netty编码解码，拆包粘包，心跳，重连，序列化

　　载入门之后，更多的细节进行整理。

一：序列化

1.顺序

　　进入：从上到下，走inbound

　　出站：从下往上，走outbound

2.String序列化

　　客户端往服务端发送string，然后服务端进行解码出来

　　NettyServer：

package com.jun.netty.codec.string;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.string.StringDecoder;

public class NettyServer {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup boosGroup = new NioEventLoopGroup(1);
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        try{
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(boosGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            ChannelPipeline pipeline = socketChannel.pipeline();
                            pipeline.addLast(new StringDecoder());
                            pipeline.addLast(new ServerHandler());
                        }
                    });
            System.out.println("netty server start");
            ChannelFuture channelFuture = serverBootstrap.bind(9000).sync();
            channelFuture.channel().closeFuture().sync();
        }finally {
            boosGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

　　处理器：

package com.jun.netty.codec.string;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class ServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("从客户端读取的数据："+ msg.toString());
    }
}

　　NettyClient：

package com.jun.netty.codec.string;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.string.StringEncoder;

public class NettyClient {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            ChannelPipeline pipeline = socketChannel.pipeline();
                            pipeline.addLast(new StringEncoder());
                            pipeline.addLast(new ClientHandler());
                        }
                    });
            System.out.println("netty client start");
            ChannelFuture ch = bootstrap.connect("127.0.0.1", 9000).sync();
            ch.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }
}

　　处理器

package com.jun.netty.codec.string;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class ClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush("hello server");
    }
}

　　效果：

3.Object序列化

　　客户端往服务端发送object，然后服务端进行解码出来

　　NettyServer：

package com.jun.netty.codec.object;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.serialization.ClassResolver;
import io.netty.handler.codec.serialization.ClassResolvers;
import io.netty.handler.codec.serialization.ObjectDecoder;
import io.netty.handler.codec.string.StringDecoder;

public class NettyServer {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup boosGroup = new NioEventLoopGroup(1);
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        try{
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(boosGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            ChannelPipeline pipeline = socketChannel.pipeline();
                            pipeline.addLast(new ObjectDecoder(10240, ClassResolvers.cacheDisabled(null)));
                            pipeline.addLast(new ServerHandler());
                        }
                    });
            System.out.println("netty server start");
            ChannelFuture channelFuture = serverBootstrap.bind(9000).sync();
            channelFuture.channel().closeFuture().sync();
        }finally {
            boosGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

　　处理器：

package com.jun.netty.codec.object;

import com.jun.netty.model.User;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class ServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("从客户端读取到Object：" + ((User)msg).toString());
    }
}

　　NettyClient

package com.jun.netty.codec.object;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.serialization.ObjectEncoder;
import io.netty.handler.codec.string.StringEncoder;

public class NettyClient {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            ChannelPipeline pipeline = socketChannel.pipeline();
                            pipeline.addLast(new ObjectEncoder());
                            pipeline.addLast(new ClientHandler());
                        }
                    });
            System.out.println("netty client start");
            ChannelFuture ch = bootstrap.connect("127.0.0.1", 9000).sync();
            ch.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }
}

　　处理器

package com.jun.netty.codec.object;

import com.jun.netty.model.User;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class ClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush(new User(1,"jun"));
    }
}

4.protostuff序列化

　　先做一个protostuff

　　protostuff是一个基于protobuf实现的序列化方法，它较于protobuf最明显的好处是，在几乎不损耗性能的情况下做到了不用我们写.proto文件来实现序列化。使用它也非常简单，代码如下：

　　引入依赖：

<!-- protostuff依赖包 begin -->
        <dependency>
            <groupId>com.dyuproject.protostuff</groupId>
            <artifactId>protostuff-api</artifactId>
            <version>1.0.10</version>
        </dependency>
        <dependency>
            <groupId>com.dyuproject.protostuff</groupId>
            <artifactId>protostuff-core</artifactId>
            <version>1.0.10</version>
        </dependency>
        <dependency>
            <groupId>com.dyuproject.protostuff</groupId>
            <artifactId>protostuff-runtime</artifactId>
            <version>1.0.10</version>
        </dependency>
        <!-- protostuff依赖包 end -->

