Netty 粘包半包

什么是 TCP 粘包半包？

假设客户端分别发送了两个数据包 D1 和 D2 给服务端，由于服务端一次读取到的字节

数是不确定的，故可能存在以下 4 种情况。

（1）服务端分两次读取到了两个独立的数据包，分别是 D1 和 D2 ，没有粘包和拆包；

（2）服务端一次接收到了两个数据包， D1 和 D2 粘合在一起，被称为 TCP 粘包；

（3）服务端分两次读取到了两个数据包，第一次读取到了完整的 D1 包和 D2 包的部分

内容，第二次读取到了 D2 包的剩余内容，这被称为 TCP 拆包；

（

4 ）服务端分两次读取到了两个数据包，第一次读取到了 D1 包的部分内容 D1_1 ，第

二次读取到了 D1 包的剩余内容 D1_2 和 D2 包的整包。

如果此时服务端 TCP 接收滑窗非常小，而数据包 D1 和 D2 比较大，很有可能会发生第

五种可能，即服务端分多次才能将 D1 和 D2 包接收完全，期间发生多次拆包。

服务端

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.util.CharsetUtil;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.net.InetSocketAddress;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 类说明：基于Netty的服务器
 */

public class EchoSvrStickyHalf {
    private static final Logger LOG = LoggerFactory.getLogger(EchoSvrStickyHalf.class);

    private final int port;

    public EchoSvrStickyHalf(int port) {
        this.port = port;
    }

    public static void main(String[] args) throws InterruptedException {
        int port = 9999;
        EchoSvrStickyHalf echoSvrStickyHalf = new EchoSvrStickyHalf(port);
        LOG.info("服务器即将启动");
        echoSvrStickyHalf.start();
        LOG.info("服务器关闭");
    }

    public void start() throws InterruptedException {
        /*线程组*/
        EventLoopGroup group  = new NioEventLoopGroup();
        try {
            /*服务端启动必备*/
            ServerBootstrap b = new ServerBootstrap();
            b.group(group)
                    .channel(NioServerSocketChannel.class)
                    .localAddress(new InetSocketAddress(port))
                    .childHandler(new ChannelInitializer() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new EchoSvrSHHandler());
                        }
                    });

            /*异步绑定到服务器，sync()会阻塞到完成*/
            ChannelFuture f = b.bind().sync();
            LOG.info("服务器启动完成。");
            /*阻塞当前线程，直到服务器的ServerChannel被关闭*/
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }

    public class EchoSvrSHHandler extends ChannelInboundHandlerAdapter {

        private AtomicInteger counter = new AtomicInteger(0);

        /*** 服务端读取到网络数据后的处理*/
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            ByteBuf in = (ByteBuf)msg;
            String request = in.toString(CharsetUtil.UTF_8);
            System.out.println("Server Accept["+request
                    +"] and the counter is:"+counter.incrementAndGet());
            String resp = "Hello,"+request+". Welcome to Netty World!"
                    + System.getProperty("line.separator");
            ctx.writeAndFlush(Unpooled.copiedBuffer(resp.getBytes()));
        }

//    /*** 服务端读取完成网络数据后的处理*/
//    @Override
//    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
//        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
//    }

        /*** 发生异常后的处理*/
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            cause.printStackTrace();
            ctx.close();
        }
    }
}

客户端

import cn.tuling.nettybasic.echo.EchoClientHandler;
import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.util.CharsetUtil;

import java.net.InetSocketAddress;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 类说明：基于Netty的客户端
 */
public class EchoCliStickyHalf {

    private final int port;
    private final String host;

    public EchoCliStickyHalf(int port, String host) {
        this.port = port;
        this.host = host;
    }

    public void start() throws InterruptedException {

        /*线程组*/
        EventLoopGroup group  = new NioEventLoopGroup();
        try {
            /*客户端启动必备，和服务器的不同点*/
            Bootstrap b = new Bootstrap();
            b.group(group)
                    .channel(NioSocketChannel.class)/*指定使用NIO的通信模式*/
                    /*指定服务器的IP地址和端口，和服务器的不同点*/
                    .remoteAddress(new InetSocketAddress(host,port))
                    /*和服务器的不同点*/
                    .handler(new ChannelInitializer() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new EchoCliSHHandler());

