import java.io.BufferedOutputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

import java.net.URL;

import java.net.URLClassLoader;

import java.util.jar.JarEntry;

import java.util.jar.JarOutputStream;

/*

 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

/**

 * A ByteClassLoader is used to define classes from collections of bytes, as

 * well as loading classes in the usual way. It includes options to write the

 * classes to files in a jar, or to read the classes from jars in a later or

 * debugging run.

 *

 * If Boolean property byteclassloader.verbose is true, be chatty about jar

 * file operations.

 *

 */

public class ByteClassLoader extends URLClassLoader {

    final static boolean verbose

            = Boolean.getBoolean("byteclassloader.verbose");

    final boolean read;

    final JarOutputStream jos;

    final String jar_name;

    /**

     * Make a new ByteClassLoader.

     *

     * @param jar_name  Basename of jar file to be read/written by this classloader.

     * @param read      If true, read classes from jar file instead of from parameter.

     * @param write     If true, write classes to jar files for offline study/use.

     *

     * @throws FileNotFoundException

     * @throws IOException

     */

    public ByteClassLoader(String jar_name, boolean read, boolean write)

            throws FileNotFoundException, IOException {

        super(read

                ? new URL[]{new URL("file:" + jar_name + ".jar")}

                : new URL[0]);

        this.read = read;

        this.jar_name = jar_name;

        this.jos = write

                ? new JarOutputStream(

                new BufferedOutputStream(

                new FileOutputStream(jar_name + ".jar"))) : null;

        if (read && write) {

            throw new Error("At most one of read and write may be true.");

        }

    }

    private static void writeJarredFile(JarOutputStream jos, String file, String suffix, byte[] bytes) {

        String fileName = file.replace(".", "/") + "." + suffix;

        JarEntry ze = new JarEntry(fileName);

        try {

            ze.setSize(bytes.length);

            jos.putNextEntry(ze);

            jos.write(bytes);

            jos.closeEntry();

        } catch (IOException e) {

            throw new RuntimeException(e);

        }

    }

    /**

     * (pre)load class name using classData for the definition.

     *

     * @param name

     * @param classData

     * @return

     */

    public Class<?> loadBytes(String name, byte[] classData) throws ClassNotFoundException {

        if (jos != null) {

            if (verbose) {

                System.out.println("ByteClassLoader: writing " + name);

            }

            writeJarredFile(jos, name, "class", classData);

        }

        Class<?> clazz = null;

        if (read) {

            if (verbose) {

                System.out.println("ByteClassLoader: reading " + name + " from " + jar_name);

            }

            clazz = loadClass(name);

        } else {

            clazz = defineClass(name, classData, 0, classData.length);

            resolveClass(clazz);

        }

        return clazz;

    }

    public void close() {

        if (jos != null) {

            try {

                if (verbose) {

                    System.out.println("ByteClassLoader: closing " + jar_name);

                }

                jos.close();

            } catch (IOException ex) {

            }

        }

    }

}