shortintegerdecodingstate.java

mina是以Java实现的一个开源的网络程序框架

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 *  Licensed to the Apache Software Foundation (ASF) under one
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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 decodes <code>short</code> values in big-endian 
 * order (high bytes come first).
 * 
 * @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 ShortIntegerDecodingState implements DecodingState {
    
    private int highByte;
    private int counter;

    /**
     * {@inheritDoc}
     */
    public DecodingState decode(IoBuffer in, ProtocolDecoderOutput out)
            throws Exception {
        
        while (in.hasRemaining()) {
            switch (counter) {
            case 0:
                highByte = in.getUnsigned();
                break;
            case 1:
                counter = 0;
                return finishDecode((short) ((highByte << 8) | in.getUnsigned()), out);
            default:
                throw new InternalError();
            }

            counter ++;
        }
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public DecodingState finishDecode(ProtocolDecoderOutput out)
            throws Exception {
        throw new ProtocolDecoderException(
                "Unexpected end of session while waiting for a short integer.");
    }

    /**
     * Invoked when this state has consumed a complete <code>short</code>.
     * 
     * @param value the short.
     * @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(short value,
            ProtocolDecoderOutput out) throws Exception;
}