1 /*
2  * Licensed to the Apache Software Foundation (ASF) under one or more
3  * contributor license agreements.  See the NOTICE file distributed with
4  * this work for additional information regarding copyright ownership.
5  * The ASF licenses this file to You under the Apache License, Version 2.0
6  * (the "License"); you may not use this file except in compliance with
7  * the License.  You may obtain a copy of the License at
8  *
9  *      http://www.apache.org/licenses/LICENSE-2.0
10  *
11  *  Unless required by applicable law or agreed to in writing, software
12  *  distributed under the License is distributed on an "AS IS" BASIS,
13  *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  *  See the License for the specific language governing permissions and
15  *  limitations under the License.
16  *
17  */
18 package org.apache.bcel.util;
19 
20 import java.io.ByteArrayInputStream;
21 import java.io.IOException;
22 import java.util.Hashtable;
23 
24 import org.apache.bcel.Constants;
25 import org.apache.bcel.classfile.ClassParser;
26 import org.apache.bcel.classfile.ConstantClass;
27 import org.apache.bcel.classfile.ConstantPool;
28 import org.apache.bcel.classfile.ConstantUtf8;
29 import org.apache.bcel.classfile.JavaClass;
30 import org.apache.bcel.classfile.Utility;
31 
32 /**
33  * <p>Drop in replacement for the standard class loader of the JVM. You can use it
34  * in conjunction with the JavaWrapper to dynamically modify/create classes
35  * as they're requested.</p>
36  *
37  * <p>This class loader recognizes special requests in a distinct
38  * format, i.e., when the name of the requested class contains with
39  * "$$BCEL$$" it calls the createClass() method with that name
40  * (everything bevor the $$BCEL$$ is considered to be the package
41  * name. You can subclass the class loader and override that
42  * method. "Normal" classes class can be modified by overriding the
43  * modifyClass() method which is called just before defineClass().</p>
44  *
45  * <p>There may be a number of packages where you have to use the
46  * default class loader (which may also be faster). You can define the
47  * set of packages where to use the system class loader in the
48  * constructor. The default value contains "java.", "sun.",
49  * "javax."</p>
50  *
51  * @version $Id$
52  * @see JavaWrapper
53  * @see ClassPath
54  * @deprecated 6.0 Do not use - does not work
55  */
56 @Deprecated
57 public class ClassLoader extends java.lang.ClassLoader {
58 
59     private static final String BCEL_TOKEN = "$$BCEL$$";
60 
61     public static final String[] DEFAULT_IGNORED_PACKAGES = {
62             "java.", "javax.", "sun."
63     };
64 
65     private final Hashtable<String, Class<?>> classes = new Hashtable<>();
66     // Hashtable is synchronized thus thread-safe
67     private final String[] ignored_packages;
68     private Repository repository = SyntheticRepository.getInstance();
69 
70 
71     /** Ignored packages are by default ( "java.", "sun.",
72      * "javax."), i.e. loaded by system class loader
73      */
ClassLoader()74     public ClassLoader() {
75         this(DEFAULT_IGNORED_PACKAGES);
76     }
77 
78 
79     /** @param deferTo delegate class loader to use for ignored packages
80      */
ClassLoader(final java.lang.ClassLoader deferTo)81     public ClassLoader(final java.lang.ClassLoader deferTo) {
82         super(deferTo);
83         this.ignored_packages = DEFAULT_IGNORED_PACKAGES;
84         this.repository = new ClassLoaderRepository(deferTo);
85     }
86 
87 
88     /** @param ignored_packages classes contained in these packages will be loaded
89      * with the system class loader
90      */
ClassLoader(final String[] ignored_packages)91     public ClassLoader(final String[] ignored_packages) {
92         this.ignored_packages = ignored_packages;
93     }
94 
95 
96     /** @param ignored_packages classes contained in these packages will be loaded
97      * with the system class loader
98      * @param deferTo delegate class loader to use for ignored packages
99      */
ClassLoader(final java.lang.ClassLoader deferTo, final String[] ignored_packages)100     public ClassLoader(final java.lang.ClassLoader deferTo, final String[] ignored_packages) {
101         this(ignored_packages);
102         this.repository = new ClassLoaderRepository(deferTo);
103     }
104 
105     @Override
loadClass( final String class_name, final boolean resolve )106     protected Class<?> loadClass( final String class_name, final boolean resolve ) throws ClassNotFoundException {
107         Class<?> cl = null;
108         /* First try: lookup hash table.
109          */
110         if ((cl = classes.get(class_name)) == null) {
111             /* Second try: Load system class using system class loader. You better
112              * don't mess around with them.
113              */
114             for (final String ignored_package : ignored_packages) {
115                 if (class_name.startsWith(ignored_package)) {
116                     cl = getParent().loadClass(class_name);
117                     break;
118                 }
119             }
120             if (cl == null) {
121                 JavaClass clazz = null;
122                 /* Third try: Special request?
123                  */
124                 if (class_name.contains(BCEL_TOKEN)) {
125                     clazz = createClass(class_name);
126                 } else { // Fourth try: Load classes via repository
127                     if ((clazz = repository.loadClass(class_name)) != null) {
128                         clazz = modifyClass(clazz);
129                     } else {
130                         throw new ClassNotFoundException(class_name);
131                     }
132                 }
133                 if (clazz != null) {
134                     final byte[] bytes = clazz.getBytes();
135                     cl = defineClass(class_name, bytes, 0, bytes.length);
136                 } else {
137                     cl = Class.forName(class_name);
138                 }
139             }
140             if (resolve) {
141                 resolveClass(cl);
142             }
143         }
144         classes.put(class_name, cl);
145         return cl;
146     }
147 
148 
149     /** Override this method if you want to alter a class before it gets actually
150      * loaded. Does nothing by default.
151      */
modifyClass( final JavaClass clazz )152     protected JavaClass modifyClass( final JavaClass clazz ) {
153         return clazz;
154     }
155 
156 
157     /**
158      * Override this method to create you own classes on the fly. The
159      * name contains the special token $$BCEL$$. Everything before that
160      * token is considered to be a package name. You can encode your own
161      * arguments into the subsequent string. You must ensure however not
162      * to use any "illegal" characters, i.e., characters that may not
163      * appear in a Java class name too<br>
164      *
165      * The default implementation interprets the string as a encoded compressed
166      * Java class, unpacks and decodes it with the Utility.decode() method, and
167      * parses the resulting byte array and returns the resulting JavaClass object.
168      *
169      * @param class_name compressed byte code with "$$BCEL$$" in it
170      */
createClass( final String class_name )171     protected JavaClass createClass( final String class_name ) {
172         final int index = class_name.indexOf(BCEL_TOKEN);
173         final String real_name = class_name.substring(index + BCEL_TOKEN.length());
174         JavaClass clazz = null;
175         try {
176             final byte[] bytes = Utility.decode(real_name, true);
177             final ClassParser parser = new ClassParser(new ByteArrayInputStream(bytes), "foo");
178             clazz = parser.parse();
179         } catch (final IOException e) {
180             e.printStackTrace();
181             return null;
182         }
183         // Adapt the class name to the passed value
184         final ConstantPool cp = clazz.getConstantPool();
185         final ConstantClass cl = (ConstantClass) cp.getConstant(clazz.getClassNameIndex(),
186                 Constants.CONSTANT_Class);
187         final ConstantUtf8 name = (ConstantUtf8) cp.getConstant(cl.getNameIndex(),
188                 Constants.CONSTANT_Utf8);
189         name.setBytes(class_name.replace('.', '/'));
190         return clazz;
191     }
192 }
193