Netty是什么

Netty是一个java开源框架。Netty提供异步的、事件驱动的网络应用程序框架和工具，用以快速开发高性能、高可靠性的网络服务器和客户端程序。

也就是说，Netty 是一个基于NIO的客户、服务器端编程框架，使用Netty 可以确保你快速和简单的开发出一个网络应用，例如实现了某种协议的客户，服务端应用。Netty相当简化和流线化了网络应用的编程开发过程，例如，TCP和UDP的socket服务开发。

“快速”和“简单”并不意味着会让你的最终应用产生维护性或性能上的问题。Netty 是一个吸收了多种协议的实现经验，这些协议包括FTP,SMTP,HTTP，各种二进制，文本协议，并经过相当精心设计的项目，最终，Netty 成功的找到了一种方式，在保证易于开发的同时还保证了其应用的性能，稳定性和伸缩性。

https://www.oschina.net/p/netty

Server端

public class TimeServer {

    public void bind(int port) throws Exception {

        EventLoopGroup bossGroup = new NioEventLoopGroup();

        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {

            // 配置服务器的NIO线程租

            ServerBootstrap bootstrap = new ServerBootstrap();

            bootstrap.group(bossGroup, workerGroup)

                    .channel(NioServerSocketChannel.class)

                    .option(ChannelOption.SO_BACKLOG, 1024)

                    .childHandler(new ChildChannelHandler());

            // 绑定端口，同步等待成功

            ChannelFuture future = bootstrap.bind(port).sync();

            // 等待服务端监听端口关闭

            future.channel().closeFuture().sync();

        } catch (Exception e) {

            e.printStackTrace();

        } finally {

            // 优雅退出，释放线程池资源

            bossGroup.shutdownGracefully();

            workerGroup.shutdownGracefully();

        }

    }

    private class ChildChannelHandler extends ChannelInitializer<SocketChannel> {

        @Override

        protected void initChannel(SocketChannel arg0) throws Exception {

            System.out.println("server initChannel..");

            arg0.pipeline().addLast(new TimerServerHandler());

        }

    }

    public static void main(String[] args) throws Exception {

        int port = 9000;

        new TimeServer().bind(port);

    }

}

public class TimerServerHandler extends ChannelHandlerAdapter {

    @Override

    public void channelRead(ChannelHandlerContext ctx, Object msg)

            throws Exception {

        System.out.println("server channelRead..");

        ByteBuf buf = (ByteBuf) msg;

        byte[] req = new byte[buf.readableBytes()];

        buf.readBytes(req);

        String body = new String(req, "UTF-8");

        System.out.println("The time server receive order:" + body);

        String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(

                System.currentTimeMillis()).toString() : "BAD ORDER";

        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());

        ctx.write(resp);

    }

    @Override

    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {

        System.out.println("server channelReadComplete..");

        ctx.flush();//刷新后才将数据发出到SocketChannel

    }

    @Override

    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)

            throws Exception {

        System.out.println("server exceptionCaught..");

        ctx.close();

    }

}

Client端

public class TimeClient {

    public void connect(int port, String host) throws Exception {

        // 配置客户端NIO线程组

        EventLoopGroup group = new NioEventLoopGroup();

        try {

            Bootstrap bootstrap = new Bootstrap();

            bootstrap.group(group).channel(NioSocketChannel.class)

                    .option(ChannelOption.TCP_NODELAY, true)

                    .handler(new ChannelInitializer<SocketChannel>() {

                        @Override

                        protected void initChannel(SocketChannel socketChannel)

                                throws Exception {

                            System.out.println("client initChannel..");

                            socketChannel.pipeline().addLast(new TimeClientHandler());

                        }

                    });

            // 发起异步连接操作

            ChannelFuture future = bootstrap.connect(host, port).sync();

            // 等待客户端链路关闭

            future.channel().closeFuture().sync();

        } finally {

            // 优雅退出，释放NIO线程组

            group.shutdownGracefully();

        }

    }

    public static void main(String[] args) throws Exception {

        int port = 9000;

        new TimeClient().connect(port, "127.0.0.1");

    }

}

public class TimeClientHandler extends ChannelHandlerAdapter implements ChannelHandler{

    private static final Logger logger = Logger

            .getLogger(TimeClientHandler.class.getName());

    private final ByteBuf firstMessage;

    public TimeClientHandler() {

        byte[] req = "QUERY TIME ORDER".getBytes();

        firstMessage = Unpooled.buffer(req.length);

        firstMessage.writeBytes(req);

    }

    @Override

    public void channelActive(ChannelHandlerContext ctx) throws Exception {

        //与服务端建立连接后

        System.out.println("client channelActive..");

        ctx.writeAndFlush(firstMessage);

    }

    @Override

    public void channelRead(ChannelHandlerContext ctx, Object msg)

            throws Exception {

        System.out.println("client channelRead..");

        //服务端返回消息后

        ByteBuf buf = (ByteBuf) msg;

        byte[] req = new byte[buf.readableBytes()];

        buf.readBytes(req);

        String body = new String(req, "UTF-8");

        System.out.println("Now is :" + body);

    }

    @Override

    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)

            throws Exception {

        System.out.println("client exceptionCaught..");

        // 释放资源

        logger.warn("Unexpected exception from downstream:"

                + cause.getMessage());

        ctx.close();

    }

}