Netty粘包、拆包

1.什么是拆包、粘包

（1）拆包、粘包介绍

TCP是个“流”协议，所谓流，就是没有界限的一串数据。大家可以想想河里的流水，是连成一片的，其间并没有分界线。TCP底层并不了解上层业务数据的具体含义，它会根据TCP缓冲区的实际情况进行包的划分，所以在业务上认为，一个完整的包可能会被TCP拆分成多个包进行发送，也有可能把多个小的包封装成一个大的数据包发送，这就是所谓的TCP粘包和拆包问题。

（2）图解

（3）代码模拟

1. 服务端Server

   package com.xm.netty.demo02;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 {     EventLoopGroup g1 = new NioEventLoopGroup();     EventLoopGroup g2 = new NioEventLoopGroup();     try {         ServerBootstrap bootstrap = new ServerBootstrap();          bootstrap                 .group(g1,g2)                 .channel(NioServerSocketChannel.class)                 .localAddress(new InetSocketAddress( port))                 .childHandler(new ChannelInitializer() {                     @Override                     protected void initChannel(Channel ch) throws Exception {                         ch.pipeline().addLast(new ServerHandler());                     }                 });          ChannelFuture future = bootstrap.bind().sync();          future.channel().closeFuture().sync();     } finally {         g1.shutdownGracefully().sync();         g2.shutdownGracefully().sync();     } }}

2. 服务端ServerHandler

   package com.xm.netty.demo02;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;import io.netty.util.CharsetUtil;public class ServerHandler extends ChannelHandlerAdapter { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {     ByteBuf in = (ByteBuf) msg;     String str = in.toString(CharsetUtil.UTF_8);     System.out.println("Server:"+str);     str = "服务器返回--->"+ str;     ctx.writeAndFlush(Unpooled.copiedBuffer(str.getBytes())); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {     cause.printStackTrace();     ctx.close(); } @Override public void channelActive(ChannelHandlerContext ctx) throws Exception {     System.out.println(DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(LocalDateTime.now())+"一个客户端连接!"); }}

3. 客户端Client

   package com.xm.netty.demo02;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;import io.netty.bootstrap.Bootstrap;import io.netty.buffer.Unpooled;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
         
          () {                     @Override                     protected void initChannel(SocketChannel ch) throws Exception {                         ch.pipeline().addLast(new ClientHandler());                     }                 });         ChannelFuture future = bootstrap.connect().sync();         for(int i=10;i<20;i++) {             String str = DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(LocalDateTime.now()) + "---- " +i+"<<<";             future.channel().writeAndFlush(Unpooled.copiedBuffer(str.getBytes()));         }         future.channel().closeFuture().sync();     } finally {         group.shutdownGracefully().sync();     } }}
         

4. 客户端ClientHandler

   package com.xm.netty.demo02;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerAdapter;import io.netty.channel.ChannelHandlerContext;import io.netty.util.CharsetUtil;import io.netty.util.ReferenceCountUtil;public class ClientHandler extends ChannelHandlerAdapter { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {     try {         ByteBuf in = (ByteBuf) msg;         String str = in.toString(CharsetUtil.UTF_8);         System.out.println("Client:"+str);     } finally {         ReferenceCountUtil.release(msg);     } } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {     cause.printStackTrace();     ctx.close(); } @Override public void channelActive(ChannelHandlerContext ctx) throws Exception {     System.out.println(DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(LocalDateTime.now())+"  已连接上服务器！"); }}

5. 添加依赖

           
          
           4.0.0
            
          
           com.xm
            
          
           netty
            
          
           0.0.1-SNAPSHOT
            
             
                
            
             io.netty
                 
            
             netty-all
                 
            
             5.0.0.Alpha2
             
             
          
         

6. 预期结果

   1）服务器

   2018-10-11T18:37:19.857一个客户端连接!

   Server:2018-10-11T18:37:19.855---- 10<<<

   Server:2018-10-11T18:37:20.377---- 11<<<

   Server:2018-10-11T18:37:20.877---- 12<<<

   Server:2018-10-11T18:37:21.378---- 13<<<

   Server:2018-10-11T18:37:21.879---- 14<<<

   Server:2018-10-11T18:37:22.379---- 15<<<

   Server:2018-10-11T18:37:22.879---- 16<<<

   Server:2018-10-11T18:37:23.38---- 17<<<

   Server:2018-10-11T18:37:23.881---- 18<<<

   Server:2018-10-11T18:37:24.382---- 19<<<

   （2）客户端

   2018-10-11T18:37:19.855 已连接上服务器！

   Client:服务器返回--->2018-10-11T18:37:19.855---- 10<<<

   Client:服务器返回--->2018-10-11T18:37:20.377---- 11<<<

   Client:服务器返回--->2018-10-11T18:37:20.877---- 12<<<

   Client:服务器返回--->2018-10-11T18:37:21.378---- 13<<<

   Client:服务器返回--->2018-10-11T18:37:21.879---- 14<<<

   Client:服务器返回--->2018-10-11T18:37:22.379---- 15<<<

   Client:服务器返回--->2018-10-11T18:37:22.879---- 16<<<

   Client:服务器返回--->2018-10-11T18:37:23.38---- 17<<<

   Client:服务器返回--->2018-10-11T18:37:23.881---- 18<<<

   Client:服务器返回--->2018-10-11T18:37:24.382---- 19<<<

7. 实际结果

   （1）服务器

   2018-10-11T18:35:40.988一个客户端连接!

   Server:2018-10-11T18:35:40.986---- 10<<<2018-10-11T18:35:41.01---- 11<<<2018-10-11T18:35:41.01---- 12<<<2018-10-11T18:35:41.01---- 13<<<2018-10-11T18:35:41.01---- 14<<<2018-10-11T18:35:41.01---- 15<<<2018-10-11T18:35:41.01---- 16<<<2018-10-11T18:35:41.01---- 17<<<2018-10-11T18:35:41.01---- 18<<<2018-10-11T18:35:41.01---- 19<<<

   （2）客户端

   2018-10-11T18:35:40.986 已连接上服务器！

   Client:服务器返回--->2018-10-11T18:35:40.986---- 10<<<2018-10-11T18:35:41.01---- 11<<<2018-10-11T18:35:41.01---- 12<<<2018-10-11T18:35:41.01---- 13<<<2018-10-11T18:35:41.01---- 14<<<2018-10-11T18:35:41.01---- 15<<<2018-10-11T18:35:41.01---- 16<<<2018-10-11T18:35:41.01---- 17<<<2018-10-11T18:35:41.01---- 18<<<2018-10-11T18:35:41.01---- 19<<<