                        }
                    });
            /*异步连接到服务器，sync()会阻塞到完成，和服务器的不同点*/
            ChannelFuture f = b.connect().sync();
            f.channel().closeFuture().sync();/*阻塞当前线程，直到客户端的Channel被关闭*/
        } finally {
            group.shutdownGracefully().sync();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new EchoCliStickyHalf(9999,"127.0.0.1").start();
    }

    public class EchoCliSHHandler extends SimpleChannelInboundHandler {

        private AtomicInteger counter = new AtomicInteger(0);

        /*** 客户端读取到网络数据后的处理*/
        protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
            System.out.println("client Accept["+msg.toString(CharsetUtil.UTF_8)
                    +"] and the counter is:"+counter.incrementAndGet());
        }

        /*** 客户端被通知channel活跃后，做事*/
        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            //ByteBuf msg = null;
            String request = "a,b,c,d,e";
            final ByteBufAllocator alloc = ctx.alloc();
            ByteBuf msg = null;
            /*我们希望服务器接受到100个这样的报文*/
            for(int i=0;i<100;i++){
                ByteBuf byteBuf = alloc.buffer();
                msg = alloc.buffer(request.length());
                msg.writeBytes(request.getBytes());
                ctx.writeAndFlush(msg);
            }
        }

        /*** 发生异常后的处理*/
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            cause.printStackTrace();
            ctx.close();
        }
    }
}

TCP 粘包/半包发生的原因

由于 TCP 协议本身的机制（面向连接的可靠地协议 - 三次握手机制）客户端与服务器会

维持一个连接（ Channel ），数据在连接不断开的情况下，可以持续不断地将多个数据包发 往服务器，但是如果发送的网络数据包太小，那么他本身会启用 Nagle 算法（可配置是否启

用）对较小的数据包进行合并（基于此， TCP 的网络延迟要 UDP 的高些）然后再发送（超

时或者包大小足够）。那么这样的话，服务器在接收到消息（数据流）的时候就无法区分哪

些数据包是客户端自己分开发送的，这样产生了粘包；服务器在接收到数据库后，放到缓冲

区中，如果消息没有被及时从缓存区取走，下次在取数据的时候可能就会出现一次取出多个

数据包的情况，造成粘包现象

UDP ：本身作为无连接的不可靠的传输协议（适合频繁发送较小的数据包），他不会对

数据包进行合并发送（也就没有 Nagle 算法之说了），他直接是一端发送什么数据，直接就

发出去了，既然他不会对数据合并，每一个数据包都是完整的（数据 +UDP 头 +IP 头等等发一

次数据封装一次）也就没有粘包一说了。

分包产生的原因就简单的多：就是一个数据包被分成了多次接收。

更具体的原因至少包括：

1. 应用程序写入数据的字节大小大于套接字发送缓冲区的大小

2. 进行 MSS 大小的 TCP 分段。 MSS 是最大报文段长度的缩写。 MSS 是 TCP 报文段中的

数据字段的最大长度。数据字段加上 TCP 首部才等于整个的 TCP 报文段。所以 MSS 并不是

TCP 报文段的最大长度，而是： MSS=TCP 报文段长度 -TCP 首部长度

解决粘包半包

由于底层的 TCP 无法理解上层的业务数据，所以在底层是无法保证数据包不被拆分和重

组的，这个问题只能通过上层的应用协议栈设计来解决，根据业界的主流协议的解决方案，

可以归纳如下。

（1） 在包尾增加分割符，比如回车换行符进行分割，例如 FTP 协议

 String request = "a,b,c,d,e" +   System.getProperty("line.separator");

