Netty是建立在NIO基础之上，Netty在NIO之上又提供了更高层次的抽象。
在Netty里面，Accept连接可以使用单独的线程池去处理，读写操作又是另外的线程池来处理。
Accept连接和读写操作也可以使用同一个线程池来进行处理。而请求处理逻辑既可以使用单独的线程池进行处理，也可以跟放在读写线程一块处理。线程池中的每一个线程都是NIO线程。用户可以根据实际情况进行组装，构造出满足系统需求的并发模型。
Netty提供了内置的常用编解码器，包括行编解码器［一行一个请求］，前缀长度编解码器［前N个字节定义请求的字节长度］，可重放解码器［记录半包消息的状态］，HTTP编解码器，WebSocket消息编解码器等等
Netty提供了一些列生命周期回调接口，当一个完整的请求到达时，当一个连接关闭时，当一个连接建立时，用户都会收到回调事件，然后进行逻辑处理。
Netty可以同时管理多个端口，可以使用NIO客户端模型，这些对于RPC服务是很有必要的。
Netty除了可以处理TCP Socket之外，还可以处理UDP Socket。
在消息读写过程中，需要大量使用ByteBuffer，Netty对ByteBuffer在性能和使用的便捷性上都进行了优化和抽象。
代码：
服务端：
package com.kinson.netty.server;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.Channel;import io.netty.channel.ChannelOption;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.nio.NioServerSocketChannel;/** * descripiton:服务端 * * @author: www.iknowba.cn * @date: 2018/3/23 * @time: 15:37 * @modifier: * @since: */public class NettyServer { ???/** ????* 端口 ????*/ ???private int port; ???public NettyServer(int port) { ???????this.port = port; ???} ???public void run() { ???????//EventLoopGroup是用来处理IO操作的多线程事件循环器 ???????//负责接收客户端连接线程 ???????EventLoopGroup bossGroup = new NioEventLoopGroup(); ???????//负责处理客户端i/o事件、task任务、监听任务组 ???????EventLoopGroup workerGroup = new NioEventLoopGroup(); ???????//启动 NIO 服务的辅助启动类 ???????ServerBootstrap bootstrap = new ServerBootstrap(); ???????bootstrap.group(bossGroup, workerGroup); ???????//配置 Channel ???????bootstrap.channel(NioServerSocketChannel.class); ???????bootstrap.childHandler(new ServerIniterHandler()); ???????//BACKLOG用于构造服务端套接字ServerSocket对象， ???????// 标识当服务器请求处理线程全满时，用于临时存放已完成三次握手的请求的队列的最大长度 ???????bootstrap.option(ChannelOption.SO_BACKLOG, 1024); ???????//是否启用心跳保活机制 ???????bootstrap.childOption(ChannelOption.SO_KEEPALIVE, true); ???????try { ???????????//绑定服务端口监听 ???????????Channel channel = bootstrap.bind(port).sync().channel(); ???????????System.out.println("server run in port " + port); ???????????//服务器关闭监听 ???????????/*channel.closeFuture().sync()实际是如何工作: ???????????channel.closeFuture()不做任何操作，只是简单的返回channel对象中的closeFuture对象，对于每个Channel对象，都会有唯一的一个CloseFuture，用来表示关闭的Future， ???????????所有执行channel.closeFuture().sync()就是执行的CloseFuturn的sync方法，从上面的解释可以知道，这步是会将当前线程阻塞在CloseFuture上*/ ???????????channel.closeFuture().sync(); ???????} catch (InterruptedException e) { ???????????e.printStackTrace(); ???????} finally { ???????????//关闭事件流组 ???????????bossGroup.shutdownGracefully(); ???????????workerGroup.shutdownGracefully(); ???????} ???} ???public static void main(String[] args) { ???????new NettyServer(8899).run(); ???}}服务端业务逻辑处理：
package com.kinson.netty.server;import io.netty.channel.Channel;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.SimpleChannelInboundHandler;import io.netty.channel.group.ChannelGroup;import io.netty.channel.group.DefaultChannelGroup;import io.netty.util.concurrent.GlobalEventExecutor;/** * descripiton: 服务器的处理逻辑 * * @author: www.iknowba.cn * @date: 2018/3/23 * @time: 15:50 * @modifier: * @since: */public class ServerHandler extends SimpleChannelInboundHandler<String> { ???/** ????* 所有的活动用户 ????*/ ???public static final ChannelGroup group = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE); ???/** ????* 读取消息通道 ????* ????* @param context ????* @param s ????* @throws Exception ????*/ ???