netty 解决粘包拆包问题

netty server

TimeServer

package com.zhaowb.netty.ch4_3;

import io.netty.bootstrap.ServerBootstrap;
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.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

public class TimeServer {

    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, 1024)
                    .childHandler(new ChildChannelHandler());

            // 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();
        } catch (Exception e) {
            // 退出，释放线程池资源
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    private class ChildChannelHandler extends ChannelInitializer<SocketChannel> {
        @Override
        protected void initChannel(SocketChannel ch) throws Exception {
            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
            ch.pipeline().addLast(new StringDecoder());
            ch.pipeline().addLast(new TimeServerHandler());
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;

        if (args != null && args.length > 0) {
            try {
                port = Integer.valueOf(args[0]);
            } catch (NumberFormatException e) {
            }
        }
        new TimeServer().bind(port);
    }
}

TimeServerHandler

package com.zhaowb.netty.ch4_3;

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 TimeServerHandler extends ChannelHandlerAdapter {

    private int counter;

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

        String body = (String) msg;

        System.out.println("The time server receive order : " + body + " ; the counter is :  " + ++counter);
        String currentTime = "QUERY TIME ORDER"
                .equalsIgnoreCase(body) ? new Date(
                System.currentTimeMillis()).toString()
                : "BAD ORDER";
        currentTime = currentTime + System.getProperty("line.separator");
        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.writeAndFlush(resp);
    }

    /**
     * 当监听到端口时调用 channelActive 打印 "连接成功！"
     *
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("连接成功！");
    }

    /**
     * 当出现异常时，关闭连接
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println("出现异常，关闭");
        ctx.close();
    }
}

netty client

TimeClient

package com.zhaowb.netty.ch4_3;

import io.netty.bootstrap.Bootstrap;
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.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;

public class TimeClient {

    public void connect(int port, String host) throws Exception {

        //配置客户端 NIO 线程组
        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 {

                            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new TimeClientHandler());
                        }
                    });
            // 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 {
            // 释放 NIO 线程组
            group.shutdownGracefully();

        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;

        if (args != null && args.length > 0) {
            try {
                port = Integer.valueOf(args[0]);
            } catch (NumberFormatException e) {
            }
        }
        new TimeClient().connect(port, "127.0.0.1");
    }
}

TimeClientHandler

package com.zhaowb.netty.ch4_3;

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

import java.util.logging.Logger;

public class TimeClientHandler extends ChannelHandlerAdapter {

    private static final Logger logger = Logger.getLogger(TimeClientHandler.class.getName());

    private int counter;

    private byte[] req;


    public TimeClientHandler() {
       req = ("QUERY TIME ORDER" + System.getProperty("line.separator")).getBytes();
    }

    /**
     * 当连接成功时，调用 writeAndFlush 发送 firstMessage 到服务端
     *
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ByteBuf message = null;
        for (int i = 0; i < 100; i++){
            message = Unpooled.buffer(req.length);
            message.writeBytes(req);
            ctx.writeAndFlush(message);
        }
    }

    /**
     * 当服务端的有数据发送过来时，调用 channelRead 接受数据，并打印
     *
     * @param ctx
     * @param msg
     * @throws Exception
     */
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

        String body = (String) msg;
        System.out.println("Now is : " + body + " ; the counter is : " + ++counter);
    }

    /**
     * 出现异常时，打印错误，并关闭
     *
     * @param ctx
     * @param cause
     * @throws Exception
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        logger.warning("Unexpected  Exception  from downstream : " + cause.getMessage());
        ctx.close();
    }
}

解决粘包拆包问题的关键是使用了

ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
ch.pipeline().addLast(new StringDecoder());

这个程序的运行还是有一些理想的情况，在发送的数据结尾添加System.getProperty("line.separator")，如果没有，将会无法解析

​ LineBasedFrameDecoder: 的工作原理是它一次遍历 ByteBuf 中的刻度字节，判断看是否有 “ ” 或者 " ",

如果有就以此位置为结束位置，从可读索引到结束位置区间的字节就组成了一行，它是以换行符为结束标志 的解码器，支持携带结束符或者不携带结束符两种解码方式，同时支持配置单行的最大长度。如果连续读取到最大长度后仍没有发现换行符，就会抛出异常，同时忽略掉之前读到的异常码流。

​ StringDecoder: 的功能非常简单，就是将接收到的对象转换成字符串，然后继续调用后面的 handle。

​ LineBasedFrameDecoder + StringDecoder 组合就是换行切换的文本编辑器，被设计出来用来支持 TCP 的粘包和拆包。