a FactoryBean
which retrieves a
static
or non-static field value. It is typically
used for retrieving public
static
final
constants, which may then be used to set a
property value or constructor arg for another bean.
Find below an example which shows how a static
field is exposed, by
using the staticField
property:
<bean id="myField" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean"> <property name="staticField" value="java.sql.Connection.TRANSACTION_SERIALIZABLE"/> </bean>
There is also a convenience usage form where the static
field is specified as the bean name:
<bean id="java.sql.Connection.TRANSACTION_SERIALIZABLE" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean"/>
This does mean that there is no longer any choice in what the bean id is (so any other bean that refers to it will also have to use this longer name), but this form is very concise to define, and very convenient to use as an inner bean since the id doesn't have to be specified for the bean reference:
<bean id="..." class="..."> <property name="isolation"> <bean id="java.sql.Connection.TRANSACTION_SERIALIZABLE" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean" /> </property> </bean>
It is also possible to access a non-static (instance) field of another bean,
as described in the API documentation for the
FieldRetrievingFactoryBean
class.
Injecting enum values into beans as either property or constructor arguments is very
easy to do in Spring, in that you don't actually have to do
anything or know anything about the Spring internals (or even about classes such
as the FieldRetrievingFactoryBean
). Let's look at an example
to see how easy injecting an enum value is; consider this JDK 5 enum:
package javax.persistence; public enum PersistenceContextType { TRANSACTION, EXTENDED }
Now consider a setter of type PersistenceContextType
:
package example; public class Client { private PersistenceContextType persistenceContextType; public void setPersistenceContextType(PersistenceContextType type) { this.persistenceContextType = type; } }
.. and the corresponding bean definition:
<bean class="example.Client"> <property name="persistenceContextType" value="TRANSACTION" /> </bean>
This works for classic type-safe emulated enums (on JDK 1.4 and JDK 1.3) as well; Spring will automatically attempt to match the string property value to a constant on the enum class.
Before...
<!-- target bean to be referenced by name --> <bean id="testBean" class="org.springframework.beans.TestBean" scope="prototype"> <property name="age" value="10"/> <property name="spouse"> <bean class="org.springframework.beans.TestBean"> <property name="age" value="11"/> </bean> </property> </bean> <!-- will result in 10, which is the value of property 'age' of bean 'testBean' --> <bean id="testBean.age" class="org.springframework.beans.factory.config.PropertyPathFactoryBean"/>
The above configuration uses a Spring FactoryBean
implementation, the PropertyPathFactoryBean
, to
create a bean (of type int
) called
'testBean.age'
that has a value equal to the 'age'
property of the 'testBean'
bean.
After...
<!-- target bean to be referenced by name --> <bean id="testBean" class="org.springframework.beans.TestBean" scope="prototype"> <property name="age" value="10"/> <property name="spouse"> <bean class="org.springframework.beans.TestBean"> <property name="age" value="11"/> </bean> </property> </bean> <!-- will result in 10, which is the value of property 'age' of bean 'testBean' --> <util:property-path id="name" path="testBean.age"/>
The value of the 'path'
attribute of the
<property-path/>
tag follows the form 'beanName.beanProperty'
.
PropertyPathFactoryBean
is a
FactoryBean
that evaluates a property path on a given
target object. The target object can be specified directly or via a bean
name. This value may then be used in another bean definition as a property
value or constructor argument.
Here's an example where a path is used against another bean, by name:
// target bean to be referenced by name
<bean id="person" class="org.springframework.beans.TestBean" scope="prototype">
<property name="age" value="10"/>
<property name="spouse">
<bean class="org.springframework.beans.TestBean">
<property name="age" value="11"/>
</bean>
</property>
</bean>
// will result in 11, which is the value of property 'spouse.age' of bean 'person'
<bean id="theAge"
class="org.springframework.beans.factory.config.PropertyPathFactoryBean">
<property name="targetBeanName" value="person"/>
<property name="propertyPath" value="spouse.age"/>
</bean>
In this example, a path is evaluated against an inner bean:
<!-- will result in 12, which is the value of property 'age' of the inner bean -->
<bean id="theAge"
class="org.springframework.beans.factory.config.PropertyPathFactoryBean">
<property name="targetObject">
<bean class="org.springframework.beans.TestBean">
<property name="age" value="12"/>
</bean>
</property>
<property name="propertyPath" value="age"/>
</bean>
There is also a shortcut form, where the bean name is the property path.
<!-- will result in 10, which is the value of property 'age' of bean 'person' -->
<bean id="person.age"
class="org.springframework.beans.factory.config.PropertyPathFactoryBean"/>
This form does mean that there is no choice in the name of the bean. Any reference to it will also have to use the same id, which is the path. Of course, if used as an inner bean, there is no need to refer to it at all:
<bean id="..." class="..."> <property name="age"> <bean id="person.age" class="org.springframework.beans.factory.config.PropertyPathFactoryBean"/> </property> </bean>
The result type may be specifically set in the actual definition. This is not necessary for most use cases, but can be of use for some. Please see the Javadocs for more info on this feature.
Before...
<!-- creates a java.util.Properties
instance with values loaded from the supplied location -->
<bean id="jdbcConfiguration" class="org.springframework.beans.factory.config.PropertiesFactoryBean">
<property name="location" value="classpath:com/foo/jdbc-production.properties"/>
</bean>
The above configuration uses a Spring FactoryBean
implementation, the PropertiesFactoryBean
, to
instantiate a java.util.Properties
instance with values loaded from
the supplied Resource
location).
After...
<!-- creates a java.util.Properties
instance with values loaded from the supplied location -->
<util:properties id="jdbcConfiguration" location="classpath:com/foo/jdbc-production.properties"/>
Before...
<!-- creates a java.util.List
instance with values loaded from the supplied 'sourceList'
-->
<bean id="emails" class="org.springframework.beans.factory.config.ListFactoryBean">
<property name="sourceList">
<list>
<value>pechorin@hero.org</value>
<value>raskolnikov@slums.org</value>
<value>stavrogin@gov.org</value>
<value>porfiry@gov.org</value>
</list>
</property>
</bean>
The above configuration uses a Spring FactoryBean
implementation, the ListFactoryBean
, to
create a java.util.List
instance initialized
with values taken from the supplied 'sourceList'
.
After...
<!-- creates a java.util.List
instance with values loaded from the supplied 'sourceList'
-->
<util:list id="emails">
<value>pechorin@hero.org</value>
<value>raskolnikov@slums.org</value>
<value>stavrogin@gov.org</value>
<value>porfiry@gov.org</value>
</util:list>
You can also explicitly control the exact type of List
that will be instantiated and populated via the use of the 'list-class'
attribute on the <util:list/>
element. For example, if we
really need a java.util.LinkedList
to be instantiated, we could
use the following configuration:
<util:list id="emails" list-class="java.util.LinkedList"> <value>jackshaftoe@vagabond.org</value> <value>eliza@thinkingmanscrumpet.org</value> <value>vanhoek@pirate.org</value> <value>d'Arcachon@nemesis.org</value> </util:list>
If no 'list-class'
attribute is supplied, a
List
implementation will be chosen by the container.
Finally, you can also control the merging behavior using the
'merge'
attribute of the <util:list/>
element; collection merging is described in more detail in the section entitled
Section 3.3.2.4.1, “Collection merging”.
Before...
<!-- creates a java.util.Map
instance with values loaded from the supplied 'sourceMap'
-->
<bean id="emails" class="org.springframework.beans.factory.config.MapFactoryBean">
<property name="sourceMap">
<map>
<entry key="pechorin" value="pechorin@hero.org"/>
<entry key="raskolnikov" value="raskolnikov@slums.org"/>
<entry key="stavrogin" value="stavrogin@gov.org"/>
<entry key="porfiry" value="porfiry@gov.org"/>
</map>
</property>
</bean>
The above configuration uses a Spring FactoryBean
implementation, the MapFactoryBean
, to
create a java.util.Map
instance initialized
with key-value pairs taken from the supplied 'sourceMap'
.
After...
<!-- creates a java.util.Map
instance with values loaded from the supplied 'sourceMap'
-->
<util:map id="emails">
<entry key="pechorin" value="pechorin@hero.org"/>
<entry key="raskolnikov" value="raskolnikov@slums.org"/>
<entry key="stavrogin" value="stavrogin@gov.org"/>
<entry key="porfiry" value="porfiry@gov.org"/>
</util:map>
You can also explicitly control the exact type of Map
that will be instantiated and populated via the use of the 'map-class'
attribute on the <util:map/>
element. For example, if we
really need a java.util.TreeMap
to be instantiated, we could
use the following configuration:
<util:map id="emails" map-class="java.util.TreeMap"> <entry key="pechorin" value="pechorin@hero.org"/> <entry key="raskolnikov" value="raskolnikov@slums.org"/> <entry key="stavrogin" value="stavrogin@gov.org"/> <entry key="porfiry" value="porfiry@gov.org"/> </util:map>
If no 'map-class'
attribute is supplied, a
Map
implementation will be chosen by the container.
Finally, you can also control the merging behavior using the
'merge'
attribute of the <util:map/>
element; collection merging is described in more detail in the section entitled
Section 3.3.2.4.1, “Collection merging”.
Before...
<!-- creates a java.util.Set
instance with values loaded from the supplied 'sourceSet'
-->
<bean id="emails" class="org.springframework.beans.factory.config.SetFactoryBean">
<property name="sourceSet">
<set>
<value>pechorin@hero.org</value>
<value>raskolnikov@slums.org</value>
<value>stavrogin@gov.org</value>
<value>porfiry@gov.org</value>
</set>
</property>
</bean>
The above configuration uses a Spring FactoryBean
implementation, the SetFactoryBean
, to
create a java.util.Set
instance initialized
with values taken from the supplied 'sourceSet'
.
After...
