Netty固定长度解码器

绝地灬酷狼 2022-05-13 10:04 225阅读 0赞

FixedLengthFrameDecoder是固定长度解码器，它根据指定的长度自动对消息进行解码，开发者不需要考虑TCP拆包/粘包问题。  
下面通过一个例子进行说明。

服务端：  
在服务端的ChannelPipleline中增加FixedLengthFrameDecoder，长度设置为20，然后依次增加字符串解码器和自定义的EchoServerHandler。

/** * 使用FixedLengthFrameDecoder解码器解决TCP粘包/拆包问题。 * * @author j.tommy * @version 1.0 * @date 2017/11/18 */
    public class EchoServer { 
        public static void main(String[] args) {
            EventLoopGroup bossGroup = new NioEventLoopGroup();
            EventLoopGroup workerGroup = new NioEventLoopGroup();
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            socketChannel.pipeline().addLast(new FixedLengthFrameDecoder(20)); // 固定长度解码器，长度设置为20
                            socketChannel.pipeline().addLast(new StringDecoder());
                            socketChannel.pipeline().addLast(new EchoServerHandler());
                        }
                    });
            try {
                ChannelFuture f = b.bind(8899).sync();
                f.channel().closeFuture().sync();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                bossGroup.shutdownGracefully();
                workerGroup.shutdownGracefully();
            }
        }
    }
    class EchoServerHandler extends ChannelHandlerAdapter {
        private int counter;
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            ctx.close();
        }
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            String body = (String) msg;
            System.out.println("接收到客户端请求：" + body + ",counter=" + ++counter);
            // 响应客户端
            ByteBuf resp = Unpooled.copiedBuffer(body.getBytes());
            ctx.write(resp);
        }
        @Override
        public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
            ctx.flush();
        }
    }

客户端：  
在客户端的ChannelPipleline中增加FixedLengthFrameDecoder，长度设置为20，然后依次增加字符串解码器和自定义的EchoClientHandler。

/** * @author j.tommy * @version 1.0 * @date 2017/11/18 */
    public class EchoClient { 
        public static void main(String[] args) {
            EventLoopGroup group = new NioEventLoopGroup();
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY,true).handler(new ChannelInitializer<SocketChannel>() {
                protected void initChannel(SocketChannel socketChannel) throws Exception {
                    socketChannel.pipeline().addLast(new FixedLengthFrameDecoder(20));
                    socketChannel.pipeline().addLast(new StringDecoder());
                    socketChannel.pipeline().addLast(new EchoClientHandler());
                }
            });
            try {
                ChannelFuture f = b.connect("127.0.0.1",8899).sync();
                f.channel().closeFuture().sync();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            finally {
                group.shutdownGracefully();
            }
        }
    }
    class EchoClientHandler extends ChannelHandlerAdapter {
        private int counter = 0;
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            ctx.close();
        }
        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            String req = "hello,this message is from client.";
            ByteBuf sendBuf = null;
            for (int i=0;i<100;i++) {
                sendBuf = Unpooled.copiedBuffer(req.getBytes());
                ctx.writeAndFlush(sendBuf);
            }
        }
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            String resp = (String) msg;
            System.out.println("接收到服务端响应："  + resp + ",counter=" + ++counter);
        }
    }

示例中，客户端发送的消息是hello,this message is from client.  
因为按照固定长度截取，所以服务端接收到的是这样的：  
![41553604.jpg][]

参考《Netty权威指南》

[41553604.jpg]: http://omh46px9n.bkt.clouddn.com/17-11-18/41553604.jpg