Communicate over MQTT topics

For the complete code, see MqttSample.java in the demo.

Publish messages

For more information, see MqttPublishRequest.

• Without an acknowledgement

  Use this method when a device sends a message and does not require an acknowledgement from IoT Platform, or when IoT Platform sends a reply that the device does not need to process.

  // Publish the message.
  MqttPublishRequest request = new MqttPublishRequest();
  // Specify whether to require an acknowledgement.
  request.isRPC = false;
  // Set the topic. The device uses this topic to send messages to IoT Platform. The following topic is an example. Replace it with your device's topic.
  request.topic = "/a18wP******/LightSwitch/user/update";
  // Set the QoS level.
  request.qos = 0;
  String data = "hello world"; // TODO: Set the data to publish.
  request.payloadObj = data;
  LinkKit.getInstance().publish(request, new IConnectSendListener() {
      @Override
      public void onResponse(ARequest aRequest, AResponse aResponse) {
          // The message is successfully submitted to the operating system's send buffer.
          // The message may fail to reach the cloud due to network fluctuations or other issues.
          // If the mobile originated message has a corresponding mobile terminated reply, use the reply message to confirm that the mobile originated message was received.
      }
      @Override
      public void onFailure(ARequest aRequest, AError aError) {
          // The message failed to be published.
      }
  });                       

  Parameter	Example	Description
  isRPC	false	Specifies whether the request is an RPC request. If it is, the system waits for a message from the replyTopic before sending a response. The default value is false, which means no acknowledgement is required.
  topic	/a18wP******/LightSwitch/user/update	A topic to which the device has publish permissions, used to send messages to IoT Platform.
  qos	0	The Quality of Service (QoS) level for the MQTT request. The default value is 0.
  payloadObj	{"id":"160865432","method":"thing.event.property.post","params":{"LightSwitch":1},"version":"1.0"}	The data to publish. The data can be in any format. If the format is a JSON string, the value of the id field must be unique for each message. Use auto-increment to set the ID. For example, if the id is 160865432, the next id must be 160865433.

• Return acknowledgement

  • Use this method when messages from a device are forwarded to your server, which then sends reply messages back to the device.

  • Also applies when you use an Alink protocol topic that requires a server-side reply.

  // Publish the message.
  MqttPublishRequest request = new MqttPublishRequest();
  // Specify whether to require an acknowledgement. Set to true to expect a mobile terminated reply from IoT Platform.
  request.isRPC = true;
  // Set the QoS level.
  request.qos = 0;
  // Set the topic. The device uses this topic to send messages to IoT Platform. The following topic is an example. Replace it with your device's topic.
  request.topic = "/a18wP******/LightSwitch/user/update";
  // Set the topic for replies from IoT Platform. If not set, the default is topic + "_reply".
  request.replyTopic = "/a18wP******/LightSwitch/user/update_reply";
  String data = "hello world"; // TODO: Set the data to send.
  request.payloadObj = data;
  LinkKit.getInstance().publish(request, new IConnectSendListener() {
      @Override
      public void onResponse(ARequest aRequest, AResponse aResponse) {
          // The message was published successfully.
      }
      @Override
      public void onFailure(ARequest aRequest, AError aError) {
          // The message failed to be published.
      }  
  });                    

  Parameter	Example	Description
  isRPC	true	Specifies whether the request is an RPC request. If it is, the system waits for a message from the replyTopic before sending a response. Set this to true to expect a mobile terminated reply from IoT Platform.
  qos	0	The Quality of Service (QoS) level for the MQTT request. The default value is 0.
  topic	/a18wP******/LightSwitch/user/update	A topic to which the device has publish permissions, used to send messages to IoT Platform.
  replyTopic	/a18wP******/LightSwitch/user/update_reply	The topic for replies from IoT Platform. If not set, the default is topic + "_reply".
  payloadObj	{"id":"160865432","method":"thing.event.property.post","params":{"LightSwitch":1},"version":"1.0"}	The data to publish. The data must be in a JSON string format. The value of the id field must be unique for each message. Use auto-increment to set the ID. For example, if the id is 160865432, the next id must be 160865433.

Subscribe to messages

Subscribe to a topic to receive its messages. IoT Platform saves the subscription and forwards messages published to that topic to the device. For more information, see MqttSubscribeRequest.

After you subscribe to a topic, mobile terminated messages are passed to the `IConnectNotifyListener` object. For more information, see Connection status and mobile terminated message listener in Authentication and connection.

Sample code:

// Subscribe to a topic.
MqttSubscribeRequest subscribeRequest = new MqttSubscribeRequest();
// Replace subTopic with the topic to which you want to subscribe.
subscribeRequest.topic = subTopic;
subscribeRequest.isSubscribe = true;
LinkKit.getInstance().subscribe(subscribeRequest, new IConnectSubscribeListener() {
    @Override
    public void onSuccess() {
        // The subscription is successful.
    }
    @Override
    public void onFailure(AError aError) {
        // The subscription failed.
    }
});                    

If a device no longer needs messages from a topic, unsubscribe from it. Otherwise, the subscription persists and the device continues to receive messages. For more information, see Unsubscribe from a topic below.

Unsubscribe

// Unsubscribe
MqttSubscribeRequest unsubRequest = new MqttSubscribeRequest();
// Replace unSubTopic with the topic from which you want to unsubscribe.
unsubRequest.topic = unSubTopic;
unsubRequest.isSubscribe = false;
LinkKit.getInstance().unsubscribe(unsubRequest, new IConnectUnscribeListener() {
    @Override
    public void onSuccess() {
        // The unsubscription is successful.
    }
    @Override
    public void onFailure(AError aError) {
        // The unsubscription failed.
    }
});