1、Netty是什么？
本质：JBoss做的一个Jar包
目的：快速开发高性能、高可靠性的网络服务器和客户端程序
优点：提供异步的、事件驱动的网络应用程序框架和工具
通俗的说：一个好使的处理Socket的东东
2、Netty的异步事件驱动模型主要涉及到下面几个核心的概念
Channel：表示一个与socket关联的通道
ChannelPipeline： 管道，一个Channel拥有一个ChannelPipeline，ChannelPipeline维护着一个处理链（严格的说是两 个：upstream、downstream），处理链是由很 多通道处理器ChannelHandler所构成，每个ChannelHandler处理完以 后会传递给链中的下一个通道处理器继续处理。
ChannelHandler：通道处理器，用户可以定义自己的处理句柄来处理每个请求，或发出请求前进行预处理，典型的有编码/解码器：decoder、encoder。
ChannelEvent：事件，是整个模型的处理对象，当产生或触发（fire）一个事件时，该事件会沿着ChannelPipeline处理链依次被处理。 ChannelFuture： 异步结果，这个是异步事件处理的关键，当一个事件被处理时，可以直接以ChannelFuture的形式直接返回，不用在当前操作中被阻塞。可以通过 ChannelFuture得到最终的执行结果，具体的做法是在ChannelFuture添加监听器listener，当操作最终被执行完 后，listener会被触发，我们可以在listener的回调函数中预定义我们的业务代码。
ChannelPipeline实际上维持了两个处理链：upstream、downstream。 Upstream一般处理来自Channel的读事件，而downstream一般处理向Channel的写事件。需要注意的是，这两个处理链是相互独立 的，在upstream链中传递到最后一个ChannelHandler处理后，不会再传递到downstream链中继续处理。
在downstream链的末端会有个ChannelSink处理，用户可以自定义这个ChannelSink的实现，系统也有个默认的实现，当downstream链中最后一个ChannelHandler处理完后会被传递给这个ChannelSink进行最后的处理。
3、Demo
3.1、NettyServer.java
package com.jacky.server;import java.util.concurrent.TimeUnit;import org.apache.log4j.Logger;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelOption;import io.netty.channel.ChannelPipeline;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.LengthFieldBasedFrameDecoder;import io.netty.handler.timeout.IdleStateHandler;public class NettyServer { private static Logger logger = Logger.getLogger(NettyServer.class); private int port; public NettyServer(int port) { this.port = port; bind(); } private void bind() { EventLoopGroup boss = new NioEventLoopGroup(); EventLoopGroup worker = new NioEventLoopGroup(); try { ServerBootstrap bootstrap = new ServerBootstrap(); bootstrap.group(boss, worker); bootstrap.channel(NioServerSocketChannel.class); bootstrap.option(ChannelOption.SO_BACKLOG, 1024); //连接数 bootstrap.option(ChannelOption.TCP_NODELAY, true); //不延迟，消息立即发送 bootstrap.childOption(ChannelOption.SO_KEEPALIVE, true); //长连接 bootstrap.childHandler(new ChannelInitializer () { @Override protected void initChannel(SocketChannel socketChannel) throws Exception { ChannelPipeline p = socketChannel.pipeline(); p.addLast(new NettyServerHandler()); } }); ChannelFuture f = bootstrap.bind(port).sync(); if (f.isSuccess()) { logger.debug("启动Netty服务成功，端口号：" + this.port); } // 关闭连接 f.channel().closeFuture().sync(); } catch (Exception e) { logger.error("启动Netty服务异常，异常信息：" + e.getMessage()); e.printStackTrace(); } finally { boss.shutdownGracefully(); worker.shutdownGracefully(); } } public static void main(String[] args) throws InterruptedException { NettyServer server= new NettyServer(9999); }} 3.2、NettyServerHandler.java
package com.jacky.server;import java.io.UnsupportedEncodingException;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;public class NettyServerHandler extends ChannelHandlerAdapter { @Override public void channelRead(ChannelHandlerContext context, Object msg) { ByteBuf buf = (ByteBuf) msg; String recieved = getMessage(buf); System.out.println("服务器接收到消息：" + recieved); try { context.writeAndFlush(getSendByteBuf("APPLE")); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } } /* * 从ByteBuf中获取信息 使用UTF-8编码返回 */ private String getMessage(ByteBuf buf) { byte[] con = new byte[buf.readableBytes()]; buf.readBytes(con); try { return new String(con, "UTF-8"); } catch (UnsupportedEncodingException e) { e.printStackTrace(); return null; } } private ByteBuf getSendByteBuf(String message) throws UnsupportedEncodingException { byte[] req = message.getBytes("UTF-8"); ByteBuf pingMessage = Unpooled.buffer(); pingMessage.writeBytes(req); return pingMessage; }} 3.3、NettyClient.java
package com.jacky.client;import java.util.concurrent.TimeUnit;import io.netty.bootstrap.Bootstrap;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.NioSocketChannel;import io.netty.handler.codec.LengthFieldBasedFrameDecoder;import io.netty.handler.timeout.IdleStateHandler;public class NettyClient { /* * 服务器端口号 */ private int port; /* * 服务器IP */ private String host; public NettyClient(int port, String host) throws InterruptedException { this.port = port; this.host = host; start(); } private void start() throws InterruptedException { EventLoopGroup eventLoopGroup = new NioEventLoopGroup(); try { Bootstrap bootstrap = new Bootstrap(); bootstrap.channel(NioSocketChannel.class); bootstrap.option(ChannelOption.SO_KEEPALIVE, true); bootstrap.group(eventLoopGroup); bootstrap.remoteAddress(host, port); bootstrap.handler(new ChannelInitializer () { @Override protected void initChannel(SocketChannel socketChannel) throws Exception { socketChannel.pipeline().addLast(new NettyClientHandler()); } }); ChannelFuture future = bootstrap.connect(host, port).sync(); if (future.isSuccess()) { SocketChannel socketChannel = (SocketChannel) future.channel(); System.out.println("----------------connect server success----------------"); } future.channel().closeFuture().sync(); } finally { eventLoopGroup.shutdownGracefully(); } } public static void main(String[] args) throws InterruptedException { NettyClient client = new NettyClient(9999, "localhost"); }} 3.4、NettyClientHandler.java
package com.jacky.client;import java.io.UnsupportedEncodingException;import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.TimeUnit;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;public class NettyClientHandler extends ChannelHandlerAdapter { private ByteBuf firstMessage; @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { byte[] data = "服务器，给我一个APPLE".getBytes(); firstMessage=Unpooled.buffer(); firstMessage.writeBytes(data); ctx.writeAndFlush(firstMessage); } @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ByteBuf buf = (ByteBuf) msg; String rev = getMessage(buf); System.out.println("客户端收到服务器数据:" + rev); } private String getMessage(ByteBuf buf) { byte[] con = new byte[buf.readableBytes()]; buf.readBytes(con); try { return new String(con, "UTF-8"); } catch (UnsupportedEncodingException e) { e.printStackTrace(); return null; } }}