mqtt 服务端开发

MQTT是一种轻量级的消息传输协议，常用于物联网设备之间的通信。下面是使用Netty+SpringBoot方式开发MQTT服务端程序的步骤：

1.添加依赖

在pom.xml文件中添加以下依赖：

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.1.25.Final</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>org.eclipse.paho</groupId>
    <artifactId>org.eclipse.paho.client.mqttv3</artifactId>
    <version>1.2.5</version>
</dependency>

2.编写配置类

创建一个配置类，配置Netty的线程池和端口号等信息：

@Configuration
public class NettyConfig {

    @Value("${netty.port}")
    private int port;

    @Value("${netty.boss.thread.count}")
    private int bossCount;

    @Value("${netty.worker.thread.count}")
    private int workerCount;

    @Bean(name = "bossGroup", destroyMethod = "shutdownGracefully")
    public NioEventLoopGroup bossGroup() {
        return new NioEventLoopGroup(bossCount);
    }

    @Bean(name = "workerGroup", destroyMethod = "shutdownGracefully")
    public NioEventLoopGroup workerGroup() {
        return new NioEventLoopGroup(workerCount);
    }

    @Bean(name = "mqttServerBootstrap")
    public ServerBootstrap bootstrap() {
        ServerBootstrap bootstrap = new ServerBootstrap();
        bootstrap.group(bossGroup(), workerGroup())
                .channel(NioServerSocketChannel.class)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        ChannelPipeline pipeline = ch.pipeline();
                        pipeline.addLast("decoder", new MqttDecoder());
                        pipeline.addLast("encoder", MqttEncoder.INSTANCE);
                        pipeline.addLast("handler", new MqttServerHandler());
                    }
                });
        return bootstrap;
    }

    @Bean(name = "tcpSocketAddress")
    public InetSocketAddress tcpPort() {
        return new InetSocketAddress(port);
    }
}

3.编写服务端处理程序

创建一个MqttServerHandler类，继承SimpleChannelInboundHandler类，重写channelRead0方法，处理客户端发送的消息：

@Component
@ChannelHandler.Sharable
public class MqttServerHandler extends SimpleChannelInboundHandler<MqttMessage> {

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, MqttMessage msg) throws Exception {
        // 处理客户端发送的消息
        // ...
    }
}

4.启动服务端

创建一个MqttServer类，启动Netty服务端：

@Component
public class MqttServer {

    @Autowired
    private ServerBootstrap bootstrap;

    @Autowired
    private InetSocketAddress tcpSocketAddress;

    private ChannelFuture serverChannelFuture;

    @PostConstruct
    public void start() throws InterruptedException {
        serverChannelFuture = bootstrap.bind(tcpSocketAddress).sync();
        if (serverChannelFuture.isSuccess()) {
            System.out.println("MQTT server started on port " + tcpSocketAddress.getPort() + " and ready for connections...");
        }
    }

    @PreDestroy
    public void stop() throws InterruptedException {
        serverChannelFuture.channel().closeFuture().sync();
    }
}

5.配置端口号

在application.properties文件中配置Netty的端口号：

netty.port=1883

以上就是使用Netty+SpringBoot方式开发MQTT服务端程序的步骤。