Netty学习之五—— 粘包/拆包 之 分隔符解码器DelimiterBasedFrameDecoder的应用

DelimiterBasedFrameDecoder 应用开发

通过对 DelimiterBasedFrameDecoder 的使用，可以自动完成以分隔符作为码流结束标识的消息的解码。

演示程序以经典的 Echo 服务为例。EchoServer 接收到 EchoClient 的请求消息后，将其打印出来，然后将原始消息返回给客户端，消息以“$_” 作为分隔符。

服务端代码：

package com.netty.echo;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
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.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

public class EchoServer {
    public void bind(int port) throws Exception {
        // 配置服务端的 NIO 线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 100)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes());
                            /**
                             * 第一个参数：1024 表示单条记录的最大长度，当达到最大长度仍然没有找到
                             *              分隔符，就抛出 TooLongFrameException 异常，防止异常码流缺失
                             *              分隔符导致内存溢出，这是Netty解码器的可靠性保证。
                             * 第二个参数：是分隔符
                             */
                            ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter));
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new EchoServerHandler());
                        }
                    });
            // 绑定端口，同步等待成功
            ChannelFuture f = b.bind(port).sync();

            // 等待服务端监听端口关闭
            f.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }


    public static void main(String[] args) throws Exception {
        int port = 8080;
        new EchoServer().bind(port);
    }
}

package com.netty.echo;


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

import java.util.Date;

public class EchoServerHandler extends ChannelHandlerAdapter {
    private int counter;

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.close();
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String body = (String) msg;
        System.out.println("This is " + ++counter + " times receive client : [" + body + "]");
        body += "$_";
        ByteBuf resp = Unpooled.copiedBuffer(body.getBytes());
        ctx.writeAndFlush(resp);
    }
}

客户端代码：

package com.netty.echo;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
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 io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;

public class EchoClient {
    public void connect(int port, String host) throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try{
            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 {
                            ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes());
                            /**
                             * 第一个参数：1024 表示单条记录的最大长度，当达到最大长度仍然没有找到
                             *              分隔符，就抛出 TooLongFrameException 异常，防止异常码流缺失
                             *              分隔符导致内存溢出，这是Netty解码器的可靠性保证。
                             * 第二个参数：是分隔符
                             */
                            ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter));
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new EchoClientHandler());
                        }
                    });
            // 发起异步连接操作
            ChannelFuture f = b.connect(host, port).sync();

            // 等待客户端链路关闭
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;
        new EchoClient().connect(port, "127.0.0.1");
    }
}

package com.netty.echo;

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

public class EchoClientHandler extends ChannelHandlerAdapter {

    private int counter;
    static final String ECHO_REQ = "Hi , Netty Server .$_";

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.close();
    }

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

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("This is " + ++counter + " times receive server : [" + msg + "]");
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }
}

运行结果：

服务端：客户端：