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.Constants; 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 * @version $Id: ClassLoader.java 1806200 2017-08-25 16:33:06Z ggregory $ 052 * @see JavaWrapper 053 * @see ClassPath 054 * @deprecated 6.0 Do not use - does not work 055 */ 056@Deprecated 057public class ClassLoader extends java.lang.ClassLoader { 058 059 private static final String BCEL_TOKEN = "$$BCEL$$"; 060 061 public static final String[] DEFAULT_IGNORED_PACKAGES = { 062 "java.", "javax.", "sun." 063 }; 064 065 private final Hashtable<String, Class<?>> classes = new Hashtable<>(); 066 // Hashtable is synchronized thus thread-safe 067 private final String[] ignored_packages; 068 private Repository repository = SyntheticRepository.getInstance(); 069 070 071 /** Ignored packages are by default ( "java.", "sun.", 072 * "javax."), i.e. loaded by system class loader 073 */ 074 public ClassLoader() { 075 this(DEFAULT_IGNORED_PACKAGES); 076 } 077 078 079 /** @param deferTo delegate class loader to use for ignored packages 080 */ 081 public ClassLoader(final java.lang.ClassLoader deferTo) { 082 super(deferTo); 083 this.ignored_packages = DEFAULT_IGNORED_PACKAGES; 084 this.repository = new ClassLoaderRepository(deferTo); 085 } 086 087 088 /** @param ignored_packages classes contained in these packages will be loaded 089 * with the system class loader 090 */ 091 public ClassLoader(final String[] ignored_packages) { 092 this.ignored_packages = ignored_packages; 093 } 094 095 096 /** @param ignored_packages classes contained in these packages will be loaded 097 * with the system class loader 098 * @param deferTo delegate class loader to use for ignored packages 099 */ 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 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 */ 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 */ 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}