从ClassLoader获取类文件

/*

 * Copyright 2014 NAVER Corp.

 *

 * Licensed 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 com.nowjava;

import java.io.Closeable;
/** from 
n o w j a v a . c o m - 时  代  Java**/

import java.io.IOException;

import java.io.InputStream;


import java.nio.ByteBuffer;

import java.nio.channels.Channels;

import java.nio.channels.ReadableByteChannel;


public class Main {

    public static byte[] getClassFile(ClassLoader classLoader,

            String className) {

        if (classLoader == null) {

            classLoader = ClassLoader.getSystemClassLoader();

        }

        if (className == null) {

            throw new NullPointerException("className must not be null");

        }/*from 时 代 J a v a - N o w J a v a . c o m*/


        final InputStream is = classLoader.getResourceAsStream(className

                .replace('.', '/') + ".class");

        if (is == null) {

            throw new RuntimeException("No such class file: " + className);

        }


        ReadableByteChannel channel = Channels.newChannel(is);

        ByteBuffer buffer;


        try {

            buffer = ByteBuffer.allocate(is.available());


            while (channel.read(buffer) >= 0) {

                if (buffer.remaining() == 0) {

                    buffer.flip();

                    ByteBuffer newBuffer = ByteBuffer.allocate(buffer

                            .capacity() * 2);

                    newBuffer.put(buffer);

                    buffer = newBuffer;

                }

            }

        } catch (IOException e) {

            throw new RuntimeException(e);

        }