在 MQTT java 中使用 qos = 0 发布消息时程序挂起

Question

我正在 thingstream 中处理 mqtt 客户端。当我尝试使用 qos = 0 将消息发布到主题时，消息已发送，但程序仅挂在那里。然后我尝试使用 qos = 1 发送消息。消息发送成功，程序也没有挂起。但是在发送另一条消息时，我收到中断异常。谁能帮我吗。

下面是我用来发布消息的sn-p。

MqttMessage message = new MqttMessage(command);
message.setPayload(command);
message.setQos(1);
mqttClient.publish(topic, message);
System.out.println("Message published");

使用的库 - o​​rg.eclipse.paho.client.mqttv3-1.2.0

mqtt客户端初始化代码

public void connect() {

    try {
        mqttClient = new MqttClient(serverUri, clientId);
        //mqttClient.setTimeToWait(10000);
    } catch (MqttException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }

    mqttClient.setCallback(new MqttCallbackExtended() {
        @Override
        public void messageArrived(String topic, MqttMessage mqttMessage) throws Exception {
            // TODO Auto-generated method stub
            System.out.println("messageArrived: " + topic.toString());
            System.out.println(mqttMessage.toString());
            System.out.println(mqttMessage.getPayload());
        }

        @Override
        public void deliveryComplete(IMqttDeliveryToken arg0) {
            // TODO Auto-generated method stub
            System.out.println("deliveryComplete: " + arg0.getMessageId());
        }

        @Override
        public void connectionLost(Throwable arg0) {
            // TODO Auto-generated method stub
            System.out.println("---Connection lost1");
            // Toast.makeText(App.getContext(), "Connection
            // lost",Toast.LENGTH_SHORT).show();

        }

        @Override
        public void connectComplete(boolean arg0, String arg1) {
            // TODO Auto-generated method stub
            System.out.println("connectComplete");
            try {
                mqttClient.subscribe("device/+/publish");
            } catch (MqttException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            try {
                commands.sendCommand(Commands.GET_STATUS, null, "device/identity:85111741-5789-3010-85c9-be4a7204e5d3");
            } catch (MqttException | InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }
    });

    MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
    mqttConnectOptions.setAutomaticReconnect(true);
    mqttConnectOptions.setCleanSession(true);
    mqttConnectOptions.setUserName(username);
    mqttConnectOptions.setPassword(password.toCharArray());
    mqttConnectOptions.setKeepAliveInterval(30);
    mqttConnectOptions.setConnectionTimeout(60);
    mqttConnectOptions.setMqttVersion(MqttConnectOptions.MQTT_VERSION_3_1_1);

    try {
        mqttClient.connect(mqttConnectOptions);
    } catch (MqttSecurityException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (MqttException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

Answer 1

不要在主线程中发送，而是使用另一个线程来发布消息。

Thread thread = new Thread() {
   public void run() {
       mqttClient.publish(topic, message);
   }  
};
thread.start(); 

Answer 2

问题实际上可能不是 qos 值，而是您的客户端与 MQTT 服务器的连接是否良好/稳定。如前所述herepublish

... 是一个阻塞方法，一旦发布完成就返回

发布可能未完成。检查您是否连接到您的 MQTT 服务器，以及您的 MQTT 客户端是否已成功连接到 MQTT 服务器。

您也可以在调用周围加上try... catch ... 语句来查看是否有异常被抛出：

try {
  mqttClient.publish(topic, message);
} catch(Exception e) {
  e.printStackTrace();
}