<netty权威指南>笔记-分隔符解码器处理半包问题

最新推荐文章于 2025-09-23 19:46:59 发布

原创最新推荐文章于 2025-09-23 19:46:59 发布 · 3.5k 阅读

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CC 4.0 BY-SA版权

本文介绍如何使用Netty的DelimiterBasedFrameDecoder和StringDecoder解决分隔符消息的半包问题。通过示例展示了客户端和服务端正确配置解码器的重要性，避免粘包和半包现象。

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概述

在以回车换行结尾的消息如何处理半包问题一文中介绍了如何处理以回车换行的消息的半包问题,如果消息用分隔符来切割的,那么如何处理半包问题呢?可以组合使用

DelimiterBasedFrameDecoder
StringDecoder

来处理半包问题。

netty分隔符解码器

服务端代码

package nettyguide.encode.delimiter.server;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

public class SocketServer {
    public static void main(String[] args) throws InterruptedException {
        EventLoopGroup parentGroup = new NioEventLoopGroup();
        EventLoopGroup childGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(parentGroup, childGroup)
                    .channel(NioServerSocketChannel.class)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new SocketServerInitializer());

            ChannelFuture channelFuture = serverBootstrap.bind(8899).sync();
            channelFuture.channel().closeFuture().sync();
        }
        finally {
            parentGroup.shutdownGracefully();
            childGroup.shutdownGracefully();
        }
    }
}

package nettyguide.encode.delimiter.server;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;


public class SocketServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        // 告诉DelimiterBasedFrameDecoder以$_作为分隔符
        ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes());
        ChannelPipeline pipeline = ch.pipeline();
        //这里的1024,表示单条消息的最大长度,当达到长度后,还没有找到分隔符,则抛出TooLongFrameException
        pipeline.addLast(new DelimiterBasedFrameDecoder(1024,delimiter));
        pipeline.addLast(new StringDecoder());
        pipeline.addLast(new SocketServerHandler());
    }
}

package nettyguide.encode.delimiter.server;

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

public class SocketServerHandler extends ChannelInboundHandlerAdapter {
    private int counter;

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        //打印客户端发送的数据
        String body = (String)msg;
        System.out.println("This is " + ++counter + " times receive from client:"+body+"");
        body = body + "$_";
        ByteBuf byteBuf = Unpooled.copiedBuffer(body.getBytes());
        ctx.writeAndFlush(byteBuf);
    }
}

客户端代码

package nettyguide.encode.delimiter.client;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

public class SocketClient {
    public static void main(String[] args) throws InterruptedException {
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();

        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup)
                    .channel(NioSocketChannel.class)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .handler(new SocketClientInitializer());

            ChannelFuture channelFuture = bootstrap.connect("localhost", 8899).sync();
            channelFuture.channel().closeFuture().sync();
        }
        finally {
            eventLoopGroup.shutdownGracefully();
        }
    }
}

package nettyguide.encode.delimiter.client;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;

public class SocketClientInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes());
        ChannelPipeline pipeline = ch.pipeline();
        //这里的1024,表示单条消息的最大长度,当达到长度后,还没有找到分隔符,则抛出TooLongFrameException
        pipeline.addLast(new DelimiterBasedFrameDecoder(1024,delimiter));
        pipeline.addLast(new StringDecoder());
        pipeline.addLast(new SocketClientHandler());
    }
}

package nettyguide.encode.delimiter.client;

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

public class SocketClientHandler extends ChannelInboundHandlerAdapter {
    private int counter;
    private static String req = "Hi Sam.Welcome to Netty home.$_";
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String body = (String)msg;
        System.out.println("This is " + ++counter + " times receive from server:"+body+"");
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        for (int i = 0; i < 10; i++) {
            ctx.writeAndFlush(Unpooled.copiedBuffer(req.getBytes()));
        }
    }
 }

运行服务端和客户端代码,服务端打印的信息如下

This is 1 times receive from client:Hi Sam.Welcome to Netty home.
This is 2 times receive from client:Hi Sam.Welcome to Netty home.
This is 3 times receive from client:Hi Sam.Welcome to Netty home.
This is 4 times receive from client:Hi Sam.Welcome to Netty home.
This is 5 times receive from client:Hi Sam.Welcome to Netty home.
This is 6 times receive from client:Hi Sam.Welcome to Netty home.
This is 7 times receive from client:Hi Sam.Welcome to Netty home.
This is 8 times receive from client:Hi Sam.Welcome to Netty home.
This is 9 times receive from client:Hi Sam.Welcome to Netty home.
This is 10 times receive from client:Hi Sam.Welcome to Netty home.