　　使用：

package com.jun.netty.utils;

import com.dyuproject.protostuff.LinkedBuffer;
import com.dyuproject.protostuff.ProtostuffIOUtil;
import com.dyuproject.protostuff.Schema;
import com.dyuproject.protostuff.runtime.RuntimeSchema;
import com.jun.netty.model.User;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * protostuff 序列化工具类，基于protobuf封装
 */
public class ProtostuffUtil {

    private static Map<Class<?>, Schema<?>> cachedSchema = new ConcurrentHashMap<Class<?>, Schema<?>>();

    private static <T> Schema<T> getSchema(Class<T> clazz) {
        @SuppressWarnings("unchecked")
        Schema<T> schema = (Schema<T>) cachedSchema.get(clazz);
        if (schema == null) {
            schema = RuntimeSchema.getSchema(clazz);
            if (schema != null) {
                cachedSchema.put(clazz, schema);
            }
        }
        return schema;
    }

    /**
     * 序列化
     *
     * @param obj
     * @return
     */
    public static <T> byte[] serializer(T obj) {
        @SuppressWarnings("unchecked")
        Class<T> clazz = (Class<T>) obj.getClass();
        LinkedBuffer buffer = LinkedBuffer.allocate(LinkedBuffer.DEFAULT_BUFFER_SIZE);
        try {
            Schema<T> schema = getSchema(clazz);
            return ProtostuffIOUtil.toByteArray(obj, schema, buffer);
        } catch (Exception e) {
            throw new IllegalStateException(e.getMessage(), e);
        } finally {
            buffer.clear();
        }
    }

    /**
     * 反序列化
     *
     * @param data
     * @param clazz
     * @return
     */
    public static <T> T deserializer(byte[] data, Class<T> clazz) {
        try {
            T obj = clazz.newInstance();
            Schema<T> schema = getSchema(clazz);
            ProtostuffIOUtil.mergeFrom(data, obj, schema);
            return obj;
        } catch (Exception e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
    }

    public static void main(String[] args) {
        byte[] userBytes = ProtostuffUtil.serializer(new User(1, "caojun"));
        User user = ProtostuffUtil.deserializer(userBytes, User.class);
        System.out.println(user);
    }
}

　　在实际中使用：

　　NettyServer:

package com.jun.netty.codec.protostuff;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.serialization.ClassResolvers;
import io.netty.handler.codec.serialization.ObjectDecoder;

public class NettyServer {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup boosGroup = new NioEventLoopGroup(1);
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        try{
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(boosGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            ChannelPipeline pipeline = socketChannel.pipeline();
                            pipeline.addLast(new ServerHandler());
                        }
                    });
            System.out.println("netty server start");
            ChannelFuture channelFuture = serverBootstrap.bind(9000).sync();
            channelFuture.channel().closeFuture().sync();
        }finally {
            boosGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

　　处理器：

package com.jun.netty.codec.protostuff;

import com.jun.netty.model.User;
import com.jun.netty.utils.ProtostuffUtil;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class ServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf buf = (ByteBuf) msg;
        byte[] bytes = new byte[buf.readableBytes()];
        buf.readBytes(bytes);
        System.out.println("从客户端读取到Object：" + ProtostuffUtil.deserializer(bytes, User.class));

    }
}

　　NettyClient

package com.jun.netty.codec.protostuff;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.serialization.ObjectEncoder;

public class NettyClient {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            ChannelPipeline pipeline = socketChannel.pipeline();
                            pipeline.addLast(new ClientHandler());
                        }
                    });
            System.out.println("netty client start");
            ChannelFuture ch = bootstrap.connect("127.0.0.1", 9000).sync();
            ch.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }
}

　　处理器

package com.jun.netty.codec.protostuff;

import com.jun.netty.model.User;
import com.jun.netty.utils.ProtostuffUtil;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class ClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ByteBuf buf = Unpooled.copiedBuffer(ProtostuffUtil.serializer(new User(1, "junjun")));
        ctx.writeAndFlush(buf);

    }
}

二：拆包粘包

1.说明

　　TCP是一个流协议，就是没有界限的一长串二进制数据。TCP作为传输层协议并不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数据包的划分，所以在业务上认为是一个完整的包，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。面向流的通信是无消息保护边界的。

