    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one
    003 * or more contributor license agreements.  See the NOTICE file
    004 * distributed with this work for additional information
    005 * regarding copyright ownership.  The ASF licenses this file
    006 * to you under the Apache License, Version 2.0 (the
    007 * "License"); you may not use this file except in compliance
    008 * with the License.  You may obtain a copy of the License at
    009 *
    010 *   https://www.apache.org/licenses/LICENSE-2.0
    011 *
    012 * Unless required by applicable law or agreed to in writing,
    013 * software distributed under the License is distributed on an
    014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    015 * KIND, either express or implied.  See the License for the
    016 * specific language governing permissions and limitations
    017 * under the License.
    018 */
    019package org.apache.bcel.util;
    020
    021import java.io.ByteArrayInputStream;
    022import java.io.IOException;
    023import java.util.Hashtable;
    024
    025import org.apache.bcel.Const;
    026import org.apache.bcel.classfile.ClassParser;
    027import org.apache.bcel.classfile.ConstantClass;
    028import org.apache.bcel.classfile.ConstantPool;
    029import org.apache.bcel.classfile.ConstantUtf8;
    030import org.apache.bcel.classfile.JavaClass;
    031import org.apache.bcel.classfile.Utility;
    032
    033/**
    034 * <p>
    035 * Drop in replacement for the standard class loader of the JVM. You can use it in conjunction with the JavaWrapper to
    036 * dynamically modify/create classes as they're requested.
    037 * </p>
    038 *
    039 * <p>
    040 * This class loader recognizes special requests in a distinct format, i.e., when the name of the requested class
    041 * contains with "$$BCEL$$" it calls the createClass() method with that name (everything bevor the $$BCEL$$ is
    042 * considered to be the package name. You can subclass the class loader and override that method. "Normal" classes class
    043 * can be modified by overriding the modifyClass() method which is called just before defineClass().
    044 * </p>
    045 *
    046 * <p>
    047 * There may be a number of packages where you have to use the default class loader (which may also be faster). You can
    048 * define the set of packages where to use the system class loader in the constructor. The default value contains
    049 * "java.", "sun.", "javax."
    050 * </p>
    051 *
    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 = {"java.", "javax.", "sun."};
    062
    063    private final Hashtable<String, Class<?>> classes = new Hashtable<>();
    064    // Hashtable is synchronized thus thread-safe
    065    private final String[] ignoredPackages;
    066    private Repository repository = SyntheticRepository.getInstance();
    067
    068    /**
    069     * Ignored packages are by default ( "java.", "sun.", "javax."), i.e. loaded by system class loader
    070     */
    071    public ClassLoader() {
    072        this(DEFAULT_IGNORED_PACKAGES);
    073    }
    074
    075    /**
    076     * @param deferTo delegate class loader to use for ignored packages
    077     */
    078    public ClassLoader(final java.lang.ClassLoader deferTo) {
    079        super(deferTo);
    080        this.ignoredPackages = DEFAULT_IGNORED_PACKAGES;
    081        this.repository = new ClassLoaderRepository(deferTo);
    082    }
    083
    084    /**
    085     * @param ignoredPackages classes contained in these packages will be loaded with the system class loader
    086     * @param deferTo delegate class loader to use for ignored packages
    087     */
    088    public ClassLoader(final java.lang.ClassLoader deferTo, final String[] ignoredPackages) {
    089        this(ignoredPackages);
    090        this.repository = new ClassLoaderRepository(deferTo);
    091    }
    092
    093    /**
    094     * @param ignoredPackages classes contained in these packages will be loaded with the system class loader
    095     */
    096    public ClassLoader(final String[] ignoredPackages) {
    097        this.ignoredPackages = ignoredPackages;
    098    }
    099
    100    /**
    101     * Override this method to create you own classes on the fly. The name contains the special token $$BCEL$$. Everything
    102     * before that token is considered to be a package name. You can encode your own arguments into the subsequent string.
    103     * You must ensure however not to use any "illegal" characters, i.e., characters that may not appear in a Java class
    104     * name too
    105     * <p>
    106     * The default implementation interprets the string as a encoded compressed Java class, unpacks and decodes it with the
    107     * Utility.decode() method, and parses the resulting byte array and returns the resulting JavaClass object.
    108     * </p>
    109     *
    110     * @param className compressed byte code with "$$BCEL$$" in it
    111     */
    112    protected JavaClass createClass(final String className) {
    113        final int index = className.indexOf(BCEL_TOKEN);
    114        final String realName = className.substring(index + BCEL_TOKEN.length());
    115        JavaClass clazz = null;
    116        try {
    117            final byte[] bytes = Utility.decode(realName, true);
    118            final ClassParser parser = new ClassParser(new ByteArrayInputStream(bytes), "foo");
    119            clazz = parser.parse();
    120        } catch (final IOException e) {
    121            e.printStackTrace();
    122            return null;
    123        }
    124        // Adapt the class name to the passed value
    125        final ConstantPool cp = clazz.getConstantPool();
    126        final ConstantClass cl = cp.getConstant(clazz.getClassNameIndex(), Const.CONSTANT_Class, ConstantClass.class);
    127        final ConstantUtf8 name = cp.getConstantUtf8(cl.getNameIndex());
    128        name.setBytes(Utility.packageToPath(className));
    129        return clazz;
    130    }
    131
    132    @Override
    133    protected Class<?> loadClass(final String className, final boolean resolve) throws ClassNotFoundException {
    134        Class<?> cl = null;
    135        /*
    136         * First try: lookup hash table.
    137         */
    138        if ((cl = classes.get(className)) == null) {
    139            /*
    140             * Second try: Load system class using system class loader. You better don't mess around with them.
    141             */
    142            for (final String ignoredPackage : ignoredPackages) {
    143                if (className.startsWith(ignoredPackage)) {
    144                    cl = getParent().loadClass(className);
    145                    break;
    146                }
    147            }
    148            if (cl == null) {
    149                JavaClass clazz = null;
    150                /*
    151                 * Third try: Special request?
    152                 */
    153                if (className.contains(BCEL_TOKEN)) {
    154                    clazz = createClass(className);
    155                } else { // Fourth try: Load classes via repository
    156                    if ((clazz = repository.loadClass(className)) == null) {
    157                        throw new ClassNotFoundException(className);
    158                    }
    159                    clazz = modifyClass(clazz);
    160                }
    161                if (clazz != null) {
    162                    final byte[] bytes = clazz.getBytes();
    163                    cl = defineClass(className, bytes, 0, bytes.length);
    164                } else {
    165                    cl = Class.forName(className);
    166                }
    167            }
    168            if (resolve) {
    169                resolveClass(cl);
    170            }
    171        }
    172        classes.put(className, cl);
    173        return cl;
    174    }
    175
    176    /**
    177     * Override this method if you want to alter a class before it gets actually loaded. Does nothing by default.
    178     */
    179    protected JavaClass modifyClass(final JavaClass clazz) {
    180        return clazz;
    181    }
    182}