"C:\Program Files\Java\jdk1.8.0_131\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\lib\idea_rt.jar=57393:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\rt.jar;C:\Users\Administrator\Desktop\新建文件夹\24-Netty使用和常用组件辨析（一）-Mark\ketang-tl-netty\netty-basic\target\classes;C:\Users\Administrator\.m2\repository\com\google\protobuf\protobuf-java\2.6.1\protobuf-java-2.6.1.jar;C:\Users\Administrator\.m2\repository\org\msgpack\msgpack\0.6.12\msgpack-0.6.12.jar;C:\Users\Administrator\.m2\repository\com\googlecode\json-simple\json-simple\1.1.1\json-simple-1.1.1.jar;C:\Users\Administrator\.m2\repository\org\javassist\javassist\3.18.1-GA\javassist-3.18.1-GA.jar;C:\Users\Administrator\.m2\repository\de\javakaffee\kryo-serializers\0.42\kryo-serializers-0.42.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\kryo\4.0.0\kryo-4.0.0.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\reflectasm\1.11.3\reflectasm-1.11.3.jar;C:\Users\Administrator\.m2\repository\org\ow2\asm\asm\5.0.4\asm-5.0.4.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\minlog\1.3.0\minlog-1.3.0.jar;C:\Users\Administrator\.m2\repository\org\objenesis\objenesis\2.2\objenesis-2.2.jar;C:\Users\Administrator\.m2\repository\io\netty\netty-all\4.1.42.Final\netty-all-4.1.42.Final.jar;C:\Users\Administrator\.m2\repository\junit\junit\4.11\junit-4.11.jar;C:\Users\Administrator\.m2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar;C:\Users\Administrator\.m2\repository\org\slf4j\slf4j-api\1.7.30\slf4j-api-1.7.30.jar;C:\Users\Administrator\.m2\repository\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;C:\Users\Administrator\.m2\repository\ch\qos\logback\logback-core\1.2.4\logback-core-1.2.4.jar" cn.tuling.nettybasic.splicing.demo.EchoCliStickyHalf
client Accept[Hello,a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,] and the counter is:1
client Accept[d,e
a. Welcome to Netty World!
Hello,,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
a,b,c,d,e
. Welcome to Netty World!
] and the counter is:2

（自定义分割符）

服务端

package cn.tuling.nettybasic.splicing.delimiter;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.util.CharsetUtil;
import java.net.InetSocketAddress;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 类说明：
 */
public class DelimiterEchoServer {

    public static final String DELIMITER_SYMBOL = "@~";
    public static final int PORT = 9997;

    public static void main(String[] args) throws InterruptedException {
        DelimiterEchoServer delimiterEchoServer = new DelimiterEchoServer();
        System.out.println("服务器即将启动");
        delimiterEchoServer.start();
    }

    public void start() throws InterruptedException {
        final DelimiterServerHandler serverHandler = new DelimiterServerHandler();
        EventLoopGroup group = new NioEventLoopGroup();/*线程组*/
        try {
            ServerBootstrap b = new ServerBootstrap();/*服务端启动必须*/
            b.group(group)/*将线程组传入*/
                .channel(NioServerSocketChannel.class)/*指定使用NIO进行网络传输*/
                .localAddress(new InetSocketAddress(PORT))/*指定服务器监听端口*/
                /*服务端每接收到一个连接请求，就会新启一个socket通信，也就是channel，
                所以下面这段代码的作用就是为这个子channel增加handle*/
                .childHandler(new ChannelInitializerImp());
            ChannelFuture f = b.bind().sync();/*异步绑定到服务器，sync()会阻塞直到完成*/
            System.out.println("服务器启动完成，等待客户端的连接和数据.....");
            f.channel().closeFuture().sync();/*阻塞直到服务器的channel关闭*/
        } finally {
            group.shutdownGracefully().sync();/*优雅关闭线程组*/
        }
    }

    private class ChannelInitializerImp extends ChannelInitializer {

        @Override
        protected void initChannel(Channel ch) throws Exception {
            ByteBuf delimiter = Unpooled.copiedBuffer(DELIMITER_SYMBOL.getBytes());
            ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,
                    delimiter));
            ch.pipeline().addLast(new DelimiterServerHandler());
        }
    }
    @ChannelHandler.Sharable
    public class DelimiterServerHandler extends ChannelInboundHandlerAdapter {

        private AtomicInteger counter = new AtomicInteger(0);

        /*** 服务端读取到网络数据后的处理*/
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            ByteBuf in = (ByteBuf) msg;
            String request = in.toString(CharsetUtil.UTF_8);
            System.out.println("Server Accept["+request
                    +"] and the counter is:"+counter.incrementAndGet());
            String resp = "Hello,"+request+". Welcome to Netty World!"
                    + DelimiterEchoServer.DELIMITER_SYMBOL;
            ctx.writeAndFlush(Unpooled.copiedBuffer(resp.getBytes()));
            //ctx.close();
        }

