我也遇到类似的问题，请高手指点啊！

这个示例直接抄袭自某书，运行结果却不甚理想，请教诸位大虾 
server 部分 
package network; 
import java.io.*; 
import java.nio.channels.*; 
import java.nio.*; 
import java.nio.charset.*; 
import java.net.*; 
import java.util.*; 
/** * 
*/ 
public class EchoServer { 
      
/** 
  * @param args 
  */ 
  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("server start"); 
  
  } 
  
  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("receive connet from: "+socketChannel.socket().getIn 
etAddress()+":"+socketChannel.socket().getPort()); 
      socketChannel.configureBlocking(false); 
      ByteBuffer buffer=ByteBuffer.allocate(1024); 
      socketChannel.register(selector, SelectionKey.OP_READ|SelectionKey.OP_W 
RITE,buffer); 
      } 
      if(key.isReadable()){ 
      receive(key); 
      } 
      if(key.isWritable()){ 
      send(key); 
      } 
    } 
    catch(IOException e){ 
      e.printStackTrace(); 
      try{ 
      if(key!=null){ 
        key.cancel(); 
        key.channel().close(); 
      } 
      } 
      catch(Exception ex){e.printStackTrace();} 
    } 
    } 
    
  } 
  
  } 
  public void send(SelectionKey key)throws IOException{ 
  ByteBuffer buffer=(ByteBuffer)key.attachment(); 
  SocketChannel socketChannel=(SocketChannel)key.channel(); 
  String data=decode(buffer); 
  if(data.indexOf("\r\n")==-1)return; 
  String outputData=data.substring(0, data.indexOf("\n")+1); 
  System.out.print(outputData); 
  ByteBuffer outputBuffer=encode("echo:"+outputData); 
  while(outputBuffer.hasRemaining()) 
    socketChannel.write(outputBuffer); 
  ByteBuffer temp=encode(outputData); 
  buffer.position(temp.limit()); 
  buffer.compact(); 
  if(outputData.equalsIgnoreCase("bye\r\n")){ 
    key.cancel(); 
    socketChannel.close(); 
    System.out.println("stop connect with the host"); 
  } 
  } 
  
  public void receive(SelectionKey key)throws IOException{ 
  ByteBuffer buffer=(ByteBuffer)key.attachment(); 
  SocketChannel socketChannel=(SocketChannel)key.channel(); 
  ByteBuffer readBuffer=ByteBuffer.allocate(32); 
  socketChannel.read(readBuffer); 
  readBuffer.flip(); 
  buffer.limit(buffer.capacity()); 
  buffer.put(readBuffer); 
  
  } 
  
  public String decode(ByteBuffer buffer){ 
  CharBuffer charBuffer=charset.decode(buffer); 
  return charset.toString(); 
  } 
  public ByteBuffer encode(String str){ 
  return charset.encode(str); 
  } 
  
public static void main(String[] args)throws Exception { 
  // TODO 自动生成方法存根 
        EchoServer server=new EchoServer(); 
        server.service(); 
} } 
客户端部分 
package network; 
import java.io.*; 
import java.nio.channels.*; 
import java.nio.*; 
import java.nio.charset.*; 
import java.net.*; 
import java.util.*; public class EchoClient { 
    private SocketChannel socketChannel=null; 
    private ByteBuffer sendBuffer=ByteBuffer.allocate(1024); 
    private ByteBuffer receiveBuffer=ByteBuffer.allocate(1024); 
    private Charset charset=Charset.forName("GBK"); 
    private Selector selector; 
    
    public EchoClient()throws IOException { 
    socketChannel=SocketChannel.open(); 
    InetAddress ia= InetAddress.getLocalHost(); 
    InetSocketAddress isa=new InetSocketAddress(ia,8000); 
    socketChannel.connect(isa); 
    socketChannel.configureBlocking(false); 
    System.out.println("get connect successfully with server."); 
    selector=Selector.open(); 
    } 
/** 
  * @param args 
  */ 
public static void main(String[] args) throws IOException{ 
  
  final EchoClient client=new EchoClient(); 
  Thread receiver=new Thread(){ 
  public void run(){ 
    client.receiveFromUser(); 
  } 
  }; 
  receiver.start(); 
  client.talk(); } public void receiveFromUser(){ 
  try{ 
  BufferedReader localReader=new BufferedReader(new InputStreamReader(System. 
in)); 
  String msg=null; 
  while((msg=localReader.readLine())!=null){ 
    synchronized(sendBuffer){ 
    sendBuffer.put(encode(msg+"\r\n")); 
    } 
    if(msg.equalsIgnoreCase("bye")) 
    break; 
  } 
  } 
  catch(IOException e){ 
  e.printStackTrace(); 
  } 
} public void talk()throws IOException{ 
  socketChannel.register(selector, SelectionKey.OP_READ|SelectionKey.OP_WRITE) 
; 
  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.isReadable()){ 
      receive(key); 
      } 
      if(key.isWritable()){ 
      send(key); 
      } 
    } 
    catch(IOException e){ 
      e.printStackTrace(); 
      try{ 
      if(key!=null){ 
        key.cancel(); 
        key.channel().close(); 
      } 
      } 
      catch(Exception ex){e.printStackTrace();} 
    } 
    } 
    
  } 
}   public void send(SelectionKey key)throws IOException{ 
  
  SocketChannel socketChannel=(SocketChannel)key.channel(); 
  synchronized(sendBuffer){ 
    sendBuffer.flip(); 
    socketChannel.write(sendBuffer); 
    sendBuffer.compact(); 
  } 
  } 
  
  public void receive(SelectionKey key)throws IOException{ 
  
  SocketChannel socketChannel=(SocketChannel)key.channel(); 
      socketChannel.read(receiveBuffer); 
  receiveBuffer.flip(); 
  String receiveData=decode(receiveBuffer); 
  if(receiveData.indexOf("\n")==-1)return; 
  String outputData=receiveData.substring(0,receiveData.indexOf("\n")+1); 
  if(outputData.equalsIgnoreCase("echo:bye\r\n")){ 
    key.cancel(); 
    socketChannel.close(); 
    System.out.println("stop connect with the server"); 
    selector.close(); 
    System.exit(0); 
  } 
  ByteBuffer temp=encode(outputData); 
  receiveBuffer.position(temp.limit()); 
  receiveBuffer.compact(); 
  
  } 
  public String decode(ByteBuffer buffer){ 
  CharBuffer charBuffer=charset.decode(buffer); 
  return charset.toString(); 
  } 
  public ByteBuffer encode(String str){ 
  return charset.encode(str); 
  } 
} 
server控制台输出：server start 
receive connet from: /192.168.88.34:1278 
Exception in thread "main" java.nio.BufferOverflowException 
at java.nio.HeapByteBuffer.put(Unknown Source) 
at network.EchoServer.receive(EchoServer.java:103) 
at network.EchoServer.service(EchoServer.java:55) 
at network.EchoServer.main(EchoServer.java:118) 
client控制台输出： 
get connect successfully with server. 
hi 
java.io.IOException: 远程主机强迫关闭了一个现有的连接。 
at sun.nio.ch.SocketDispatcher.read0(Native Method) 
at sun.nio.ch.SocketDispatcher.read(Unknown Source) 
at sun.nio.ch.IOUtil.readIntoNativeBuffer(Unknown Source) 
at sun.nio.ch.IOUtil.read(Unknown Source) 
at sun.nio.ch.SocketChannelImpl.read(Unknown Source) 
at network.EchoClient.receive(EchoClient.java:108) 
at network.EchoClient.talk(EchoClient.java:74) 
at network.EchoClient.main(EchoClient.java:40)