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 }
This page was automatically generated by Maven