一、简介
Netty是基于Java NIO client-server的网络应用框架，使用Netty可以快速开发网络应用，例如服务器和客户端协议。Netty提供了一种新的方式来开发网络应用程序，这种新的方式使它很容易使用和具有很强的扩展性。Netty的内部实现是很复杂的，但是Netty提供了简单易用的API从网络处理代码中解耦业务逻辑。Netty是完全基于NIO实现的，所以整个Netty都是异步的。
网络应用程序通常需要有较高的可扩展性，无论是Netty还是其他的基于Java Nio的框架，都会提供可扩展性的解决方案。Netty中一个关键组成部分是它的异步特性，本片文章将讨论同步（阻塞）和异步（非阻塞）的IO来说明为什么使用异步代码解决扩展性问题以及如何使用异步。
二、入门程序
2.1创建服务端
2.1.1创建HelloServer
package com.zy.netty.example;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.ChannelFuture;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.nio.NioServerSocketChannel;public class HelloServer { ???/** ????* 服务端监听的端口地址 ????*/ ???private static final int portNumber = 7878; ???public static void main(String[] args) throws InterruptedException { ???????EventLoopGroup bossGroup = new NioEventLoopGroup(); ???????EventLoopGroup workerGroup = new NioEventLoopGroup(); ???????try { ???????????ServerBootstrap b = new ServerBootstrap(); ???????????b.group(bossGroup, workerGroup); ???????????b.channel(NioServerSocketChannel.class); ???????????b.childHandler(new HelloServerInitializer()); ???????????// 服务器绑定端口监听 ???????????ChannelFuture f = b.bind(portNumber).sync(); ???????????// 监听服务器关闭监听 ???????????f.channel().closeFuture().sync(); ???????????// 可以简写为 ???????????/* b.bind(portNumber).sync().channel().closeFuture().sync(); */ ???????} finally { ???????????bossGroup.shutdownGracefully(); ???????????workerGroup.shutdownGracefully(); ???????} ???}}2.1.2创建和实现HelloServerInitializer
package com.zy.netty.example;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelPipeline;import io.netty.channel.socket.SocketChannel;import io.netty.handler.codec.DelimiterBasedFrameDecoder;import io.netty.handler.codec.Delimiters;import io.netty.handler.codec.string.StringDecoder;import io.netty.handler.codec.string.StringEncoder;public class HelloServerInitializer extends ChannelInitializer<SocketChannel> { ???@Override ???protected void initChannel(SocketChannel ch) throws Exception { ???????ChannelPipeline pipeline = ch.pipeline(); ???????// 以("\n")为结尾分割的 解码器 ???????pipeline.addLast("framer", new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter())); ???????// 字符串解码 和 编码 ???????pipeline.addLast("decoder", new StringDecoder()); ???????pipeline.addLast("encoder", new StringEncoder()); ???????// 自己的逻辑Handler ???????pipeline.addLast("handler", new HelloServerHandler()); ???}}2.1.3创建ServerHandler
package com.zy.netty.example;import java.net.InetAddress;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.SimpleChannelInboundHandler;public class HelloServerHandler extends SimpleChannelInboundHandler<String> {/* ???@Override ???protected void channelRead(ChannelHandlerContext ctx, String msg) throws Exception { ???????// 收到消息直接打印输出 ???????System.out.println(ctx.channel().remoteAddress() + " Say : " + msg); ???????// 返回客户端消息 - 我已经接收到了你的消息 ???????ctx.writeAndFlush("Received your message !\n"); ???}*/ ???/* ????* ?????* 覆盖 channelActive 方法 在channel被启用的时候触发 (在建立连接的时候) ????* ?????* channelActive 和 channelInActive 在后面的内容中讲述，这里先不做详细的描述 ????*/ ???@Override ???public void channelActive(ChannelHandlerContext ctx) throws Exception { ???????System.out.println("RamoteAddress : " + ctx.channel().remoteAddress() + " active !"); ???????ctx.writeAndFlush("Welcome to " + InetAddress.getLocalHost().getHostName() + " service!\n"); ???????super.channelActive(ctx); ???} ???@Override ???protected void messageReceived(ChannelHandlerContext ctx, String msg) throws Exception { ???????System.out.println(ctx.channel().remoteAddress() + " Say : " + msg); ???????// 返回客户端消息 - 我已经接收到了你的消息 ???????ctx.writeAndFlush("Received your message !\n"); ???}}2.2Client客户端
