Netty解决TCP粘包/拆包问题 - 按行分隔字符串解码器

服务端

package org.zln.netty.five.timer;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 时间服务器服务端
 * Created by sherry on 16/11/5.
 */
public class TimerServer {
    /**
     * 服务端绑定端口号
     */
    private int PORT;

    public TimerServer(int PORT) {
        this.PORT = PORT;
    }

    /**
     * 日志
     */
    private static Logger logger = LoggerFactory.getLogger(TimerServer.class);

    public void bind() {
        /*
        NioEventLoopGroup是线程池组
        包含了一组NIO线程,专门用于网络事件的处理
        bossGroup:服务端,接收客户端连接
        workGroup:进行SocketChannel的网络读写
         */
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workGroup = new NioEventLoopGroup();
        try {
            /*
            ServerBootstrap:用于启动NIO服务的辅助类,目的是降低服务端的开发复杂度
             */
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)//配置TCP参数,能够设置很多,这里就只设置了backlog=1024,
                    .childHandler(new TimerServerInitializer());//绑定I/O事件处理类
            logger.debug("绑定端口号:" + PORT + ",等待同步成功");
            /*
            bind:绑定端口
            sync:同步阻塞方法,等待绑定完成,完成后返回 ChannelFuture ,主要用于通知回调
             */
            ChannelFuture channelFuture = serverBootstrap.bind(PORT).sync();
            logger.debug("等待服务端监听窗口关闭");
            /*
             closeFuture().sync():为了阻塞,服务端链路关闭后才退出.也是一个同步阻塞方法
             */
            channelFuture.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            logger.error(e.getMessage(), e);
        } finally {
            logger.debug("优雅退出,释放线程池资源");
            bossGroup.shutdownGracefully();
            workGroup.shutdownGracefully();
        }
    }
}

TimerServer

 package org.zln.netty.five.timer;

 import io.netty.channel.ChannelInitializer;
 import io.netty.channel.ChannelPipeline;
 import io.netty.channel.socket.SocketChannel;
 import io.netty.handler.codec.LineBasedFrameDecoder;
 import io.netty.handler.codec.string.StringDecoder;

 /**
  * Created by sherry on 16/11/5.
  */
 public class TimerServerInitializer extends ChannelInitializer<SocketChannel> {
     @Override
     protected void initChannel(SocketChannel socketChannel) throws Exception {

         ChannelPipeline pipeline = socketChannel.pipeline();

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

     }
 }

TimerServerInitializer

 package org.zln.netty.five.timer;

 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 import java.text.SimpleDateFormat;
 import java.util.Date;

 /**
  * Handler主要用于对网络事件进行读写操作,是真正的业务类
  * 通常只需要关注 channelRead 和 exceptionCaught 方法
  * Created by sherry on 16/11/5.
  */
 public class TimerServerHandler extends ChannelHandlerAdapter {

     /**
      * 日志
      */
     private Logger logger = LoggerFactory.getLogger(TimerServerHandler.class);

     private static int count = 0;

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

         String body = (String) msg;
         logger.debug("第  "+(++count)+"  次收到请求  -  "+body);

         String timeNow = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss SSS").format(new Date())+System.lineSeparator();

         //获取发送给客户端的数据
         ByteBuf resBuf = Unpooled.copiedBuffer(timeNow.getBytes("UTF-8"));

         ctx.writeAndFlush(resBuf);
     }

     @Override
     public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
         //将消息发送队列中的消息写入到SocketChannel中发送给对方
         logger.debug("channelReadComplete");
         ctx.flush();
     }

     @Override
     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
         //发生异常时,关闭 ChannelHandlerContext,释放ChannelHandlerContext 相关的句柄等资源
         logger.error(cause.getMessage(),cause);
         ctx.close();
     }
 }