2.解决方案

1）消息定长度，传输的数据大小固定长度，例如每段的长度固定为100字节，如果不够空位补空格

2）在数据包尾部添加特殊分隔符，比如下划线，中划线等，这种方法简单易行，但选择分隔符的时候一定要注意每条数据的内部一定不能出现分隔符。

3）发送长度：发送每条数据的时候，将数据的长度一并发送，比如可以选择每条数据的前4位是数据的长度，应用层处理时可以根据长度来判断每条数据的开始和结束。

Netty提供了多个解码器，可以进行分包的操作，如下：

LineBasedFrameDecoder （回车换行分包）
DelimiterBasedFrameDecoder（特殊分隔符分包）
FixedLengthFrameDecoder（固定长度报文来分包）

3.展示粘包与拆包

　　使用聊天chat包的程序。

　　先启动服务端，进行转发程序

　　启动启动一个客户端1。

　　再修改客户端的程序，然后启动，作为客户端2。

package com.tuling.netty.chat;

import io.netty.bootstrap.Bootstrap;
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.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

public class ChatClient {

    public static void main(String[] args) throws Exception {

        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            //pipeline.addLast(new DelimiterBasedFrameDecoder(1024, Unpooled.copiedBuffer("_"
                            // .getBytes())));
                            //向pipeline加入解码器
                            pipeline.addLast("decoder", new StringDecoder());
                            //向pipeline加入编码器
                            pipeline.addLast("encoder", new StringEncoder());
                            //加入自己的业务处理handler
                            pipeline.addLast(new ChatClientHandler());
                        }
                    });
            ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 9000).sync();
            //得到 channel
            Channel channel = channelFuture.channel();
            System.out.println("========" + channel.localAddress() + "========");
            //客户端需要输入信息， 创建一个扫描器
//            Scanner scanner = new Scanner(System.in);
//            while (scanner.hasNextLine()) {
//                String msg = scanner.nextLine();
//                //通过 channel 发送到服务器端
//                channel.writeAndFlush(msg);
//            }
            for (int i = 0; i < 200; i++) {
                channel.writeAndFlush("hello，诸葛!" + "_");
            }
        } finally {
            group.shutdownGracefully();
        }
    }
}

　　在客户端1小效果：

D:\jdk1.8.0_202\bin\java.exe -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:52388,suspend=y,server=n -javaagent:C:\Users\Administrator\.IntelliJIdea2019.3\system\captureAgent\debugger-agent.jar -Dfile.encoding=UTF-8 -classpath "D:\jdk1.8.0_202\jre\lib\charsets.jar;D:\jdk1.8.0_202\jre\lib\deploy.jar;D:\jdk1.8.0_202\jre\lib\ext\access-bridge-64.jar;D:\jdk1.8.0_202\jre\lib\ext\cldrdata.jar;D:\jdk1.8.0_202\jre\lib\ext\dnsns.jar;D:\jdk1.8.0_202\jre\lib\ext\jaccess.jar;D:\jdk1.8.0_202\jre\lib\ext\jfxrt.jar;D:\jdk1.8.0_202\jre\lib\ext\localedata.jar;D:\jdk1.8.0_202\jre\lib\ext\nashorn.jar;D:\jdk1.8.0_202\jre\lib\ext\sunec.jar;D:\jdk1.8.0_202\jre\lib\ext\sunjce_provider.jar;D:\jdk1.8.0_202\jre\lib\ext\sunmscapi.jar;D:\jdk1.8.0_202\jre\lib\ext\sunpkcs11.jar;D:\jdk1.8.0_202\jre\lib\ext\zipfs.jar;D:\jdk1.8.0_202\jre\lib\javaws.jar;D:\jdk1.8.0_202\jre\lib\jce.jar;D:\jdk1.8.0_202\jre\lib\jfr.jar;D:\jdk1.8.0_202\jre\lib\jfxswt.jar;D:\jdk1.8.0_202\jre\lib\jsse.jar;D:\jdk1.8.0_202\jre\lib\management-agent.jar;D:\jdk1.8.0_202\jre\lib\plugin.jar;D:\jdk1.8.0_202\jre\lib\resources.jar;D:\jdk1.8.0_202\jre\lib\rt.jar;C:\Users\Administrator\Desktop\netty\30-深入Hotspot源码与Linux内核理解NIO与Epoll-诸葛\netty(2)\netty\target\classes;C:\Users\zhuge\.m2\repository\com\dyuproject\protostuff\protostuff-api\1.0.10\protostuff-api-1.0.10.jar;C:\Users\zhuge\.m2\repository\com\dyuproject\protostuff\protostuff-core\1.0.10\protostuff-core-1.0.10.jar;C:\Users\zhuge\.m2\repository\com\dyuproject\protostuff\protostuff-runtime\1.0.10\protostuff-runtime-1.0.10.jar;C:\Users\zhuge\.m2\repository\com\dyuproject\protostuff\protostuff-collectionschema\1.0.10\protostuff-collectionschema-1.0.10.jar;C:\Users\zhuge\.m2\repository\io\netty\netty-all\4.1.35.Final\netty-all-4.1.35.Final.jar;D:\IntelliJ IDEA 2019.3.1\lib\idea_rt.jar" com.tuling.netty.chat.ChatClient
Connected to the target VM, address: '127.0.0.1:52388', transport: 'socket'
========/127.0.0.1:52431========
[ 客户端 ]/127.0.0.1:52482 上线了 2022-09-22 21:43:22
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息
：hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_hello，诸葛!_hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 发送了消息：hello，诸葛!_
[ 客户端 ]/127.0.0.1:52482 下线了

