1 package org.apache.bcel.util;
2
3 /* ====================================================================
4 * The Apache Software License, Version 1.1
5 *
6 * Copyright (c) 2001 The Apache Software Foundation. All rights
7 * reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 *
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 *
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in
18 * the documentation and/or other materials provided with the
19 * distribution.
20 *
21 * 3. The end-user documentation included with the redistribution,
22 * if any, must include the following acknowledgment:
23 * "This product includes software developed by the
24 * Apache Software Foundation (http://www.apache.org/)."
25 * Alternately, this acknowledgment may appear in the software itself,
26 * if and wherever such third-party acknowledgments normally appear.
27 *
28 * 4. The names "Apache" and "Apache Software Foundation" and
29 * "Apache BCEL" must not be used to endorse or promote products
30 * derived from this software without prior written permission. For
31 * written permission, please contact apache@apache.org.
32 *
33 * 5. Products derived from this software may not be called "Apache",
34 * "Apache BCEL", nor may "Apache" appear in their name, without
35 * prior written permission of the Apache Software Foundation.
36 *
37 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
38 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
39 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
40 * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
41 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
42 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
43 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
44 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
45 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
46 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
47 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
48 * SUCH DAMAGE.
49 * ====================================================================
50 *
51 * This software consists of voluntary contributions made by many
52 * individuals on behalf of the Apache Software Foundation. For more
53 * information on the Apache Software Foundation, please see
54 * <http://www.apache.org/>.
55 */
56
57 import java.util.Hashtable;
58 import java.io.*;
59 import org.apache.bcel.*;
60 import org.apache.bcel.classfile.*;
61
62 /***
63 * <p>Drop in replacement for the standard class loader of the JVM. You can use it
64 * in conjunction with the JavaWrapper to dynamically modify/create classes
65 * as they're requested.</p>
66 *
67 * <p>This class loader recognizes special requests in a distinct
68 * format, i.e., when the name of the requested class contains with
69 * "$$BCEL$$" it calls the createClass() method with that name
70 * (everything bevor the $$BCEL$$ is considered to be the package
71 * name. You can subclass the class loader and override that
72 * method. "Normal" classes class can be modified by overriding the
73 * modifyClass() method which is called just before defineClass().</p>
74 *
75 * <p>There may be a number of packages where you have to use the default
76 * class loader (which may also be faster). You can define the set of packages
77 * where to use the system class loader in the constructor. The default value contains
78 * "java.", "sun.", "javax."</p>
79 *
80 * @version $Id: ClassLoader.java,v 1.6 2002/06/13 09:32:50 enver Exp $
81 * @author <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
82 * @see JavaWrapper
83 * @see ClassPath
84 */
85 public class ClassLoader extends java.lang.ClassLoader {
86 private Hashtable classes = new Hashtable(); // Hashtable is synchronized thus thread-safe
87 privateb> String[] ignored_packages = {
88 "java.", "javax.", "sun."
89 };
90 private Repository repository = SyntheticRepository.getInstance();
91 private java.lang.ClassLoader deferTo = ClassLoader.getSystemClassLoader();
92
93 public ClassLoader() {
94 }
95
96 public ClassLoader(java.lang.ClassLoader deferTo) {
97 this.deferTo = deferTo;
98 this.repository = new ClassLoaderRepository(deferTo);
99 }
100
101 /*** @param ignored_packages classes contained in these packages will be loaded
102 * with the system class loader
103 */
104 publicClassLoader(String[] ignored_packages) {/package-summary.html">b> ClassLoader(String[] ignored_packages) {
105 addIgnoredPkgs(ignored_packages);
106 }
107
108 publicClassLoader(java/lang/ClassLoader deferTo, String [] ignored_packages) {/package-summary.html">b> ClassLoader(java.lang.ClassLoader deferTo, String [] ignored_packages) {
109 this.deferTo = deferTo;
110 this.repository = new ClassLoaderRepository(deferTo);
111
112 addIgnoredPkgs(ignored_packages);
113 }
114
115 privateb> void addIgnoredPkgs(String[] ignored_packages) {
116 String[] new_p = new String[ignored_packages.length + this.ignored_packages.length];
117
118 System.arraycopy(this.ignored_packages, 0, new_p, 0, this.ignored_packages.length);
119 System.arraycopy(ignored_packages, 0, new_p, this.ignored_packages.length,
120 ignored_packages.length);
121
122 this.ignored_packages = new_p;
123 }
124
125 protected Class loadClass(String class_name, boolean resolve)
126 throws ClassNotFoundException
127 {
128 Class cl = null;
129
130 /* First try: lookup hash table.
131 */
132 if((cl=(Class)classes.get(class_name)) == null) {
133 /* Second try: Load system class using system class loader. You better
134 * don't mess around with them.
135 */
136 for(int i=0; i < ignored_packages.length; i++) {
137 if(class_name.startsWith(ignored_packages[i])) {
138 cl = deferTo.loadClass(class_name);
139 break;
140 }
141 }
142
143 if(cl == null) {
144 JavaClass clazz = null;
145
146 /* Third try: Special request?
147 */
148 if(class_name.indexOf("$$BCEL$$") >= 0)
149 clazz = createClass(class_name);
150 else { // Fourth try: Load classes via repository
151 if ((clazz = repository.loadClass(class_name)) != null) {
152 clazz = modifyClass(clazz);
153 }
154 else
155 throw new ClassNotFoundException(class_name);
156 }
157
158 if(clazz != null) {
159 byte[] bytes = clazz.getBytes();
160 cl = defineClass(class_name, bytes, 0, bytes.length);
161 } else // Fourth try: Use default class loader
162 cl = Class.forName(class_name);
163 }
164
165 if(resolve)
166 resolveClass(cl);
167 }
168
169 classes.put(class_name, cl);
170
171 return cl;
172 }
173
174 /*** Override this method if you want to alter a class before it gets actually
175 * loaded. Does nothing by default.
176 */
177 protected JavaClass modifyClass(JavaClass clazz) {
178 return clazz;
179 }
180
181 /***
182 * Override this method to create you own classes on the fly. The
183 * name contains the special token $$BCEL$$. Everything before that
184 * token is consddered to be a package name. You can encode you own
185 * arguments into the subsequent string. You must regard however not
186 * to use any "illegal" characters, i.e., characters that may not
187 * appear in a Java class name too<br>
188 *
189 * The default implementation interprets the string as a encoded compressed
190 * Java class, unpacks and decodes it with the Utility.decode() method, and
191 * parses the resulting byte array and returns the resulting JavaClass object.
192 *
193 * @param class_name compressed byte code with "$$BCEL$$" in it
194 */
195 protected JavaClass createClass(String class_name) {
196 int index = class_name.indexOf("$$BCEL$$");
197 String real_name = class_name.substring(index + 8);
198
199 JavaClass clazz = null;
200 try {
201 byte[] bytes = Utility.decode(real_name, true);
202 ClassParser parser = new ClassParser(new ByteArrayInputStream(bytes), "foo");
203
204 clazz = parser.parse();
205 } catch(Throwable e) {
206 e.printStackTrace();
207 return null;
208 }
209
210 // Adapt the class name to the passed value
211 ConstantPool cp = clazz.getConstantPool();
212
213 ConstantClass cl = (ConstantClass)cp.getConstant(clazz.getClassNameIndex(),
214 Constants.CONSTANT_Class);
215 ConstantUtf8 name = (ConstantUtf8)cp.getConstant(cl.getNameIndex(),
216 Constants.CONSTANT_Utf8);
217 name.setBytes(class_name.replace('.', '/'));
218
219 return clazz;
220 }
221 }
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