netty权威指南学习笔记五——分隔符和定长解码器的应用

　　　　TCP以流的方式进行数据传输，上层应用协议为了对消息进行区分，通常采用以下4中方式：

1. 1. 消息长度固定，累计读取到长度综合为定长LEN的报文后，就认为读取到了一个完整的消息，将计数器置位，重新开始读取下一个数据报；
   2. 将回车换行符作为消息结束符，例如FTP协议，这种方式在文本协议中应用比较广泛；
   3. 将特殊的分隔符作为消息的结束标志，回车换行符就是一种特殊的分隔符；
   4. 通过在消息头中定义长度字段来标识消息的总长度。

　　DelimiterBaseFrameDecoder——分隔符解码器，FixedLengthFrameDecoder——定长解码器

下面我们采用#为分隔符进行代码练习运行。

EchoServer服务端代码

 package com.decoder;

 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.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 InterruptedException {
         NioEventLoopGroup bossGroup = new NioEventLoopGroup();
         NioEventLoopGroup workGroup = new NioEventLoopGroup();
         try {
             ServerBootstrap b = new ServerBootstrap();
             b.group(bossGroup,workGroup)
                     .channel(NioServerSocketChannel.class)
                     .option(ChannelOption.SO_BACKLOG,100)
                     .childHandler(new LoggingHandler(LogLevel.INFO))
                     .childHandler(new ChannelInitializer<SocketChannel>() {
                         @Override
                         protected void initChannel(SocketChannel socketChannel) throws Exception {
                             ByteBuf delimiter = Unpooled.copiedBuffer("#".getBytes());//创建一个分隔符，确定为结束标志
                             socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,delimiter))
                                     .addLast(new StringDecoder())
                                     .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();
             workGroup.shutdownGracefully();
         }
     }
     public static void main(String[] args) throws InterruptedException {
         int port = 8080;
         if(args.length>0&&args!=null){
             port = Integer.parseInt(args[0]);
         }
         new EchoServer().bind(port);

     }
 }

服务端处理IO代码

 package com.decoder;

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

 public class EchoServerHandler extends ChannelInboundHandlerAdapter {
     int count;
     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
         String body = (String) msg;
         System.out.println("This is"+ ++count +" times server receive client request.");
         body += "#";
         ByteBuf echo = Unpooled.copiedBuffer(body.getBytes());
         ctx.writeAndFlush(echo);
     }

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

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

客户端发送消息代码

 package com.decoder;

 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.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 connection(int port,String host) throws InterruptedException {
         NioEventLoopGroup workGroup = new NioEventLoopGroup();
         try {
             Bootstrap b = new Bootstrap();
             b.group(workGroup)
                     .channel(NioSocketChannel.class)
                     .option(ChannelOption.TCP_NODELAY,true)
                     .handler(new ChannelInitializer<SocketChannel>() {
                         @Override
                         protected void initChannel(SocketChannel socketChannel) throws Exception {
                             ByteBuf delimiter = Unpooled.copiedBuffer("#".getBytes());
                             socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,delimiter))
                                     .addLast(new StringDecoder())
                                     .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 {
             workGroup.shutdownGracefully();
         }
     }
     public static void main(String[] args) throws InterruptedException {
         int port = 8080;
         if(args.length>0&&args!=null){
             System.out.println(args[0]);
             port = Integer.parseInt(args[0]);
         }
         new EchoClient().connection(port,"127.0.0.1");
     }
 }

客户端处理IO代码

 package com.decoder;

 import io.netty.buffer.Unpooled;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelInboundHandlerAdapter;

 public class EchoClientHandler extends ChannelInboundHandlerAdapter {
     private int count;
     static final String ECHO_REQ = "hello,zuixiaoyao,welcome here!#";

     @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 {
         String body = (String) msg;
         System.out.println("this is client receive msg"+ ++count +"times:【"+body+"】");
     }

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

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

运行结果

服务端

客户端

若采用定长解码器，运行上面代码看看会发生什么，我们只需要对上面服务器中解码器换为定长解码器即可，解码器最大长度设置为20，看看

修改的服务端代码如下：

  @Override
                         protected void initChannel(SocketChannel socketChannel) throws Exception {
                             ByteBuf delimiter = Unpooled.copiedBuffer("#".getBytes());//创建一个分隔符，确定为结束标志
                             socketChannel.pipeline()
 //                                    .addLast(new DelimiterBasedFrameDecoder(1024,delimiter))
 //                                    修改为定长解码器
                                     .addLast(new FixedLengthFrameDecoder(20))
                                     .addLast(new StringDecoder())
                                     .addLast(new EchoServerHandler());
                         }

运行后如下：

服务端结果

客户端结果

我们发现所有运行返回的代码都不超过20字符。这就是按照定长解析的，但是解析的比较乱，具体的原理还需深入学习后才知道，暂时不表。

按书上的操作，输入一行超过20字符的命令请求时，只返回一个20字符定长的数据显示。