4.自定义

　　新定义传输协议：

package com.jun.netty.model;
/**
 * 自定义传输协议包
 */
public class MessageProtocol {
    /**
     * 长度
     */
    private int len;

    /**
     * 二进制内容
     */
    private byte[] content;

    public int getLen() {
        return len;
    }

    public void setLen(int len) {
        this.len = len;
    }

    public byte[] getContent() {
        return content;
    }

    public void setContent(byte[] content) {
        this.content = content;
    }
}

　　server

package com.jun.netty.splitandstickpacket;

import com.jun.netty.splitandstickpacket.code.NettyMessageDecode;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class NettyServer {
    public static void main(String[] args) {
        NioEventLoopGroup boosGroup = new NioEventLoopGroup(1);
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();
        try{
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(boosGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            ChannelPipeline pipeline = socketChannel.pipeline();
                            pipeline.addLast(new NettyMessageDecode());
                            pipeline.addLast(new NettyServerHandler());
                        }
                    });
            System.out.println("netty server start");
            ChannelFuture future = serverBootstrap.bind(9000).sync();
            future.channel().closeFuture().sync();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            boosGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

　　解码器

package com.jun.netty.splitandstickpacket.code;

import com.jun.netty.model.MessageProtocol;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;

import java.util.List;

/**
 * 信息解码器
 */
public class NettyMessageDecode extends ByteToMessageDecoder {
    private int length = 0;

    @Override
    protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf, List<Object> list) throws Exception {
        System.out.println("服务端接收到的数据" + byteBuf);
        if (byteBuf.readableBytes() >= 4) {
            if (length == 0) {
                length = byteBuf.readInt();
            }
            if (byteBuf.readableBytes() < length) {
                System.out.println("读取到的数据不符合length长度");
                return;
            }
            byte[] content = new byte[length];
            if (byteBuf.readableBytes() >= length) {
                byteBuf.readBytes(content);

                // 将信息组装成dto，传递给下一个业务处理器
                MessageProtocol messageProtocol = new MessageProtocol();
                messageProtocol.setLen(length);
                messageProtocol.setContent(content);
                list.add(messageProtocol);
            }
            length = 0;
        }
    }
}

　　处理器

package com.jun.netty.splitandstickpacket;

import com.jun.netty.model.MessageProtocol;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.util.CharsetUtil;

public class NettyServerHandler extends SimpleChannelInboundHandler<MessageProtocol> {
    private int count;

