decoderabstractmessage.java

利用mina框架写的一个通信实例。初学者的一个好教程。

/*
 *   @(#) $Id: AbstractMessageDecoder.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.decode;

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.ProtocolDecoderOutput;
import org.apache.mina.protocol.ProtocolSession;
import org.apache.mina.protocol.ProtocolViolationException;
import org.apache.mina.protocol.codec.MessageDecoder;
import org.apache.mina.protocol.codec.MessageDecoderResult;

/**
 * A {@link MessageDecoder} that decodes message header and forwards the
 * decoding 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 DecoderAbstractMessage implements MessageDecoder {

	protected int head_len;// first

	protected int head_command;// second

	protected int head_sequence;// third

	private boolean readHeader;// complete read header

	protected DecoderAbstractMessage(int head_command) {
		this.head_command = head_command;
	}

	// 判断是否可以，decode．
	public MessageDecoderResult decodable(ProtocolSession session, ByteBuffer in) {
		// System.out.println("--info DecoderAbstractMessage begin " + this);

		// set byte order
		in.order(Constants.BYTE_ORDER);

		// Return NEED_DATA if the whole header is not read yet.
		if (in.remaining() < Constants.HEADER_LEN_SUM) {
			return MessageDecoderResult.NEED_DATA;
		}

		// skip
		int len = in.getInt();

		// check command id
		int command = in.getInt();
		if (head_command == command) {
			return MessageDecoderResult.OK;
		}

		// System.out.println("--info DecoderAbstractMessage end" + this);

		// Return NOT_OK if not matches.
		return MessageDecoderResult.NOT_OK;

	}

	public MessageDecoderResult decode(ProtocolSession session, ByteBuffer in,
			ProtocolDecoderOutput out) throws ProtocolViolationException {

		// Try to skip header if not read.

		if (!readHeader) {
			this.head_len = in.getInt();// head_len
			this.head_command = in.getInt();// command
			this.head_sequence = in.getInt(); // sequence
			readHeader = true;

			System.out.println("--info DecoderAbstractMessage decode head_len:"
					+ this.head_len);
			System.out
					.println("--info DecoderAbstractMessage decode head_command:"
							+ this.head_command);
			System.out
					.println("--info DecoderAbstractMessage decode head_sequence:"
							+ this.head_sequence);

		}

		// Try to decode body
		AbstractMessage message = decodeBody(session, in);

		// Return NEED_DATA if the body is not fully read.
		if (message == null) {
			return MessageDecoderResult.NEED_DATA;
		} else {
			readHeader = false; // reset readHeader for the next decode
		}

		message.setHead_len(this.head_len);
		message.setHead_command(this.head_command);
		message.setHead_sequence(this.head_sequence);

		out.write(message);
		return MessageDecoderResult.OK;
	}

	/**
	 * @return <tt>null</tt> if the whole body is not read yet
	 */
	protected abstract AbstractMessage decodeBody(ProtocolSession session,
			ByteBuffer in);
}