encoderabstractmessage.java

利用mina框架写的一个通信实例。初学者的一个好教程。

/*
 *   @(#) $Id: AbstractMessageEncoder.java 357871 2005-12-20 01:56:40Z trustin $
 *
 *   Copyright 2004 The Apache Software Foundation
 *
 *   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 org.apache.mina.examples.call.encode;

import org.apache.mina.common.ByteBuffer;
import org.apache.mina.examples.call.Constants;
import org.apache.mina.examples.call.message.AbstractMessage;
import org.apache.mina.protocol.ProtocolEncoderOutput;
import org.apache.mina.protocol.ProtocolSession;
import org.apache.mina.protocol.ProtocolViolationException;
import org.apache.mina.protocol.codec.MessageEncoder;

/**
 * A {@link MessageEncoder} that encodes message header and forwards the
 * encoding of body to a subclass.
 * 
 * @author The Apache Directory Project
 * @version $Rev: 357871 $, $Date: 2005-12-20 10:56:40 +0900 (Tue, 20 Dec 2005) $
 */

public abstract class EncoderAbstractMessage implements MessageEncoder {

	// private int totalMsgLen;
	private final int head_command;

	// private int sequenceID;

	protected EncoderAbstractMessage(int commandID) {
		this.head_command = commandID;
	}

	public void encode(ProtocolSession session, Object message,
			ProtocolEncoderOutput out) throws ProtocolViolationException {
		// System.out.println(this + "--info EncoderAbstractMessage begin");
		AbstractMessage msg = (AbstractMessage) message;
		ByteBuffer buf = ByteBuffer.allocate(msg.getHead_len(), true);

		buf.order(Constants.BYTE_ORDER);
		buf.setAutoExpand(true); // Enable auto-expand for easier encoding

		// Encode a header
		buf.putInt(msg.getHead_len());
		buf.putInt(msg.getHead_command());
		buf.putInt(msg.getHead_sequence());

		// Encode a body
		encodeBody(session, msg, buf);
		buf.flip();
		out.write(buf);
		// System.out.println(this + "--info EncoderAbstractMessage end");
	}

	protected abstract void encodeBody(ProtocolSession session,
			AbstractMessage message, ByteBuffer out);
}