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<SocketChannel>() {
   
   						@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

   <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>5.0.0.Alpha2</version>
   
   	</dependency>
   
     </dependencies>
   
   </project>
   
   

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<<<

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