    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, MessageProtocol messageProtocol) throws Exception {
        System.out.println("服务端接收到的数据长度=" + messageProtocol.getLen());
        System.out.println("服务端接收到的数据=" + new String(messageProtocol.getContent(), CharsetUtil.UTF_8));
        System.out.println("服务端接收到的消息包的数量=" + (++this.count));
    }
}

　　client

package com.jun.netty.splitandstickpacket;

import com.jun.netty.splitandstickpacket.code.NettyMessageEncode;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

public class NettyClient {
    public static void main(String[] args) {
        NioEventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            ChannelPipeline pipeline = socketChannel.pipeline();
                            pipeline.addLast(new NettyMessageEncode());
                            pipeline.addLast(new NettyClientHandler());
                        }
                    });
            System.out.println("netty client start");
            ChannelFuture future = bootstrap.connect("127.0.0.1", 9000).sync();
            future.channel().closeFuture().sync();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            group.shutdownGracefully();
        }
    }
}

　　处理器

package com.jun.netty.splitandstickpacket;

import com.jun.netty.model.MessageProtocol;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.util.CharsetUtil;

public class NettyClientHandler extends SimpleChannelInboundHandler<MessageProtocol> {
    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, MessageProtocol messageProtocol) throws Exception {

    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        for (int i=0; i< 100; i++){
            String msg = "你好啊，netty";
            MessageProtocol messageProtocol = new MessageProtocol();
            messageProtocol.setLen(msg.getBytes(CharsetUtil.UTF_8).length);
            messageProtocol.setContent(msg.getBytes(CharsetUtil.UTF_8));
            ctx.writeAndFlush(messageProtocol);
        }
    }
}

　　编码器

package com.jun.netty.splitandstickpacket.code;

import com.jun.netty.model.MessageProtocol;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;

/**
 * 信息编码器
 */
public class NettyMessageEncode extends MessageToByteEncoder<MessageProtocol> {
    @Override
    protected void encode(ChannelHandlerContext channelHandlerContext, MessageProtocol messageProtocol, ByteBuf byteBuf) throws Exception {
        byteBuf.writeInt(messageProtocol.getLen());
        byteBuf.writeBytes(messageProtocol.getContent());
    }
}

三：心跳检测机制

1.client

package com.jun.netty.heartbeat;

import io.netty.bootstrap.Bootstrap;
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.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

import java.util.Random;

public class HeatBeatClient {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {

                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            ChannelPipeline pipeline = socketChannel.pipeline();
                            pipeline.addLast(new StringEncoder());
                            pipeline.addLast(new StringDecoder());
                            pipeline.addLast(new HeatBeatClientHandler());
                        }
                    });
            System.out.println("netty client start");
            Channel channel = bootstrap.connect("127.0.0.1", 9000).sync().channel();
            String text = "packet heatBeat";
            Random random = new Random();
            while (channel.isActive()) {
                int num = random.nextInt(8);
                Thread.sleep(num * 1000);
                channel.writeAndFlush(text);
            }
        } finally {
            group.shutdownGracefully();
        }
    }

    static class HeatBeatClientHandler extends SimpleChannelInboundHandler<String> {

        @Override
        protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
            System.out.println(" client received :" + msg);
            if (msg != null && msg.equals("idle close")) {
                System.out.println(" 服务端关闭连接，客户端也关闭");
                ctx.channel().closeFuture();
            }
        }
    }
}

2.server

package com.tuling.netty.heartbeat;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.handler.timeout.IdleStateHandler;

import java.util.concurrent.TimeUnit;

public class HeartBeatServer {

    public static void main(String[] args) throws Exception {
        EventLoopGroup boss = new NioEventLoopGroup();
        EventLoopGroup worker = new NioEventLoopGroup();
        try {
            ServerBootstrap bootstrap = new ServerBootstrap();
            bootstrap.group(boss, worker)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            pipeline.addLast("decoder", new StringDecoder());
                            pipeline.addLast("encoder", new StringEncoder());
                            //IdleStateHandler的readerIdleTime参数指定超过3秒还没收到客户端的连接，
                            //会触发IdleStateEvent事件并且交给下一个handler处理，下一个handler必须
                            //实现userEventTriggered方法处理对应事件
                            pipeline.addLast(new IdleStateHandler(3, 0, 0, TimeUnit.SECONDS));
                            pipeline.addLast(new HeartBeatServerHandler());
                        }
                    });
            System.out.println("netty server start。。");
            ChannelFuture future = bootstrap.bind(9000).sync();
            future.channel().closeFuture().sync();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            worker.shutdownGracefully();
            boss.shutdownGracefully();
        }
    }
}

