/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 */
package org.apache.bcel.util;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.util.Hashtable;

import org.apache.bcel.Const;
import org.apache.bcel.classfile.ClassParser;
import org.apache.bcel.classfile.ConstantClass;
import org.apache.bcel.classfile.ConstantPool;
import org.apache.bcel.classfile.ConstantUtf8;
import org.apache.bcel.classfile.JavaClass;
import org.apache.bcel.classfile.Utility;

Drop in replacement for the standard class loader of the JVM. You can use it
in conjunction with the JavaWrapper to dynamically modify/create classes
as they're requested.
This class loader recognizes special requests in a distinct
format, i.e., when the name of the requested class contains with
"$$BCEL$$" it calls the createClass() method with that name
(everything bevor the $$BCEL$$ is considered to be the package
name. You can subclass the class loader and override that
method. "Normal" classes class can be modified by overriding the
modifyClass() method which is called just before defineClass().
There may be a number of packages where you have to use the
default class loader (which may also be faster). You can define the
set of packages where to use the system class loader in the
constructor. The default value contains "java.", "sun.",
"javax."
See Also:
JavaWrapper
ClassPath
Deprecated:
6.0 Do not use - does not work/**
 * <p>Drop in replacement for the standard class loader of the JVM. You can use it
 * in conjunction with the JavaWrapper to dynamically modify/create classes
 * as they're requested.</p>
 *
 * <p>This class loader recognizes special requests in a distinct
 * format, i.e., when the name of the requested class contains with
 * "$$BCEL$$" it calls the createClass() method with that name
 * (everything bevor the $$BCEL$$ is considered to be the package
 * name. You can subclass the class loader and override that
 * method. "Normal" classes class can be modified by overriding the
 * modifyClass() method which is called just before defineClass().</p>
 *
 * <p>There may be a number of packages where you have to use the
 * default class loader (which may also be faster). You can define the
 * set of packages where to use the system class loader in the
 * constructor. The default value contains "java.", "sun.",
 * "javax."</p>
 *
 * @see JavaWrapper
 * @see ClassPath
 * @deprecated 6.0 Do not use - does not work
 */
@Deprecated
public class ClassLoader extends java.lang.ClassLoader {

    private static final String BCEL_TOKEN = "$$BCEL$$";

    public static final String[] DEFAULT_IGNORED_PACKAGES = {
            "java.", "javax.", "sun."
    };

    private final Hashtable<String, Class<?>> classes = new Hashtable<>();
    // Hashtable is synchronized thus thread-safe
    private final String[] ignored_packages;
    private Repository repository = SyntheticRepository.getInstance();


    
Ignored packages are by default ( "java.", "sun.",
"javax."), i.e. loaded by system class loader
/** Ignored packages are by default ( "java.", "sun.",
     * "javax."), i.e. loaded by system class loader
     */
    public ClassLoader() {
        this(DEFAULT_IGNORED_PACKAGES);
    }


    
Params:
deferTo – delegate class loader to use for ignored packages/** @param deferTo delegate class loader to use for ignored packages
     */
    public ClassLoader(final java.lang.ClassLoader deferTo) {
        super(deferTo);
        this.ignored_packages = DEFAULT_IGNORED_PACKAGES;
        this.repository = new ClassLoaderRepository(deferTo);
    }


    
Params:
ignored_packages – classes contained in these packages will be loaded
with the system class loader/** @param ignored_packages classes contained in these packages will be loaded
     * with the system class loader
     */
    public ClassLoader(final String[] ignored_packages) {
        this.ignored_packages = ignored_packages;
    }


    
Params:
ignored_packages – classes contained in these packages will be loaded
with the system class loader
deferTo – delegate class loader to use for ignored packages/** @param ignored_packages classes contained in these packages will be loaded
     * with the system class loader
     * @param deferTo delegate class loader to use for ignored packages
     */
    public ClassLoader(final java.lang.ClassLoader deferTo, final String[] ignored_packages) {
        this(ignored_packages);
        this.repository = new ClassLoaderRepository(deferTo);
    }

    @Override
    protected Class<?> loadClass( final String class_name, final boolean resolve ) throws ClassNotFoundException {
        Class<?> cl = null;
        /* First try: lookup hash table.
         */
        if ((cl = classes.get(class_name)) == null) {
            /* Second try: Load system class using system class loader. You better
             * don't mess around with them.
             */
            for (final String ignored_package : ignored_packages) {
                if (class_name.startsWith(ignored_package)) {
                    cl = getParent().loadClass(class_name);
                    break;
                }
            }
            if (cl == null) {
                JavaClass clazz = null;
                /* Third try: Special request?
                 */
                if (class_name.contains(BCEL_TOKEN)) {
                    clazz = createClass(class_name);
                } else { // Fourth try: Load classes via repository
                    if ((clazz = repository.loadClass(class_name)) != null) {
                        clazz = modifyClass(clazz);
                    } else {
                        throw new ClassNotFoundException(class_name);
                    }
                }
                if (clazz != null) {
                    final byte[] bytes = clazz.getBytes();
                    cl = defineClass(class_name, bytes, 0, bytes.length);
                } else {
                    cl = Class.forName(class_name);
                }
            }
            if (resolve) {
                resolveClass(cl);
            }
        }
        classes.put(class_name, cl);
        return cl;
    }


    
Override this method if you want to alter a class before it gets actually
loaded. Does nothing by default.
/** Override this method if you want to alter a class before it gets actually
     * loaded. Does nothing by default.
     */
    protected JavaClass modifyClass( final JavaClass clazz ) {
        return clazz;
    }


    
Override this method to create you own classes on the fly. The
name contains the special token $$BCEL$$. Everything before that
token is considered to be a package name. You can encode your own
arguments into the subsequent string. You must ensure however not
to use any "illegal" characters, i.e., characters that may not
appear in a Java class name too

The default implementation interprets the string as a encoded compressed
Java class, unpacks and decodes it with the Utility.decode() method, and
parses the resulting byte array and returns the resulting JavaClass object.

Params:
class_name – compressed byte code with "$$BCEL$$" in it/**
     * Override this method to create you own classes on the fly. The
     * name contains the special token $$BCEL$$. Everything before that
     * token is considered to be a package name. You can encode your own
     * arguments into the subsequent string. You must ensure however not
     * to use any "illegal" characters, i.e., characters that may not
     * appear in a Java class name too
     * <p>
     * The default implementation interprets the string as a encoded compressed
     * Java class, unpacks and decodes it with the Utility.decode() method, and
     * parses the resulting byte array and returns the resulting JavaClass object.
     * </p>
     *
     * @param class_name compressed byte code with "$$BCEL$$" in it
     */
    protected JavaClass createClass( final String class_name ) {
        final int index = class_name.indexOf(BCEL_TOKEN);
        final String real_name = class_name.substring(index + BCEL_TOKEN.length());
        JavaClass clazz = null;
        try {
            final byte[] bytes = Utility.decode(real_name, true);
            final ClassParser parser = new ClassParser(new ByteArrayInputStream(bytes), "foo");
            clazz = parser.parse();
        } catch (final IOException e) {
            e.printStackTrace();
            return null;
        }
        // Adapt the class name to the passed value
        final ConstantPool cp = clazz.getConstantPool();
        final ConstantClass cl = (ConstantClass) cp.getConstant(clazz.getClassNameIndex(),
                Const.CONSTANT_Class);
        final ConstantUtf8 name = (ConstantUtf8) cp.getConstant(cl.getNameIndex(),
                Const.CONSTANT_Utf8);
        name.setBytes(class_name.replace('.', '/'));
        return clazz;
    }
}