        /*** 服务端读取完成网络数据后的处理*/
        @Override
        public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
            System.out.println("channelReadComplete------");
            //ctx.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
        }

        /*** 发生异常后的处理*/
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            cause.printStackTrace();
            ctx.close();
        }
    }
}

客户端

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.util.CharsetUtil;

import java.net.InetSocketAddress;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 作者：Mark
 * 类说明：
 */
public class DelimiterEchoClient {

    private final String host;

    public DelimiterEchoClient(String host) {
        this.host = host;
    }

    public void start() throws InterruptedException {
        EventLoopGroup group = new NioEventLoopGroup();/*线程组*/
        try {
            final Bootstrap b = new Bootstrap();;/*客户端启动必须*/
            b.group(group)/*将线程组传入*/
                    .channel(NioSocketChannel.class)/*指定使用NIO进行网络传输*/
                    .remoteAddress(new InetSocketAddress(host,DelimiterEchoServer.PORT))/*配置要连接服务器的ip地址和端口*/
                    .handler(new ChannelInitializerImp());
            ChannelFuture f = b.connect().sync();
            System.out.println("已连接到服务器.....");
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }

    private class ChannelInitializerImp extends ChannelInitializer {

        @Override
        protected void initChannel(Channel ch) throws Exception {
            ByteBuf delimiter = Unpooled.copiedBuffer(
                    DelimiterEchoServer.DELIMITER_SYMBOL.getBytes());
            ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,
                    delimiter));
            ch.pipeline().addLast(new DelimiterClientHandler());
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new DelimiterEchoClient("127.0.0.1").start();
    }

    public class DelimiterClientHandler extends SimpleChannelInboundHandler {

        private AtomicInteger counter = new AtomicInteger(0);

        /*** 客户端读取到网络数据后的处理*/
        protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
            System.out.println("client Accept["+msg.toString(CharsetUtil.UTF_8)
                    +"] and the counter is:"+counter.incrementAndGet());
        }

        /*** 客户端被通知channel活跃后，做事*/
        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            ByteBuf msg = null;
            String request = "a,b,c,d"
                    + DelimiterEchoServer.DELIMITER_SYMBOL;
            for(int i=0;i<10;i++){
                msg = Unpooled.buffer(request.length());
                msg.writeBytes(request.getBytes());
                ctx.writeAndFlush(msg);
                System.out.println("发送数据到服务器");
            }
        }

        /*** 发生异常后的处理*/
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            cause.printStackTrace();
            ctx.close();
        }
    }
}

"C:\Program Files\Java\jdk1.8.0_131\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\lib\idea_rt.jar=62139:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\rt.jar;C:\Users\Administrator\Desktop\新建文件夹\24-Netty使用和常用组件辨析（一）-Mark\ketang-tl-netty\netty-basic\target\classes;C:\Users\Administrator\.m2\repository\com\google\protobuf\protobuf-java\2.6.1\protobuf-java-2.6.1.jar;C:\Users\Administrator\.m2\repository\org\msgpack\msgpack\0.6.12\msgpack-0.6.12.jar;C:\Users\Administrator\.m2\repository\com\googlecode\json-simple\json-simple\1.1.1\json-simple-1.1.1.jar;C:\Users\Administrator\.m2\repository\org\javassist\javassist\3.18.1-GA\javassist-3.18.1-GA.jar;C:\Users\Administrator\.m2\repository\de\javakaffee\kryo-serializers\0.42\kryo-serializers-0.42.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\kryo\4.0.0\kryo-4.0.0.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\reflectasm\1.11.3\reflectasm-1.11.3.jar;C:\Users\Administrator\.m2\repository\org\ow2\asm\asm\5.0.4\asm-5.0.4.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\minlog\1.3.0\minlog-1.3.0.jar;C:\Users\Administrator\.m2\repository\org\objenesis\objenesis\2.2\objenesis-2.2.jar;C:\Users\Administrator\.m2\repository\io\netty\netty-all\4.1.42.Final\netty-all-4.1.42.Final.jar;C:\Users\Administrator\.m2\repository\junit\junit\4.11\junit-4.11.jar;C:\Users\Administrator\.m2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar;C:\Users\Administrator\.m2\repository\org\slf4j\slf4j-api\1.7.30\slf4j-api-1.7.30.jar;C:\Users\Administrator\.m2\repository\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;C:\Users\Administrator\.m2\repository\ch\qos\logback\logback-core\1.2.4\logback-core-1.2.4.jar" cn.tuling.nettybasic.splicing.delimiter.DelimiterEchoClient
已连接到服务器.....
发送数据到服务器
发送数据到服务器
发送数据到服务器
发送数据到服务器
发送数据到服务器
发送数据到服务器
发送数据到服务器
发送数据到服务器
发送数据到服务器
发送数据到服务器
client Accept[Hello,a,b,c,d. Welcome to Netty World!] and the counter is:1
client Accept[Hello,a,b,c,d. Welcome to Netty World!] and the counter is:2
client Accept[Hello,a,b,c,d. Welcome to Netty World!] and the counter is:3
client Accept[Hello,a,b,c,d. Welcome to Netty World!] and the counter is:4
client Accept[Hello,a,b,c,d. Welcome to Netty World!] and the counter is:5
client Accept[Hello,a,b,c,d. Welcome to Netty World!] and the counter is:6
client Accept[Hello,a,b,c,d. Welcome to Netty World!] and the counter is:7
client Accept[Hello,a,b,c,d. Welcome to Netty World!] and the counter is:8
client Accept[Hello,a,b,c,d. Welcome to Netty World!] and the counter is:9
client Accept[Hello,a,b,c,d. Welcome to Netty World!] and the counter is:10

