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Netty3:分隔符和定长解码器
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回顾TCP粘包/拆包问题解决方案
上文详细说了TCP粘包/拆包问题产生的原因及解决方式,并以LineBasedFrameDecoder为例演示了粘包/拆包问题的实际解决方案,本文再介绍两种粘包/拆包问题的解决方案:分隔符和定长解码器。在开始本文之前,先回顾一下解决粘包/拆包问题的几个方式:
- 消息长度固定,累计读取到长度总和为定长LEN的报文后,就认为读取到了一个完整的消息,将计数器重置,重新读取下一个消息
- 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
- 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结束分隔符
- 通过在消息头中定义长度字段来标志消息的总长度
Netty对上面4种方式做了统一的抽象,提供了4种解码器来解决对应的问题,使用起来非常方便,有了这些解码器,用户不需要自己对读取的报文进行人工解码,也不需要考虑TCP的粘包和拆包。
基于DelimiterBasedFrameDecoder的TCP粘包/拆包解决方案
使用DelimiterBasedFrameDecoder,我们可以自动完成以分隔符作为码流结束标志的消息的解码,下面通过例子来学习下DelimiterBasedFrameDecoder的使用。
首先写一个EchoServer,和TimeServer差不多,主要是加上了DelimiterBasedFrameDecoder,分隔符定为"¥_":
1 public class EchoServer { 2 3 public void bind(int port) throws Exception { 4// NIO线程组 5 EventLoopGroup bossGroup = new NioEventLoopGroup(); 6 EventLoopGroup workerGroup = new NioEventLoopGroup(); 7 8try { 9 ServerBootstrap b = new ServerBootstrap(); 10 b.group(bossGroup, workerGroup) 11 .channel(NioServerSocketChannel.class) 12 .option(ChannelOption.SO_BACKLOG, 1024) 13 .childHandler(new ChildChannelHandler()); 1415// 绑定端口,同步等待成功16 ChannelFuture f = b.bind(port).sync(); 17// 等待服务端监听端口关闭18 f.channel().closeFuture().sync(); 19 } finally { 20// 优雅退出,释放线程池资源21 bossGroup.shutdownGracefully(); 22 workerGroup.shutdownGracefully(); 23 } 24 } 2526privateclass ChildChannelHandler extends ChannelInitializer<SocketChannel> { 27 @Override 28protectedvoid initChannel(SocketChannel arg0) throws Exception { 29 ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes()); 3031 arg0.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter)); 32 arg0.pipeline().addLast(new StringDecoder()); 33 arg0.pipeline().addLast(new EchoServerHandler()); 34 } 35 } 3637 }
接着是EchoServerHandler,将接收到的消息打印出来,并记录收到的消息次数:
1 public class EchoServerHandler extends ChannelHandlerAdapter { 2 3privateint counter = 0; 4 5 @Override 6publicvoid channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { 7 String body = (String)msg; 8 System.out.println("This is " + ++counter + " times receive client:[" + body + "]"); 910 body += "$_"; 11 ByteBuf echo = Unpooled.copiedBuffer(body.getBytes()); 12 ctx.writeAndFlush(echo); 13 } 1415 @Override 16publicvoid exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { 17 cause.printStackTrace(); 18 ctx.close(); 19 } 2021 }
收到消息之后,将消息加上"$_"回给客户端。看下客户端EchoClient的写法,也是一样,加上DelimiterBasedFrameDecoder:
1 public class EchoClient { 2 3 public void connect(int port, String host) throws Exception { 4 EventLoopGroup group = new NioEventLoopGroup(); 5try { 6 Bootstrap b = new Bootstrap(); 7 8 b.group(group) 9 .channel(NioSocketChannel.class) 10 .option(ChannelOption.TCP_NODELAY, true) 11 .handler(new ChannelInitializer<SocketChannel>() { 12protectedvoid initChannel(SocketChannel ch) throws Exception { 13 ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes()); 1415 ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter)); 16 ch.pipeline().addLast(new StringDecoder()); 17 ch.pipeline().addLast(new EchoClientHandler()); 18 }; 19 }); 2021// 发起异步连接操作22 ChannelFuture f = b.connect(host, port).sync(); 23// 等待客户端连接关闭24 f.channel().closeFuture().sync(); 25 } finally { 26// 优雅退出,释放NIO线程组27 group.shutdownGracefully(); 28 } 29 } 3031 }
写一个EchoClientHandler,发送10条消息到Server并记录从Server回来的数据:
1 public class EchoClientHandler extends ChannelHandlerAdapter { 2 3privateint counter; 4 5privatestaticfinal String ECHO_REQ = "Hi, RickyXu, Welcome to Netty.$_"; 6 7public EchoClientHandler() { 8 9 } 1011 @Override 12publicvoid channelActive(ChannelHandlerContext ctx) throws Exception { 13for (int i = 0; i < 10; i++) { 14 ctx.writeAndFlush(Unpooled.copiedBuffer(ECHO_REQ.getBytes())); 15 } 16 } 1718 @Override 19publicvoid channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { 20 System.out.println("This is" + ++counter + " times receive server:[" + msg + "]"); 21 } 2223 @Override 24publicvoid channelReadComplete(ChannelHandlerContext ctx) throws Exception { 25 ctx.flush(); 26 } 2728 @Override 29publicvoid exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { 30 cause.printStackTrace(); 31 ctx.close(); 32 } 3334 }
先运行服务端代码再运行客户端代码,看下服务端收到的数据为:
This is 1 times receive client:[Hi, RickyXu, Welcome to Netty.] This is 2 times receive client:[Hi, RickyXu, Welcome to Netty.] This is 3 times receive client:[Hi, RickyXu, Welcome to Netty.] This is 4 times receive client:[Hi, RickyXu, Welcome to Netty.] This is 5 times receive client:[Hi, RickyXu, Welcome to Netty.] This is 6 times receive client:[Hi, RickyXu, Welcome to Netty.] This is 7 times receive client:[Hi, RickyXu, Welcome to Netty.] This is 8 times receive client:[Hi, RickyXu, Welcome to Netty.] This is 9 times receive client:[Hi, RickyXu, Welcome to Netty.] This is 10 times receive client:[Hi, RickyXu, Welcome to Netty.]
