Agfdhyk

Device side mqtt publishes data to mosquitto broker installed on Raspberry Pi to a topic.
how to subscribe the data from the mosquitto broker in 2 ways.

Normal google example search gives me code samples. But what i want is 2 ways i thought one is MQTT API to subscribe providing topic which listens every time checking whether data has arrived or not which reduces the CPU performance and speed.

So, Other is if a message has arrived in the topic then it should call back saying message arrived instead of me going and looking into topic everytime checking is cumbersome. The second way increases CPU performance.

MemoryPersistence memoryPersistence = new MemoryPersistence();



    MqttConnectOptions conOpt = new MqttConnectOptions();

    conOpt.setUserName("mqttuser");

    conOpt.setPassword(new String("mqttpassword").toCharArray());

    conOpt.setCleanSession(true);



    try {



        MqttAsyncClient mqttAsyncClient = new MqttAsyncClient("tcp://localhost:1883", "1883", memoryPersistence);

        mqttAsyncClient.setCallback(new MqttConnectionCallback());



        if (!mqttAsyncClient.isConnected()) {

            IMqttToken token = mqttAsyncClient.connect(conOpt);

            logger.info();

            System.out.println("Connected");

        }



    } catch (MqttException e) {

        e.printStackTrace();

        System.out.println("Unable to set up client: "+e.toString());

        System.exit(1);

    }

this is my listener class overridden method

@Override

public void messageArrived(String topic, MqttMessage msgData) throws Exception {



    String time = new Timestamp(System.currentTimeMillis()).toString();

    System.out.println("Time:t" +time +

                           "  Topic:t" + topic +

                           "  Message:t" + new String(msgData.getPayload()) +

                           "  QoS:t" + msgData.getQos());

}

Need some clearance from coding side how this is accompolished in asynchronous ways.
Please correct if my understanding is wrong, specifically on how listener listenes on topicname and how the binding is done.

You need to use the subscribe() method on the mqttAsyncClient object (after connection has completed)

You can call this multiple times to subscribe to multiple topics.

Messages will be delivered to the messageArrived() callback and you can use the topic argument to determine which subscription the message arrived from.