最近在学习netty，看了几天的博客之后，打算自己写一个练手的程序。

这个程序很简单：客户端发送一个ping，服务端会相应地回复一个pong，当监测到服务端失去连接后，即断开。

整个代码分为client与server两部分，结构如下：

引入netty包：

    	
     
      io.netty
     	
     
      netty-all
     	
     
      4.1.15.Final
     
    

client端：

PingClient.java

package org.attempt.netty4.demo001.client;import io.netty.bootstrap.Bootstrap;import io.netty.channel.Channel;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelOption;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.SocketChannel;import io.netty.channel.socket.nio.NioSocketChannel;import io.netty.handler.codec.string.StringDecoder;import io.netty.handler.codec.string.StringEncoder;public class PingClient {    /** 服务器IP地址 */    private String host = "127.0.0.1";    /** 服务器端口 */    private int port = 8000;    private EventLoopGroup group = null;    private Bootstrap b = null;    private Channel channel = null;    public PingClient() throws Exception {        group = new NioEventLoopGroup();        b = new Bootstrap();        b.group(group)                .option(ChannelOption.SO_KEEPALIVE, true)                .channel(NioSocketChannel.class)                .handler(new ChannelInitializer
    
     () {                    @Override                    protected void initChannel(SocketChannel channel) throws Exception {                        channel.pipeline()                                //字符串解码和编码                                .addLast(new StringDecoder())                                .addLast(new StringEncoder())                                //客户端的逻辑                                .addLast(new PingClientHandler());                    }                });    }    public Channel getChannel() throws Exception {        if(null == channel || !channel.isActive()) {            channel = b.connect(host, port).sync().channel();        }        return channel;    }    public static void main(String[] args) throws Exception {        PingClient client = null;        try {            client = new PingClient();            Channel channel = client.getChannel();            while(true) {                //输出channel的状态，对应于close()                System.out.println(channel.isOpen());                //判断连接状态                if(channel.isActive()) {                    channel.writeAndFlush("ping");                } else {                    System.out.println("失去连接，关闭客户端");                    channel.close();                    break;                }                Thread.sleep(5000);            }        } finally {            if(null != client) {                client.stop();            }        }    }    public void stop() {        if(null != group) {            //优雅退出，释放线程池资源            group.shutdownGracefully();        }    }}
    

PingClientHandler.java

package org.attempt.netty4.demo001.client;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.SimpleChannelInboundHandler;public class PingClientHandler extends SimpleChannelInboundHandler {    @Override    protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {        System.out.println("receive from server: " + msg.toString());    }}

server端： PongServer.java

package org.attempt.netty4.demo001.server;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelOption;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.SocketChannel;import io.netty.channel.socket.nio.NioServerSocketChannel;import io.netty.handler.codec.string.StringDecoder;import io.netty.handler.codec.string.StringEncoder;public class PongServer {    public static void main(String[] args) throws Exception {        int port = 8000;        if (args != null && args.length > 0) {            try {                port = Integer.valueOf(args[0]);            } catch (NumberFormatException e) {                //采用默认值            }        }        new PongServer().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 ChannelInitializer
    
     () {                        @Override                        protected void initChannel(SocketChannel channel) throws Exception {                            channel.pipeline()                            //字符串解码和编码                            .addLast(new StringDecoder())                            .addLast(new StringEncoder())                            //服务器的逻辑                            .addLast(new PongServerHandler());                        }                    });            //绑定端口，同步等待成功            ChannelFuture f = b.bind(port).sync();            //等待服务器监听端口关闭            f.channel().closeFuture().sync();        } finally {            //优雅退出，释放线程池资源            bossGroup.shutdownGracefully();            workerGroup.shutdownGracefully();        }    }}
    

PongServerHandler.java

package org.attempt.netty4.demo001.server;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.SimpleChannelInboundHandler;/** * @author admin * @date 2018-09-06 22:48 */public class PongServerHandler extends SimpleChannelInboundHandler {    @Override    protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {        System.out.println("receive from client: " + msg.toString());        //返回客户端消息        if(msg.toString().equals("ping")) {            ctx.writeAndFlush("pong");        } else {            ctx.writeAndFlush("UNKONWN");        }    }}

运行，先启动server端，再启动client端，结果如下：

• server端：

receive from client: pingreceive from client: pingreceive from client: pingreceive from client: pingreceive from client: pingProcess finished with exit code -1

• client端：

truereceive from server: pongtruereceive from server: pongtruereceive from server: pongtruereceive from server: pongtruereceive from server: pongfalse失去连接，关闭客户端

代码中的一些类及用法，后面再说。