客户端打印的信息如下

This is 1 times receive from server:Hi Sam.Welcome to Netty home.
This is 2 times receive from server:Hi Sam.Welcome to Netty home.
This is 3 times receive from server:Hi Sam.Welcome to Netty home.
This is 4 times receive from server:Hi Sam.Welcome to Netty home.
This is 5 times receive from server:Hi Sam.Welcome to Netty home.
This is 6 times receive from server:Hi Sam.Welcome to Netty home.
This is 7 times receive from server:Hi Sam.Welcome to Netty home.
This is 8 times receive from server:Hi Sam.Welcome to Netty home.
This is 9 times receive from server:Hi Sam.Welcome to Netty home.
This is 10 times receive from server:Hi Sam.Welcome to Netty home.

结果很正常,客户端发送10次,服务端接收到信息后,也往客户端发送了10次请求。半包问题得到解决了。

现在来做个试验,如果把客户端代码中SocketClientInitializer类中的

pipeline.addLast(new DelimiterBasedFrameDecoder(1024,delimiter));

注释掉,会发生什么事情呢?

注释掉后运行服务端代码和客户端代码,服务端打印信息如下

This is 1 times receive from client:Hi Sam.Welcome to Netty home.
This is 2 times receive from client:Hi Sam.Welcome to Netty home.
This is 3 times receive from client:Hi Sam.Welcome to Netty home.
This is 4 times receive from client:Hi Sam.Welcome to Netty home.
This is 5 times receive from client:Hi Sam.Welcome to Netty home.
This is 6 times receive from client:Hi Sam.Welcome to Netty home.
This is 7 times receive from client:Hi Sam.Welcome to Netty home.
This is 8 times receive from client:Hi Sam.Welcome to Netty home.
This is 9 times receive from client:Hi Sam.Welcome to Netty home.
This is 10 times receive from client:Hi Sam.Welcome to Netty home.

也是10次,跟我们的预期一样,但是客户端却发生了粘包。客户端打印信息如下

This is 1 times receive from server:Hi Sam.Welcome to Netty home.$_
This is 2 times receive from server:Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_
This is 3 times receive from server:Hi Sam.Welcome to Netty home.$_
This is 4 times receive from server:Hi Sam.Welcome to Netty home.$_
This is 5 times receive from server:Hi Sam.Welcome to Netty home.$_
This is 6 times receive from server:Hi Sam.Welcome to Netty home.$_
This is 7 times receive from server:Hi Sam.Welcome to Netty home.$_

总共才发送了7次请求给服务端,部分数据在客户端发生了粘包。但是由于服务端仍然使用了

pipeline.addLast(new DelimiterBasedFrameDecoder(1024,delimiter));

所有服务端是能够正确解析的。仍然是打印10次。

如果是把服务端类中的SocketServerInitializer中的

pipeline.addLast(new DelimiterBasedFrameDecoder(1024,delimiter));

注释掉。但是客户端中的保留。又会是什么效果呢?继续运行代码看效果。

服务端打印如下

This is 1 times receive from client:Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_Hi Sam.Welcome to Netty home.$_

客户端打印如下

This is 1 times receive from server:Hi Sam.Welcome to Netty home.
This is 2 times receive from server:Hi Sam.Welcome to Netty home.
This is 3 times receive from server:Hi Sam.Welcome to Netty home.
This is 4 times receive from server:Hi Sam.Welcome to Netty home.
This is 5 times receive from server:Hi Sam.Welcome to Netty home.
This is 6 times receive from server:Hi Sam.Welcome to Netty home.
This is 7 times receive from server:Hi Sam.Welcome to Netty home.
This is 8 times receive from server:Hi Sam.Welcome to Netty home.
This is 9 times receive from server:Hi Sam.Welcome to Netty home.
This is 10 times receive from server:Hi Sam.Welcome to Netty home.