consumetoendofsessiondecodingstate.java

mina是以Java实现的一个开源的网络程序框架

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 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
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 *    http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.mina.filter.codec.statemachine;

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.filter.codec.ProtocolDecoderException;
import org.apache.mina.filter.codec.ProtocolDecoderOutput;

/**
 * {@link DecodingState} which consumes all received bytes until the session is
 * closed.
 *
 * @author The Apache MINA Project ([e-mail])
 * @version $Rev: 671827 $, $Date: 2008-06-26 10:49:48 +0200 (Thu, 26 Jun 2008) $
 */
public abstract class ConsumeToEndOfSessionDecodingState implements DecodingState {

    private IoBuffer buffer;
    private final int maxLength;
    
    /**
     * Creates a new instance using the specified maximum length.
     * 
     * @param maxLength the maximum number of bytes which will be consumed. If
     *        this max is reached a {@link ProtocolDecoderException} will be 
     *        thrown by {@link #decode(IoBuffer, ProtocolDecoderOutput)}.
     */
    public ConsumeToEndOfSessionDecodingState(int maxLength) {
        this.maxLength = maxLength;
    }

    /**
     * {@inheritDoc}
     */
    public DecodingState decode(IoBuffer in, ProtocolDecoderOutput out)
            throws Exception {
        if (buffer == null) {
            buffer = IoBuffer.allocate(256).setAutoExpand(true);
        }

        if (buffer.position() + in.remaining() > maxLength) {
            throw new ProtocolDecoderException("Received data exceeds " + maxLength + " byte(s).");
        }
        buffer.put(in);
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public DecodingState finishDecode(ProtocolDecoderOutput out)
            throws Exception {
        try {
            if (buffer == null) {
                buffer = IoBuffer.allocate(0);
            }
            buffer.flip();
            return finishDecode(buffer, out);
        } finally {
            buffer = null;
        }
    }

    /**
     * Invoked when this state has consumed all bytes until the session is 
     * closed.
     * 
     * @param product the bytes read.
     * @param out the current {@link ProtocolDecoderOutput} used to write 
     *        decoded messages.
     * @return the next state if a state transition was triggered (use 
     *         <code>this</code> for loop transitions) or <code>null</code> if 
     *         the state machine has reached its end.
     * @throws Exception if the read data violated protocol specification.
     */
    protected abstract DecodingState finishDecode(IoBuffer product,
            ProtocolDecoderOutput out) throws Exception;
}