注意:@ChannelHandler.Sharable注解

@ChannelHandler.Sharable注解的作用是标注一个 ChannelHandler实例可以被多个通道安全地共享，另外如果没有使用该注解修饰的ChannelHandler，那该ChannelHandler每次添加到通道的流水线都必须创建一个新的Handler实例；

Sharable的意思是在多个通道的流水线可以加入同一个ChannelHandler业务处理器实例，而这种共享操作， Netty默认是不允许的；

换句话说，如果一个Handler没有使用@ChannelHandler.Sharable注解修饰，并试图将同一个Handler实例添加到多个ChannelPipeline通道流水线，或在同一个ChannelPipeline通道流水线中添加同一个Handler实例时， Netty将会抛出异常；

2 ）消息定长，例如每个报文的大小为固定长度 200 字节，如果不够，空位补空格；

服务端

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.util.CharsetUtil;

import java.net.InetSocketAddress;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 类说明：
 */
public class FixedLengthEchoServer {

    public static final String RESPONSE = "Welcome to Netty!";
    public static final int PORT = 9996;

    public static void main(String[] args) throws InterruptedException {
        FixedLengthEchoServer fixedLengthEchoServer = new FixedLengthEchoServer();
        System.out.println("服务器即将启动");
        fixedLengthEchoServer.start();
    }

    public void start() throws InterruptedException {
        final FixedLengthServerHandler serverHandler = new FixedLengthServerHandler();
        EventLoopGroup group = new NioEventLoopGroup();/*线程组*/
        try {
            ServerBootstrap b = new ServerBootstrap();/*服务端启动必须*/
            b.group(group)/*将线程组传入*/
                .channel(NioServerSocketChannel.class)/*指定使用NIO进行网络传输*/
                .localAddress(new InetSocketAddress(PORT))/*指定服务器监听端口*/
                /*服务端每接收到一个连接请求，就会新启一个socket通信，也就是channel，
                所以下面这段代码的作用就是为这个子channel增加handle*/
                .childHandler(new ChannelInitializerImp());
            ChannelFuture f = b.bind().sync();/*异步绑定到服务器，sync()会阻塞直到完成*/
            System.out.println("服务器启动完成，等待客户端的连接和数据.....");
            f.channel().closeFuture().sync();/*阻塞直到服务器的channel关闭*/
        } finally {
            group.shutdownGracefully().sync();/*优雅关闭线程组*/
        }
    }

    private class ChannelInitializerImp extends ChannelInitializer {

        @Override
        protected void initChannel(Channel ch) throws Exception {
            ch.pipeline().addLast(
                    new FixedLengthFrameDecoder(
                            FixedLengthEchoClient.REQUEST.length()));
            ch.pipeline().addLast(new FixedLengthServerHandler());
        }
    }
    @ChannelHandler.Sharable
    public class FixedLengthServerHandler extends ChannelInboundHandlerAdapter {

        private AtomicInteger counter = new AtomicInteger(0);

