NIO因为其高效性，成为了服务端的首选，大大提高了服务端的响应效率。以下是一个简单的DEMO。服务端：

    package com.liuc.io;                import java.io.IOException;        import java.net.InetSocketAddress;        import java.nio.ByteBuffer;        import java.nio.channels.SelectionKey;        import java.nio.channels.Selector;        import java.nio.channels.ServerSocketChannel;        import java.nio.channels.SocketChannel;        import java.nio.charset.Charset;        import java.util.Iterator;        import java.util.Set;                import org.apache.log4j.Logger;                public class NIOServer extends Thread {            private Logger log=Logger.getLogger(NIOServer.class);            private boolean stop=false;            private String ip="localhost";            private int port=9999;            private Selector selector;            private ByteBuffer buffer=ByteBuffer.allocate(1024);            private Charset gbkCharset = Charset.forName( "GB2312" );              public NIOServer() {                try {                    selector=Selector.open();                    ServerSocketChannel ssc=ServerSocketChannel.open();                    InetSocketAddress address=new InetSocketAddress(ip, port);                    //ServerSocket绑定IP                    ssc.socket().bind(address);                    //设置为非阻塞模式                    ssc.configureBlocking(false);                    //向选择器注册                    ssc.register(selector,SelectionKey.OP_ACCEPT);                      System.out.println("Listen to port:"+port);                } catch (IOException e) {                    log.error(e);                }                            }                    @Override            public void run() {                System.out.println("deal with request");                while(!stop){                        String content="HelloWorld";                        try {                            int numKeys = selector.select();                            Set<SelectionKey> selectionKeys=selector.selectedKeys();                            Iterator<SelectionKey> iterator=selectionKeys.iterator();                            while (iterator.hasNext()) {                                 SelectionKey key = iterator.next();                                 iterator.remove();                                 dealRequest(key,content);                            }                        } catch (IOException e) {                            log.equals(e);                        }                                        }            }                        private void dealRequest(SelectionKey key,String contentToSend) {                try {                                          StringBuffer clientContent=new StringBuffer();                      if(key.isAcceptable()){//测试此键的通道是否已准备好接受新的套接字连接。                          ServerSocketChannel ssc=(ServerSocketChannel) key.channel();                          SocketChannel sc=ssc.accept();                          sc.configureBlocking(false);                          sc.register(selector, SelectionKey. OP_READ);                      }else if(key.isReadable()) {//测试此键的通道是否已准备好进行读取。                           SocketChannel sc=(SocketChannel) key.channel();                          while(true){//读取全部数据                              buffer.clear();                              int r=sc.read(buffer);                              buffer.flip();                              byte[] temp=new byte[r];                              if (r<=0) {                                break;                              }                              clientContent.append(gbkCharset.decode(buffer).toString());                                                       }                          //获取全部的数据                          String content=clientContent.toString();                          String[] info=content.split(",");//用户名密码验证                          System.out.println("客户端的验证请求为:"+content);                                      sc.register(selector, SelectionKey.OP_WRITE);                                                }else if(key.isWritable()){//测试此键的通道是否已准备好进行写入                        System.out.println("要发送的消息为"+contentToSend);                        buffer.clear();                        buffer.put(contentToSend.getBytes());                        buffer.flip();                        SocketChannel sc = (SocketChannel)key.channel();                        sc.write(buffer);                        buffer.flip();                        //发送完信息后关闭连接                        key.cancel();                        sc.close();                    }                                    } catch (IOException e) {                    System.out.println(e);                    //客户端断开连接，所以从Selector中取消注册                     key.cancel();                    if(key.channel() != null)                        try {                            key.channel().close();                            log.debug("the client socket is closed!");                            //System.out.println("the client socket is closed!");                        } catch (IOException e1) {                            e1.printStackTrace();                        }                }            }                                    public static void main(String[] args){                new NIOServer().start();            }                }  

    package com.liuc.io;                import java.io.IOException;        import java.io.InputStream;        import java.io.OutputStream;        import java.net.Socket;        import java.net.UnknownHostException;                public class NIOClient {                    /**            * @param args            */            public static void main(String[] args) {                Socket socket=null;                OutputStream outputStream=null;                InputStream inputStream=null;                try {                    socket=new Socket("localhost", 9999);                    outputStream=socket.getOutputStream();                    String sendContent="HelloWorld";                    outputStream.write(sendContent.getBytes());                    outputStream.flush();                                                            inputStream=socket.getInputStream();                    byte[] bytes=new byte[1024];                    int n=inputStream.read(bytes);                    System.out.println(new String(bytes));                                                        } catch (UnknownHostException e) {                    e.printStackTrace();                } catch (IOException e) {                    e.printStackTrace();                }finally{                    try {                            if(inputStream!=null){                                inputStream.close();                            }                            if (outputStream!=null) {                                outputStream.close();                            }                            if (socket!=null) {                                socket.close();                            }                    } catch (IOException e) {                        e.printStackTrace();                    }                                    }                                    }                }