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The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.

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/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project 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.jboss.netty.handler.codec.serialization;

import java.io.ObjectOutputStream;
import java.io.StreamCorruptedException;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBufferInputStream;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.frame.LengthFieldBasedFrameDecoder;

/**
 * A decoder which deserializes the received {@link ChannelBuffer}s into Java
 * objects.
 * 
 * Please note that the serialized form this decoder expects is not
 * compatible with the standard {@link ObjectOutputStream}.  Please use
 * {@link ObjectEncoder} or {@link ObjectEncoderOutputStream} to ensure the
 * interoperability with this decoder.
 *
 * @apiviz.landmark
 * @apiviz.has org.jboss.netty.handler.codec.serialization.ObjectDecoderInputStream - - - compatible with
 */
public class ObjectDecoder extends LengthFieldBasedFrameDecoder {

    private final ClassResolver classResolver;

    /**
     * Creates a new decoder whose maximum object size is {@code 1048576}
     * bytes.  If the size of the received object is greater than
     * {@code 1048576} bytes, a {@link StreamCorruptedException} will be
     * raised.
     *
     * @param classResolver  the {@link ClassResolver} to use for this decoder
     */
    public ObjectDecoder(ClassResolver classResolver) {
        this(1048576, classResolver);
    }

    /**
     * Creates a new decoder with the specified maximum object size.
     *
     * @param maxObjectSize  the maximum byte length of the serialized object.
     *                       if the length of the received object is greater
     *                       than this value, {@link StreamCorruptedException}
     *                       will be raised.
     * @param classResolver    the {@link ClassResolver} which will load the class
     *                       of the serialized object
     */
    public ObjectDecoder(int maxObjectSize, ClassResolver classResolver) {
        super(maxObjectSize, 0, 4, 0, 4);
        if (classResolver == null) {
            throw new NullPointerException("classResolver");
        }
        this.classResolver = classResolver;
    }

    @Override
    protected Object decode(
            ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {

        ChannelBuffer frame = (ChannelBuffer) super.decode(ctx, channel, buffer);
        if (frame == null) {
            return null;
        }

        return new CompactObjectInputStream(
                new ChannelBufferInputStream(frame), classResolver).readObject();
    }

    @Override
    protected ChannelBuffer extractFrame(ChannelBuffer buffer, int index, int length) {
        return buffer.slice(index, length);
    }
}