Netty入门

1.Netty介绍

（1）百度百科介绍：

Netty是由JBOSS提供的一个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相当于简化和流线化了网络应用的编程开发过程，例如：基于TCP和UDP的socket服务开发。
“快速”和“简单”并不用产生维护性或性能上的问题。Netty 是一个吸收了多种协议（包括FTP、SMTP、HTTP等各种二进制文本协议）的实现经验，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。

（2）官网介绍：netty.io

Netty is an asynchronous event-driven network application framework
for rapid development of maintainable high performance protocol servers & clients.

（3）参考资料：

1. 参考书籍：Netty实战（Norman Maurer & Marvin Allen Wolfthal）
2. 参考官方文档：https://netty.io/wiki/user-guide.html
3. 参考网址：https://ifeve.com/tag/netty/

2.程序功能概述

客户端向服务器发送HelloNetty-Server!服务器向客户端返回Hello Netty-Client!

3.程序实现

1. 服务端ChannelHandler

   package com.xm.netty;
   
   import io.netty.buffer.ByteBuf;
   import io.netty.buffer.Unpooled;
   import io.netty.channel.ChannelFutureListener;
   import io.netty.channel.ChannelHandlerContext;
   import io.netty.channel.ChannelInboundHandlerAdapter;
   import io.netty.util.CharsetUtil;
   
   public class ServerHandler extends ChannelInboundHandlerAdapter {
   
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf in = (ByteBuf) msg;
        System.out.println("服务器接收："+in.toString(CharsetUtil.UTF_8));
        in.clear();
        String str = "Hello Netty-Client!";
        in.writeBytes(str.getBytes());
        ctx.write(in);
    }
   
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
    }   
   
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
   
   }
   

2. 服务端Server

   package com.xm.netty;
   
   import java.net.InetSocketAddress;
   
   import io.netty.bootstrap.ServerBootstrap;
   import io.netty.channel.Channel;
   import io.netty.channel.ChannelFuture;
   import io.netty.channel.ChannelInitializer;
   import io.netty.channel.EventLoopGroup;
   import io.netty.channel.nio.NioEventLoopGroup;
   import io.netty.channel.socket.nio.NioServerSocketChannel;
   
   public class Server {
   
    private final int port;
   
    public Server(int port) {
        this.port = port;
    }
   
    public static void main(String[] args) {
        int port = 8989;
        try {
            new Server(port).start();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
   
    private void start() throws InterruptedException {
         final ServerHandler serverHandler = new ServerHandler();
         EventLoopGroup group = new NioEventLoopGroup();
         try {
            ServerBootstrap bootstrap = new ServerBootstrap();
             bootstrap
                    .group(group)
                    .channel(NioServerSocketChannel.class)
                    .localAddress(new InetSocketAddress( port))
                    .childHandler(new ChannelInitializer() {
                        @Override
                        protected void initChannel(Channel ch) throws Exception {
                            ch.pipeline().addLast(serverHandler);
                        }
                    });
             ChannelFuture future = bootstrap.bind().sync();
             future.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
   
    }
   
   }
   

3. 客户端ChannelHandler

   package com.xm.netty;
   
   import io.netty.buffer.ByteBuf;
   import io.netty.buffer.Unpooled;
   import io.netty.channel.ChannelHandlerContext;
   import io.netty.channel.SimpleChannelInboundHandler;
   import io.netty.util.CharsetUtil;
   
   public class ClientHandler extends SimpleChannelInboundHandler<ByteBuf> {
   
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush(Unpooled.copiedBuffer("Hello Netty-Server!",CharsetUtil.UTF_8));
    }
   
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
        System.out.println("客户端接收到消息："+msg.toString(CharsetUtil.UTF_8));
    }
   
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
   
   }
   

4. 客户端Client

   package com.xm.netty;
   
   import io.netty.bootstrap.Bootstrap;
   import io.netty.channel.ChannelFuture;
   import io.netty.channel.ChannelInitializer;
   import io.netty.channel.EventLoopGroup;
   import io.netty.channel.nio.NioEventLoopGroup;
   import io.netty.channel.socket.SocketChannel;
   import io.netty.channel.socket.nio.NioSocketChannel;
   
   public class Client {
   
    private final int port;
    private final String host;
   
   
   
    public Client(int port, String host) {
        this.port = port;
        this.host = host;
    }
   
   
   
    public static void main(String[] args) {
   
        String host = "127.0.0.1";
        int port = 8989;
        try {
            new Client(port, host).start();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
   
    }
   
   
   
    private void start() throws InterruptedException {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap
                    .group(group)
                    .channel(NioSocketChannel.class)
                    .remoteAddress(host, port)
                    .handler(new ChannelInitializer<SocketChannel>() {
   
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new ClientHandler());
                        }
   
                    });
   
            ChannelFuture future = bootstrap.connect().sync();
            future.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
   
    }
   
   }
   

5. 导入依赖

   <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>com.xm</groupId>
     <artifactId>netty</artifactId>
     <version>0.0.1-SNAPSHOT</version>
   
     <dependencies>
   
   
   <dependency>
       <groupId>io.netty</groupId>
       <artifactId>netty-all</artifactId>
       <version>4.1.16.Final</version>
   </dependency>
   
   
     </dependencies>
   </project>

4.运行结果：

1. 服务端：

   服务器接收：Hello Netty-Server!

2. 客户端：

   客户端接收到消息：Hello Netty-Client!