185 lines
7.0 KiB
Java
185 lines
7.0 KiB
Java
/*
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* Copyright 2000-2004 The Apache Software Foundation
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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*/
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package org.apache.bcel.util;
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import java.io.ByteArrayInputStream;
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import java.util.Hashtable;
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import org.apache.bcel.Constants;
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import org.apache.bcel.classfile.ClassParser;
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import org.apache.bcel.classfile.ConstantClass;
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import org.apache.bcel.classfile.ConstantPool;
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import org.apache.bcel.classfile.ConstantUtf8;
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import org.apache.bcel.classfile.JavaClass;
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import org.apache.bcel.classfile.Utility;
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/**
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* <p>Drop in replacement for the standard class loader of the JVM. You can use it
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* in conjunction with the JavaWrapper to dynamically modify/create classes
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* as they're requested.</p>
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*
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* <p>This class loader recognizes special requests in a distinct
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* format, i.e., when the name of the requested class contains with
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* "$$BCEL$$" it calls the createClass() method with that name
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* (everything bevor the $$BCEL$$ is considered to be the package
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* name. You can subclass the class loader and override that
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* method. "Normal" classes class can be modified by overriding the
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* modifyClass() method which is called just before defineClass().</p>
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*
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* <p>There may be a number of packages where you have to use the
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* default class loader (which may also be faster). You can define the
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* set of packages where to use the system class loader in the
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* constructor. The default value contains "java.", "sun.",
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* "javax."</p>
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*
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* @version $Id: ClassLoader.java 386056 2006-03-15 11:31:56Z tcurdt $
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* @author <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
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* @see JavaWrapper
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* @see ClassPath
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*/
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public class ClassLoader extends java.lang.ClassLoader {
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public static final String[] DEFAULT_IGNORED_PACKAGES = {
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"java.", "javax.", "sun."
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};
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private Hashtable classes = new Hashtable(); // Hashtable is synchronized thus thread-safe
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private String[] ignored_packages;
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private Repository repository = SyntheticRepository.getInstance();
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/** Ignored packages are by default ( "java.", "sun.",
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* "javax."), i.e. loaded by system class loader
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*/
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public ClassLoader() {
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this(DEFAULT_IGNORED_PACKAGES);
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}
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/** @param deferTo delegate class loader to use for ignored packages
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*/
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public ClassLoader(java.lang.ClassLoader deferTo) {
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super(deferTo);
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this.ignored_packages = DEFAULT_IGNORED_PACKAGES;
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this.repository = new ClassLoaderRepository(deferTo);
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}
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/** @param ignored_packages classes contained in these packages will be loaded
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* with the system class loader
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*/
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public ClassLoader(String[] ignored_packages) {
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this.ignored_packages = ignored_packages;
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}
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/** @param ignored_packages classes contained in these packages will be loaded
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* with the system class loader
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* @param deferTo delegate class loader to use for ignored packages
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*/
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public ClassLoader(java.lang.ClassLoader deferTo, String[] ignored_packages) {
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this(ignored_packages);
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this.repository = new ClassLoaderRepository(deferTo);
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}
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protected Class loadClass( String class_name, boolean resolve ) throws ClassNotFoundException {
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Class cl = null;
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/* First try: lookup hash table.
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*/
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if ((cl = (Class) classes.get(class_name)) == null) {
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/* Second try: Load system class using system class loader. You better
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* don't mess around with them.
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*/
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for (int i = 0; i < ignored_packages.length; i++) {
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if (class_name.startsWith(ignored_packages[i])) {
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cl = getParent().loadClass(class_name);
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break;
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}
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}
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if (cl == null) {
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JavaClass clazz = null;
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/* Third try: Special request?
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*/
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if (class_name.indexOf("$$BCEL$$") >= 0) {
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clazz = createClass(class_name);
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} else { // Fourth try: Load classes via repository
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if ((clazz = repository.loadClass(class_name)) != null) {
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clazz = modifyClass(clazz);
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} else {
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throw new ClassNotFoundException(class_name);
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}
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}
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if (clazz != null) {
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byte[] bytes = clazz.getBytes();
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cl = defineClass(class_name, bytes, 0, bytes.length);
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} else {
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cl = Class.forName(class_name);
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}
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}
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if (resolve) {
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resolveClass(cl);
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}
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}
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classes.put(class_name, cl);
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return cl;
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}
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/** Override this method if you want to alter a class before it gets actually
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* loaded. Does nothing by default.
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*/
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protected JavaClass modifyClass( JavaClass clazz ) {
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return clazz;
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}
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/**
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* Override this method to create you own classes on the fly. The
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* name contains the special token $$BCEL$$. Everything before that
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* token is consddered to be a package name. You can encode you own
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* arguments into the subsequent string. You must regard however not
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* to use any "illegal" characters, i.e., characters that may not
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* appear in a Java class name too<br>
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*
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* The default implementation interprets the string as a encoded compressed
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* Java class, unpacks and decodes it with the Utility.decode() method, and
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* parses the resulting byte array and returns the resulting JavaClass object.
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*
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* @param class_name compressed byte code with "$$BCEL$$" in it
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*/
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protected JavaClass createClass( String class_name ) {
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int index = class_name.indexOf("$$BCEL$$");
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String real_name = class_name.substring(index + 8);
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JavaClass clazz = null;
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try {
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byte[] bytes = Utility.decode(real_name, true);
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ClassParser parser = new ClassParser(new ByteArrayInputStream(bytes), "foo");
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clazz = parser.parse();
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} catch (Throwable e) {
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e.printStackTrace();
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return null;
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}
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// Adapt the class name to the passed value
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ConstantPool cp = clazz.getConstantPool();
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ConstantClass cl = (ConstantClass) cp.getConstant(clazz.getClassNameIndex(),
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Constants.CONSTANT_Class);
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ConstantUtf8 name = (ConstantUtf8) cp.getConstant(cl.getNameIndex(),
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Constants.CONSTANT_Utf8);
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name.setBytes(class_name.replace('.', '/'));
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return clazz;
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}
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}
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