<!-- creates a java.util.Set
instance with values loaded from the supplied 'sourceSet'
-->
<util:set id="emails">
<value>pechorin@hero.org</value>
<value>raskolnikov@slums.org</value>
<value>stavrogin@gov.org</value>
<value>porfiry@gov.org</value>
</util:set>
You can also explicitly control the exact type of Set
that will be instantiated and populated via the use of the 'set-class'
attribute on the <util:set/>
element. For example, if we
really need a java.util.TreeSet
to be instantiated, we could
use the following configuration:
<util:set id="emails" set-class="java.util.TreeSet"> <value>pechorin@hero.org</value> <value>raskolnikov@slums.org</value> <value>stavrogin@gov.org</value> <value>porfiry@gov.org</value> </util:set>
If no 'set-class'
attribute is supplied, a
Set
implementation will be chosen by the container.
Finally, you can also control the merging behavior using the
'merge'
attribute of the <util:set/>
element; collection merging is described in more detail in the section entitled
Section 3.3.2.4.1, “Collection merging”.
The jee
tags deal with JEE (Java Enterprise Edition)-related
configuration issues, such as looking up a JNDI object and defining EJB references.
To use the tags in the jee
schema, you need to have
the following preamble at the top of your Spring XML configuration file;
the emboldened text in the following snippet references the correct schema so that
the tags in the jee
namespace are available to you.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jee="http://www.springframework.org/schema/jee"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-2.5.xsd">
<!-- <bean/>
definitions here -->
</beans>
Before...
<bean id="dataSource" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="jdbc/MyDataSource"/> </bean> <bean id="userDao" class="com.foo.JdbcUserDao"> <!-- Spring will do the cast automatically (as usual) --> <property name="dataSource" ref="dataSource"/> </bean>
After...
<jee:jndi-lookup id="dataSource" jndi-name="jdbc/MyDataSource"/> <bean id="userDao" class="com.foo.JdbcUserDao"> <!-- Spring will do the cast automatically (as usual) --> <property name="dataSource" ref="dataSource"/> </bean>
Before...
<bean id="simple" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="jdbc/MyDataSource"/> <property name="jndiEnvironment"> <props> <prop key="foo">bar</prop> </props> </property> </bean>
After...
<jee:jndi-lookup id="simple" jndi-name="jdbc/MyDataSource"> <jee:environment>foo=bar</jee:environment> </jee:jndi-lookup>
Before...
<bean id="simple" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="jdbc/MyDataSource"/> <property name="jndiEnvironment"> <props> <prop key="foo">bar</prop> <prop key="ping">pong</prop> </props> </property> </bean>
After...
<jee:jndi-lookup id="simple" jndi-name="jdbc/MyDataSource">
<!-- newline-separated, key-value pairs for the environment (standard Properties
format) -->
<jee:environment>
foo=bar
ping=pong
</jee:environment>
</jee:jndi-lookup>
Before...
<bean id="simple" class="org.springframework.jndi.JndiObjectFactoryBean"> <property name="jndiName" value="jdbc/MyDataSource"/> <property name="cache" value="true"/> <property name="resourceRef" value="true"/> <property name="lookupOnStartup" value="false"/> <property name="expectedType" value="com.myapp.DefaultFoo"/> <property name="proxyInterface" value="com.myapp.Foo"/> </bean>
After...
<jee:jndi-lookup id="simple" jndi-name="jdbc/MyDataSource" cache="true" resource-ref="true" lookup-on-startup="false" expected-type="com.myapp.DefaultFoo" proxy-interface="com.myapp.Foo"/>
The <jee:local-slsb/>
tag configures a
reference to an EJB Stateless SessionBean.
Before...
<bean id="simple" class="org.springframework.ejb.access.LocalStatelessSessionProxyFactoryBean"> <property name="jndiName" value="ejb/RentalServiceBean"/> <property name="businessInterface" value="com.foo.service.RentalService"/> </bean>
After...
<jee:local-slsb id="simpleSlsb" jndi-name="ejb/RentalServiceBean" business-interface="com.foo.service.RentalService"/>
<bean id="complexLocalEjb" class="org.springframework.ejb.access.LocalStatelessSessionProxyFactoryBean"> <property name="jndiName" value="ejb/RentalServiceBean"/> <property name="businessInterface" value="com.foo.service.RentalService"/> <property name="cacheHome" value="true"/> <property name="lookupHomeOnStartup" value="true"/> <property name="resourceRef" value="true"/> </bean>
After...
<jee:local-slsb id="complexLocalEjb" jndi-name="ejb/RentalServiceBean" business-interface="com.foo.service.RentalService" cache-home="true" lookup-home-on-startup="true" resource-ref="true">
The <jee:remote-slsb/>
tag configures a
reference to a remote
EJB Stateless SessionBean.
Before...
<bean id="complexRemoteEjb" class="org.springframework.ejb.access.SimpleRemoteStatelessSessionProxyFactoryBean"> <property name="jndiName" value="ejb/MyRemoteBean"/> <property name="businessInterface" value="com.foo.service.RentalService"/> <property name="cacheHome" value="true"/> <property name="lookupHomeOnStartup" value="true"/> <property name="resourceRef" value="true"/> <property name="homeInterface" value="com.foo.service.RentalService"/> <property name="refreshHomeOnConnectFailure" value="true"/> </bean>
After...
<jee:remote-slsb id="complexRemoteEjb" jndi-name="ejb/MyRemoteBean" business-interface="com.foo.service.RentalService" cache-home="true" lookup-home-on-startup="true" resource-ref="true" home-interface="com.foo.service.RentalService" refresh-home-on-connect-failure="true">
The lang
tags deal with exposing objects that have been
written in a dynamic language such as JRuby or Groovy as beans in the Spring
container.
These tags (and the dynamic language support) are comprehensively covered
in the chapter entitled Chapter 24, Dynamic language support. Please do consult that
chapter for full details on this support and the lang
tags
themselves.
In the interest of completeness, to use the tags in the lang
schema, you need to have the following preamble at the top of your Spring XML
configuration file; the emboldened text in the following snippet references the
correct schema so that the tags in the lang
namespace are
available to you.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:lang="http://www.springframework.org/schema/lang"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang-2.5.xsd">
<!-- <bean/>
definitions here -->
</beans>
The jms
tags deal with configuring JMS-related
beans such as Spring's MessageListenerContainers.
These tags are detailed in the section of the JMS chapter
entitled Section 19.6, “JMS Namespace Support”. Please do consult that
chapter for full details on this support and the jms
tags
themselves.
In the interest of completeness, to use the tags in the jms
schema, you need to have the following preamble at the top of your Spring XML
configuration file; the emboldened text in the following snippet references the
correct schema so that the tags in the jms
namespace are
available to you.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jms="http://www.springframework.org/schema/jms"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/jms http://www.springframework.org/schema/jms/spring-jms-2.5.xsd">
<!-- <bean/>
definitions here -->
</beans>
The tx
tags deal with configuring all of those
beans in Spring's comprehensive support for transactions. These tags are
covered in the chapter entitled Chapter 9, Transaction management.
![]() | Tip |
---|---|
You are strongly encouraged to look at the
|
In the interest of completeness, to use the tags in the tx
schema, you need to have the following preamble at the top of your Spring XML
configuration file; the emboldened text in the following snippet references the
correct schema so that the tags in the tx
namespace are
available to you.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd">
<!-- <bean/>
definitions here -->
</beans>
![]() | Note |
---|---|
Often when using the tags in the |
The aop
tags deal with configuring all things
AOP in Spring: this includes Spring's own proxy-based AOP framework and Spring's
integration with the AspectJ AOP framework. These tags are
comprehensively covered in the chapter entitled Chapter 6, Aspect Oriented Programming with Spring.
In the interest of completeness, to use the tags in the aop
schema, you need to have the following preamble at the top of your Spring XML
configuration file; the emboldened text in the following snippet references the
correct schema so that the tags in the aop
namespace are
available to you.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:aop="http://www.springframework.org/schema/aop"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd">
<!-- <bean/>
definitions here -->
</beans>
The context
tags deal with ApplicationContext
configuration that relates to plumbing - that is, not usually beans that are important to an end-user
but rather beans that do a lot of grunt work in Spring, such as BeanfactoryPostProcessors
.
The following snippet references the correct schema so that the tags in the context
namespace are available to you.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<!-- <bean/>
definitions here -->
</beans>
![]() | Note |
---|---|
The |
This element activates the replacement of ${...}
placeholders, resolved
against the specified properties file (as a Spring resource location).
This element is a convenience mechanism that sets up a
PropertyPlaceholderConfigurer
for you; if you need more control over the PropertyPlaceholderConfigurer
, just
define one yourself explicitly.
Activates the Spring infrastructure for various annotations to be detected in bean classes:
Spring's @Required
and @Autowired
, as well as
JSR 250's @PostConstruct
, @PreDestroy
and
@Resource
(if available), and JPA's
@PersistenceContext
and @PersistenceUnit
(if available). Alternatively, you can choose to activate the individual
BeanPostProcessors
for those annotations explictly.
![]() | Note |
---|---|
This element does not activate processing of Spring's
|
This element is detailed in the section entitled Section 3.11, “Annotation-based configuration”.
This element is detailed in the section entitled Section 6.8.4, “Load-time weaving with AspectJ in the Spring Framework”.
This element is detailed in the section entitled Section 6.8.1, “Using AspectJ to dependency inject domain objects with Spring”.
This element is detailed in the section entitled Section 20.4.3, “The <context:mbean-export/>
element”.
The tool
tags are for use when you want to add
tooling-specific metadata to your custom configuration elements. This metadata
can then be consumed by tools that are aware of this metadata, and the tools can
then do pretty much whatever they want with it (validation, etc.).
The tool
tags are not documented in this release of
Spring as they are currently undergoing review. If you are a third party tool
vendor and you would like to contribute to this review process, then do mail
the Spring mailing list. The currently supported tool
tags can be found in the file 'spring-tool-2.5.xsd'
in the
'src/org/springframework/beans/factory/xml'
directory of the
Spring source distribution.
Last but not least we have the tags in the beans
schema.
These are the same tags that have been in Spring since the very dawn of the framework.
Examples of the various tags in the beans
schema are not shown here
because they are quite comprehensively covered in the section entitled Section 3.3.2, “Dependencies and configuration in detail”
(and indeed in that entire chapter).
One thing that is new to the beans tags themselves in Spring 2.0 is the idea
of arbitrary bean metadata. In Spring 2.0 it is now possible to add zero or more
key / value pairs to <bean/>
XML definitions. What, if
anything, is done with this extra metadata is totally up to your own custom logic (and
so is typically only of use if you are writing your own custom tags as described in
the appendix entitled Appendix B, Extensible XML authoring).
