基于head和body的自定义数据编解码器

收集医院设备信息时由于消息为较短的json字符串，所以我们使用netty的自定义协议进行简单的数据接收。

协议约定为：head（实际消息的字节长度）+body（实际需要解析的json数据）

解码器如下，分为两步骤，最后我们获取json字符串进行处理，如果想要使用byte[]直接解析，请忽略第二个解码处理器：

/**
 * Created by zzq on 2019/12/26.
 * <p>
 * ReplayingDecoder如果字节读取失败会抛出异常，则父类会自动捕获异常，重新调用decode直到能够重复调用
 */
public class CustomDataFrameDecoder extends ReplayingDecoder<Void> {
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        int bodyLength = in.readInt();//直接将头部数据获取，得知body的长度，此时ByteBuf中readIndex会向后移动
        byte bodyTmp[] = new byte[bodyLength];
        ByteBuf body = in.readBytes(bodyLength);
        body.readBytes(bodyTmp);//将body存入字节数组

        CustomDataFrame customDataFrame = new CustomDataFrame(bodyLength, bodyTmp);
        out.add(customDataFrame);
    }
}

/**
 * Created by zzq on 2019/12/26.
 */
public class CustomDataFrameToStrDecoder extends MessageToMessageDecoder<CustomDataFrame> {
    @Override
    protected void decode(ChannelHandlerContext ctx, CustomDataFrame msg, List out) throws Exception {
        if (msg != null) {
            String bodyStr = new String(msg.getBody(), Charset.forName("UTF-8"));
            out.add(bodyStr);
        }
    }
}

 服务端如下：

  EventLoopGroup parent = new NioEventLoopGroup(1);
        EventLoopGroup children = new NioEventLoopGroup();

        ServerBootstrap serverBootstrap = new ServerBootstrap();
        serverBootstrap.group(parent, children)
                .channel(NioServerSocketChannel.class)
                .handler(new LoggingHandler(LogLevel.DEBUG))
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        ChannelPipeline pipeline = ch.pipeline();
                        pipeline.addLast(new CustomDataFrameDecoder());
                        pipeline.addLast(new CustomDataFrameToStrDecoder());
                        pipeline.addLast(new SimpleChannelInboundHandler<String>() {
                            @Override
                            protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
                                System.out.println("收到客户端消息：" + msg);
                                String res = msg + "你好";
                                ctx.channel().writeAndFlush(res);
                            }

                            @Override
                            public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
                                super.exceptionCaught(ctx, cause);
                                ctx.close();
                            }

                            @Override
                            public void channelUnregistered(ChannelHandlerContext ctx) throws Exception {
                                String clientAddress = ctx.channel().remoteAddress().toString();
                                System.out.println("*通信管道注销成功 :" + clientAddress);
                            }

                            @Override
                            public void channelInactive(ChannelHandlerContext ctx) throws Exception {
                                String clientAddress = ctx.channel().remoteAddress().toString();
                                System.out.println("*通信管道关闭" + clientAddress);
                            }

                            @Override
                            public void handlerAdded(ChannelHandlerContext ctx) throws Exception {//客户端连接建立
                                System.out.println("客户端连接建立");
                            }

                            @Override
                            public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {//客户端失去连接
                                System.out.println("客户端失去连接");
                            }
                        });
                        pipeline.addLast(new CustomDataFrameEncoder());
                    }
                });
        ChannelFuture channelFuture = null;
        try {
            channelFuture = serverBootstrap.bind(9099).sync();
            channelFuture.channel().closeFuture().sync();

        } catch (InterruptedException e) {
            channelFuture.channel().close();
            parent.shutdownGracefully();
            children.shutdownGracefully();
        }

为了测试服务端，编写了客户端代码如下：

 EventLoopGroup eventLoopGroup = new NioEventLoopGroup(1);

        Bootstrap bootstrap = new Bootstrap();
        bootstrap.group(eventLoopGroup);
        bootstrap.channel(NioSocketChannel.class)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        ChannelPipeline pipeline = ch.pipeline();
                        pipeline.addLast(new CustomDataFrameDecoder());
                        pipeline.addLast(new CustomDataFrameToStrDecoder());
                        pipeline.addLast(new SimpleChannelInboundHandler<String>() {
                            @Override
                            protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
                                System.out.println("收到服务端返回的消息");
                                System.out.println(msg);
                            }

                            @Override
                            public void channelActive(final ChannelHandlerContext ctx) throws Exception {
                                super.channelActive(ctx);
                                new Thread(new Runnable() {
                                    @Override
                                    public void run() {
                                        for (; ; ) {
                                            try {
                                                Thread.sleep(2000);
                                            } catch (Exception e) {

                                            }

                                            String msg = "{a:b,i:p}" + UUID.randomUUID().toString();
                                            System.out.println("客户端发送消息：" + msg);
                                            ctx.channel().writeAndFlush(msg);
                                        }
                                    }
                                }).start();

                            }

                            @Override
                            public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
                                super.exceptionCaught(ctx, cause);
                                ctx.close();
                            }
                        });
                        pipeline.addLast(new CustomDataFrameEncoder());
                    }
                });
        try {
            bootstrap.connect("127.0.0.1", 9099).sync().channel().closeFuture().sync();
        } catch (Exception e) {
            eventLoopGroup.shutdownGracefully();
        }

数据接收和发送需要使用到解码器的同时，还需要使用编码器，编码器如下：

/**
 * Created by zzq on 2019/12/26.
 */
public class CustomDataFrameEncoder extends MessageToByteEncoder<String> {
    @Override
    protected void encode(ChannelHandlerContext ctx, String msg, ByteBuf out) throws Exception {
        byte body[] = msg.getBytes(Charset.forName("UTF-8"));
        int bodyLength = body.length;
        out.writeInt(bodyLength);//向输出参数中添加数据
        out.writeBytes(body);
    }
}

但实际我们的服务端是不需要像客户端响应数据的，我们直接在数据接收端使用自定义线程池异步处理数据即可。