Netty学习之六—— 粘包/拆包 之 固定长度解码器FixedLengthFrameDecoder的应用

FixedLengthFrameDecoder 是固定长度解码器，它能够按照指定的长度对消息进行自动解码，开发者不需要考虑 TCP的粘包/拆包问题，非常实用。

客户端代码：

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.FixedLengthFrameDecoder;
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 {
                            /**
                             * 固定长度解码器。无论一次收到多少数据包，它都会按照构造函数中设置的固定长度进行解码，
                             * 如果是半包消息，FixedLengthFrameDecoder 会缓存半包消息等待下个包到达后进行拼包，
                             * 直到读取到一个完整的包。
                             */
                            ch.pipeline().addLast(new FixedLengthFrameDecoder(20));
                            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.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;

public class EchoServerHandler extends ChannelHandlerAdapter {

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

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("Receive client : [" + msg + "]");
    }
}

客户端：

采用telnet命令连接 服务端，发送消息，具体步骤是：

1、打开cmd窗口，运行命令 telnet localhost 8080;

2、成功连接后，随便输入数据然后回车发送到服务端，可以尝试多发几次长短包，测试粘包的情况。