TCP粘包和拆包

（1）TCP是面向连接的，面向流的，提供可靠性服务。收发两端（客户端和服务端）都要有一一成对的socket，因此，发送端为了将多个发给接收端的包，更有效的发给对方，使用了优化方法（Nagle算法），将多次间隔较小且数据量小的数据，合并成一个大的数据块，然后进行封包。这样做虽然提高了效率，但是接收端难于分辨出完整的数据包，因为面向流的通信是无消息保护边界的。
（2）由于TCP无消息保护边界，需要在接收端处理消息边界问题，也就是我们所说的粘包和拆包问题。
（3）TCP粘包、拆包图解
在这里插入图片描述
下面我们通过Netty实验还原场景：
我们通过这样的方法来还原粘包和拆包场景，客户端循环想服务端发送10条消息，服务端每次接收到消息即想客户端返回一个UUID，我们可以通过观察，这10条消息服务端接收过程中并不是一次性接收的，并且每次发送接收结果不一，说明部分消息发生了粘包现象（拆包现象）

服务端：
MyServer

package com.sgg.Netty.TCP;

import com.sgg.Netty.simple.NettyServerhandler;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class MyServer {
    public static void main(String[] args) throws InterruptedException {
        //创建BossGroup和WorkerGroup
        //说明
        //1、创建两个线程组BossGroup和WorkerGroup
        //2、BossGroup只负责处理请求，真正和客户端的业务处理会交给WorkerGroup
        //3、两个都是无限循环
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        //创建服务端的启动对象，配置启动参数
        ServerBootstrap bootstrap = new ServerBootstrap();

        //使用链式变成来进行设置
        bootstrap.group(bossGroup,workerGroup)       //设置两个线程组
                .channel(NioServerSocketChannel.class)     //使用NioServerSocketChannel作为服务器的通道实现
                .option(ChannelOption.SO_BACKLOG,128)       //设置线程队列的连接个数
                .childOption(ChannelOption.SO_KEEPALIVE,true)       //设置保持活动连接状态
                .childHandler(new MyServerInitializer());

        System.out.println(".....服务器准备好了");

        // Future-Listener机制

        //绑定一个端口并且同步，生成一个ChannelFuture对象
        ChannelFuture cf = bootstrap.bind(6668).sync();
        //给cf注册监听器，监控我们关心的事件
        cf.addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture channelFuture) throws Exception {
                if(cf.isSuccess()){
                    System.out.println("监听端口成功");
                }else{
                    System.out.println("监听端口失败");
                }
            }
        });

        //对关闭通道进行监听
        cf.channel().closeFuture().sync();

    }
}

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MyServerInitializer

package com.sgg.Netty.TCP;


import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;

public class MyServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel socketChannel) throws Exception {
        ChannelPipeline pipeline = socketChannel.pipeline();
        pipeline.addLast(new MyServerhandler());
    }
}

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MyServerhandler

package com.sgg.Netty.TCP;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.nio.charset.Charset;
import java.util.UUID;

public class MyServerhandler extends SimpleChannelInboundHandler<ByteBuf> {
    private int count;

    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf) throws Exception {
        //
        byte[] buffer = new byte[byteBuf.readableBytes()];
        byteBuf.readBytes(buffer);
        //将buffer转成字符串
        String message = new String(buffer, Charset.forName("utf-8"));

        System.out.println("服务器接收到数据"+ message);
        System.out.println("服务器端接收到消息="+ (++this.count));

        //服务端回送数据给客户端，回送 一个随机的ID
        ByteBuf responseByteBuf = Unpooled.copiedBuffer(UUID.randomUUID().toString()+"  ",Charset.forName("utf-8"));
        channelHandlerContext.writeAndFlush(responseByteBuf);

    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

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MyClient

package com.sgg.Netty.TCP;

import com.sgg.Netty.http.TestServerInitializer;
import com.sgg.Netty.simple.NettyClienthandler;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

public class MyClient {
    public static void main(String[] args) throws InterruptedException {
        //客户端需要一个事件循环组
        NioEventLoopGroup eventLoopGroup = new NioEventLoopGroup();

        try {
            //创建客户端启动对象
            //注意客户端不是ServerBootstrap，是Bootstrap
            Bootstrap bootstrap = new Bootstrap();

            //设置相关参数
            bootstrap.group(eventLoopGroup)
                    .channel(NioSocketChannel.class)
                    .handler(new MyClientInitializer());
            System.out.println("客户端OK");
            //启动客户端
            ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 6668).sync();
            //给关闭通道进行监听
            channelFuture.channel().closeFuture().sync();
        } finally {
            //关闭
            eventLoopGroup.shutdownGracefully();
        }
    }
}

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MyClientInitializer

package com.sgg.Netty.TCP;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;

public class MyClientInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel socketChannel) throws Exception {
        ChannelPipeline pipeline = socketChannel.pipeline();
        pipeline.addLast(new MyClienthandler());
    }
}

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MyClienthandler

package com.sgg.Netty.TCP;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.nio.charset.Charset;

public class MyClienthandler extends SimpleChannelInboundHandler<ByteBuf> {


    private int count;

    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf) throws Exception {
        byte[] buffer = new byte[byteBuf.readableBytes()];
        byteBuf.readBytes(buffer);

        String message = new String(buffer,Charset.forName("utf-8"));
        System.out.println("客户端接收到消息="+message);
        System.out.println("客户端接收消息数量="+(++this.count));
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        //使用客户端发送10条数据
        for(int i=0;i<10;i++){
            ByteBuf buffer =  Unpooled.copiedBuffer("hello,server"+i, Charset.forName("utf-8"));
            ctx.writeAndFlush(buffer);
        }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

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最终我们可以看到：
服务端入下，同样客户端返回的随机数个数与接收次数统一
在这里插入图片描述那么我们怎么解决TCP的粘包和拆包呢？？