一、前言

netty是什么？根据自己的理解，就是一句话：非阻塞、基于事件驱动的网络应用服务开发框架，可以用来开发高性能、高可靠的服务端和客户端网络程序。关于netty架构的介绍，可参考Netty框架入门的介绍，本文做为入门篇，通过实例代码介绍如何使用netty。

首先配置开发环境，开发环境使用的是IDEA，新建个空的MAVEN项目，在pom.xml中添加依赖。

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>zkh360</groupId>
  <artifactId>zkh-netty</artifactId>
  <version>1.0-SNAPSHOT</version>

  <dependencies>
    <!-- https://mvnrepository.com/artifact/io.netty/netty-all -->
    <dependency>
      <groupId>io.netty</groupId>
      <artifactId>netty-all</artifactId>
      <version>4.1.36.Final</version>
    </dependency>
  </dependencies>

</project>

echo server是回显服务，用户输入什么，服务器将输入信息返回给客户端。EchoServer代码如下：

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;

/**
 * @Author:Mark
 * @Email: yunxiang.lon@gmail.com
 * @Description:
 * @Date: Created on 20:52 2019/6/5
 * @Modify by: 
 */
public class EchoServer {
    private int port;

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

    public void run() throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup(); // (1)
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap(); // (2)
            b.group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class) // (3)
                .childHandler(new ChannelInitializer<SocketChannel>() { // (4)
                    @Override
                    public void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(new DiscardServerHandler());
                    }
                })
                .option(ChannelOption.SO_BACKLOG, 128)          // (5)
                .childOption(ChannelOption.SO_KEEPALIVE, true); // (6)

            // Bind and start to accept incoming connections.
            ChannelFuture f = b.bind(port).sync(); // (7)

            // Wait until the server socket is closed.
            // In this example, this does not happen, but you can do that to gracefully
            // shut down your server.
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8090;
        if (args.length > 0) {
            port = Integer.parseInt(args[0]);
        }

        new DiscardServer(port).run();
    }

}

服务器端消息处理代码如下

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.ReferenceCountUtil;

/**
 * @Author:Mark
 * @Email: yunxiang.lon@gmail.com
 * @Description:
 * @Date: Created on 20:34 2019/6/5
 * @Modify by: 
 */
public class EchoServerHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg){
        ctx.write(msg); //(1)
        ctx.close(); //(2)
    }


    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause){
        // Close the connection when an exception is raised.
        cause.printStackTrace();
        ctx.close();
    }

}

运行服务端程序，telnet 27.0.0.1 8090，输入，显示如下：