Netty 系列一（核心组件和实例）.

public class EchoServer {

    private final int port;

    public EchoServer(int port) {
        this.port = port;
    }

    public void start() throws InterruptedException {
        final EchoServerHandler serverHandler = new EchoServerHandler();
        //1、创建EventLoopGroup以进行事件的处理，如接受新连接以及读/写数据
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            //2、创建ServerBootstrap，引导和绑定服务器
            ServerBootstrap bootstrap = new ServerBootstrap();
            bootstrap.group(group, group)
                    //3、指定所使用的NIO传输Channel
                    .channel(NioServerSocketChannel.class)
                    //4、使用指定的端口设置套接字地址
                    .localAddress(new InetSocketAddress(port))
                    //5、添加一个 EchoServerHandler 到子 Channel的 ChannelPipeline
                    //当一个新的连接被接受时，一个新的子Channel将会被创建，而 ChannelInitializer 将会把一个你的EchoServerHandler 的实例添加到该 Channel 的 ChannelPipeline 中
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) {
                            ChannelPipeline pipeline = ch.pipeline();
                            pipeline.addLast(serverHandler);
                        }
                    });
            //6、异步地绑定服务器，调用sync()方法阻塞等待直到绑定完成
            ChannelFuture channelFuture = bootstrap.bind().sync();
            System.out.println(EchoServer.class.getName() + "started and listening for connections on" + channelFuture.channel().localAddress());
            //7、获取 Channel 的 CloseFuture，并且阻塞当前线程直到它完成
            channelFuture.channel().closeFuture().sync();

        } finally {
            //8、关闭 EventLoopGroup 释放所有的资源
            group.shutdownGracefully().sync();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new EchoServer(9999).start();
    }
}

public class EchoClient {

    private final String host;
    private final int port;

    public EchoClient(String host, int port) {
        this.host = host;
        this.port = port;
    }

    public void start() throws InterruptedException {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            //创建Bootstrap
            Bootstrap bootstrap = new Bootstrap();
            //指定 EventLoopGroup 以处理客户端事件；适应于NIO的实现
            bootstrap.group(group)
                    //适用于NIO传输的Channel类型
                    .channel(NioSocketChannel.class)
                    .remoteAddress(new InetSocketAddress(host, port))
                    //在创建Channel时，向ChannelPipeline中添加一个EchoClientHandler实例
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new EchoClientHandler());
                        }
                    });
            //连接到远程节点，阻塞等待直到连接完成
            ChannelFuture channelFuture = bootstrap.connect().sync();
            //阻塞，直到Channel 关闭
            channelFuture.channel().closeFuture().sync();
        } finally {
            //关闭线程池并且释放所有的资源
            group.shutdownGracefully().sync();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new EchoClient("127.0.0.1", 9999).start();

        System.out.println("------------------------------------");

        new EchoClient("127.0.0.1", 9999).start();

        System.out.println("------------------------------------");

        new EchoClient("127.0.0.1", 9999).start();
    }


}