java NIO使用示例

package com.mine;

import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.nio.ByteBuffer;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;

public class SelectorDemo {

    public static int PORT_NUMBER = 1234;

    public static void main(String[] argv) throws Exception {
        new SelectorDemo().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(); // 新建一个通道
        ServerSocket serverSocket = serverChannel.socket(); // 从通道获得一个socket连接
        Selector selector = Selector.open(); // 新建一个选择器
        serverSocket.bind(new InetSocketAddress(port)); // 把socket连接绑定到一个端口上
        serverChannel.configureBlocking(false); // 设置通道为非阻塞模式，只有非阻塞模式才能使用nio带来的好处，socket通道能设置为非阻塞的，文件通道不能设置为非阻塞的
        serverChannel.register(selector, SelectionKey.OP_ACCEPT); //把这个通道注册到一个选择器上，感兴趣的操作时OP_ACCEPT，等待连接
        while (true) {// 从选择器中循环选择已经准备好的选择器键，键就是保持通道跟选择器的对应关系
            int n = selector.select();  //从选择器中获得已经准备好的选择器键的个数
            if (n == 0) {
                continue; // nothing to do
            }// Get an iterator over the set of selected keys
            Iterator it = selector.selectedKeys().iterator(); // 遍历所有已经准备好的选择器键
            while (it.hasNext()) {
                SelectionKey key = (SelectionKey) it.next(); 
                if (key.isAcceptable()) { //如果该键是等待连接的状态
                    ServerSocketChannel server = (ServerSocketChannel) key.channel(); //从改键中获取已经准备连接好的server socket通道
                    SocketChannel channel = server.accept(); //从server socket通道获得本次socket连接
                    registerChannel(selector, channel, SelectionKey.OP_READ); //把该连接注册为可读的操作状态
                    sayHello(channel);//往该socket连接发送数据
                }// Is there data to read on this channel?
                if (key.isReadable()) { //下次当该链接为可读的时候
                    readDataFromSocket(key);//接收该socket链接的数据，并显示
                }// Remove key from selected set; it's been handled
                it.remove();//删除本次已经执行过的准备好的键，下次再执行selector.select()，仍然能选出所有已经准备好的键
            }
        }
    }

    protected void registerChannel(Selector selector, SelectableChannel channel, int ops) throws Exception {
        if (channel == null) {
            return; 
        }
        channel.configureBlocking(false); //设置通道为非阻塞模式 
        channel.register(selector, ops);//把该连接注册为可读的操作状态
    }

    private ByteBuffer buffer = ByteBuffer.allocateDirect(1024);


    protected void readDataFromSocket(SelectionKey key) throws Exception {
        SocketChannel socketChannel = (SocketChannel) key.channel();
        int count;
        buffer.clear(); 
        while ((count = socketChannel.read(buffer)) > 0) { //从通道里面独处数据
            buffer.flip(); //标准该通道的数据是可读的
            while (buffer.hasRemaining()) {
                socketChannel.write(buffer);//往通道里面写数据
            }
            buffer.clear(); 
            if (count < 0) {
                socketChannel.close();
            }
        }
    }
    private void sayHello(SocketChannel channel) throws Exception {
        buffer.clear();
        buffer.put("Hi there!\r\n".getBytes());
        buffer.flip();
        channel.write(buffer);
    }
}

执行该程序，用telnet登陆本机的1234端口，你输入一个字符，程序把接收到的字符发送出去。