　　处理器

package com.jun.netty.heartbeat;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.timeout.IdleStateEvent;

public class HeatBeatServerHandler extends SimpleChannelInboundHandler<String> {
    int readIdleTimes = 0;

    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, String s) throws Exception {
        if ("packet heatBeat".equals(s)) {
            System.out.println("回复ok");
            channelHandlerContext.channel().writeAndFlush("ok");
        } else {
            System.out.println("其他信息");
        }
    }

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        IdleStateEvent event = (IdleStateEvent) evt;
        String eventType = "";
        switch (event.state()) {
            case ALL_IDLE:
                eventType = "读写空闲";
                break;
            case READER_IDLE:
                readIdleTimes++;
                eventType = "读空闲";
                break;
            case WRITER_IDLE:
                eventType = "写空闲";
                break;
        }

        System.out.println(ctx.channel().remoteAddress() + "超时事件" + eventType);
        if (readIdleTimes > 3) {
            System.out.println("[server]读空闲超过3次，关闭连接，释放更多资源");
            ctx.channel().writeAndFlush("idle close");
            ctx.channel().close();
        }
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.err.println("=== " + ctx.channel().remoteAddress() + " is active ===");
    }
}

3.效果

"D:\IntelliJ IDEA 2019.3.1\jbr\bin\java.exe" -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:51972,suspend=y,server=n -javaagent:C:\Users\Administrator\.IntelliJIdea2019.3\system\captureAgent\debugger-agent.jar -Dfile.encoding=UTF-8 -classpath "E:\study\mygitee\netty-pro\target\classes;C:\Users\Administrator\.m2\repository\io\netty\netty-all\4.1.35.Final\netty-all-4.1.35.Final.jar;C:\Users\Administrator\.m2\repository\com\dyuproject\protostuff\protostuff-api\1.0.10\protostuff-api-1.0.10.jar;C:\Users\Administrator\.m2\repository\com\dyuproject\protostuff\protostuff-core\1.0.10\protostuff-core-1.0.10.jar;C:\Users\Administrator\.m2\repository\com\dyuproject\protostuff\protostuff-runtime\1.0.10\protostuff-runtime-1.0.10.jar;C:\Users\Administrator\.m2\repository\com\dyuproject\protostuff\protostuff-collectionschema\1.0.10\protostuff-collectionschema-1.0.10.jar;D:\IntelliJ IDEA 2019.3.1\lib\idea_rt.jar" com.jun.netty.heartbeat.HeartBeatServer
Connected to the target VM, address: '127.0.0.1:51972', transport: 'socket'
OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended
netty server start
=== /127.0.0.1:52060 is active ===
/127.0.0.1:52060超时事件读空闲
回复ok
/127.0.0.1:52060超时事件读空闲
其他信息
回复ok
/127.0.0.1:52060超时事件读空闲
/127.0.0.1:52060超时事件读空闲
[server]读空闲超过3次，关闭连接，释放更多资源
Disconnected from the target VM, address: '127.0.0.1:51972', transport: 'socket'

Process finished with exit code 130

四：重连

1.server

package com.jun.netty.reconnect;

import com.jun.netty.reconnect.handler.NettyClientHandler;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
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;

import java.util.concurrent.TimeUnit;

public class NettyClient {
    private String host;
    private int port;
    private Bootstrap bootstrap;
    private EventLoopGroup eventLoopGroup;

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

    /**
     * 初始化
     */
    private void init() {
        eventLoopGroup = new NioEventLoopGroup();
        //创建客户端启动对象
        // bootstrap 可重用, 只需在NettyClient实例化的时候初始化即可.
        bootstrap = new Bootstrap();
        bootstrap.group(eventLoopGroup)
                .channel(NioSocketChannel.class)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        //加入处理器
                        ch.pipeline().addLast(new NettyClientHandler(NettyClient.this));
                    }
                });
    }

    /**
     * 连接
     */
    public void connect() throws InterruptedException {
        System.out.println("netty client start。。");
        //启动客户端去连接服务器端
        ChannelFuture cf = bootstrap.connect(host, port);
        cf.addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) throws Exception {
                if (!future.isSuccess()) {
                    //重连交给后端线程执行
                    future.channel().eventLoop().schedule(() -> {
                        System.err.println("重连服务端...");
                        try {
                            connect();
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }, 3000, TimeUnit.MILLISECONDS);
                } else {
                    System.out.println("服务端连接成功...");
                }
            }
        });
        //对通道关闭进行监听
        cf.channel().closeFuture().sync();
    }