@Override ???protected void channelRead0(ChannelHandlerContext context, String s) ???????????throws Exception { ???????Channel channel = context.channel(); ???????//当有用户发送消息的时候，对其他的用户发送消息 ???????for (Channel ch : group) { ???????????if (ch == channel) { ???????????????ch.writeAndFlush("[you]: " + s + "\n"); ???????????} else { ???????????????ch.writeAndFlush("[" + channel.remoteAddress() + "]: " + s + "\n"); ???????????} ???????} ???????System.out.println("[" + channel.remoteAddress() + "]: " + s + "\n"); ???} ???/** ????* 处理新加的消息通道 ????* ????* @param ctx ????* @throws Exception ????*/ ???@Override ???public void handlerAdded(ChannelHandlerContext ctx) throws Exception { ???????Channel channel = ctx.channel(); ???????for (Channel ch : group) { ???????????if (ch == channel) { ???????????????ch.writeAndFlush("[" + channel.remoteAddress() + "] coming"); ???????????} ???????} ???????group.add(channel); ???} ???/** ????* 处理退出消息通道 ????* ????* @param ctx ????* @throws Exception ????*/ ???@Override ???public void handlerRemoved(ChannelHandlerContext ctx) throws Exception { ???????Channel channel = ctx.channel(); ???????for (Channel ch : group) { ???????????if (ch == channel) { ???????????????ch.writeAndFlush("[" + channel.remoteAddress() + "] leaving"); ???????????} ???????} ???????group.remove(channel); ???} ???/** ????* 在建立连接时发送消息 ????* ????* @param ctx ????* @throws Exception ????*/ ???@Override ???public void channelActive(ChannelHandlerContext ctx) throws Exception { ???????Channel channel = ctx.channel(); ???????boolean active = channel.isActive(); ???????if (active) { ???????????System.out.println("[" + channel.remoteAddress() + "] is online"); ???????} else { ???????????System.out.println("[" + channel.remoteAddress() + "] is offline"); ???????} ???????ctx.writeAndFlush("[server]: welcome"); ???} ???/** ????* 退出时发送消息 ????* ????* @param ctx ????* @throws Exception ????*/ ???@Override ???public void channelInactive(ChannelHandlerContext ctx) throws Exception { ???????Channel channel = ctx.channel(); ???????if (!channel.isActive()) { ???????????System.out.println("[" + channel.remoteAddress() + "] is offline"); ???????} else { ???????????System.out.println("[" + channel.remoteAddress() + "] is online"); ???????} ???} ???/** ????* 异常捕获 ????* ????* @param ctx ????* @param e ????* @throws Exception ????*/ ???@Override ???public void exceptionCaught(ChannelHandlerContext ctx, Throwable e) throws Exception { ???????Channel channel = ctx.channel(); ???????System.out.println("[" + channel.remoteAddress() + "] leave the room"); ???????ctx.close().sync(); ???}}服务端处理器注册：
package com.kinson.netty.server;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelPipeline;import io.netty.channel.socket.SocketChannel;import io.netty.handler.codec.string.StringDecoder;import io.netty.handler.codec.string.StringEncoder;/** * descripiton: 服务器初始化 * * @author: www.iknowba.cn * @date: 2018/3/23 * @time: 15:46 * @modifier: * @since: */public class ServerIniterHandler extends ChannelInitializer<SocketChannel> { ???@Override ???protected void initChannel(SocketChannel socketChannel) throws Exception { ???????//管道注册handler ???????ChannelPipeline pipeline = socketChannel.pipeline(); ???????//编码通道处理 ???????pipeline.addLast("decode", new StringDecoder()); ???????//转码通道处理 ???????pipeline.addLast("encode", new StringEncoder()); ???????//聊天服务通道处理 ???????pipeline.addLast("chat", new ServerHandler()); ???}}客户端：