Find below an example of the <meta/>
tag in the context
of a surrounding <bean/>
(please note that without any logic
to interpret it the metadata is effectively useless as-is).
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="foo" class="x.y.Foo">
<meta key="cacheName" value="foo"/>
<property name="name" value="Rick"/>
</bean>
</beans>
In the case of the above example, you would assume that there is some logic that will consume the bean definition and set up some caching infrastructure using the supplied metadata.
This final section documents the steps involved in setting up a number of popular Java IDEs to effect the easier editing of Spring's XML Schema-based configuration files. If your favourite Java IDE or editor is not included in the list of documented IDEs, then please do raise an issue and an example with your favorite IDE/editor may be included in the next release.
The following steps illustrate setting up Eclipse to be XSD-aware. The assumption in the following steps is that you already have an Eclipse project open (either a brand new project or an already existing one).
![]() | Note |
---|---|
The following steps were created using Eclipse 3.2. The setup will probably be the same (or similar) on an earlier or later version of Eclipse. |
Step One
Create a new XML file. You can name this file whatever you want. In the
example below, the file is named 'context.xml'
.
Copy and paste the following text into the file so that it matches the screenshot.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.5.xsd"> </beans>
Step Two
As can be seen in the above screenshot (unless you have a customised version of Eclipse with the correct plugins) the XML file will be treated as plain text. There is no XML editing support out of the box in Eclipse, and as such there is not even any syntax highlighting of elements and attributes. To address this, you will have to install an XML editor plugin for Eclipse...
Table A.1. Eclipse XML editors
XML Editor | Link |
---|---|
The Eclipse Web Tools Platform (WTP) | http://www.eclipse.org/webtools/ |
A list of Eclipse XML plugins | http://eclipse-plugins.2y.net/eclipse/plugins.jsp?category=XML |
Unfortunately, precisely because there is no standard XML editor for Eclipse, there are (bar the one below) no further steps showing you how to configure XML Schema support in Eclipse... each XML editor plugin would require its very own dedicated section, and this is Spring reference documentation, not Eclipse XML editor documentation. You will have to read the documentation that comes with your XML editor plugin (good luck there) and figure it out for yourself.
Spring IDE
There is a dedicated Spring Framework plugin for Eclipse called Spring IDE and it is pretty darn cool. (There's a considered and non-biased opinion for you!) This plugin makes using Spring even easier, and it has more than just support for the core Spring Framework... Spring Web Flow is supported too. Details of how to install Spring IDE can be found on the Spring IDE installation page.
Web Tools Platform (WTP) for Eclipse
If you are using the Web Tools Platform (WTP) for Eclipse, you don't need to do anything other than open a Spring XML configuration file using the WTP platform's XML editor. As can be seen in the screenshot below, you immediately get some slick IDE-level support for autocompleting tags and suchlike.
The following steps illustrate setting up the IntelliJ IDEA IDE to be XSD-aware. The assumption in the following steps is that you already have an IDEA project open (either a brand new project or an already existing one).
Repeat as required for setting up IDEA to reference the other Spring XSD files.
Step One
Create a new XML file (you can name this file whatever you want). In the
example below, the file is named 'context.xml'
. Copy and paste
the following text into the file so that it matches the screenshot.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.5.xsd"> </beans>
Step Two
As can be seen in the above screenshot, the XML file has a number of nasty red contextual error markers. To rectify this, IDEA has to be made aware of the location of the referenced XSD namespace(s).
To do this, simply position the cursor over the squiggly red area (see the screenshot below); then press the Alt-Enter keystroke combination, and press the Enter key again when the popup becomes active to fetch the external resource.
Step Three
If the external resource could not be fetched (maybe no active Internet
connection is available), you can manually configure the resource to
reference a local copy of the XSD file. Simply open up the 'Settings'
dialog
(using the Ctrl-A-S keystroke combination or via the 'File|Settings'
menu),
and click on the 'Resources'
button.
Step Four
As can be seen in the following screenshot, this will bring up a dialog
that allows you to add an explicit reference to a local copy of the
util
schema file. (You can find all of the various Spring
XSD files in the 'src'
directory of the Spring distribution.)
Step Five
Clicking the 'Add'
button will bring up another dialog
that allows you to explicitly to associate a namespace URI with the path to the
relevant XSD file. As can be seen in the following screenshot, the
'http://www.springframework.org/schema/util'
namespace
is being associated with the file resource
'C:\bench\spring\src\org\springframework\beans\factory\xml\spring-util-2.5.xsd'
.
Step Six
Exiting out of the nested dialogs by clicking the 'OK'
button
will then bring back the main editing window, and as can be seen in the
following screenshot, the contextual error markers have disappeared; typing
the '<'
character into the editing window now also
brings up a handy dropdown box that contains all of the imported tags from
the util
namespace.
This final section details integration issues that may arise when you switch over to using the above XSD-style for Spring 2.0 configuration.
This section is quite small at the moment (and hopefully it will stay that way). It has been included in the Spring documentation as a convenience to Spring users so that if you encounter an issue when switching over to the XSD-style in some specific environment you can refer to this section for the authoritative answer.
If you are using the XSD-style for Spring 2.0 XML configuration and deploying to v.3 of Caucho's Resin application server, you will need to set some configuration options prior to startup so that an XSD-aware parser is available to Spring.
Please do read this resource, http://www.caucho.com/resin-3.0/xml/jaxp.xtp#xerces, for further details.
Since version 2.0, Spring has featured a mechanism for schema-based extensions to the basic Spring XML format for defining and configuring beans. This section is devoted to detailing how you would go about writing your own custom XML bean definition parsers and integrating such parsers into the Spring IoC container.
To facilitate the authoring of configuration files using a schema-aware XML editor, Spring's extensible XML configuration mechanism is based on XML Schema. If you are not familiar with Spring's current XML configuration extensions that come with the standard Spring distribution, please first read the appendix entitled Appendix A, XML Schema-based configuration.
Creating new XML configuration extensions can be done by following these (relatively) simple steps:
Authoring an XML schema to describe your custom element(s).
Coding a custom NamespaceHandler
implementation (this is an easy step, don't worry).
Coding one or more BeanDefinitionParser
implementations (this is where the real work is done).
Registering the above artifacts with Spring (this too is an easy step).
What follows is a description of each of these steps. For the example, we will create
an XML extension (a custom XML element) that allows us to configure objects of the type
SimpleDateFormat
(from the java.text
package)
in an easy manner. When we are done, we will be able to define bean definitions of type
SimpleDateFormat
like this:
<myns:dateformat id="dateFormat" pattern="yyyy-MM-dd HH:mm" lenient="true"/>
(Don't worry about the fact that this example is very simple; much more detailed examples follow afterwards. The intent in this first simple example is to walk you through the basic steps involved.)
Creating an XML configuration extension for use with Spring's IoC container
starts with authoring an XML Schema to describe the extension. What follows
is the schema we'll use to configure SimpleDateFormat
objects.
<!-- myns.xsd (inside package org/springframework/samples/xml) --> <?xml version="1.0" encoding="UTF-8"?> <xsd:schema xmlns="http://www.mycompany.com/schema/myns" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:beans="http://www.springframework.org/schema/beans" targetNamespace="http://www.mycompany.com/schema/myns" elementFormDefault="qualified" attributeFormDefault="unqualified"> <xsd:import namespace="http://www.springframework.org/schema/beans"/> <xsd:element name="dateformat"> <xsd:complexType> <xsd:complexContent> <xsd:extension base="beans:identifiedType"> <xsd:attribute name="lenient" type="xsd:boolean"/> <xsd:attribute name="pattern" type="xsd:string" use="required"/> </xsd:extension> </xsd:complexContent> </xsd:complexType> </xsd:element> </xsd:schema>
(The emphasized line contains an extension base for all tags that
will be identifiable (meaning they have an id
attribute
that will be used as the bean identifier in the container). We are able to use this
attribute because we imported the Spring-provided 'beans'
namespace.)
The above schema will be used to configure SimpleDateFormat
objects, directly in an XML application context file using the
<myns:dateformat/>
element.
<myns:dateformat id="dateFormat" pattern="yyyy-MM-dd HH:mm" lenient="true"/>
Note that after we've created the infrastructure classes, the above snippet of XML
will essentially be exactly the same as the following XML snippet. In other words,
we're just creating a bean in the container, identified by the name
'dateFormat'
of type SimpleDateFormat
, with a
couple of properties set.
<bean id="dateFormat" class="java.text.SimpleDateFormat"> <constructor-arg value="yyyy-HH-dd HH:mm"/> <property name="lenient" value="true"/> </bean>
![]() | Note |
---|---|
The schema-based approach to creating configuration format allows for tight integration with an IDE that has a schema-aware XML editor. Using a properly authored schema, you can use autocompletion to have a user choose between several configuration options defined in the enumeration. |
In addition to the schema, we need a NamespaceHandler
that will parse all elements of this specific namespace Spring encounters
while parsing configuration files. The NamespaceHandler
should in our case take care of the parsing of the myns:dateformat
element.
The NamespaceHandler
interface is pretty simple in that
it features just three methods:
init()
- allows for initialization of
the NamespaceHandler
and will be called by Spring
before the handler is used
BeanDefinition parse(Element, ParserContext)
-
called when Spring encounters a top-level element (not nested inside a bean definition
or a different namespace). This method can register bean definitions itself and/or
return a bean definition.
BeanDefinitionHolder decorate(Node, BeanDefinitionHolder, ParserContext)
-
called when Spring encounters an attribute or nested element of a different namespace.
The decoration of one or more bean definitions is used for example with the
out-of-the-box scopes Spring 2.0 supports.
We'll start by highlighting a simple example, without using decoration, after which
we will show decoration in a somewhat more advanced example.
Although it is perfectly possible to code your own
NamespaceHandler
for the entire namespace
(and hence provide code that parses each and every element in the namespace),
it is often the case that each top-level XML element in a Spring XML
configuration file results in a single bean definition (as in our
case, where a single <myns:dateformat/>
element
results in a single SimpleDateFormat
bean definition).
Spring features a number of convenience classes that support this scenario.