    /**
     * 启动
     */
    public static void main(String[] args) throws InterruptedException {
        NettyClient nettyClient = new NettyClient("127.0.0.1", 9000);
        nettyClient.connect();
    }


}

　　处理器1

package com.jun.netty.reconnect.handler;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class LifeCycleInBoundHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx)
            throws Exception {
        System.out.println("channelActive: channel准备就绪");
        super.channelActive(ctx);
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx)
            throws Exception {
        System.out.println("channelInactive: channel被关闭");
        super.channelInactive(ctx);
    }
}

　　处理器2

package com.jun.netty.reconnect.handler;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.CharsetUtil;

public class NettyServerHandler extends ChannelInboundHandlerAdapter {
    /**
     * 读取客户端发送的数据
     */
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("服务器读取线程 " + Thread.currentThread().getName());
        ByteBuf buf = (ByteBuf) msg;
        System.out.println("客户端发送消息是:" + buf.toString(CharsetUtil.UTF_8));
    }

    /**
     * 数据读取完毕处理方法
     */
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ByteBuf buf = Unpooled.copiedBuffer("HelloClient".getBytes(CharsetUtil.UTF_8));
        ctx.writeAndFlush(buf);
    }

    /**
     * 处理异常, 一般是需要关闭通道
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.close();
    }
}

2.client

package com.jun.netty.reconnect;

import com.jun.netty.reconnect.handler.NettyClientHandler;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
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;

import java.util.concurrent.TimeUnit;

public class NettyClient {
    private String host;
    private int port;
    private Bootstrap bootstrap;
    private EventLoopGroup eventLoopGroup;

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

    /**
     * 初始化
     */
    private void init() {
        eventLoopGroup = new NioEventLoopGroup();
        //创建客户端启动对象
        // bootstrap 可重用, 只需在NettyClient实例化的时候初始化即可.
        bootstrap = new Bootstrap();
        bootstrap.group(eventLoopGroup)
                .channel(NioSocketChannel.class)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        //加入处理器
                        ch.pipeline().addLast(new NettyClientHandler(NettyClient.this));
                    }
                });
    }

    /**
     * 连接
     */
    public void connect() throws InterruptedException {
        System.out.println("netty client start。。");
        //启动客户端去连接服务器端
        ChannelFuture cf = bootstrap.connect(host, port);
        cf.addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) throws Exception {
                if (!future.isSuccess()) {
                    //重连交给后端线程执行
                    future.channel().eventLoop().schedule(() -> {
                        System.err.println("重连服务端...");
                        try {
                            connect();
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }, 3000, TimeUnit.MILLISECONDS);
                } else {
                    System.out.println("服务端连接成功...");
                }
            }
        });
        //对通道关闭进行监听
        cf.channel().closeFuture().sync();
    }

    /**
     * 启动
     */
    public static void main(String[] args) throws InterruptedException {
        NettyClient nettyClient = new NettyClient("127.0.0.1", 9000);
        nettyClient.connect();
    }


}

　　处理器

package com.jun.netty.reconnect.handler;

import com.jun.netty.reconnect.NettyClient;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.CharsetUtil;

public class NettyClientHandler extends ChannelInboundHandlerAdapter {
    private NettyClient nettyClient;

    public NettyClientHandler(NettyClient nettyClient) {
        this.nettyClient = nettyClient;
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        System.err.println("运行中断开重连。。。");
        nettyClient.connect();
    }

    /**
     * 当客户端连接服务器完成就会触发该方法
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ByteBuf buf = Unpooled.copiedBuffer("HelloServer".getBytes(CharsetUtil.UTF_8));
        ctx.writeAndFlush(buf);
    }

    //当通道有读取事件时会触发，即服务端发送数据给客户端
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf buf = (ByteBuf) msg;
        System.out.println("收到服务端的消息:" + buf.toString(CharsetUtil.UTF_8));
        System.out.println("服务端的地址： " + ctx.channel().remoteAddress());
    }
}

　　效果

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原文地址：https://www.cnblogs.com/juncaoit/p/16707813.html