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2.Netty的粘包、拆包（一）

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

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();
		}
	}

}

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!");
	}
	

}

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();
		}
	
	}

}

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！");
	}
	

}

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>

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<<<
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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原文地址：https://www.cnblogs.com/TimerHotel/p/netty02.html