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Customizing JMeter to suit your needs.

Extensible Interfaces

There are five basic objects in JMeter which provide extensibility:

• Visualizers represent the sampling data which is recorded.
• Timers specify the delay between samples.
• SamplerControllers hold information about all the test cases to be sampled, and overall information about how the test is conducted.
• Samplers are the classes that actually do the sampling of a particular protocol.
• TestSamples hold information about a particular test case to be sampled.

Visualizers

The Visualizer interface exists in the org.apache.jmeter.visualizers package. JMeter maintains an instance of each visualizer it is aware of for each thread group currently available to the user. A visualizer provides a method of recording the data which JMeter generates. A visualizer may represent the data graphically (GraphVisualizer), persistently (FileVisualizer) or both (TBD). The visualizer contains three methods:

add(SampleResult result) adds data to the visualization.

JMeter calls the add method to include new data in the visualizer. The visualizer should add the data into its data representation.

clear() clears all data in the visualizer currently

JMeter calls clear when the user requests that all visualizers be cleared. When the clear method is called the visualizer should clear all data from its representation and re-initialize itself.

getControlPanel() obtains the GUI for the visualizer

JMeter calls getControlPanel at start up time to prepare the visualizer for display.

Timers

Timers provide a framework for delaying in between samples. This is important in order to obtain a true balanced load on a function rather than a calm-STORM-calm-STORM-calm... pattern. Timers contain two methods:

delay() wait for a Timer specific amount of time

JMeter calls this function prior to every sample. The Timer should wait for a period of time and then return.

set() prepare for sampling

JMeter calls this function prior to the begining of a test session. The timer should initialize itself, read any values from its UI and prepare for operation.

SamplerControllers

The sampler controller is by far the most complicated, but also the most powerful, interface in JMeter. It allows a user to customize what, where and when JMeter tests. It provides six methods:

start()

JMeter calls this immediatly prior to starting a test. It is most often use to disable the SamplerController's GUI.

stop()

JMeter calls this when a user requests a stop to a test. It is most often used to re-enable the SamplerController's GUI.

getControlPanel() Get the GUI for the SamplerController

JMeter calls this at start up to create the its GUI. This is how a user enters information into the SamplerController.

getName() Get the SamplerController's display name.

JMeter uses this name in the list of SamplerControllers that it displays.

getDefaultThreadGroups()

Gets the default list of threadgroups.

getSampleThreads(String threadGroup,int numThreads)

When the user hits start, use this method to get all the JMeterThread objects you want for a threadgroup. Each JMeterThread object implements Runnable and it is used to sample the test entries.

Samplers

Samplers are simple - they are the objects that know the protocol of that which you wish to sample. The HTTPSampler knows how to request a URL from a web server, for instance. The interface for Sampler is as follows:

public SampleResult sample(Entry e)

JMeterThread implementations will loop through all the test samples given to them, and call the sample method on the Sampler (also given to them) for each test entry. SampleResult is essentially a Map containing information about the sampling (timing data is included, as well as the test response from the url).

TestSample

TestSamples are objects that collect information from users about each test sample the user wants to test. The TestSample object is also responsible for serving up its test entries. The interface:

public java.awt.Container getGUI()

Returns the GUI used to collect information from the user.

public Entry[] getEntries()

Gets a list of entries to be sampled from the TestSample object

public String[] getThreadGroups()

Get all the thread groups the user selected for this TestSample

public void setThreadGroups(String[] threadGroups)

Set the thread groups the user may choose from

public String getName()

Get a name for this TestSample

public void setName(String name)

Set the name for this TestSample

public void reset()

inform the test sample that a sampling run is starting