    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 */
    017package org.apache.bcel.util;
    018
    019import java.io.ByteArrayInputStream;
    020import java.io.IOException;
    021import java.util.Hashtable;
    022
    023import org.apache.bcel.Const;
    024import org.apache.bcel.classfile.ClassParser;
    025import org.apache.bcel.classfile.ConstantClass;
    026import org.apache.bcel.classfile.ConstantPool;
    027import org.apache.bcel.classfile.ConstantUtf8;
    028import org.apache.bcel.classfile.JavaClass;
    029import org.apache.bcel.classfile.Utility;
    030
    031/**
    032 * <p>
    033 * Drop in replacement for the standard class loader of the JVM. You can use it in conjunction with the JavaWrapper to
    034 * dynamically modify/create classes as they're requested.
    035 * </p>
    036 *
    037 * <p>
    038 * This class loader recognizes special requests in a distinct format, i.e., when the name of the requested class
    039 * contains with "$$BCEL$$" it calls the createClass() method with that name (everything bevor the $$BCEL$$ is
    040 * considered to be the package name. You can subclass the class loader and override that method. "Normal" classes class
    041 * can be modified by overriding the modifyClass() method which is called just before defineClass().
    042 * </p>
    043 *
    044 * <p>
    045 * There may be a number of packages where you have to use the default class loader (which may also be faster). You can
    046 * define the set of packages where to use the system class loader in the constructor. The default value contains
    047 * "java.", "sun.", "javax."
    048 * </p>
    049 *
    050 * @see JavaWrapper
    051 * @see ClassPath
    052 * @deprecated 6.0 Do not use - does not work
    053 */
    054@Deprecated
    055public class ClassLoader extends java.lang.ClassLoader {
    056
    057    private static final String BCEL_TOKEN = "$$BCEL$$";
    058
    059    public static final String[] DEFAULT_IGNORED_PACKAGES = {"java.", "javax.", "sun."};
    060
    061    private final Hashtable<String, Class<?>> classes = new Hashtable<>();
    062    // Hashtable is synchronized thus thread-safe
    063    private final String[] ignoredPackages;
    064    private Repository repository = SyntheticRepository.getInstance();
    065
    066    /**
    067     * Ignored packages are by default ( "java.", "sun.", "javax."), i.e. loaded by system class loader
    068     */
    069    public ClassLoader() {
    070        this(DEFAULT_IGNORED_PACKAGES);
    071    }
    072
    073    /**
    074     * @param deferTo delegate class loader to use for ignored packages
    075     */
    076    public ClassLoader(final java.lang.ClassLoader deferTo) {
    077        super(deferTo);
    078        this.ignoredPackages = DEFAULT_IGNORED_PACKAGES;
    079        this.repository = new ClassLoaderRepository(deferTo);
    080    }
    081
    082    /**
    083     * @param ignoredPackages classes contained in these packages will be loaded with the system class loader
    084     * @param deferTo delegate class loader to use for ignored packages
    085     */
    086    public ClassLoader(final java.lang.ClassLoader deferTo, final String[] ignoredPackages) {
    087        this(ignoredPackages);
    088        this.repository = new ClassLoaderRepository(deferTo);
    089    }
    090
    091    /**
    092     * @param ignoredPackages classes contained in these packages will be loaded with the system class loader
    093     */
    094    public ClassLoader(final String[] ignoredPackages) {
    095        this.ignoredPackages = ignoredPackages;
    096    }
    097
    098    /**
    099     * Override this method to create you own classes on the fly. The name contains the special token $$BCEL$$. Everything
    100     * before that token is considered to be a package name. You can encode your own arguments into the subsequent string.
    101     * You must ensure however not to use any "illegal" characters, i.e., characters that may not appear in a Java class
    102     * name too
    103     * <p>
    104     * The default implementation interprets the string as a encoded compressed Java class, unpacks and decodes it with the
    105     * Utility.decode() method, and parses the resulting byte array and returns the resulting JavaClass object.
    106     * </p>
    107     *
    108     * @param className compressed byte code with "$$BCEL$$" in it
    109     */
    110    protected JavaClass createClass(final String className) {
    111        final int index = className.indexOf(BCEL_TOKEN);
    112        final String realName = className.substring(index + BCEL_TOKEN.length());
    113        JavaClass clazz = null;
    114        try {
    115            final byte[] bytes = Utility.decode(realName, true);
    116            final ClassParser parser = new ClassParser(new ByteArrayInputStream(bytes), "foo");
    117            clazz = parser.parse();
    118        } catch (final IOException e) {
    119            e.printStackTrace();
    120            return null;
    121        }
    122        // Adapt the class name to the passed value
    123        final ConstantPool cp = clazz.getConstantPool();
    124        final ConstantClass cl = cp.getConstant(clazz.getClassNameIndex(), Const.CONSTANT_Class, ConstantClass.class);
    125        final ConstantUtf8 name = cp.getConstantUtf8(cl.getNameIndex());
    126        name.setBytes(className.replace('.', '/'));
    127        return clazz;
    128    }
    129
    130    @Override
    131    protected Class<?> loadClass(final String className, final boolean resolve) throws ClassNotFoundException {
    132        Class<?> cl = null;
    133        /*
    134         * First try: lookup hash table.
    135         */
    136        if ((cl = classes.get(className)) == null) {
    137            /*
    138             * Second try: Load system class using system class loader. You better don't mess around with them.
    139             */
    140            for (final String ignoredPackage : ignoredPackages) {
    141                if (className.startsWith(ignoredPackage)) {
    142                    cl = getParent().loadClass(className);
    143                    break;
    144                }
    145            }
    146            if (cl == null) {
    147                JavaClass clazz = null;
    148                /*
    149                 * Third try: Special request?
    150                 */
    151                if (className.contains(BCEL_TOKEN)) {
    152                    clazz = createClass(className);
    153                } else { // Fourth try: Load classes via repository
    154                    if ((clazz = repository.loadClass(className)) == null) {
    155                        throw new ClassNotFoundException(className);
    156                    }
    157                    clazz = modifyClass(clazz);
    158                }
    159                if (clazz != null) {
    160                    final byte[] bytes = clazz.getBytes();
    161                    cl = defineClass(className, bytes, 0, bytes.length);
    162                } else {
    163                    cl = Class.forName(className);
    164                }
    165            }
    166            if (resolve) {
    167                resolveClass(cl);
    168            }
    169        }
    170        classes.put(className, cl);
    171        return cl;
    172    }
    173
    174    /**
    175     * Override this method if you want to alter a class before it gets actually loaded. Does nothing by default.
    176     */
    177    protected JavaClass modifyClass(final JavaClass clazz) {
    178        return clazz;
    179    }
    180}