In this example, we'll make use the NamespaceHandlerSupport
class:
package org.springframework.samples.xml;
import org.springframework.beans.factory.xml.NamespaceHandlerSupport;
public class MyNamespaceHandler extends NamespaceHandlerSupport {
public void init() {
registerBeanDefinitionParser("dateformat", new SimpleDateFormatBeanDefinitionParser());
}
}
The observant reader will notice that there isn't actually a whole lot of
parsing logic in this class. Indeed... the NamespaceHandlerSupport
class has a built in notion of delegation. It supports the registration of any number
of BeanDefinitionParser
instances, to which it will delegate
to when it needs to parse an element in it's namespace. This clean separation of concerns
allows a NamespaceHandler
to handle the orchestration
of the parsing of all of the custom elements in it's namespace,
while delegating to BeanDefinitionParsers
to do the grunt work of the
XML parsing; this means that each BeanDefinitionParser
will
contain just the logic for parsing a single custom element, as we can see in the next step
A BeanDefinitionParser
will be used if the
NamespaceHandler
encounters an XML element of the type
that has been mapped to the specific bean definition parser (which is 'dateformat'
in this case). In other words, the BeanDefinitionParser
is
responsible for parsing one distinct top-level XML element defined in the
schema. In the parser, we'll have access to the XML element (and thus it's subelements too)
so that we can parse our custom XML content, as can be seen in the following example:
package org.springframework.samples.xml; import org.springframework.beans.factory.support.BeanDefinitionBuilder; import org.springframework.beans.factory.xml.AbstractSingleBeanDefinitionParser; import org.springframework.util.StringUtils; import org.w3c.dom.Element; import java.text.SimpleDateFormat; public class SimpleDateFormatBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {protected Class getBeanClass(Element element) { return SimpleDateFormat.class;
} protected void doParse(Element element, BeanDefinitionBuilder bean) { // this will never be null since the schema explicitly requires that a value be supplied String pattern = element.getAttribute("pattern"); bean.addConstructorArg(pattern); // this however is an optional property String lenient = element.getAttribute("lenient"); if (StringUtils.hasText(lenient)) { bean.addPropertyValue("lenient", Boolean.valueOf(lenient)); } } }
In this simple case, this is all that we need to do. The creation of our single
BeanDefinition
is handled by the AbstractSingleBeanDefinitionParser
superclass, as is the extraction and setting of the bean definition's unique identifier.
The coding is finished! All that remains to be done is to somehow make the Spring XML
parsing infrastructure aware of our custom element; we do this by registering our custom
namespaceHandler
and custom XSD file in two special purpose
properties files. These properties files are both placed in a
'META-INF'
directory in your application, and can, for
example, be distributed alongside your binary classes in a JAR file. The Spring XML parsing
infrastructurewill automatically pick up your new extension by consuming these special
properties files, the formats of which are detailed below.
The properties file called 'spring.handlers'
contains a mapping
of XML Schema URIs to namespace handler classes. So for our example, we need to write the
following:
http\://www.mycompany.com/schema/myns=org.springframework.samples.xml.MyNamespaceHandler
(The ':'
character is a valid delimiter in the Java properties format,
and so the ':'
character in the URI needs to be escaped with a backslash.)
The first part (the key) of the key-value pair is the URI associated with your custom namespace
extension, and needs to match exactly the value of the
'targetNamespace'
attribute as specified in your custom XSD schema.
The properties file called 'spring.schemas'
contains a mapping
of XML Schema locations (referred to along with the schema declaration in XML files
that use the schema as part of the 'xsi:schemaLocation'
attribute)
to classpath resources. This file is needed to prevent Spring from
absolutely having to use a default EntityResolver
that requires
Internet access to retrieve the schema file. If you specify the mapping in this properties file,
Spring will search for the schema on the classpath (in this case 'myns.xsd'
in the 'org.springframework.samples.xml'
package):
http\://www.mycompany.com/schema/myns/myns.xsd=org/springframework/samples/xml/myns.xsd
The upshot of this is that you are encouraged to deploy your XSD file(s) right alongside
the NamespaceHandler
and BeanDefinitionParser
classes on the classpath.
Using a custom extension that you yourself have implemented is no different from
using one of the 'custom' extensions that Spring provides straight out of the box. Find below
an example of using the custom <dateformat/>
element developed in the
previous steps in a Spring XML configuration file.
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:myns="http://www.mycompany.com/schema/myns" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.mycompany.com/schema/myns http://www.mycompany.com/schema/myns/myns.xsd"> <!-- as a top-level bean --> <myns:dateformat id="defaultDateFormat" pattern="yyyy-MM-dd HH:mm" lenient="true"/> <bean id="jobDetailTemplate" abstract="true"> <property name="dateFormat"> <!-- as an inner bean --> <myns:dateformat pattern="HH:mm MM-dd-yyyy"/> </property> </bean> </beans>
Find below some much meatier examples of custom XML extensions.
This example illustrates how you might go about writing the various artifacts required to satisfy a target of the following configuration:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:foo="http://www.foo.com/schema/component"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.foo.com/schema/component http://www.foo.com/schema/component/component.xsd">
<foo:component id="bionic-family" name="Bionic-1">
<foo:component name="Sport-1"/>
<foo:component name="Rock-1"/>
</foo:component>
</beans>
The above configuration actually nests custom extensions within each other. The class
that is actually configured by the above <foo:component/>
element is the Component
class (shown directly below). Notice
how the Component
class does not expose
a setter method for the 'components'
property; this makes it hard
(or rather impossible) to configure a bean definition for the Component
class using setter injection.
package com.foo;
import java.util.ArrayList;
import java.util.List;
public class Component {
private String name;
private List components = new ArrayList();
// mmm, there is no setter method for the 'components'
public void addComponent(Component component) {
this.components.add(component);
}
public List getComponents() {
return components;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
The typical solution to this issue is to create a custom FactoryBean
that exposes a setter property for the 'components'
property.
package com.foo; import org.springframework.beans.factory.FactoryBean; import java.util.Iterator; import java.util.List; public class ComponentFactoryBean implements FactoryBean { private Component parent; private List children; public void setParent(Component parent) { this.parent = parent; } public void setChildren(List children) { this.children = children; } public Object getObject() throws Exception { if (this.children != null && this.children.size() > 0) { for (Iterator it = children.iterator(); it.hasNext();) { Component childComponent = (Component) it.next(); this.parent.addComponent(childComponent); } } return this.parent; } public Class getObjectType() { return Component.class; } public boolean isSingleton() { return true; } }
This is all very well, and does work nicely, but exposes a lot of Spring plumbing to the end user. What we are going to do is write a custom extension that hides away all of this Spring plumbing. If we stick to the steps described previously, we'll start off by creating the XSD schema to define the structure of our custom tag.
<?xml version="1.0" encoding="UTF-8" standalone="no"?> <xsd:schema xmlns="http://www.foo.com/schema/component" xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.foo.com/schema/component" elementFormDefault="qualified" attributeFormDefault="unqualified"> <xsd:element name="component"> <xsd:complexType> <xsd:choice minOccurs="0" maxOccurs="unbounded"> <xsd:element ref="component"/> </xsd:choice> <xsd:attribute name="id" type="xsd:ID"/> <xsd:attribute name="name" use="required" type="xsd:string"/> </xsd:complexType> </xsd:element> </xsd:schema>
We'll then create a custom NamespaceHandler
.
package com.foo; import org.springframework.beans.factory.xml.NamespaceHandlerSupport; public class ComponentNamespaceHandler extends NamespaceHandlerSupport { public void init() { registerBeanDefinitionParser("component", new ComponentBeanDefinitionParser()); } }
Next up is the custom BeanDefinitionParser
. Remember
that what we are creating is a BeanDefinition
describing
a ComponentFactoryBean
.
package com.foo; import org.springframework.beans.factory.support.AbstractBeanDefinition; import org.springframework.beans.factory.support.BeanDefinitionBuilder; import org.springframework.beans.factory.support.ManagedList; import org.springframework.beans.factory.xml.AbstractBeanDefinitionParser; import org.springframework.beans.factory.xml.ParserContext; import org.springframework.util.xml.DomUtils; import org.w3c.dom.Element; import java.util.List; public class ComponentBeanDefinitionParser extends AbstractBeanDefinitionParser { protected AbstractBeanDefinition parseInternal(Element element, ParserContext parserContext) { BeanDefinitionBuilder factory = BeanDefinitionBuilder.rootBeanDefinition(ComponentFactoryBean.class); BeanDefinitionBuilder parent = parseComponent(element); factory.addPropertyValue("parent", parent.getBeanDefinition()); List childElements = DomUtils.getChildElementsByTagName(element, "component"); if (childElements != null && childElements.size() > 0) { parseChildComponents(childElements, factory); } return factory.getBeanDefinition(); } private static BeanDefinitionBuilder parseComponent(Element element) { BeanDefinitionBuilder component = BeanDefinitionBuilder.rootBeanDefinition(Component.class); component.addPropertyValue("name", element.getAttribute("name")); return component; } private static void parseChildComponents(List childElements, BeanDefinitionBuilder factory) { ManagedList children = new ManagedList(childElements.size()); for (int i = 0; i < childElements.size(); ++i) { Element childElement = (Element) childElements.get(i); BeanDefinitionBuilder child = parseComponent(childElement); children.add(child.getBeanDefinition()); } factory.addPropertyValue("children", children); } }
Lastly, the various artifacts need to be registered with the Spring XML infrastructure.
# in 'META-INF/spring.handlers'
http\://www.foo.com/schema/component=com.foo.ComponentNamespaceHandler
# in 'META-INF/spring.schemas'
http\://www.foo.com/schema/component/component.xsd=com/foo/component.xsd
Writing your own custom parser and the associated artifacts isn't hard, but sometimes it is not the right thing to do. Consider the scenario where you need to add metadata to already existing bean definitions. In this case you certainly don't want to have to go off and write your own entire custom extension; rather you just want to add an additional attribute to the existing bean definition element.
