    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 * @version $Id$
    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                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}