java NIO selector ServerSocketChannel 例子

1、概述
Selector（选择器）是Java NIO中能够检测一到多个NIO通道，并能够知晓通道是否为诸如读写事件做好准备的组件。这样，一个单独的线程可以管理多个channel，从而管理多个网络连接。
Java NIO中的 ServerSocketChannel 是一个可以监听新进来的TCP连接的通道, 就像标准IO中的ServerSocket一样。

2、例子
例子的思路，初始化ServerSocketChannel ，将ServerSocketChannel 注册到Selector，Selector监听ServerSocketChannel的accept事件，由ServerSocketChannel accept而产生的SocketChannel，再将SocketChannel的read事件注册到Selector。

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.util.Iterator;

public class MyNioServer {

    private Selector selector;

    public static void main(String[] args){
        new MyNioServer().start();
    }

    //初始化类
    public void start(){
        try {
            ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
            serverSocketChannel.configureBlocking(false);
            serverSocketChannel.socket().bind(new InetSocketAddress(9999));
            selector = Selector.open();
            serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
            //循环等待服务
            while(true){
                //至少有一个channel准备就绪
                selector.select();
                //channel状态遍历
                Iterator<?> it = selector.selectedKeys().iterator();
                while (it.hasNext()){
                    SelectionKey key =(SelectionKey) it.next();
                    if(key.isReadable()){
                        readData(key);
                    }else if(key.isAcceptable()){
                        connectEven(key);
                    }
                    it.remove();
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //连接处理
    public void connectEven(SelectionKey key){
        try {
            ServerSocketChannel server = (ServerSocketChannel)key.channel();
            SocketChannel channel = server.accept();
            channel.configureBlocking(false);
            //获得远程连接的IP地址
            System.out.println("已有连接，连接的ip地址是"+ channel.socket().getInetAddress());
            channel.register(selector,SelectionKey.OP_READ);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //数据读取处理
    public void readData(SelectionKey key){
        SocketChannel socketChannel = (SocketChannel) key.channel();
        ByteBuffer buf = ByteBuffer.allocate(1024);
        try {
            int readSize = socketChannel.read(buf);
            if(readSize>0){
                byte[] data = buf.array();
                String msg = new String(data,"UTF-8").trim();
                System.out.println(msg);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

使用网络助手调试，调试结果如图：