By way of another example, let's say that the service class that you are defining a bean definition for a service object that will (unknown to it) be accessing a clustered JCache, and you want to ensure that the named JCache instance is eagerly started within the surrounding cluster:
<bean id="checkingAccountService" class="com.foo.DefaultCheckingAccountService" jcache:cache-name="checking.account"> <!-- other dependencies here... --> </bean>
What we are going to do here is create another BeanDefinition
when the 'jcache:cache-name'
attribute is parsed; this
BeanDefinition
will then initialize the named JCache
for us. We will also modify the existing BeanDefinition
for the
'checkingAccountService'
so that it will have a dependency on this
new JCache-initializing BeanDefinition
.
package com.foo;
public class JCacheInitializer {
private String name;
public JCacheInitializer(String name) {
this.name = name;
}
public void initialize() {
// lots of JCache API calls to initialize the named cache...
}
}
Now onto the custom extension. Firstly, the authoring of the XSD schema describing the custom attribute (quite easy in this case).
<?xml version="1.0" encoding="UTF-8" standalone="no"?> <xsd:schema xmlns="http://www.foo.com/schema/jcache" xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.foo.com/schema/jcache" elementFormDefault="qualified"> <xsd:attribute name="cache-name" type="xsd:string"/> </xsd:schema>
Next, the associated NamespaceHandler
.
package com.foo; import org.springframework.beans.factory.xml.NamespaceHandlerSupport; public class JCacheNamespaceHandler extends NamespaceHandlerSupport { public void init() { super.registerBeanDefinitionDecoratorForAttribute("cache-name", new JCacheInitializingBeanDefinitionDecorator()); } }
Next, the parser. Note that in this case, because we are going to be parsing an XML
attribute, we write a BeanDefinitionDecorator
rather than a
BeanDefinitionParser
.
package com.foo; import org.springframework.beans.factory.config.BeanDefinitionHolder; import org.springframework.beans.factory.support.AbstractBeanDefinition; import org.springframework.beans.factory.support.BeanDefinitionBuilder; import org.springframework.beans.factory.xml.BeanDefinitionDecorator; import org.springframework.beans.factory.xml.ParserContext; import org.w3c.dom.Attr; import org.w3c.dom.Node; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class JCacheInitializingBeanDefinitionDecorator implements BeanDefinitionDecorator { private static final String[] EMPTY_STRING_ARRAY = new String[0]; public BeanDefinitionHolder decorate( Node source, BeanDefinitionHolder holder, ParserContext ctx) { String initializerBeanName = registerJCacheInitializer(source, ctx); createDependencyOnJCacheInitializer(holder, initializerBeanName); return holder; } private void createDependencyOnJCacheInitializer(BeanDefinitionHolder holder, String initializerBeanName) { AbstractBeanDefinition definition = ((AbstractBeanDefinition) holder.getBeanDefinition()); String[] dependsOn = definition.getDependsOn(); if (dependsOn == null) { dependsOn = new String[]{initializerBeanName}; } else { List dependencies = new ArrayList(Arrays.asList(dependsOn)); dependencies.add(initializerBeanName); dependsOn = (String[]) dependencies.toArray(EMPTY_STRING_ARRAY); } definition.setDependsOn(dependsOn); } private String registerJCacheInitializer(Node source, ParserContext ctx) { String cacheName = ((Attr) source).getValue(); String beanName = cacheName + "-initializer"; if (!ctx.getRegistry().containsBeanDefinition(beanName)) { BeanDefinitionBuilder initializer = BeanDefinitionBuilder.rootBeanDefinition(JCacheInitializer.class); initializer.addConstructorArg(cacheName); ctx.getRegistry().registerBeanDefinition(beanName, initializer.getBeanDefinition()); } return beanName; } }
Lastly, the various artifacts need to be registered with the Spring XML infrastructure.
# in 'META-INF/spring.handlers'
http\://www.foo.com/schema/jcache=com.foo.JCacheNamespaceHandler
# in 'META-INF/spring.schemas'
http\://www.foo.com/schema/jcache/jcache.xsd=com/foo/jcache.xsd
Find below links to further resources concerning XML Schema and the extensible XML support described in this chapter.
<!-- Spring XML Beans DTD, version 2.0 Authors: Rod Johnson, Juergen Hoeller, Alef Arendsen, Colin Sampaleanu, Rob Harrop This defines a simple and consistent way of creating a namespace of JavaBeans objects, managed by a Spring BeanFactory, read by XmlBeanDefinitionReader (with DefaultBeanDefinitionDocumentReader). This document type is used by most Spring functionality, including web application contexts, which are based on bean factories. Each "bean" element in this document defines a JavaBean. Typically the bean class is specified, along with JavaBean properties and/or constructor arguments. A bean instance can be a "singleton" (shared instance) or a "prototype" (independent instance). Further scopes can be provided by extended bean factories, for example in a web environment. References among beans are supported, that is, setting a JavaBean property or a constructor argument to refer to another bean in the same factory (or an ancestor factory). As alternative to bean references, "inner bean definitions" can be used. Singleton flags of such inner bean definitions are effectively ignored: Inner beans are typically anonymous prototypes. There is also support for lists, sets, maps, and java.util.Properties as bean property types or constructor argument types. For simple purposes, this DTD is sufficient. As of Spring 2.0, XSD-based bean definitions are supported as more powerful alternative. XML documents that conform to this DTD should declare the following doctype: <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd"> --> <!-- The document root. A document can contain bean definitions only, imports only, or a mixture of both (typically with imports first). --> <!ELEMENT beans ( description?, (import | alias | bean)* )> <!-- Default values for all bean definitions. Can be overridden at the "bean" level. See those attribute definitions for details. --> <!ATTLIST beans default-lazy-init (true | false) "false"> <!ATTLIST beans default-autowire (no | byName | byType | constructor | autodetect) "no"> <!ATTLIST beans default-dependency-check (none | objects | simple | all) "none"> <!ATTLIST beans default-init-method CDATA #IMPLIED> <!ATTLIST beans default-destroy-method CDATA #IMPLIED> <!ATTLIST beans default-merge (true | false) "false"> <!-- Element containing informative text describing the purpose of the enclosing element. Always optional. Used primarily for user documentation of XML bean definition documents. --> <!ELEMENT description (#PCDATA)> <!-- Specifies an XML bean definition resource to import. --> <!ELEMENT import EMPTY> <!-- The relative resource location of the XML bean definition file to import, for example "myImport.xml" or "includes/myImport.xml" or "../myImport.xml". --> <!ATTLIST import resource CDATA #REQUIRED> <!-- Defines an alias for a bean, which can reside in a different definition file. --> <!ELEMENT alias EMPTY> <!-- The name of the bean to define an alias for. --> <!ATTLIST alias name CDATA #REQUIRED> <!-- The alias name to define for the bean. --> <!ATTLIST alias alias CDATA #REQUIRED> <!-- Allows for arbitrary metadata to be attached to a bean definition. --> <!ELEMENT meta EMPTY> <!-- Specifies the key name of the metadata parameter being defined. --> <!ATTLIST meta key CDATA #REQUIRED> <!-- Specifies the value of the metadata parameter being defined as a String. --> <!ATTLIST meta value CDATA #REQUIRED> <!-- Defines a single (usually named) bean. A bean definition may contain nested tags for constructor arguments, property values, lookup methods, and replaced methods. Mixing constructor injection and setter injection on the same bean is explicitly supported. --> <!ELEMENT bean ( description?, (meta | constructor-arg | property | lookup-method | replaced-method)* )> <!-- Beans can be identified by an id, to enable reference checking. There are constraints on a valid XML id: if you want to reference your bean in Java code using a name that's illegal as an XML id, use the optional "name" attribute. If neither is given, the bean class name is used as id (with an appended counter like "#2" if there is already a bean with that name). --> <!ATTLIST bean id ID #IMPLIED> <!-- Optional. Can be used to create one or more aliases illegal in an id. Multiple aliases can be separated by any number of spaces, commas, or semi-colons (or indeed any mixture of the three). --> <!ATTLIST bean name CDATA #IMPLIED> <!-- Each bean definition must specify the fully qualified name of the class, except if it pure serves as parent for child bean definitions. --> <!ATTLIST bean class CDATA #IMPLIED> <!-- Optionally specify a parent bean definition. Will use the bean class of the parent if none specified, but can also override it. In the latter case, the child bean class must be compatible with the parent, i.e. accept the parent's property values and constructor argument values, if any. A child bean definition will inherit constructor argument values, property values and method overrides from the parent, with the option to add new values. If init method, destroy method, factory bean and/or factory method are specified, they will override the corresponding parent settings. The remaining settings will always be taken from the child definition: depends on, autowire mode, dependency check, scope, lazy init. --> <!ATTLIST bean parent CDATA #IMPLIED> <!-- The scope of this bean: typically "singleton" (one shared instance, which will be returned by all calls to getBean() with the id), or "prototype" (independent instance resulting from each call to getBean(). Default is "singleton". Singletons are most commonly used, and are ideal for multi-threaded service objects. Further scopes, such as "request" or "session", might be supported by extended bean factories (for example, in a web environment). Note: This attribute will not be inherited by child bean definitions. Hence, it needs to be specified per concrete bean definition. Inner bean definitions inherit the singleton status of their containing bean definition, unless explicitly specified: The inner bean will be a singleton if the containing bean is a singleton, and a prototype if the containing bean has any other scope. --> <!ATTLIST bean scope CDATA #IMPLIED> <!-- Is this bean "abstract", i.e. not meant to be instantiated itself but rather just serving as parent for concrete child bean definitions. Default is "false". Specify "true" to tell the bean factory to not try to instantiate that particular bean in any case. Note: This attribute will not be inherited by child bean definitions. Hence, it needs to be specified per abstract bean definition. --> <!ATTLIST bean abstract (true | false) #IMPLIED> <!-- If this bean should be lazily initialized. If false, it will get instantiated on startup by bean factories that perform eager initialization of singletons. Note: This attribute will not be inherited by child bean definitions. Hence, it needs to be specified per concrete bean definition. --> <!ATTLIST bean lazy-init (true | false | default) "default"> <!-- Indicates whether or not this bean should be considered when looking for candidates to satisfy another beans autowiring requirements. --> <!ATTLIST bean autowire-candidate (true | false) #IMPLIED> <!-- Optional attribute controlling whether to "autowire" bean properties. This is an automagical process in which bean references don't need to be coded explicitly in the XML bean definition file, but Spring works out dependencies. There are 5 modes: 1. "no" The traditional Spring default. No automagical wiring. Bean references must be defined in the XML file via the <ref> element. We recommend this in most cases as it makes documentation more explicit. 2. "byName" Autowiring by property name. If a bean of class Cat exposes a dog property, Spring will try to set this to the value of the bean "dog" in the current factory. If there is no matching bean by name, nothing special happens; use dependency-check="objects" to raise an error in that case. 3. "byType" Autowiring if there is exactly one bean of the property type in the bean factory. If there is more than one, a fatal error is raised, and you can't use byType autowiring for that bean. If there is none, nothing special happens; use dependency-check="objects" to raise an error in that case. 4. "constructor" Analogous to "byType" for constructor arguments. If there isn't exactly one bean of the constructor argument type in the bean factory, a fatal error is raised. 5. "autodetect" Chooses "constructor" or "byType" through introspection of the bean class. If a default constructor is found, "byType" gets applied. The latter two are similar to PicoContainer and make bean factories simple to configure for small namespaces, but doesn't work as well as standard Spring behaviour for bigger applications. Note that explicit dependencies, i.e. "property" and "constructor-arg" elements, always override autowiring. Autowire behavior can be combined with dependency checking, which will be performed after all autowiring has been completed. Note: This attribute will not be inherited by child bean definitions. Hence, it needs to be specified per concrete bean definition. --> <!ATTLIST bean autowire (no | byName | byType | constructor | autodetect | default) "default"> <!