        /*** 服务端读取到网络数据后的处理*/
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            ByteBuf in = (ByteBuf) msg;
            String request = in.toString(CharsetUtil.UTF_8);
            System.out.println("Server Accept["+request
                    +"] and the counter is:"+counter.incrementAndGet());
            ctx.writeAndFlush(Unpooled.copiedBuffer(
                    FixedLengthEchoServer.RESPONSE.getBytes()));
        }

        /*** 发生异常后的处理*/
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            cause.printStackTrace();
            ctx.close();
        }
    }
}

客户端

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.util.CharsetUtil;

import java.net.InetSocketAddress;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 类说明：
 */
public class FixedLengthEchoClient {

    public final static String REQUEST = "a,b,c,d,e";

    private final String host;

    public FixedLengthEchoClient(String host) {
        this.host = host;
    }

    public void start() throws InterruptedException {
        EventLoopGroup group = new NioEventLoopGroup();/*线程组*/
        try {
            final Bootstrap b = new Bootstrap();;/*客户端启动必须*/
            b.group(group)/*将线程组传入*/
                    .channel(NioSocketChannel.class)/*指定使用NIO进行网络传输*/
                    .remoteAddress(new InetSocketAddress(host,FixedLengthEchoServer.PORT))/*配置要连接服务器的ip地址和端口*/
                    .handler(new ChannelInitializerImp());
            ChannelFuture f = b.connect().sync();
            System.out.println("已连接到服务器.....");
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }

    private class ChannelInitializerImp extends ChannelInitializer {

        @Override
        protected void initChannel(Channel ch) throws Exception {
            ch.pipeline().addLast(
                    new FixedLengthFrameDecoder(
                            FixedLengthEchoServer.RESPONSE.length()));
            ch.pipeline().addLast(new FixedLengthClientHandler());
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new FixedLengthEchoClient("127.0.0.1").start();
    }
    public class FixedLengthClientHandler extends SimpleChannelInboundHandler {

        private AtomicInteger counter = new AtomicInteger(0);

        /*** 客户端读取到网络数据后的处理*/
        protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
            System.out.println("client Accept[" + msg.toString(CharsetUtil.UTF_8)
                    + "] and the counter is:" + counter.incrementAndGet());
        }

        /*** 客户端被通知channel活跃后，做事*/
        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            ByteBuf msg = null;
            for (int i = 0; i < 10; i++) {
                msg = Unpooled.buffer(FixedLengthEchoClient.REQUEST.length());
                msg.writeBytes(FixedLengthEchoClient.REQUEST.getBytes());
                ctx.writeAndFlush(msg);
            }
        }

        /*** 发生异常后的处理*/
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            cause.printStackTrace();
            ctx.close();
        }
    }
}

