java NIO多路复用简单实例

To set up a Selector to monitor three Socket channels, you'd do something like this

Selector selector = Selector.open();
channel1.register (selector, SelectionKey.OP_READ);
channel2.register (selector, SelectionKey.OP_WRITE);
channel3.register (selector, SelectionKey.OP_READ |
SelectionKey.OP_WRITE);
// Wait up to 10 seconds for a channel to become ready
readyCount = selector.select (10000);

package com.ronsoft.books.nio.channels;
import java.nio.ByteBuffer;
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.net.Socket;
import java.net.ServerSocket;
import java.net.InetSocketAddress;
import java.util.Iterator;
/**
* Simple echo-back server which listens for incoming stream connections
* and echoes back whatever it reads. A single Selector object is used to
* listen to the server socket (to accept new connections) and all the
* active socket channels.
*
* @author Ron Hitchens ([e-mail])
*/
public class SelectSockets
{
   public static int PORT_NUMBER = 1234;
   public static void main (String [] argv)
   throws Exception
   {
     new SelectSockets().go (argv);
   }  
   public void go (String [] argv)
   throws Exception
   {
    int port = PORT_NUMBER;
    if (argv.length > 0) { // Override default listen port
        port = Integer.parseInt (argv [0]);
    }
    System.out.println ("Listening on port " + port);
    // Allocate an unbound server socket channel
    ServerSocketChannel serverChannel = ServerSocketChannel.open();
    // Get the associated ServerSocket to bind it with
    ServerSocket serverSocket = serverChannel.socket();
    // Create a new Selector for use below
    Selector selector = Selector.open();
    // Set the port the server channel will listen to
    serverSocket.bind (new InetSocketAddress (port));
    // Set nonblocking mode for the listening socket
    serverChannel.configureBlocking (false);
    // Register the ServerSocketChannel with the Selector
    serverChannel.register (selector, SelectionKey.OP_ACCEPT);
    while (true) {
       // This may block for a long time. Upon returning, the
       // selected set contains keys of the ready channels.
       int n = selector.select();
       if (n == 0) {
       continue; // nothing to do
       }
        // Get an iterator over the set of selected keys
       Iterator it = selector.selectedKeys().iterator();
       // Look at each key in the selected set
       while (it.hasNext()) {
       SelectionKey key = (SelectionKey) it.next();
       // Is a new connection coming in?
       if (key.isAcceptable()) {
          ServerSocketChannel server =
          (ServerSocketChannel) key.channel();
          SocketChannel channel = server.accept();
          registerChannel (selector, channel,
           SelectionKey.OP_READ);
          sayHello (channel);
       }
       // Is there data to read on this channel?
       if (key.isReadable()) {
           readDataFromSocket (key);
       }
       // Remove key from selected set; it's been handled
       it.remove();
       }
    }
 }
     // ----------------------------------------------------------

  /**
   * Register the given channel with the given selector for
   * the given operations of interest
  */
   protected void registerChannel (Selector selector,
       SelectableChannel channel, int ops)
   throws Exception
   {
    if (channel == null) {
       return; // could happen
    }
   // Set the new channel nonblocking
    channel.configureBlocking (false);
    // Register it with the selector
    channel.register (selector, ops);
  }
   

以上只是部分代码

readDataFromSocket (key);

的内容没有列出，大家可以参考Oreilly JAVA NIO一书
本书作者给出了两种模型
始终使用一个线程处理数据，还有一种就是使用线程池工作者模式，在多核环境下使用多线程可以更大程度的提供CPU利用率。

下篇简单介绍服务器的3种并发模型