-- Optional attribute controlling whether to check whether all this beans dependencies, expressed in its properties, are satisfied. Default is no dependency checking. "simple" type dependency checking includes primitives and String; "objects" includes collaborators (other beans in the factory); "all" includes both types of dependency checking. Note: This attribute will not be inherited by child bean definitions. Hence, it needs to be specified per concrete bean definition. --> <!ATTLIST bean dependency-check (none | objects | simple | all | default) "default"> <!-- The names of the beans that this bean depends on being initialized. The bean factory will guarantee that these beans get initialized before. Note that dependencies are normally expressed through bean properties or constructor arguments. This property should just be necessary for other kinds of dependencies like statics (*ugh*) or database preparation on startup. Note: This attribute will not be inherited by child bean definitions. Hence, it needs to be specified per concrete bean definition. --> <!ATTLIST bean depends-on CDATA #IMPLIED> <!-- Optional attribute for the name of the custom initialization method to invoke after setting bean properties. The method must have no arguments, but may throw any exception. --> <!ATTLIST bean init-method CDATA #IMPLIED> <!-- Optional attribute for the name of the custom destroy method to invoke on bean factory shutdown. The method must have no arguments, but may throw any exception. Note: Only invoked on beans whose lifecycle is under full control of the factory - which is always the case for singletons, but not guaranteed for any other scope. --> <!ATTLIST bean destroy-method CDATA #IMPLIED> <!-- Optional attribute specifying the name of a factory method to use to create this object. Use constructor-arg elements to specify arguments to the factory method, if it takes arguments. Autowiring does not apply to factory methods. If the "class" attribute is present, the factory method will be a static method on the class specified by the "class" attribute on this bean definition. Often this will be the same class as that of the constructed object - for example, when the factory method is used as an alternative to a constructor. However, it may be on a different class. In that case, the created object will *not* be of the class specified in the "class" attribute. This is analogous to FactoryBean behavior. If the "factory-bean" attribute is present, the "class" attribute is not used, and the factory method will be an instance method on the object returned from a getBean call with the specified bean name. The factory bean may be defined as a singleton or a prototype. The factory method can have any number of arguments. Autowiring is not supported. Use indexed constructor-arg elements in conjunction with the factory-method attribute. Setter Injection can be used in conjunction with a factory method. Method Injection cannot, as the factory method returns an instance, which will be used when the container creates the bean. --> <!ATTLIST bean factory-method CDATA #IMPLIED> <!-- Alternative to class attribute for factory-method usage. If this is specified, no class attribute should be used. This should be set to the name of a bean in the current or ancestor factories that contains the relevant factory method. This allows the factory itself to be configured using Dependency Injection, and an instance (rather than static) method to be used. --> <!ATTLIST bean factory-bean CDATA #IMPLIED> <!-- Bean definitions can specify zero or more constructor arguments. This is an alternative to "autowire constructor". Arguments correspond to either a specific index of the constructor argument list or are supposed to be matched generically by type. Note: A single generic argument value will just be used once, rather than potentially matched multiple times (as of Spring 1.1). constructor-arg elements are also used in conjunction with the factory-method element to construct beans using static or instance factory methods. --> <!ELEMENT constructor-arg ( description?, (bean | ref | idref | value | null | list | set | map | props)? )> <!-- The constructor-arg tag can have an optional index attribute, to specify the exact index in the constructor argument list. Only needed to avoid ambiguities, e.g. in case of 2 arguments of the same type. --> <!ATTLIST constructor-arg index CDATA #IMPLIED> <!-- The constructor-arg tag can have an optional type attribute, to specify the exact type of the constructor argument. Only needed to avoid ambiguities, e.g. in case of 2 single argument constructors that can both be converted from a String. --> <!ATTLIST constructor-arg type CDATA #IMPLIED> <!-- A short-cut alternative to a child element "ref bean=". --> <!ATTLIST constructor-arg ref CDATA #IMPLIED> <!-- A short-cut alternative to a child element "value". --> <!ATTLIST constructor-arg value CDATA #IMPLIED> <!-- Bean definitions can have zero or more properties. Property elements correspond to JavaBean setter methods exposed by the bean classes. Spring supports primitives, references to other beans in the same or related factories, lists, maps and properties. --> <!ELEMENT property ( description?, meta*, (bean | ref | idref | value | null | list | set | map | props)? )> <!-- The property name attribute is the name of the JavaBean property. This follows JavaBean conventions: a name of "age" would correspond to setAge()/optional getAge() methods. --> <!ATTLIST property name CDATA #REQUIRED> <!-- A short-cut alternative to a child element "ref bean=". --> <!ATTLIST property ref CDATA #IMPLIED> <!-- A short-cut alternative to a child element "value". --> <!ATTLIST property value CDATA #IMPLIED> <!-- A lookup method causes the IoC container to override the given method and return the bean with the name given in the bean attribute. This is a form of Method Injection. It's particularly useful as an alternative to implementing the BeanFactoryAware interface, in order to be able to make getBean() calls for non-singleton instances at runtime. In this case, Method Injection is a less invasive alternative. --> <!ELEMENT lookup-method EMPTY> <!-- Name of a lookup method. This method should take no arguments. --> <!ATTLIST lookup-method name CDATA #IMPLIED> <!-- Name of the bean in the current or ancestor factories that the lookup method should resolve to. Often this bean will be a prototype, in which case the lookup method will return a distinct instance on every invocation. This is useful for single-threaded objects. --> <!ATTLIST lookup-method bean CDATA #IMPLIED> <!-- Similar to the lookup method mechanism, the replaced-method element is used to control IoC container method overriding: Method Injection. This mechanism allows the overriding of a method with arbitrary code. --> <!ELEMENT replaced-method ( (arg-type)* )> <!-- Name of the method whose implementation should be replaced by the IoC container. If this method is not overloaded, there's no need to use arg-type subelements. If this method is overloaded, arg-type subelements must be used for all override definitions for the method. --> <!ATTLIST replaced-method name CDATA #IMPLIED> <!-- Bean name of an implementation of the MethodReplacer interface in the current or ancestor factories. This may be a singleton or prototype bean. If it's a prototype, a new instance will be used for each method replacement. Singleton usage is the norm. --> <!ATTLIST replaced-method replacer CDATA #IMPLIED> <!-- Subelement of replaced-method identifying an argument for a replaced method in the event of method overloading. --> <!ELEMENT arg-type (#PCDATA)> <!-- Specification of the type of an overloaded method argument as a String. For convenience, this may be a substring of the FQN. E.g. all the following would match "java.lang.String": - java.lang.String - String - Str As the number of arguments will be checked also, this convenience can often be used to save typing. --> <!ATTLIST arg-type match CDATA #IMPLIED> <!-- Defines a reference to another bean in this factory or an external factory (parent or included factory). --> <!ELEMENT ref EMPTY> <!-- References must specify a name of the target bean. The "bean" attribute can reference any name from any bean in the context, to be checked at runtime. Local references, using the "local" attribute, have to use bean ids; they can be checked by this DTD, thus should be preferred for references within the same bean factory XML file. --> <!ATTLIST ref bean CDATA #IMPLIED> <!ATTLIST ref local IDREF #IMPLIED> <!ATTLIST ref parent CDATA #IMPLIED> <!-- Defines a string property value, which must also be the id of another bean in this factory or an external factory (parent or included factory). While a regular 'value' element could instead be used for the same effect, using idref in this case allows validation of local bean ids by the XML parser, and name completion by supporting tools. --> <!ELEMENT idref EMPTY> <!-- ID refs must specify a name of the target bean. The "bean" attribute can reference any name from any bean in the context, potentially to be checked at runtime by bean factory implementations. Local references, using the "local" attribute, have to use bean ids; they can be checked by this DTD, thus should be preferred for references within the same bean factory XML file. --> <!ATTLIST idref bean CDATA #IMPLIED> <!ATTLIST idref local IDREF #IMPLIED> <!-- Contains a string representation of a property value. The property may be a string, or may be converted to the required type using the JavaBeans PropertyEditor machinery. This makes it possible for application developers to write custom PropertyEditor implementations that can convert strings to arbitrary target objects. Note that this is recommended for simple objects only. Configure more complex objects by populating JavaBean properties with references to other beans. --> <!ELEMENT value (#PCDATA)> <!-- The value tag can have an optional type attribute, to specify the exact type that the value should be converted to. Only needed if the type of the target property or constructor argument is too generic: for example, in case of a collection element. --> <!ATTLIST value type CDATA #IMPLIED> <!-- Denotes a Java null value. Necessary because an empty "value" tag will resolve to an empty String, which will not be resolved to a null value unless a special PropertyEditor does so. --> <!ELEMENT null (#PCDATA)> <!-- A list can contain multiple inner bean, ref, collection, or value elements. Java lists are untyped, pending generics support in Java 1.5, although references will be strongly typed. A list can also map to an array type. The necessary conversion is automatically performed by the BeanFactory. --> <!ELEMENT list ( (bean | ref | idref | value | null | list | set | map | props)* )> <!-- Enable/disable merging for collections when using parent/child beans. --> <!ATTLIST list merge (true | false | default) "default"> <!-- Specify the default Java type for nested values. --> <!ATTLIST list value-type CDATA #IMPLIED> <!-- A set can contain multiple inner bean, ref, collection, or value elements. Java sets are untyped, pending generics support in Java 1.5, although references will be strongly typed. --> <!ELEMENT set ( (bean | ref | idref | value | null | list | set | map | props)* )> <!-- Enable/disable merging for collections when using parent/child beans. --> <!ATTLIST set merge (true | false | default) "default"> <!-- Specify the default Java type for nested values. --> <!ATTLIST set value-type CDATA #IMPLIED> <!-- A Spring map is a mapping from a string key to object. Maps may be empty. --> <!ELEMENT map ( (entry)* )> <!-- Enable/disable merging for collections when using parent/child beans. --> <!ATTLIST map merge (true | false | default) "default"> <!-- Specify the default Java type for nested entry keys. --> <!ATTLIST map key-type CDATA #IMPLIED> <!-- Specify the default Java type for nested entry values. --> <!ATTLIST map value-type CDATA #IMPLIED> <!-- A map entry can be an inner bean, ref, value, or collection. The key of the entry is given by the "key" attribute or child element. --> <!ELEMENT entry ( key?, (bean | ref | idref | value | null | list | set | map | props)? )> <!-- Each map element must specify its key as attribute or as child element. A key attribute is always a String value. --> <!ATTLIST entry key CDATA #IMPLIED> <!-- A short-cut alternative to a "key" element with a "ref bean=" child element. --> <!ATTLIST entry key-ref CDATA #IMPLIED> <!-- A short-cut alternative to a child element "value". --> <!ATTLIST entry value CDATA #IMPLIED> <!-- A short-cut alternative to a child element "ref bean=". --> <!ATTLIST entry value-ref CDATA #IMPLIED> <!-- A key element can contain an inner bean, ref, value, or collection. --> <!ELEMENT key ( (bean | ref | idref | value | null | list | set | map | props) )> <!-- Props elements differ from map elements in that values must be strings. Props may be empty. --> <!ELEMENT props ( (prop)* )> <!-- Enable/disable merging for collections when using parent/child beans. --> <!ATTLIST props merge (true | false | default) "default"> <!-- Element content is the string value of the property. Note that whitespace is trimmed off to avoid unwanted whitespace caused by typical XML formatting. --> <!ELEMENT prop (#PCDATA)> <!-- Each property element must specify its key. --> <!ATTLIST prop key CDATA #REQUIRED>
One of the view technologies you can use with the Spring Framework is Java Server Pages (JSPs). To help you implement views using Java Server Pages the Spring Framework provides you with some tags for evaluating errors, setting themes and outputting internationalized messages.