"C:\Program Files\Java\jdk1.8.0_131\bin\java.exe" -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:63683,suspend=y,server=n -javaagent:C:\Users\Administrator\AppData\Local\JetBrains\IntelliJIdea2020.1\captureAgent\debugger-agent.jar -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\rt.jar;C:\Users\Administrator\Desktop\新建文件夹\24-Netty使用和常用组件辨析（一）-Mark\ketang-tl-netty\netty-basic\target\classes;C:\Users\Administrator\.m2\repository\com\google\protobuf\protobuf-java\2.6.1\protobuf-java-2.6.1.jar;C:\Users\Administrator\.m2\repository\org\msgpack\msgpack\0.6.12\msgpack-0.6.12.jar;C:\Users\Administrator\.m2\repository\com\googlecode\json-simple\json-simple\1.1.1\json-simple-1.1.1.jar;C:\Users\Administrator\.m2\repository\org\javassist\javassist\3.18.1-GA\javassist-3.18.1-GA.jar;C:\Users\Administrator\.m2\repository\de\javakaffee\kryo-serializers\0.42\kryo-serializers-0.42.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\kryo\4.0.0\kryo-4.0.0.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\reflectasm\1.11.3\reflectasm-1.11.3.jar;C:\Users\Administrator\.m2\repository\org\ow2\asm\asm\5.0.4\asm-5.0.4.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\minlog\1.3.0\minlog-1.3.0.jar;C:\Users\Administrator\.m2\repository\org\objenesis\objenesis\2.2\objenesis-2.2.jar;C:\Users\Administrator\.m2\repository\io\netty\netty-all\4.1.42.Final\netty-all-4.1.42.Final.jar;C:\Users\Administrator\.m2\repository\junit\junit\4.11\junit-4.11.jar;C:\Users\Administrator\.m2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar;C:\Users\Administrator\.m2\repository\org\slf4j\slf4j-api\1.7.30\slf4j-api-1.7.30.jar;C:\Users\Administrator\.m2\repository\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;C:\Users\Administrator\.m2\repository\ch\qos\logback\logback-core\1.2.4\logback-core-1.2.4.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\lib\idea_rt.jar" cn.tuling.nettybasic.splicing.fixed.FixedLengthEchoServer
Connected to the target VM, address: '127.0.0.1:63683', transport: 'socket'
服务器即将启动
服务器启动完成，等待客户端的连接和数据.....
Server Accept[a,b,c,d,e] and the counter is:1
Server Accept[a,b,c,d,e] and the counter is:2
Server Accept[a,b,c,d,e] and the counter is:3
Server Accept[a,b,c,d,e] and the counter is:4
Server Accept[a,b,c,d,e] and the counter is:5
Server Accept[a,b,c,d,e] and the counter is:6
Server Accept[a,b,c,d,e] and the counter is:7
Server Accept[a,b,c,d,e] and the counter is:8
Server Accept[a,b,c,d,e] and the counter is:9
Server Accept[a,b,c,d,e] and the counter is:10

"C:\Program Files\Java\jdk1.8.0_131\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\lib\idea_rt.jar=63728:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\rt.jar;C:\Users\Administrator\Desktop\新建文件夹\24-Netty使用和常用组件辨析（一）-Mark\ketang-tl-netty\netty-basic\target\classes;C:\Users\Administrator\.m2\repository\com\google\protobuf\protobuf-java\2.6.1\protobuf-java-2.6.1.jar;C:\Users\Administrator\.m2\repository\org\msgpack\msgpack\0.6.12\msgpack-0.6.12.jar;C:\Users\Administrator\.m2\repository\com\googlecode\json-simple\json-simple\1.1.1\json-simple-1.1.1.jar;C:\Users\Administrator\.m2\repository\org\javassist\javassist\3.18.1-GA\javassist-3.18.1-GA.jar;C:\Users\Administrator\.m2\repository\de\javakaffee\kryo-serializers\0.42\kryo-serializers-0.42.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\kryo\4.0.0\kryo-4.0.0.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\reflectasm\1.11.3\reflectasm-1.11.3.jar;C:\Users\Administrator\.m2\repository\org\ow2\asm\asm\5.0.4\asm-5.0.4.jar;C:\Users\Administrator\.m2\repository\com\esotericsoftware\minlog\1.3.0\minlog-1.3.0.jar;C:\Users\Administrator\.m2\repository\org\objenesis\objenesis\2.2\objenesis-2.2.jar;C:\Users\Administrator\.m2\repository\io\netty\netty-all\4.1.42.Final\netty-all-4.1.42.Final.jar;C:\Users\Administrator\.m2\repository\junit\junit\4.11\junit-4.11.jar;C:\Users\Administrator\.m2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar;C:\Users\Administrator\.m2\repository\org\slf4j\slf4j-api\1.7.30\slf4j-api-1.7.30.jar;C:\Users\Administrator\.m2\repository\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;C:\Users\Administrator\.m2\repository\ch\qos\logback\logback-core\1.2.4\logback-core-1.2.4.jar" cn.tuling.nettybasic.splicing.fixed.FixedLengthEchoClient
已连接到服务器.....
client Accept[Welcome to Netty!] and the counter is:1
client Accept[Welcome to Netty!] and the counter is:2
client Accept[Welcome to Netty!] and the counter is:3
client Accept[Welcome to Netty!] and the counter is:4
client Accept[Welcome to Netty!] and the counter is:5
client Accept[Welcome to Netty!] and the counter is:6
client Accept[Welcome to Netty!] and the counter is:7
client Accept[Welcome to Netty!] and the counter is:8
client Accept[Welcome to Netty!] and the counter is:9
client Accept[Welcome to Netty!] and the counter is:10