一个非阻塞IO的java客户和服务器端交换时间的例子。

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.Selector;
import java.nio.channels.SelectionKey;
import java.nio.channels.SelectableChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;

import java.net.InetAddress;
import java.net.Socket;
import java.net.ServerSocket;
import java.net.InetSocketAddress;
import java.util.*;
import java.util.Date;
import java.util.Iterator;

public class MyServer {
 SocketChannel sc;

 ServerSocketChannel ssc;

 Selector selector;

 private static Charset charset = Charset.forName("US-ASCII");

 private static CharsetEncoder encoder = charset.newEncoder();

 private static CharsetDecoder decoder = charset.newDecoder();

 ByteBuffer br = ByteBuffer.allocate(1024);

 MyServer() {
  try {
   InetSocketAddress addr = new InetSocketAddress(InetAddress
     .getLocalHost(), 26);

   ssc = ServerSocketChannel.open();
   ssc.configureBlocking(false);
   ServerSocket ss = ssc.socket();
   ss.bind(addr);
   System.out.println("asdf");
   selector = Selector.open();
   ssc.register(selector, SelectionKey.OP_ACCEPT);

   while (true) {
    if (selector.select() > 0) {
     System.out.println("asdf");
     Set readyKeys = selector.selectedKeys();
     Iterator it = readyKeys.iterator();
     while (it.hasNext()) {
      SelectionKey sk = (SelectionKey) it.next();
      it.remove();
      if (sk.isAcceptable()) {
       sc = ssc.accept();
       sc.read(br);
       br.flip();
       CharBuffer cb = decoder.decode(br);
       System.out.print(" : " + cb);
       sc.configureBlocking(false);
       sk=sc.register(selector,0);
       sk.interestOps(SelectionKey.OP_WRITE);
       System.out.println("isaccept()");
       //selector.wakeup();
       }
      if(sk.isReadable()){
       sc.read(br);
       br.flip();
       CharBuffer cb = decoder.decode(br);
       System.out.print("is readable  : " + cb);
       sk.interestOps(SelectionKey.OP_WRITE);
       System.out.println("set write");
       //selector.wakeup();
      }
      if(sk.isWritable()){
        String now = new Date().toString();
        sc.write(encoder.encode(CharBuffer.wrap("write"+now +
        "\r\n")));
        System.out.println(sc.socket().getInetAddress() +
        " : " + now);
        sk.interestOps(SelectionKey.OP_READ);
       // selector.wakeup();
       
      }
     }
    }
   }
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   try {
    sc.close();
    ssc.close();

   } catch (Exception e) {
   }
  }

 }

 public static void main(String args[]) {
  new MyServer();
 }
} 

import java.nio.channels.SocketChannel;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.Selector;
import java.nio.channels.SelectionKey;
import java.util.*;
import java.util.Date;
import java.nio.charset.*;
import java.io.IOException;

public class MyClient {
 SocketChannel sc;

 Selector selector;

 private final int MAX_LENGTH = 1024;

 // private static Charset charset = Charset.forName("US-ASCII");

 private static Charset charset = Charset.forName("US-ASCII");

 private static CharsetDecoder decoder = charset.newDecoder();

 private static CharsetEncoder encoder = charset.newEncoder();

 private ByteBuffer r_buff = ByteBuffer.allocate(MAX_LENGTH);

 public MyClient() {
  try {
   InetSocketAddress addr = new InetSocketAddress(InetAddress
     .getLocalHost(), 26);

   sc = SocketChannel.open();
            sc.configureBlocking(false);
            sc.connect(addr);
   selector=Selector.open();
      sc.register(selector,SelectionKey.OP_CONNECT);
   System.out.println("register(selector, SelectionKey.OP_CONNECT");
   while (true) {
    int n=selector.select(30);
    //System.out.println("elector.select(30)="+n);
    if (n> 0) {
     Set set = selector.selectedKeys();
     Iterator it = set.iterator();
     while (it.hasNext()) {
      System.out.println("it.hasNext()");
      SelectionKey sk = (SelectionKey) it.next();
      it.remove();
      set.clear();
      if (sk.isConnectable()) {
       
       if(sc.isConnectionPending()){
        sc.finishConnect();
       }
       System.out.println("4");
       r_buff.clear();
       // sc.read(r_buff);
       String now = new Date().toString();
       sc.write(encoder.encode(CharBuffer.wrap(now
         + "\r\n")));

       // r_buff.flip();
       // CharBuffer cb = decoder.decode(r_buff);
       // System.out.print(" : " + cb);
       sc.register(selector,SelectionKey.OP_READ);
      }
      if(sk.isReadable()){
        sc.read(r_buff);
        r_buff.flip();
        CharBuffer cb = decoder.decode(r_buff);
        System.out.print(" : " + cb);
        sc.register(selector,SelectionKey.OP_WRITE);
      }
      if(sk.isWritable()){
       r_buff.clear();
       // sc.read(r_buff);
       String now = new Date().toString();
       sc.write(encoder.encode(CharBuffer.wrap(now
         + "\r\n")));

       // r_buff.flip();
       // CharBuffer cb = decoder.decode(r_buff);
       // System.out.print(" : " + cb);
       sc.register(selector,SelectionKey.OP_READ);
      }
     }
    }
   }
  } catch (IOException ioe) {
   ioe.printStackTrace();
  } finally {
   try {
    sc.close();
   } catch (IOException ioe) {
    System.err.println("finally sth. is wrong with br.readline() ");
   }
  }
 }

 public static void main(String args[]) {
  new MyClient();
 }
}
/*
public MyClient() {
  try {
   InetSocketAddress addr = new InetSocketAddress(InetAddress
     .getLocalHost(), 26);

   sc = SocketChannel.open();
            sc.configureBlocking(false);
            sc.connect(addr);
   if (sc.finishConnect()) {
    System.out.println("connection has been established!...");

   }
   
   r_buff.clear();
   // sc.read(r_buff);
   String now = new Date().toString();
   sc.write(encoder.encode(CharBuffer.wrap(now
     + "\r\n")));
   
   selector=Selector.open();
   SelectionKey skey = sc.register(selector,0 );
   skey.interestOps(SelectionKey.OP_CONNECT);
   System.out.println("register(selector, SelectionKey.OP_CONNECT");
   while (true) {
    System.out.println(selector.select());
    if (selector.select(50000) > 0) {
     System.out.println("selector.select(30) > 0");
     Set set = selector.selectedKeys();
     Iterator it = set.iterator();
     if (it.hasNext()) {
      System.out.println("it.hasNext()");
      SelectionKey sk = (SelectionKey) it.next();
      if (sk.isConnectable()) {
       System.out.println("4");
       r_buff.clear();
       // sc.read(r_buff);
        now = new Date().toString();
       sc.write(encoder.encode(CharBuffer.wrap(now
         + "\r\n")));

       // r_buff.flip();
       // CharBuffer cb = decoder.decode(r_buff);
       // System.out.print(" : " + cb);
       sc.register(selector,SelectionKey.OP_READ);
       selector.wakeup();
      }
     }
    }
   }
  } catch (IOException ioe) {
   System.err.println("sth. is wrong with br.readline() ");
  } finally {
   try {
    sc.close();
   } catch (IOException ioe) {
    System.err.println("finally sth. is wrong with br.readline() ");
   }
  }
 }
 */