java非阻塞socket缓冲区问题

server发送数据给client，但是重复发送，不能清除缓冲，求解，谢谢！！另外请讲解一下flip(),position()的用法。
请看send2()
package nonblock;
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;
import java.net.*;
import java.util.*;public class EchoServer{
  private Selector selector = null;
  private ServerSocketChannel serverSocketChannel = null;
  private int port = 8000;
  private Charset charset=Charset.forName("GBK");  public EchoServer()throws IOException{
    selector = Selector.open();
    serverSocketChannel= ServerSocketChannel.open();
    serverSocketChannel.socket().setReuseAddress(true);
    serverSocketChannel.configureBlocking(false);
    serverSocketChannel.socket().bind(new InetSocketAddress(port));
    System.out.println("服务器启动");
  }  public void service() throws IOException{
    serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT );
    while (selector.select() > 0 ){
      Set readyKeys = selector.selectedKeys();
      Iterator it = readyKeys.iterator();
      while (it.hasNext()){
         SelectionKey key=null;
         try{
            key = (SelectionKey) it.next();
            it.remove();            if (key.isAcceptable()) {
              ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
              SocketChannel socketChannel = (SocketChannel) ssc.accept();
              System.out.println("接收到客户连接，来自:" +
                                 socketChannel.socket().getInetAddress() +
                                 ":" + socketChannel.socket().getPort());
              socketChannel.configureBlocking(false);
              ByteBuffer buffer = ByteBuffer.allocate(1024);
              socketChannel.register(selector,
                                     SelectionKey.OP_READ |
                                     SelectionKey.OP_WRITE, buffer);
            }
            if (key.isReadable()) {
                receive(key);
            }
            if (key.isWritable()) {
                send2(key);
            }
        }catch(IOException e){
           e.printStackTrace();
           try{
               if(key!=null){
                   key.cancel();
                   key.channel().close();
               }
           }catch(Exception ex){e.printStackTrace();}
        }
      }//#while
    }//#while
  }  public void send(SelectionKey key)throws IOException{
    ByteBuffer buffer=(ByteBuffer)key.attachment();
    SocketChannel socketChannel=(SocketChannel)key.channel();
    buffer.flip();  //把极限设为位置，把位置设为0//在read或put后用
    String data=decode(buffer);
    if(data.indexOf("\r\n")==-1)return;
    String outputData=data.substring(0,data.indexOf("\n")+1);
    System.out.print(outputData);
    String data1="bbbbbbbbbb";
    ByteBuffer outputBuffer=encode("echo:"+outputData);
    while(outputBuffer.hasRemaining())
      socketChannel.write(outputBuffer);
    ByteBuffer temp=encode(outputData);
    buffer.position(temp.limit());
    buffer.compact();    if(outputData.equals("bye\r\n")){
      key.cancel();
      socketChannel.close();
      System.out.println("关闭与客户的连接");
    }
  }  public void receive(SelectionKey key)throws IOException{
    ByteBuffer buffer=(ByteBuffer)key.attachment();    SocketChannel socketChannel=(SocketChannel)key.channel();
    ByteBuffer readBuff= ByteBuffer.allocate(32);
    socketChannel.read(readBuff);
    readBuff.flip();    buffer.limit(buffer.capacity());
    buffer.put(readBuff);
  }  public String decode(ByteBuffer buffer){  //解码
    CharBuffer charBuffer= charset.decode(buffer);
    return charBuffer.toString();
  }
  public ByteBuffer encode(String str){  //编码
    return charset.encode(str);
  }  public static void main(String args[])throws Exception{
    EchoServer server = new EchoServer();
    server.service();
  }
  
  public void send2(SelectionKey key)throws IOException{
  ByteBuffer buffer=(ByteBuffer)key.attachment();
  SocketChannel socketChannel=(SocketChannel)key.channel();
  buffer.put(encode("bbbbbbbbb" + "\r\n"));
  buffer.flip(); //把极限设为位置
  socketChannel.write(buffer);//写入通道
  buffer.compact();
  buffer.clear();
  System.out.println(buffer.toString());
  }
}
/****************************************************
 * 作者：孙卫琴                                     *
 * 来源：<<Java网络编程精解>>                       *
 * 技术支持网址：www.javathinker.org                *
 ***************************************************/