前言：在阅读Netty源码前，我们先了解下Netty的基本使用方法。

一、服务端代码

public class TimeServer {        public static void main(String[] args) throws Exception {        int port = 8080;        if (args != null && args.length > 0) {            try {                port = Integer.valueOf(args[0]);            } catch (NumberFormatException e) {                // 采用默认值            }        }        new TimeServer().bind(port);    }        public void bind(int port) throws Exception {        // 配置服务端的NIO线程组        EventLoopGroup bossGroup = new NioEventLoopGroup();        EventLoopGroup workerGroup = new NioEventLoopGroup();        try {            ServerBootstrap b = new ServerBootstrap();            b.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 f = b.bind(port).sync();            // 等待服务端监听端口关闭            f.channel().closeFuture().sync();        } finally {            // 优雅退出，释放线程池资源            bossGroup.shutdownGracefully();            workerGroup.shutdownGracefully();        }    }    private class ChildChannelHandler extends ChannelInitializer
     
       {        @Override        protected void initChannel(SocketChannel arg0) throws Exception {            arg0.pipeline().addLast(new TimeServerHandler());        }    }}public class TimeServerHandler extends ChannelHandlerAdapter {    @Override    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {        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 java.util.Date(System.currentTimeMillis()).toString()                : "BAD ORDER"; 　　　　 // 创建UnpooledHeapByteBuf,同时设置对象的各个值（copy了一份byte数组放进buffer对象中）        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());        ctx.write(resp);    }    @Override    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {        ctx.flush();    }    @Override    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {        ctx.close();    }}
     

二、客户端代码

public class TimeClient {    public static void main(String[] args) throws Exception {        int port = 8080;        if (args != null && args.length > 0) {            try {                port = Integer.valueOf(args[0]);            } catch (NumberFormatException e) {                // 采用默认值            }        }        new TimeClient().connect(port, "127.0.0.1");    }    public void connect(int port, String host) throws Exception {        // 配置客户端NIO线程组        EventLoopGroup group = new NioEventLoopGroup();        try {            Bootstrap b = new Bootstrap();            b.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true)                    .handler(new ChannelInitializer
     
      () {                        @Override                        public void initChannel(SocketChannel ch) throws Exception {                            ch.pipeline().addLast(new TimeClientHandler());                        }                    });            // 发起异步连接操作            ChannelFuture f = b.connect(host, port).sync();            // 当代客户端链路关闭            f.channel().closeFuture().sync();        } finally {            // 优雅退出，释放NIO线程组            group.shutdownGracefully();        }    }}public class TimeClientHandler extends ChannelHandlerAdapter {    private static final Logger logger = Logger.getLogger(TimeClientHandler.class.getName());    private final ByteBuf firstMessage;    /**     * Creates a client-side handler.     */    public TimeClientHandler() {        byte[] req = "QUERY TIME ORDER".getBytes();        firstMessage = Unpooled.buffer(req.length);        firstMessage.writeBytes(req);    }    /**     * 当客户端连接上服务端时，会触发ChannelActive(..)     */    @Override    public void channelActive(ChannelHandlerContext ctx) {        ctx.writeAndFlush(firstMessage);    }    @Override    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {        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) {        // 释放资源        logger.warning("Unexpected exception from downstream : " + cause.getMessage());        ctx.close();    }}