TimerServerHandler

客户端

 package org.zln.netty.five.timer;

 import io.netty.bootstrap.Bootstrap;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelOption;
 import io.netty.channel.EventLoopGroup;
 import io.netty.channel.nio.NioEventLoopGroup;
 import io.netty.channel.socket.nio.NioSocketChannel;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 /**
  * 时间服务器客户端
  * Created by sherry on 16/11/5.
  */
 public class TimerClient {
     /**
      * 日志
      */
     private Logger logger = LoggerFactory.getLogger(TimerServer.class);

     private String HOST;
     private int PORT;

     public TimerClient(String HOST, int PORT) {
         this.HOST = HOST;
         this.PORT = PORT;
     }

     public void connect(){
         //配置客户端NIO线程组
         EventLoopGroup eventLoopGroup = new NioEventLoopGroup();
         try {
             Bootstrap bootstrap = new Bootstrap();
             bootstrap.group(eventLoopGroup)
                     .channel(NioSocketChannel.class)
                     .option(ChannelOption.TCP_NODELAY,true)
                     .handler(new TimerClientInitializer());
             //发起异步连接操作
             logger.debug("发起异步连接操作 - start");
             ChannelFuture channelFuture = bootstrap.connect(HOST,PORT).sync();
             logger.debug("发起异步连接操作 - end");
             //等待客户端链路关闭
             logger.debug("等待客户端链路关闭 - start");
             channelFuture.channel().closeFuture().sync();
             logger.debug("等待客户端链路关闭 - end");
         } catch (InterruptedException e) {
             logger.error(e.getMessage(),e);
         }finally {
             //优雅的关闭
             eventLoopGroup.shutdownGracefully();
         }
     }
 }

TimerClient

 package org.zln.netty.five.timer;

 import io.netty.channel.ChannelInitializer;
 import io.netty.channel.ChannelPipeline;
 import io.netty.channel.socket.SocketChannel;
 import io.netty.handler.codec.LineBasedFrameDecoder;
 import io.netty.handler.codec.string.StringDecoder;

 /**
  * Created by sherry on 16/11/5.
  */
 public class TimerClientInitializer extends ChannelInitializer<SocketChannel> {
     @Override
     protected void initChannel(SocketChannel socketChannel) throws Exception {
         ChannelPipeline pipeline = socketChannel.pipeline();
         pipeline.addLast(new LineBasedFrameDecoder(1024));
         pipeline.addLast(new StringDecoder());
         pipeline.addLast(new TimerClientHandler());
     }
 }

TimerClientInitializer

 package org.zln.netty.five.timer;

 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 import java.io.UnsupportedEncodingException;

 /**
  * Created by sherry on 16/11/5.
  */
 public class TimerClientHandler extends ChannelHandlerAdapter {

     /**
      * 日志
      */
     private Logger logger = LoggerFactory.getLogger(TimerClientHandler.class);

     private static int count = 0;

     @Override
     public void channelActive(ChannelHandlerContext ctx) throws Exception {
         logger.debug("客户端连接上了服务端");

         //发送请求
         ByteBuf reqBuf = null;
         for (int i = 0; i < 100; i++) {
             reqBuf = getReq("GET TIME"+System.lineSeparator());
             ctx.writeAndFlush(reqBuf);
         }

     }

     /**
      * 将字符串包装成ByteBuf
      * @param s
      * @return
      */
     private ByteBuf getReq(String s) throws UnsupportedEncodingException {
         byte[] data = s.getBytes("UTF-8");
         ByteBuf reqBuf = Unpooled.buffer(data.length);
         reqBuf.writeBytes(data);
         return reqBuf;
     }

     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
         String body = (String) msg;
         logger.debug("这是收到的第 "+(++count)+" 笔响应 -- "+body);
     }

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

TimerClientHandler

这里主要使用 LineBasedFrameDecoder 和 StringDecoder 来实现解决粘包问题

原理如下：

　　LineBasedFrameDecoder 依次遍历 ByteBuf 中的可读字节，判断是否有 \n 或 \r\n，如果有，就作为结束位置。从可读索引到结束位置区间的字节组成一行。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懈怠结束符两种解码方式。同时支持配置单行的最大长度。如果读取到了最大长度仍旧没有发现换行符，就会抛出异常，同时忽略掉之前读到的数据。

　　StringDecoder 的作用就是讲接收到的对象转化成字符串，然后继续调用handler。这样就不需要再handler中手动将对象转化成字符串了，直接强制转化就行。

　　LineBasedFrameDecoder+StringDecoder组合就是按行切割的文本解码器，用来解决TCP的粘包和拆包问题。