Netty权威指南 第2版学习笔记5——分隔符和定长解码器的应用

DelimiterBasedFrameDecoder

以分隔符作为码流结束标识的消息的解码
示例：Echo服务，以$_作为分隔符

EchoServer.java关键代码

@Overridepublic void initChannel(SocketChannel ch) throws Exception{    //创建分隔符缓冲对象ByteBuf，以$_为分隔符   ByteBuf delimiter=Unpooled.copiedBuffer("$_".getBytes());   //1024表示单条消息的最大长度，当达到该长度后仍然没有查找到分隔符   //就抛出TooLongFrameException异常   //第二个参数是分隔符缓冲对象   new DelimiterBasedFrameDecoder(1024,delimiter));  //后续的ChannelHandler接收到的msg对象将会是完整的消息包   ch.pipeline().addLast(new StringDecoder()); //将ByteBuf解码成字符串对象    ch.pipeline().addLast(new EchoServerHandler());  //接收到的msg消息就是解码后的字符串对象}

EchoServerHandler.java 关键代码

@Overridepublic void channelRead(ChannelHandlerContext ctx,Object msg) throws Exception{   String body=(String)msg;   System.out.println("This is " + ++counter + " times receive client : [" + body + "]");   body+="$_"; //$_已被过滤掉了，所以这里要拼接上   ByteBuf echo = Unpooled.copiedBuffer(body.getBytes());   ctx.writeAndFlush(echo);}

EchoClient.java 关键代码

@Override public void initChannel(SocketChannel ch) throws Exception{   ByteBuf delimiter=Unpooled.copiedBuffer("$_".getBytes());   ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,delimiter));   ch.pipeline().addLast(new StringDecoder());   ch.pipeline().addLast(new EchoClientHandler());}

EchoClientHandler.java 关键代码

@Overridepublic void channelActive(ChannelHandlerContext ctx){   for(int i=0;i<10;i++){      ctx.writeAndFlush(Unpooled.copiedBuffer(ECHOREQ.getBytes()));   }}

FixedLengthFrameDecoder应用开发

固定长度解码器，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

示例仍是Echo服务

EchoServer.java 关键代码

@Overridepublic void initChannel (SocketChannel ch) throws Exception{   ch.pipeline().addLast(new FixedLengthFrameDecoder(20));   ch.pipeline().addLast(new StringDecoder());   ch.pipeline().addLast(new EchoServerHandler()));}

EchoServerHandler.java 关键代码

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