第一个Netty应用

@Sharable                                        //1 标识这类的实例之间可以在 channel 里面共享
public class EchoServerHandler extends
                   ChannelInboundHandlerAdapter {

    @Override
    public void channelRead(ChannelHandlerContext ctx,
                Object msg) {
        ByteBuf in = (ByteBuf) msg;
        System.out.println("Server received: " + in.toString(CharsetUtil.UTF_8));        //2 日志消息输出到控制台
        ctx.write(in);                            //3 将所接收的消息返回给发送者。注意，这还没有冲刷数据
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER) //4 冲刷所有待审消息到远程节点。关闭通道后，操作完成
            .addListener(ChannelFutureListener.CLOSE);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx,
                    Throwable cause) {
        cause.printStackTrace();                //5 打印异常堆栈跟踪
        ctx.close();                            //6 关闭通道
    }
}

public class EchoServer {
    private final int port;

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

    public static void main(String[] args) throws Exception {
        if (args.length != 1) {
            System.err.println(
                "Usage: " + EchoServer.class.getSimpleName() +
                " <port>");
            return;
        }
        int port = Integer.parseInt(args[0]);        //1 设置端口值
        new EchoServer(port).start();                //2 启动服务器
    }

    public void start() throws Exception {
        NioEventLoopGroup group = new NioEventLoopGroup(); //3 创建 EventLoopGroup
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(group)                                //4 创建 ServerBootstrap
                .channel(NioServerSocketChannel.class)        //5 指定使用 NIO 的传输 Channel
                .localAddress(new InetSocketAddress(port))    //6 设置 socket 地址使用所选的端口
                .childHandler(new ChannelInitializer<SocketChannel>() { 
                        @Override
                        public void initChannel(SocketChannel ch) 
                            throws Exception {
                            ch.pipeline().addLast( //7 添加 EchoServerHandler 到 Channel 的 ChannelPipeline
                                new EchoServerHandler());
                        }
                    });

            ChannelFuture f = b.bind().sync();            //8 绑定的服务器sync:  等待服务器关闭
            System.out.println(EchoServer.class.getName() + " started and listen on " + f.channel().localAddress());
            f.channel().closeFuture().sync();            //9 关闭 channel 和块，直到它被关闭
        } finally {
            group.shutdownGracefully().sync();            //10 关闭 EventLoopGroup，释放所有资源
        }
    }
}

@Sharable                                //1 标记这个类的实例可以在 channel 里共享
public class EchoClientHandler extends
                   SimpleChannelInboundHandler<ByteBuf> {

    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        ctx.writeAndFlush(Unpooled.copiedBuffer("Netty rocks!", //2 当被通知该 channel 是活动的时候就发送信息
                            CharsetUtil.UTF_8));
    }

    @Override
    public void channelRead0(ChannelHandlerContext ctx,
                 ByteBuf in) {
        System.out.println("Client received: " + in.toString(CharsetUtil.UTF_8));    //3 记录接收到的消息
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx,
                    Throwable cause) {                    //4 记录日志错误并关闭 channel
        cause.printStackTrace();
        ctx.close();
    }
}

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 Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();                //1 创建 Bootstrap
            b.group(group)                                //2 指定 EventLoopGroup 来处理客户端事件。由于使用 NIO 传输，所以用到了 NioEventLoopGroup 的实现
                .channel(NioSocketChannel.class)            //3 使用的 channel 类型是一个用于 NIO 传输
                .remoteAddress(new InetSocketAddress(host, port))    //4 设置服务器的 InetSocketAddress
                .handler(new ChannelInitializer<SocketChannel>() {    //5 当建立一个连接和一个新的通道时，创建添加到 EchoClientHandler 实例 到 channel pipeline
                        @Override
                        public void initChannel(SocketChannel ch) 
                            throws Exception {
                            ch.pipeline().addLast(
                                new EchoClientHandler());
                        }
                    });

            ChannelFuture f = b.connect().sync();        //6 连接到远程，等待连接完成
            f.channel().closeFuture().sync();            //7 阻塞直到 Channel 关闭
        } finally {
            group.shutdownGracefully().sync();            //8 调用 shutdownGracefully() 来关闭线程池和释放所有资源
        }
    }

    public static void main(String[] args) throws Exception {
        if (args.length != 2) {
            System.err.println(
                "Usage: " + EchoClient.class.getSimpleName() +
                " <host> <port>");
            return;
        }

        final String host = args[0];
        final int port = Integer.parseInt(args[1]);

        new EchoClient(host, port).start();
    }
}