文章目錄

• • 一、DelimiterBasedFrameDecoder
  • • 服務端
    • • 1、EchoServer
      • 2、EchoServerChannelHandler
      • 3、EchoServerHandler
    • 客戶端
    • • 1、EchoClient
      • 2、EchoClientChannelHandler
      • 3、EchoClientHandler
  • 二、FixedLengthFrameDecoder

TCP以流的方式進行數據傳輸，上層應用協議為了對消息進行區分，一般采用如下4種方式：

1.消息長度固定，累計讀取到消息長度總和為定長Len的報文之后即認為是讀取到了一個完整的消息。計數器歸位，重新讀取。
2. 將回車換行符作為消息結束符。
3. 將特殊的分隔符作為消息分隔符，回車換行符是他的一種。
4. 通過在消息頭定義長度字段來標識消息總長度。

LineBasedframeDecoder屬于第二種，今天我們要說的DelimiterBasedFrameDecoder和FixedLengthFrameDecoder屬于第三種和第一種。DelimiterBasedFrameDecoder用來解決以特殊符號作為消息結束符的粘包問題，FixedLengthFrameDecoder用來解決定長消息的粘包問題。

一、DelimiterBasedFrameDecoder

服務端

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);} }

客戶端

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();/** 這個地方的 必須和服務端對應上。否則無法正常解碼和編碼*/ByteBuf delimiter = Unpooled.copiedBuffer("\t".getBytes());pipeline.addLast(new DelimiterBasedFrameDecoder(1024,delimiter));pipeline.addLast( new StringDecoder());pipeline.addLast( new StringEncoder());// 客戶端的邏輯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();} }

運行結果：

這里我們添加DelimiterBasedFrameDecoder解碼器并且手動指定消息分隔符為：”\t”。我們可以看一下DelimiterBasedFrameDecoder的構造方法：

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

maxFrameLength：解碼的幀的最大長度

stripDelimiter：解碼時是否去掉分隔符

failFast：為true，當frame長度超過maxFrameLength時立即報TooLongFrameException異常，為false，讀取完整個幀再報異常

delimiter：分隔符

二、FixedLengthFrameDecoder

FixedLengthFrameDecoder是固定長度解碼器，它能夠按照指定的長度對消息進行自動解碼。
用法如下：
pipeline.addLast(new FixedLengthFrameDecoder(23));//參數為一次接受的數據長度。

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