一、环境准备

开发工具eclipse/idea（本人目前正在切换为idea），maven插件

最新版的netty包maven依赖

                
     
      io.netty
                 
     
      netty-all
                 
     
      5.0.0.Alpha1
             
    

二、简单的client/server demo

功能：client端发送一个“query time order”字符串，server端接收到后返回当前服务器时间

Server端的代码

public class TimeServer {    public void bind(int port) throws  Exception{        EventLoopGroup bossGroup = new NioEventLoopGroup();        EventLoopGroup workerGroup = new NioEventLoopGroup();        ServerBootstrap b = new ServerBootstrap();        try {            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();            f.channel().closeFuture().sync();        } finally {            bossGroup.shutdownGracefully();            workerGroup.shutdownGracefully();        }    }    private class ChildChannelHandler extends ChannelInitializer
    
     {        @Override        protected void initChannel(SocketChannel ch) throws Exception {            ch.pipeline().addLast(new TimeServerHandler());            System.out.println("server add time server handler");        }    }    public static void main(String[] args) throws Exception {        int port = 8080;        new TimeServer().bind(port);    }}
    

TimeServer 首先创建了2个NioEventLoopGroup实例（NioEventLoopGroup是个线程组，它包含了一组NIO线程，专门用于网络事件的处理。），一个用于服务端接收客户端的链接，一个用于进行SokectChannel的网络读写。

ServerBootstrap是Netty用于启动NIO服务端的辅助启动类，group方法将两个线程组加入到进来。接着设置创建的Channel为NioServerSocketChannel。

然后配置NioServerSocketChannel的TCP参数，最后绑定I/O事件的处理器ChildChannelHandler。

f.channel().closeFuture().sync(); 方法进行阻塞，等待服务器链路关闭之后main函数才退出。

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("time server receive order is :"+body);        String res = "query time order".equals(body)?new Date().toString():"bad order";        ByteBuf resBuf = Unpooled.copiedBuffer(res.getBytes());        ctx.writeAndFlush(resBuf);    }    @Override    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {        System.out.println("server channel read complete……");        ctx.flush();    }    @Override    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {        System.out.println("server has exception :"+cause.getMessage());        ctx.close();    }}

TimeServerHandler 它用于对网络事件进行读写操作，通常我们只需要关注channelRead和exceptionCaught这两个方法

Client端代码

public class TimeClient {    public void connect(int port,String host) throws Exception {        EventLoopGroup group = new NioEventLoopGroup();        Bootstrap b = new Bootstrap();        try {            b.group(group).channel(NioSocketChannel.class)                    .option(ChannelOption.TCP_NODELAY, true)                    .handler(new ChannelInitializer
    
     () {                        @Override                        protected void initChannel(SocketChannel ch) throws Exception {                            ch.pipeline().addLast(new TimeClientHandler());                            System.out.println("client add time client handler");                        }                    });            //发起异步连接操作            ChannelFuture f = b.connect(host,port).sync();            f.channel().closeFuture().sync();        } finally {            group.shutdownGracefully();        }    }    public static void main(String[] args) throws Exception {        int port = 8080;        new TimeClient().connect(port,"127.0.0.1");    }}
    

首先创建客户端处理I/O读写的NioEventLoopGroup线程组，然后继续创建客户端辅助启动类Bootstrap，然后对其进行配置。它的Channel需要设置为NioSocketChannel，然后添加handler。

public class TimeClientHandler extends ChannelHandlerAdapter{    private final ByteBuf firstMessage;    public TimeClientHandler() {        byte[] res = "query time order".getBytes();        this.firstMessage = Unpooled.buffer(res.length);        firstMessage.writeBytes(res);    }    @Override    public void channelActive(ChannelHandlerContext ctx) throws Exception {        System.out.println("client channel active");        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);        System.out.println("Server time is : "+new String(req,"UTF-8"));    }    @Override    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {        System.out.println("client have exception : " + cause.getMessage());        ctx.close();    }}

这里重点关注channelActive，channelRead和exceptionCaught这三个方法。

当客户端和服务端TCP链路建立成功后，Netty的线程会调用channelActive方法，发送查询时间指令给服务端，调用ChannelHandlerContext的writeAndFlush方法将请求发送给服务端。服务端返回消息应答时，channelRead被调用。

运行效果

Server端输出

server add time server handlertime server receive order is :query time orderserver channel read complete……

Client端输出

client add time client handlerclient channel activeServer time is : Wed Dec 09 16:28:53 CST 2015

参考《Netty权威指南(第二版)》