Please note that the various tags generated by this form tag library are compliant with the XHTML-1.0-Strict specification and attendant DTD.
This appendix describes the spring.tld
tag library.
Provides BindStatus object for the given bind path. The HTML escaping flag participates in a page-wide or application-wide setting (i.e. by HtmlEscapeTag or a "defaultHtmlEscape" context-param in web.xml).
Table D.1. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
htmlEscape |
false |
true |
Set HTML escaping for this tag, as boolean value. Overrides the default HTML escaping setting for the current page. |
ignoreNestedPath |
false |
true |
Set whether to ignore a nested path, if any. Default is to not ignore. |
path |
true |
true |
The path to the bean or bean property to bind status information for. For instance account.name, company.address.zipCode or just employee. The status object will exported to the page scope, specifically for this bean or bean property |
Escapes its enclosed body content, applying HTML escaping and/or JavaScript escaping. The HTML escaping flag participates in a page-wide or application-wide setting (i.e. by HtmlEscapeTag or a "defaultHtmlEscape" context-param in web.xml).
Table D.2. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
htmlEscape |
false |
true |
Set HTML escaping for this tag, as boolean value. Overrides the default HTML escaping setting for the current page. |
javaScriptEscape |
false |
true |
Set JavaScript escaping for this tag, as boolean value. Default is false. |
Provides Errors instance in case of bind errors. The HTML escaping flag participates in a page-wide or application-wide setting (i.e. by HtmlEscapeTag or a "defaultHtmlEscape" context-param in web.xml).
Table D.3. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
htmlEscape |
false |
true |
Set HTML escaping for this tag, as boolean value. Overrides the default HTML escaping setting for the current page. |
name |
true |
true |
The name of the bean in the request, that needs to be inspected for errors. If errors are available for this bean, they will be bound under the 'errors' key. |
Sets default HTML escape value for the current page. Overrides a "defaultHtmlEscape" context-param in web.xml, if any.
Table D.4. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
defaultHtmlEscape |
true |
true |
Set the default value for HTML escaping, to be put into the current PageContext. |
Retrieves the message with the given code, or text if code isn't resolvable. The HTML escaping flag participates in a page-wide or application-wide setting (i.e. by HtmlEscapeTag or a "defaultHtmlEscape" context-param in web.xml).
Table D.5. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
arguments |
false |
true |
Set optional message arguments for this tag, as a (comma-)delimited String (each String argument can contain JSP EL), an Object array (used as argument array), or a single Object (used as single argument). |
argumentSeparator |
false |
true |
The separator character to be used for splitting the arguments string value; defaults to a 'comma' (','). |
code |
false |
true |
The code (key) to use when looking up the message. If code is not provided, the text attribute will be used. |
htmlEscape |
false |
true |
Set HTML escaping for this tag, as boolean value. Overrides the default HTML escaping setting for the current page. |
javaScriptEscape |
false |
true |
Set JavaScript escaping for this tag, as boolean value. Default is false. |
message |
false |
true |
A MessageSourceResolvable argument (direct or through JSP EL). Fits nicely when used in conjunction with Spring's own validation error classes which all implement the MessageSourceResolvable interface. For example, this allows you to iterate over all of the errors in a form, passing each error (using a runtime expression) as the value of this 'message' attribute, thus effecting the easy display of such error messages. |
scope |
false |
true |
The scope to use when exporting the result to a variable. This attribute is only used when var is also set. Possible values are page, request, session and application. |
text |
false |
true |
Default text to output when a message for the given code could not be found. If both text and code are not set, the tag will output null. |
var |
false |
true |
The string to use when binding the result to the page, request, session or application scope. If not specified, the result gets outputted to the writer (i.e. typically directly to the JSP). |
Sets a nested path to be used by the bind tag's path.
Table D.6. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
path |
true |
true |
Set the path that this tag should apply. E.g. 'customer' to allow bind paths like 'address.street' rather than 'customer.address.street'. |
Retrieves the theme message with the given code, or text if code isn't resolvable. The HTML escaping flag participates in a page-wide or application-wide setting (i.e. by HtmlEscapeTag or a "defaultHtmlEscape" context-param in web.xml).
Table D.7. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
arguments |
false |
true |
Set optional message arguments for this tag, as a (comma-)delimited String (each String argument can contain JSP EL), an Object array (used as argument array), or a single Object (used as single argument). |
argumentSeparator |
false |
true |
The separator character to be used for splitting the arguments string value; defaults to a 'comma' (','). |
code |
false |
true |
The code (key) to use when looking up the message. If code is not provided, the text attribute will be used. |
htmlEscape |
false |
true |
Set HTML escaping for this tag, as boolean value. Overrides the default HTML escaping setting for the current page. |
javaScriptEscape |
false |
true |
Set JavaScript escaping for this tag, as boolean value. Default is false. |
message |
false |
true |
A MessageSourceResolvable argument (direct or through JSP EL). |
scope |
false |
true |
The scope to use when exporting the result to a variable. This attribute is only used when var is also set. Possible values are page, request, session and application. |
text |
false |
true |
Default text to output when a message for the given code could not be found. If both text and code are not set, the tag will output null. |
var |
false |
true |
The string to use when binding the result to the page, request, session or application scope. If not specified, the result gets outputted to the writer (i.e. typically directly to the JSP). |
Provides transformation of variables to Strings, using an appropriate custom PropertyEditor from BindTag (can only be used inside BindTag). The HTML escaping flag participates in a page-wide or application-wide setting (i.e. by HtmlEscapeTag or a 'defaultHtmlEscape' context-param in web.xml).
Table D.8. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
htmlEscape |
false |
true |
Set HTML escaping for this tag, as boolean value. Overrides the default HTML escaping setting for the current page. |
scope |
false |
true |
The scope to use when exported the result to a variable. This attribute is only used when var is also set. Possible values are page, request, session and application. |
value |
true |
true |
The value to transform. This is the actual object you want to have transformed (for instance a Date). Using the PropertyEditor that is currently in use by the 'spring:bind' tag. |
var |
false |
true |
The string to use when binding the result to the page, request, session or application scope. If not specified, the result gets outputted to the writer (i.e. typically directly to the JSP). |
One of the view technologies you can use with the Spring Framework is Java Server Pages (JSPs). To help you implement views using Java Server Pages the Spring Framework provides you with some tags for evaluating errors, setting themes and outputting internationalized messages.
Please note that the various tags generated by this form tag library are compliant with the XHTML-1.0-Strict specification and attendant DTD.
This appendix describes the spring-form.tld
tag library.
checkbox
tag”checkboxes
tag”errors
tag”form
tag”hidden
tag”input
tag”label
tag”option
tag”options
tag”password
tag”radiobutton
tag”radiobuttons
tag”select
tag”textarea
tag”Renders an HTML 'input' tag with type 'checkbox'.
Table E.1. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
accesskey |
false |
true |
HTML Standard Attribute |
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used when the bound field has errors. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
dir |
false |
true |
HTML Standard Attribute |
disabled |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will disable the HTML element. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
label |
false |
true |
Value to be displayed as part of the tag |
lang |
false |
true |
HTML Standard Attribute |
onblur |
false |
true |
HTML Event Attribute |
onchange |
false |
true |
HTML Event Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onfocus |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
path |
true |
true |
Path to property for data binding |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
value |
false |
true |
HTML Optional Attribute |
Renders multiple HTML 'input' tags with type 'checkbox'.