一模一样收到10条且末尾的分隔符被忽略,客户端收到的响应为:
This is 1 times receive server:[Hi, RickyXu, Welcome to Netty.] This is 2 times receive server:[Hi, RickyXu, Welcome to Netty.] This is 3 times receive server:[Hi, RickyXu, Welcome to Netty.] This is 4 times receive server:[Hi, RickyXu, Welcome to Netty.] This is 5 times receive server:[Hi, RickyXu, Welcome to Netty.] This is 6 times receive server:[Hi, RickyXu, Welcome to Netty.] This is 7 times receive server:[Hi, RickyXu, Welcome to Netty.] This is 8 times receive server:[Hi, RickyXu, Welcome to Netty.] This is 9 times receive server:[Hi, RickyXu, Welcome to Netty.] This is 10 times receive server:[Hi, RickyXu, Welcome to Netty.]
同样收到了10条数据且忽略了末尾的换行符。
这样我们就通过一个示例演示了使用DelimiterBasedFrameDecoder解决TCP粘包/拆包,下面看一下使用FixedLengthFrameDecoder解决TCP粘包/拆包的示例。
基于FixedLengthFrameDecoder的TCP粘包/拆包解决方案
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,
同样看一下例子,先写一个EchoServer,加入FixedLengthFrameDecoder:
public class EchoServer { public void bind(int port) throws Exception { // 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(); } finally { // 优雅退出,释放线程池资源 bossGroup.shutdownGracefully(); workerGroup.shutdownGracefully(); } } privateclass ChildChannelHandler extends ChannelInitializer<SocketChannel> { @Override protectedvoid initChannel(SocketChannel arg0) throws Exception { arg0.pipeline().addLast(new FixedLengthFrameDecoder(20)); arg0.pipeline().addLast(new StringDecoder()); arg0.pipeline().addLast(new EchoServerHandler()); } } }
接着下一下EchoServerHandler,EchoServerHandler比较简单:
public class EchoServerHandler extends ChannelHandlerAdapter { @Override publicvoid channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { System.out.println("Receive client:[" + msg + "]"); } @Override publicvoid exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { cause.printStackTrace(); ctx.close(); } }
这里只打印接收到的数据,因为我们使用telnet来模拟发送请求而不是写一个EchoClient。首先telnet一下localhost 8080:
接着使用"Ctrl+]":
输入回车,这样就变成了回显模式,即输入什么看到什么,简单说一下telnet原理:
- 建立与服务器的TCP连接
- 从键盘上接收输入的字符
- 把输入的字符变成标准格式并发送给服务器
- 从服务器接收输出的信息
- 输出的信息显示在屏幕/控制台上
注意一下第2点+第3点,这里是键盘上输入一个字符就会发送这个字符到服务端的,对这点有疑问的可以在FixedLengthFrameDecoder的decode方法上打断点,就可以看到每输入一个字符,断点就会进入一次。
接着我们"0123456789"这样一直循环输入,FixedLengthFrameDecoder设置的Length是20,按照上面的解释,这样的话应该输入两轮"0123456789"即第二个9输入之后,控制台上就会打印了:
看一下控制台:
Receive client:[01234567890123456789]
没毛病,证明了FixedLengthFrameDecoder确实是按照定长接收包的,如果收到的包是半包消息,FixedLengthFrameDecoder会缓存半包消息并等待下个包到达之后进行拼包,直到读取到一个完整的包。
原文:https://www.cnblogs.com/xrq730/p/8733888.html
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