mysqlframingoutputstream.java

mysql集群

/*
 * 	This program is free software; you can redistribute it and/or modify it under the terms of 
 * the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, 
 * or (at your option) any later version. 
 * 
 * 	This program is distributed in the hope that it will be useful, 
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  
 * See the GNU General Public License for more details. 
 * 	You should have received a copy of the GNU General Public License along with this program; 
 * if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */
package com.meidusa.amoeba.mysql.io;

import java.nio.ByteBuffer;

import com.meidusa.amoeba.net.io.PacketOutputStream;

/**
 * 
 * <b> The Packet Header </b>
 * 
 * <pre>
 * Bytes                 Name
 *  -----                 ----
 *  3                     Packet Length
 *  1                     Packet Number
 * </p>
 *  <b>Packet Length:</b> The length, in bytes, of the packet
 *                 that follows the Packet Header. There
 *                 may be some special values in the most
 *                 significant byte. Since 2**24 = MB,
 *                 the maximum packet length is 16MB.
 * </P>
 *  <b>Packet Number:</b> A serial number which can be used to
 *                 ensure that all packets are present
 *                 and in order. The first packet of a
 *                 client query will have Packet Number = 0
 *                 Thus, when a new SQL statement starts, 
 *                 the packet number is re-initialised.
 *  
 * </pre>
 * 
 * @see <href a="http://forge.mysql.com/wiki/MySQL_Internals_ClientServer_Protocol#The_Packet_Header">The_Packet_Header</a>
 * 
 * @author <a href=mailto:[e-mail]>Struct chen</a>
 * 
 */
public class MysqlFramingOutputStream extends PacketOutputStream implements MySqlPacketConstant{
	protected byte packetId;
	protected boolean packetwrittenWithHead;
	
	/**
	 * 
	 * @param packetwrittenWithHead 写数据的时候是否写入包头信息，true--表示写入数据的时候已经包括了包头信息，
	 * 							   否则则需要在调用{@link #returnPacketBuffer()} 的时候需要实时生成包头信息
	 */
	public MysqlFramingOutputStream(boolean packetwrittenWithHead){
		this.packetwrittenWithHead = packetwrittenWithHead;
		resetPacket();
	}
	public ByteBuffer returnPacketBuffer ()
    {
        // flip the buffer which will limit it to it's current position
        _buffer.flip();
        if(!packetwrittenWithHead){
	        /**
	         *  包头信息：长度－－是不包含包头长度
	         */
	        int count = _buffer.limit()-HEADER_PAD.length;
	        _buffer.put((byte)(count & 0xff));
	        _buffer.put((byte) (count >>> 8));
	        _buffer.put((byte) (count >>> 16));
	        _buffer.put((byte) packetId);// packet id
        }
        _buffer.rewind();
        return _buffer;
    }
	
	public void setPacketId(byte packetId){
		this.packetId = packetId;
	}
	
	/**
	 * 
	 */
	protected void initHeader(){
		if(!packetwrittenWithHead){
			_buffer.put(HEADER_PAD);
		}
    }
}