packetoutputstream.java

来自「mysql集群」· Java 代码 · 共 114 行

/*
 * 	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.net.io;

import java.io.OutputStream;

import java.nio.BufferOverflowException;
import java.nio.ByteBuffer;

/**
 * 
 * @author <a href=mailto:[e-mail]>Struct chen</a>
 *
 */
public abstract class PacketOutputStream extends OutputStream
{
    
    /** The buffer in which we store our packet data. */
    protected ByteBuffer _buffer;

    /** The default initial size of the internal buffer. */
    protected static final int INITIAL_BUFFER_SIZE = 32;
    
    public PacketOutputStream ()
    {
        _buffer = ByteBuffer.allocate(INITIAL_BUFFER_SIZE);
        initHeader();
    }

    /**
     * Writes the specified byte to this output stream. 
     *
     * @param b the byte to be written.
     */
    public void write (int b)
    {
        try {
            _buffer.put((byte)b);
        } catch (BufferOverflowException boe) {
            expand(1);
            _buffer.put((byte)b);
        }
    }

    /**
     * Writes <code>len</code> bytes from the specified byte array
     * starting at offset <code>off</code> to this output stream.
     *
     * @param b the data.
     * @param off the start offset in the data.
     * @param len the number of bytes to write.
     */
    public void write (byte[] b, int off, int len)
    {
        // sanity check the arguments
        if ((off < 0) || (off > b.length) || (len < 0) ||
            ((off + len) > b.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return;
        }

        try {
            _buffer.put(b, off, len);
        } catch (BufferOverflowException boe) {
            expand(len);
            _buffer.put(b, off, len);
        }
    }

    /**
     * Expands our buffer to accomodate the specified capacity.
     */
    protected final void expand (int needed)
    {
        int ocapacity = _buffer.capacity();
        int ncapacity = _buffer.position() + needed;
        if (ncapacity > ocapacity) {
            // increase the buffer size in large increments
            ncapacity = Math.max(ocapacity << 1, ncapacity);
            ByteBuffer newbuf = ByteBuffer.allocate(ncapacity);
            newbuf.put((ByteBuffer)_buffer.flip());
            _buffer = newbuf;
        }
    }

    /**
     * Writes the packet length to the beginning of our buffer and returns
     * it for writing to the appropriate channel. This should be followed
     * by a call to {@link #resetPacket} when the packet has been written.
     */
    public abstract ByteBuffer returnPacketBuffer ();

    /**
     * Resets our internal buffer and prepares to write a new packet.
     */
    public void resetPacket ()
    {
        _buffer.clear();
        initHeader();
    }

    protected abstract void initHeader();
}