Table E.2. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
accesskey |
false |
true |
HTML Standard Attribute |
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used when the bound field has errors. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
delimiter |
false |
true |
Delimiter to use between each 'input' tag with type 'checkbox'. There is no delimiter by default. |
dir |
false |
true |
HTML Standard Attribute |
disabled |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will disable the HTML element. |
element |
false |
true |
Specifies the HTML element that is used to enclose each 'input' tag with type 'checkbox'. Defaults to 'span'. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
itemLabel |
false |
true |
Value to be displayed as part of the 'input' tags with type 'checkbox' |
items |
true |
true |
The Collection, Map or array of objects used to generate the 'input' tags with type 'checkbox' |
itemValue |
false |
true |
Name of the property mapped to 'value' attribute of the 'input' tags with type 'checkbox' |
lang |
false |
true |
HTML Standard Attribute |
onblur |
false |
true |
HTML Event Attribute |
onchange |
false |
true |
HTML Event Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onfocus |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
path |
true |
true |
Path to property for data binding |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
Renders field errors in an HTML 'span' tag.
Table E.3. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
delimiter |
false |
true |
Delimiter for displaying multiple error messages. Defaults to the br tag. |
dir |
false |
true |
HTML Standard Attribute |
element |
false |
true |
Specifies the HTML element that is used to render the enclosing errors. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
lang |
false |
true |
HTML Standard Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
path |
false |
true |
Path to errors object for data binding |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
Renders an HTML 'form' tag and exposes a binding path to inner tags for binding.
Table E.4. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
acceptCharset |
false |
true |
Specifies the list of character encodings for input data that is accepted by the server processing this form. The value is a space- and/or comma-delimited list of charset values. The client must interpret this list as an exclusive-or list, i.e., the server is able to accept any single character encoding per entity received. |
action |
false |
true |
HTML Required Attribute |
autocomplete |
false |
true |
Common Optional Attribute |
commandName |
false |
true |
Name of the model attribute under which the form object is exposed. Defaults to 'command'. |
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
dir |
false |
true |
HTML Standard Attribute |
enctype |
false |
true |
HTML Optional Attribute |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
lang |
false |
true |
HTML Standard Attribute |
method |
false |
true |
HTML Optional Attribute |
modelAttribute |
false |
true |
Name of the model attribute under which the form object is exposed. Defaults to 'command'. |
name |
false |
true |
HTML Standard Attribute - added for backwards compatibility cases |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
onreset |
false |
true |
HTML Event Attribute |
onsubmit |
false |
true |
HTML Event Attribute |
target |
false |
true |
HTML Optional Attribute |
title |
false |
true |
HTML Standard Attribute |
Renders an HTML 'input' tag with type 'hidden' using the bound value.
Table E.5. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
path |
true |
true |
Path to property for data binding |
Renders an HTML 'input' tag with type 'text' using the bound value.
Table E.6. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
accesskey |
false |
true |
HTML Standard Attribute |
alt |
false |
true |
HTML Optional Attribute |
autocomplete |
false |
true |
Common Optional Attribute |
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used when the bound field has errors. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
dir |
false |
true |
HTML Standard Attribute |
disabled |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will disable the HTML element. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
lang |
false |
true |
HTML Standard Attribute |
maxlength |
false |
true |
HTML Optional Attribute |
onblur |
false |
true |
HTML Event Attribute |
onchange |
false |
true |
HTML Event Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onfocus |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
onselect |
false |
true |
HTML Event Attribute |
path |
true |
true |
Path to property for data binding |
readonly |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will make the HTML element readonly. |
size |
false |
true |
HTML Optional Attribute |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
Renders a form field label in an HTML 'label' tag.
Table E.7. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used only when errors are present. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
dir |
false |
true |
HTML Standard Attribute |
for |
false |
true |
HTML Standard Attribute |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
lang |
false |
true |
HTML Standard Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
path |
true |
true |
Path to errors object for data binding |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
Renders a single HTML 'option'. Sets 'selected' as appropriate based on bound value.
Table E.8. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used when the bound field has errors. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
dir |
false |
true |
HTML Standard Attribute |
disabled |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will disable the HTML element. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
label |
false |
true |
HTML Optional Attribute |
lang |
false |
true |
HTML Standard Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
value |
true |
true |
HTML Optional Attribute |
Renders a list of HTML 'option' tags. Sets 'selected' as appropriate based on bound value.
Table E.9. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used when the bound field has errors. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
dir |
false |
true |
HTML Standard Attribute |
disabled |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will disable the HTML element. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
itemLabel |
false |
true |
Name of the property mapped to the inner text of the 'option' tag |
items |
true |
true |
The Collection, Map or array of objects used to generate the inner 'option' tags |
itemValue |
false |
true |
Name of the property mapped to 'value' attribute of the 'option' tag |
lang |
false |
true |
HTML Standard Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
Renders an HTML 'input' tag with type 'password' using the bound value.
Table E.10. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
accesskey |
false |
true |
HTML Standard Attribute |
alt |
false |
true |
HTML Optional Attribute |
autocomplete |
false |
true |
Common Optional Attribute |
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used when the bound field has errors. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
dir |
false |
true |
HTML Standard Attribute |
disabled |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will disable the HTML element. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
lang |
false |
true |
HTML Standard Attribute |
maxlength |
false |
true |
HTML Optional Attribute |
onblur |
false |
true |
HTML Event Attribute |
onchange |
false |
true |
HTML Event Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onfocus |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
onselect |
false |
true |
HTML Event Attribute |
path |
true |
true |
Path to property for data binding |
readonly |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will make the HTML element readonly. |
showPassword |
false |
true |
Is the password value to be shown? Defaults to false. |
size |
false |
true |
HTML Optional Attribute |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
Renders an HTML 'input' tag with type 'radio'.
Table E.11. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
accesskey |
false |
true |
HTML Standard Attribute |
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used when the bound field has errors. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
dir |
false |
true |
HTML Standard Attribute |
disabled |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will disable the HTML element. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
label |
false |
true |
Value to be displayed as part of the tag |
lang |
false |
true |
HTML Standard Attribute |
onblur |
false |
true |
HTML Event Attribute |
onchange |
false |
true |
HTML Event Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onfocus |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
path |
true |
true |
Path to property for data binding |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
value |
false |
true |
HTML Optional Attribute |
Renders multiple HTML 'input' tags with type 'radio'.
Table E.12. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
accesskey |
false |
true |
HTML Standard Attribute |
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used when the bound field has errors. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
delimiter |
false |
true |
Delimiter to use between each 'input' tag with type 'radio'. There is no delimiter by default. |
dir |
false |
true |
HTML Standard Attribute |
disabled |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will disable the HTML element. |
element |
false |
true |
Specifies the HTML element that is used to enclose each 'input' tag with type 'radio'. Defaults to 'span'. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
itemLabel |
false |
true |
Value to be displayed as part of the 'input' tags with type 'radio' |
items |
true |
true |
The Collection, Map or array of objects used to generate the 'input' tags with type 'radio' |
itemValue |
false |
true |
Name of the property mapped to 'value' attribute of the 'input' tags with type 'radio' |
lang |
false |
true |
HTML Standard Attribute |
onblur |
false |
true |
HTML Event Attribute |
onchange |
false |
true |
HTML Event Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onfocus |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
path |
true |
true |
Path to property for data binding |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
Renders an HTML 'select' element. Supports databinding to the selected option.
Table E.13. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
accesskey |
false |
true |
HTML Standard Attribute |
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used when the bound field has errors. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
dir |
false |
true |
HTML Standard Attribute |
disabled |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will disable the HTML element. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
itemLabel |
false |
true |
Name of the property mapped to the inner text of the 'option' tag |
items |
false |
true |
The Collection, Map or array of objects used to generate the inner 'option' tags |
itemValue |
false |
true |
Name of the property mapped to 'value' attribute of the 'option' tag |
lang |
false |
true |
HTML Standard Attribute |
multiple |
false |
true |
HTML Optional Attribute |
onblur |
false |
true |
HTML Event Attribute |
onchange |
false |
true |
HTML Event Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onfocus |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
path |
true |
true |
Path to property for data binding |
size |
false |
true |
HTML Optional Attribute |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |
Renders an HTML 'textarea'.
Table E.14. Attributes
Attribute | Required? | Runtime Expression? | Description |
---|---|---|---|
accesskey |
false |
true |
HTML Standard Attribute |
cols |
false |
true |
HTML Required Attribute |
cssClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute |
cssErrorClass |
false |
true |
Equivalent to "class" - HTML Optional Attribute. Used when the bound field has errors. |
cssStyle |
false |
true |
Equivalent to "style" - HTML Optional Attribute |
dir |
false |
true |
HTML Standard Attribute |
disabled |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will disable the HTML element. |
htmlEscape |
false |
true |
Enable/disable HTML escaping of rendered values. |
id |
false |
true |
HTML Standard Attribute |
lang |
false |
true |
HTML Standard Attribute |
onblur |
false |
true |
HTML Event Attribute |
onchange |
false |
true |
HTML Event Attribute |
onclick |
false |
true |
HTML Event Attribute |
ondblclick |
false |
true |
HTML Event Attribute |
onfocus |
false |
true |
HTML Event Attribute |
onkeydown |
false |
true |
HTML Event Attribute |
onkeypress |
false |
true |
HTML Event Attribute |
onkeyup |
false |
true |
HTML Event Attribute |
onmousedown |
false |
true |
HTML Event Attribute |
onmousemove |
false |
true |
HTML Event Attribute |
onmouseout |
false |
true |
HTML Event Attribute |
onmouseover |
false |
true |
HTML Event Attribute |
onmouseup |
false |
true |
HTML Event Attribute |
onselect |
false |
true |
HTML Event Attribute |
path |
true |
true |
Path to property for data binding |
readonly |
false |
true |
HTML Optional Attribute. Setting the value of this attribute to 'true' (without the quotes) will make the HTML element readonly. |
rows |
false |
true |
HTML Required Attribute |
tabindex |
false |
true |
HTML Standard Attribute |
title |
false |
true |
HTML Standard Attribute |