package com.kinson.netty.client;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;import org.apache.commons.lang3.StringUtils;import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;/** * descripiton: 客户端 * * @author: www.iknowba.cn * @date: 2018/3/23 * @time: 16:40 * @modifier: * @since: */public class NettyClient { ???private String ip; ???private int port; ???private boolean stop = false; ???public NettyClient(String ip, int port) { ???????this.ip = ip; ???????this.port = port; ???} ???public void run() throws IOException { ???????//设置一个多线程循环器 ???????EventLoopGroup workerGroup = new NioEventLoopGroup(); ???????//启动附注类 ???????Bootstrap bootstrap = new Bootstrap(); ???????bootstrap.group(workerGroup); ???????//指定所使用的NIO传输channel ???????bootstrap.channel(NioSocketChannel.class); ???????//指定客户端初始化处理 ???????bootstrap.handler(new ClientIniterHandler()); ???????try { ???????????//连接服务 ???????????Channel channel = bootstrap.connect(ip, port).sync().channel(); ???????????while (true) { ???????????????//向服务端发送内容 ???????????????BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); ???????????????String content = reader.readLine(); ???????????????if (StringUtils.isNotEmpty(content)) { ???????????????????if (StringUtils.equalsIgnoreCase(content, "q")) { ???????????????????????System.exit(1); ???????????????????} ???????????????????channel.writeAndFlush(content); ???????????????} ???????????} ???????} catch (InterruptedException e) { ???????????e.printStackTrace(); ???????????System.exit(1); ???????} finally { ???????????workerGroup.shutdownGracefully(); ???????} ???} ???public static void main(String[] args) throws Exception { ???????new NettyClient("127.0.0.1", 8899).run(); ???}}客户端逻辑处理：
package com.kinson.netty.client;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.SimpleChannelInboundHandler;/** * descripiton: 客户端逻辑处理 * * @author: www.iknowba.cn * @date: 2018/3/23 * @time: 16:50 * @modifier: * @since: */public class ClientHandler extends SimpleChannelInboundHandler<String> { ???@Override ???protected void channelRead0(ChannelHandlerContext ctx, String s) throws Exception { ???????//打印服务端的发送数据 ???????System.out.println(s); ???}}客户端处理器注册：
package com.kinson.netty.client;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelPipeline;import io.netty.channel.socket.SocketChannel;import io.netty.handler.codec.http.HttpClientCodec;import io.netty.handler.codec.string.StringDecoder;import io.netty.handler.codec.string.StringEncoder;/** * descripiton: 客户端处理初始化 * * @author: www.iknowba.cn * @date: 2018/3/23 * @time: 16:55 * @modifier: * @since: */public class ClientIniterHandler extends ChannelInitializer<SocketChannel> { ???@Override ???protected void initChannel(SocketChannel socketChannel) throws Exception { ???????//注册管道 ???????ChannelPipeline pipeline = socketChannel.pipeline(); ???????pipeline.addLast("decoder", new StringDecoder()); ???????pipeline.addLast("encoder", new StringEncoder()); ???????pipeline.addLast("http", new HttpClientCodec()); ???????pipeline.addLast("chat", new ClientHandler()); ???}}测试时先启动服务端，再启动客户端。。。
Netty实现客户端和服务端通信简单例子
原文地址：https://www.cnblogs.com/kingsonfu/p/Java.html