1. 思路

• 首先，我们通过一个时序图来看下如何创建一个NIO服务端并启动监听，接收多个客户端的连接，进行消息的异步读写。

0909010.png

public class NioServer
{

public static void main(String[] args)
{
    ServerSocketChannel channel = null;
    Selector selector = null;

    try
    {
        InetSocketAddress address = new InetSocketAddress(8400);
        channel = ServerSocketChannel.open();
        channel.configureBlocking(false);
        channel.socket().bind(address);

        selector = Selector.open();
        channel.register(selector, SelectionKey.OP_ACCEPT);
    } catch (IOException ex)
    {
        System.out.println("Couldn't setup server socket");
        System.out.println(ex.getMessage());
        System.exit(1);
    }

    ListenerThread listener = new ListenerThread(selector);
    listener.start();
}

}

class ListenerThread extends Thread
{
private Selector selector = null;

public ListenerThread(Selector selector)
{
    this.selector = selector;
}

public void run()
{
    while (true)
    {

        try
        {
            while (this.selector.select() > 0)
            {
                Set<SelectionKey> keys = this.selector.selectedKeys();
                Iterator<SelectionKey> iterator = keys.iterator();
                while (iterator.hasNext())
                {
                    SelectionKey key = iterator.next();

                    if (key.isAcceptable())
                    {
                        System.out.println("Accepting connection!");
                        ServerSocketChannel serverChannel = (ServerSocketChannel) key.channel();
                        SocketChannel channel = serverChannel.accept();
                        channel.configureBlocking(false);
                        channel.register(this.selector, SelectionKey.OP_READ);
                    } else if (key.isReadable())
                    {
                        System.out.println("Accpting command!");
                        SocketChannel channel = (SocketChannel) key.channel();
                        ByteBuffer _buffer = ByteBuffer.allocate(256);
                        channel.read(_buffer);
                        _buffer.flip();
                        Charset charset = Charset.forName("UTF-8");
                        CharsetDecoder decoder = charset.newDecoder();
                        CharBuffer charBuffer = decoder.decode(_buffer);
                        System.out.println(charBuffer.toString());
                        channel.register(this.selector, SelectionKey.OP_WRITE);
                    } else if (key.isWritable())
                    {
                        System.out.println("Sending response!");
                        SocketChannel channel = (SocketChannel) key.channel();
                        channel.write(ByteBuffer.wrap(new String("Hello World\n").getBytes()));
                        channel.register(this.selector, SelectionKey.OP_READ);
                    }
                    iterator.remove();
                }
            }
        } catch (IOException ex)
        {
            System.out.println("Error in poll loop");
            System.out.println(ex.getMessage());
            System.exit(1);
        }
    }
}

}

QQ截图20160704031026.png

• 在window下，通过telnet 127.0.0.1 8400 即可测试程序的运行过程与结果。