<netty权威指南>笔记-分隔符解码器处理半包问题

概述

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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。

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netty分隔符解码器

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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.

这次服务端解析出现问题了,把客户端的所有信息一次性解析出来,这是我们不希望发生的。而客户端这边在发送信息的时候,是正常的。

如果消息是有分隔符的,服务端开发的程序和客户端开发的程序,在处理这些消息时,记得使用

DelimiterBasedFrameDecoder

解码器。

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csdn code 路径

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这个项目的源代码放置在csdn code上,欢迎访问。
netty_study