《netty权威指南》之拆包粘包解决方案2-消息定长

客户端代码

package com.lyzx.netty.netty03;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.FixedLengthFrameDecoder;

public class Client {

    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup group = new NioEventLoopGroup();
        Bootstrap b = new Bootstrap();
        b.group(group)
                .channel(NioSocketChannel.class)
                .option(ChannelOption.TCP_NODELAY,true)
                .handler(new ChannelInitializer<SocketChannel>(){
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception{
                        ChannelHandler[] arr = {new FixedLengthFrameDecoder(64),new ClientHandler()};
                        ch.pipeline().addLast(arr);
                    }
                });

        ChannelFuture f = b.connect("127.0.0.1", 9988).sync();

        f.channel().closeFuture().sync();
        group.shutdownGracefully();
    }

}

客户端handler

package com.lyzx.netty.netty03;

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

public class ClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("client:channelActive____通道激活开始");
        for(int i=0;i<20;i++){
            char[] charArr = new char[64];
            Arrays.fill(charArr,' ');
            String req = "request0000000000_"+i;
            for(int j=0,count=req.length();j<count;j++){
                charArr[j] = req.charAt(j);
            }
            String reqInfo = new String(charArr);
            System.out.println("client:====================="+reqInfo+"    "+reqInfo.length());
            ctx.channel().writeAndFlush(Unpooled.copiedBuffer(reqInfo.getBytes()));
        }
        System.out.println("client:channelActive____通道激活结束");
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx,Object msg) throws Exception {
        System.out.println("client____:通道可读开始");
        ByteBuf buff = (ByteBuf)msg;
        byte[] bytes = new byte[buff.readableBytes()];
        buff.readBytes(bytes);
        System.out.println("client____response time:"+new String(bytes).trim());
        System.out.println("client____:通道可读结束");
    }

    /**
     * 类似于AOP的后置通知 在这里当通道读取完毕后关闭通道
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        System.out.println("client:通道可读完成");
//        ctx.channel().close();
//        ctx.close();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println("client:发生异常");
    }
}

服务端代码

package com.lyzx.netty.netty03;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.FixedLengthFrameDecoder;

/**
 * @author hero.li
 * 测试netty的拆包粘包问题
 * 拆包粘包的出现的底层原因是
 * TCP协议只是一个传输控制协议，TCP协议只需要把数据在客户端和服务端之间传输
 * 而并不知道这些数据的具体含义，就像水流一样，只要把数据传输成功就完成任务
 * 对于数据可能按照自己的一些规则组合更高效的传输，在组合的时候就无意中改变了
 * 上层业务数据的"规则" 这就是拆包粘包问题
 *
 * 解决方案有3 种
 * 1、分隔符
 *      只需要在客户端和服务端的消息过滤器上加上DelimiterBasedFrameDecoder的实现即可
 *      注意:在发送消息时就需要加上分隔符(客户端和服务端都要加)
 * 2、消息定长
 *      定义每一条信息都一样长，比如64个字符，如果某一条消息的大小不足64字符就手动补齐到64字符
 *      注意是手动补齐，如果不补齐那么久等到channel写到64个字符时发送出去
 *      还有一点要注意下写数据时注意用WriteAndFlush
 *
 * 3、自定义协议，报文头和报文体，其中报文头记录报文体的长度
 */
public class Server {

    public static void main(String[] args) throws InterruptedException {
        //开启两个线程组，一个用于接受客户端的请求   另一个用于异步的网络IO的读写
        NioEventLoopGroup bossGroup = new NioEventLoopGroup();
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        //Netty启动的辅助类 里面封装了客户端和服务端的链接以及如何处理选择器 selector等逻辑
        ServerBootstrap b = new ServerBootstrap();

        //传入两个线程组,设置传输块大小为1k，添加ServerHandler类型的过滤器(表示如何处理这些消息，过滤器当然要集成netty的一个接口)
        b.group(bossGroup,workerGroup)
                .channel(NioServerSocketChannel.class)
                .option(ChannelOption.SO_BACKLOG,1024)
                .childOption(ChannelOption.SO_KEEPALIVE,Boolean.TRUE)
                .childHandler(new ChannelInitializer<SocketChannel>(){
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        ChannelHandler[] arr = {new FixedLengthFrameDecoder(64),new ServerHandler()};
                        ch.pipeline().addLast(arr);
                    }
                });

        //同步等待绑定端口结束
        ChannelFuture f = b.bind(9988).sync();
        //等待服务端监听端口关闭
        f.channel().closeFuture().sync();
        //优雅的关闭线程组
        bossGroup.shutdownGracefully();
        workerGroup.shutdownGracefully();
    }
}

服务端handler

package com.lyzx.netty.netty03;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Arrays;


/**
 * 对于网事件做读写，通常只要关注channelRead()和exceptionCaught()即可
 */
public class ServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("server:channelRead____通道可读开始");
        //从msg对象中获取消息并打印
        ByteBuf buff = (ByteBuf)msg;
        byte[] bytes = new byte[buff.readableBytes()];
        buff.readBytes(bytes);
        System.out.println("server:收到的消息____:"+new String(bytes).trim());
        String datetime = LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss:SSS"));

        char[] responseCharArrData = new char[64];
        Arrays.fill(responseCharArrData,' ');
        for(int i=0,count=datetime.length();i<count;i++){
            responseCharArrData[i] = datetime.charAt(i);
        }

        String responseData = new String(responseCharArrData);
        ctx.writeAndFlush(Unpooled.copiedBuffer(responseData.getBytes()));
        System.out.println("server:channelRead____通道可读结束");
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        System.out.println("server:channelReadComplete____通道可读完成 ");
//        ctx.flush();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println("server:exceptionCaught____发生异常");
        ctx.close();
    }

}

具体代码位置 https://github.com/lyzxhero/Netty

《netty权威指南》之拆包粘包解决方案2-消息定长

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