Netty 框架学习(二)：DelimiterBasedFrameDecoder和FixedLengthFrameDecoder

文章目录

一、DelimiterBasedFrameDecoder
- 服务端
- - 1、EchoServer
  - 2、EchoServerChannelHandler
  - 3、EchoServerHandler
- 客户端
- - 1、EchoClient
  - 2、EchoClientChannelHandler
  - 3、EchoClientHandler
二、FixedLengthFrameDecoder

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，一般采用如下4种方式：

1.消息长度固定，累计读取到消息长度总和为定长Len的报文之后即认为是读取到了一个完整的消息。计数器归位，重新读取。
2. 将回车换行符作为消息结束符。
3. 将特殊的分隔符作为消息分隔符，回车换行符是他的一种。
4. 通过在消息头定义长度字段来标识消息总长度。

LineBasedframeDecoder属于第二种，今天我们要说的DelimiterBasedFrameDecoder和FixedLengthFrameDecoder属于第三种和第一种。DelimiterBasedFrameDecoder用来解决以特殊符号作为消息结束符的粘包问题，FixedLengthFrameDecoder用来解决定长消息的粘包问题。

一、DelimiterBasedFrameDecoder

服务端

1、EchoServer

/*** @author shuliangzhao* @Title: EchoServer* @ProjectName design-parent* @Description: TODO* @date 2019/8/21 20:53*/
public class EchoServer {public void start(int port) {EventLoopGroup bossGroup = new NioEventLoopGroup();EventLoopGroup workGroup = new NioEventLoopGroup();ServerBootstrap serverBootstrap = new ServerBootstrap().group(bossGroup,workGroup).channel(NioServerSocketChannel.class).childHandler(new EchoServerChannelHandler());try {ChannelFuture future = serverBootstrap.bind(port).sync();future.channel().closeFuture().sync();} catch (Exception e) {e.printStackTrace();} finally {bossGroup.shutdownGracefully();workGroup.shutdownGracefully();}}public static void main(String[] args) {new EchoServer().start(8080);}
}

2、EchoServerChannelHandler

/*** @author shuliangzhao* @Title: EchoServerChannelHandler* @ProjectName design-parent* @Description: TODO* @date 2019/8/21 20:59*/
public class EchoServerChannelHandler extends ChannelInitializer<SocketChannel> {protected void initChannel(SocketChannel socketChannel) throws Exception {ChannelPipeline pipeline = socketChannel.pipeline();ByteBuf byteBuf = Unpooled.copiedBuffer("\t".getBytes());pipeline.addLast(new DelimiterBasedFrameDecoder(1024,byteBuf));pipeline.addLast(new StringDecoder());pipeline.addLast(new StringEncoder());pipeline.addLast(new EchoServerHandler());}
}

3、EchoServerHandler

public class EchoServerHandler extends ChannelInboundHandlerAdapter {private int counter;@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {String body = (String) msg;System.out.println("server reciver oder:" + body + ";this counter is:" + ++counter);}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {super.exceptionCaught(ctx, cause);}
}

客户端

1、EchoClient

public class EchoClient {public void start(String address,int port) {EventLoopGroup group = new NioEventLoopGroup();Bootstrap bootstrap = new Bootstrap();bootstrap.group(group).channel(NioSocketChannel.class).handler(new EchoClientChannelHandler());try {ChannelFuture future = bootstrap.connect(address,port).sync();future.channel().closeFuture().sync();} catch (Exception e) {e.printStackTrace();}finally {group.shutdownGracefully();}}public static void main(String[] args) {new EchoClient().start("127.0.0.1",8080);}
}

2、EchoClientChannelHandler

public class EchoClientChannelHandler extends ChannelInitializer<SocketChannel> {protected void initChannel(SocketChannel socketChannel) throws Exception {ChannelPipeline pipeline = socketChannel.pipeline();/** 这个地方的 必须和服务端对应上。否则无法正常解码和编码*/ByteBuf delimiter = Unpooled.copiedBuffer("\t".getBytes());pipeline.addLast(new DelimiterBasedFrameDecoder(1024,delimiter));pipeline.addLast( new StringDecoder());pipeline.addLast( new StringEncoder());// 客户端的逻辑pipeline.addLast( new EchoClientHandler());}
}

3、EchoClientHandler

public class EchoClientHandler extends ChannelInboundHandlerAdapter {private byte[] req;private int counter;public EchoClientHandler() {req = ("There are moments in life when you miss\t" +"someone so much that you just want to pick\t"    +"them from your dreams and hug them for real!\t"    +"Dream what you want to dream;go where you want\t"    +"to go be what you want to be,because you have only\t"   +"one life and one chance to do all the things you want to do\t").getBytes();}@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {ByteBuf message = Unpooled.buffer(req.length);message.writeBytes(req);ctx.writeAndFlush(message);}@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {String body = (String) msg;System.out.println("client reciver is :" + body + "this is counter:" + ++counter);}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {ctx.close();}
}

运行结果：

这里我们添加DelimiterBasedFrameDecoder解码器并且手动指定消息分隔符为：”\t”。我们可以看一下DelimiterBasedFrameDecoder的构造方法：

public DelimiterBasedFrameDecoder(int maxFrameLength, boolean stripDelimiter, ByteBuf delimiter) {this(maxFrameLength, stripDelimiter, true, delimiter);
}

maxFrameLength：解码的帧的最大长度

stripDelimiter：解码时是否去掉分隔符

failFast：为true，当frame长度超过maxFrameLength时立即报TooLongFrameException异常，为false，读取完整个帧再报异常

delimiter：分隔符

二、FixedLengthFrameDecoder

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。
用法如下：
pipeline.addLast(new FixedLengthFrameDecoder(23));//参数为一次接受的数据长度。