001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 * 017 */ 018package org.apache.bcel.util; 019 020import java.io.ByteArrayInputStream; 021import java.io.IOException; 022import java.util.Hashtable; 023 024import org.apache.bcel.Const; 025import org.apache.bcel.classfile.ClassParser; 026import org.apache.bcel.classfile.ConstantClass; 027import org.apache.bcel.classfile.ConstantPool; 028import org.apache.bcel.classfile.ConstantUtf8; 029import org.apache.bcel.classfile.JavaClass; 030import org.apache.bcel.classfile.Utility; 031 032/** 033 * <p>Drop in replacement for the standard class loader of the JVM. You can use it 034 * in conjunction with the JavaWrapper to dynamically modify/create classes 035 * as they're requested.</p> 036 * 037 * <p>This class loader recognizes special requests in a distinct 038 * format, i.e., when the name of the requested class contains with 039 * "$$BCEL$$" it calls the createClass() method with that name 040 * (everything bevor the $$BCEL$$ is considered to be the package 041 * name. You can subclass the class loader and override that 042 * method. "Normal" classes class can be modified by overriding the 043 * modifyClass() method which is called just before defineClass().</p> 044 * 045 * <p>There may be a number of packages where you have to use the 046 * default class loader (which may also be faster). You can define the 047 * set of packages where to use the system class loader in the 048 * constructor. The default value contains "java.", "sun.", 049 * "javax."</p> 050 * 051 * @see JavaWrapper 052 * @see ClassPath 053 * @deprecated 6.0 Do not use - does not work 054 */ 055@Deprecated 056public class ClassLoader extends java.lang.ClassLoader { 057 058 private static final String BCEL_TOKEN = "$$BCEL$$"; 059 060 public static final String[] DEFAULT_IGNORED_PACKAGES = { 061 "java.", "javax.", "sun." 062 }; 063 064 private final Hashtable<String, Class<?>> classes = new Hashtable<>(); 065 // Hashtable is synchronized thus thread-safe 066 private final String[] ignored_packages; 067 private Repository repository = SyntheticRepository.getInstance(); 068 069 070 /** Ignored packages are by default ( "java.", "sun.", 071 * "javax."), i.e. loaded by system class loader 072 */ 073 public ClassLoader() { 074 this(DEFAULT_IGNORED_PACKAGES); 075 } 076 077 078 /** @param deferTo delegate class loader to use for ignored packages 079 */ 080 public ClassLoader(final java.lang.ClassLoader deferTo) { 081 super(deferTo); 082 this.ignored_packages = DEFAULT_IGNORED_PACKAGES; 083 this.repository = new ClassLoaderRepository(deferTo); 084 } 085 086 087 /** @param ignored_packages classes contained in these packages will be loaded 088 * with the system class loader 089 */ 090 public ClassLoader(final String[] ignored_packages) { 091 this.ignored_packages = ignored_packages; 092 } 093 094 095 /** @param ignored_packages classes contained in these packages will be loaded 096 * with the system class loader 097 * @param deferTo delegate class loader to use for ignored packages 098 */ 099 public ClassLoader(final java.lang.ClassLoader deferTo, final String[] ignored_packages) { 100 this(ignored_packages); 101 this.repository = new ClassLoaderRepository(deferTo); 102 } 103 104 @Override 105 protected Class<?> loadClass( final String class_name, final boolean resolve ) throws ClassNotFoundException { 106 Class<?> cl = null; 107 /* First try: lookup hash table. 108 */ 109 if ((cl = classes.get(class_name)) == null) { 110 /* Second try: Load system class using system class loader. You better 111 * don't mess around with them. 112 */ 113 for (final String ignored_package : ignored_packages) { 114 if (class_name.startsWith(ignored_package)) { 115 cl = getParent().loadClass(class_name); 116 break; 117 } 118 } 119 if (cl == null) { 120 JavaClass clazz = null; 121 /* Third try: Special request? 122 */ 123 if (class_name.contains(BCEL_TOKEN)) { 124 clazz = createClass(class_name); 125 } else { // Fourth try: Load classes via repository 126 if ((clazz = repository.loadClass(class_name)) != null) { 127 clazz = modifyClass(clazz); 128 } else { 129 throw new ClassNotFoundException(class_name); 130 } 131 } 132 if (clazz != null) { 133 final byte[] bytes = clazz.getBytes(); 134 cl = defineClass(class_name, bytes, 0, bytes.length); 135 } else { 136 cl = Class.forName(class_name); 137 } 138 } 139 if (resolve) { 140 resolveClass(cl); 141 } 142 } 143 classes.put(class_name, cl); 144 return cl; 145 } 146 147 148 /** Override this method if you want to alter a class before it gets actually 149 * loaded. Does nothing by default. 150 */ 151 protected JavaClass modifyClass( final JavaClass clazz ) { 152 return clazz; 153 } 154 155 156 /** 157 * Override this method to create you own classes on the fly. The 158 * name contains the special token $$BCEL$$. Everything before that 159 * token is considered to be a package name. You can encode your own 160 * arguments into the subsequent string. You must ensure however not 161 * to use any "illegal" characters, i.e., characters that may not 162 * appear in a Java class name too 163 * <p> 164 * The default implementation interprets the string as a encoded compressed 165 * Java class, unpacks and decodes it with the Utility.decode() method, and 166 * parses the resulting byte array and returns the resulting JavaClass object. 167 * </p> 168 * 169 * @param class_name compressed byte code with "$$BCEL$$" in it 170 */ 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 Const.CONSTANT_Class); 187 final ConstantUtf8 name = (ConstantUtf8) cp.getConstant(cl.getNameIndex(), 188 Const.CONSTANT_Utf8); 189 name.setBytes(class_name.replace('.', '/')); 190 return clazz; 191 } 192}