2.2.1创建HelloClient
package com.zy.netty.example;import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import io.netty.bootstrap.Bootstrap;import io.netty.channel.Channel;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.nio.NioSocketChannel;public class HelloClient { ???public static String host = "127.0.0.1"; ???public static int port = 7878; ???/** ????* @param args ????* @throws InterruptedException ????* @throws IOException ????*/ ???public static void main(String[] args) throws InterruptedException, IOException { ???????EventLoopGroup group = new NioEventLoopGroup(); ???????try { ???????????Bootstrap b = new Bootstrap(); ???????????b.group(group).channel(NioSocketChannel.class).handler(new HelloClientInitializer()); ???????????// 连接服务端 ???????????Channel ch = b.connect(host, port).sync().channel(); ???????????// 控制台输入 ???????????BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); ???????????for (;;) { ???????????????String line = in.readLine(); ???????????????if (line == null) { ???????????????????continue; ???????????????} ???????????????/* ????????????????* 向服务端发送在控制台输入的文本 并用"\r\n"结尾 之所以用\r\n结尾 是因为我们在handler中添加了 ????????????????* DelimiterBasedFrameDecoder 帧解码。 ????????????????* 这个解码器是一个根据\n符号位分隔符的解码器。所以每条消息的最后必须加上\n否则无法识别和解码 ????????????????*/ ???????????????ch.writeAndFlush(line + "\r\n"); ???????????} ???????} finally { ???????????// The connection is closed automatically on shutdown. ???????????group.shutdownGracefully(); ???????} ???}}2.2.2创建和实现HelloClientInitalizer
package com.zy.netty.example;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelPipeline;import io.netty.channel.socket.SocketChannel;import io.netty.handler.codec.DelimiterBasedFrameDecoder;import io.netty.handler.codec.Delimiters;import io.netty.handler.codec.string.StringDecoder;import io.netty.handler.codec.string.StringEncoder;public class HelloClientInitializer extends ChannelInitializer<SocketChannel>{ ???@Override ????????protected void initChannel(SocketChannel ch) throws Exception { ????????????ChannelPipeline pipeline = ch.pipeline(); ?????????????????/* ?????????????* 这个地方的 必须和服务端对应上。否则无法正常解码和编码 ?????????????* ??????????????* 解码和编码 我将会在下一张为大家详细的讲解。再次暂时不做详细的描述 ?????????????* ??????????????* */ ????????????pipeline.addLast("framer", new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter())); ????????????pipeline.addLast("decoder", new StringDecoder()); ????????????pipeline.addLast("encoder", new StringEncoder()); ?????????????????????????// 客户端的逻辑 ????????????pipeline.addLast("handler", new HelloClientHandler()); ????????}}2.2.3创建ClientHandler
package com.zy.netty.example;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.SimpleChannelInboundHandler;public class HelloClientHandler extends SimpleChannelInboundHandler<String> { ???/* ????* @Override protected void channelRead0(ChannelHandlerContext ctx, String ????* msg) throws Exception { ????* ?????* System.out.println("Server say : " + msg); } ????*/ ???@Override ???public void channelActive(ChannelHandlerContext ctx) throws Exception { ???????System.out.println("Client active "); ???????super.channelActive(ctx); ???} ???@Override ???public void channelInactive(ChannelHandlerContext ctx) throws Exception { ???????System.out.println("Client close "); ???????super.channelInactive(ctx); ???} ???@Override ???protected void messageReceived(ChannelHandlerContext ctx, String msg) throws Exception { ???????System.out.println("Server say : " + msg); ???}}以上例子是一个最简单的服务端和客户端通信的模型，主要原理是服务端和客户端监听同一个ip的端口，监听到信息作出相应的反应
Netty入门（一）
原文地址：https://www.cnblogs.com/zyxiaohuihui/p/9093137.html