Introduction

This section uses Java as an example to describe how to connect devices to the platform over MQTTS/MQTT and how to report data and deliver commands using platform APIs. For details about device access in other languages, see Obtaining Resources.

Prerequisites

• You have installed IntelliJ IDEA by following the instructions provided in Installing IntelliJ IDEA.
• You have obtained the device access address from the IoTDA console. For details, see Platform Connection Information.
• You have created a product and device on the IoTDA console. For details, see Creating a Product, Registering an Individual Device, or Registering a Batch of Devices.

Preparations

Installing IntelliJ IDEA

1. Go to the IntelliJ IDEA website to download and install a desired version. The following uses 64-bit IntelliJ IDEA 2019.2.3 Ultimate as an example.

   

2. After the download is complete, run the installation file and install IntelliJ IDEA as prompted.

Importing Sample Code

1. Download the Java demo.
2. Open the IDEA developer tool and click Import Project.

   

3. Select the downloaded Java demo and click Next.

   

4. Import the sample code.

   

Establishing a Connection

Before you connect a device or gateway to the platform, establish a connection between the device or gateway and the platform by providing the device or gateway information.

1. Before establishing a connection, modify the following parameters:

   1 2 3 4 5

   // MQTT interconnection address of the platform static String serverIp = "iot-mqtts.cn-north-4.myhuaweicloud.com"; // Device ID and secret obtained during device registration (Replace them with the actual values.) static String deviceId = "722cb****************"; static String secret = "123456789";

   • serverIp indicates the device interconnection address of the platform. To obtain this address, see Platform Interconnection Information. (After obtaining the domain name, run the ping Domain name command in the CLI to obtain the corresponding IP address.)
   • deviceId and secret indicate the device ID and secret, which can be obtained after the device is registered.
2. Use MqttClient to set up a connection. The recommended heartbeat interval for MQTT connections is 120 seconds. For details, see Constraints.

   1 2 3 4 5 6 7 8 9

   MqttConnectOptions options = new MqttConnectOptions(); options.setCleanSession(false); options.setKeepAliveInterval(120); // Set the heartbeat interval from 30 to 1200 seconds. options.setConnectionTimeout(5000); options.setAutomaticReconnect(true); options.setUserName(deviceId); options.setPassword(getPassword().toCharArray()); client = new MqttAsyncClient(url, getClientId()); client.setCallback(callback);

   Port 1883 is a non-encrypted MQTT access port, and port 8883 is an encrypted MQTTS access port (that uses SSL to load a certificate).

   1 2 3 4 5

   if (isSSL) { url = "ssl://" + serverIp + ":" + 8883; // MQTTS connection } else { url = "tcp://" + serverIp + ":" + 1883; // MQTT connection }

   To establish an MQTTS connection, load the SSL certificate of the server and add the SocketFactory parameter. The DigiCertGlobalRootCA.jks file stored in the resources directory of the demo is a certificate for verifying the platform identity. It is used for login authentication when the device connects to the platform. You can download the certificate file using the link provided in Certificates.

   1	options.setSocketFactory(getOptionSocketFactory(MqttDemo.class.getClassLoader().getResource("DigiCertGlobalRootCA.jks").getPath()));

3. Call client.connect(options, null, new IMqttActionListener()) to initiate a connection. The MqttConnectOptions object is passed.

   1	client.connect(options, null, new IMqttActionListener()

4. The password passed by calling options.setPassword() is encrypted during creation of the MqttConnectOptions object. getPassword() is used to obtain the encrypted password.

   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

   public static String getPassword() { return sha256_mac(secret, getTimeStamp()); } /* Call the SHA256 algorithm for hash calculation. */ public static String sha256_mac(String message, String tStamp) { String passWord = null; try { Mac sha256_HMAC = Mac.getInstance("HmacSHA256"); SecretKeySpec secret_key = new SecretKeySpec(tStamp.getBytes(), "HmacSHA256"); sha256_HMAC.init(secret_key);byte[] bytes = sha256_HMAC.doFinal(message.getBytes()); passWord = byteArrayToHexString(bytes); }catch (Exception e) { LOGGER.info("Error HmacSHA256 ===========" + e.getMessage()); } return passWord;

5. After the connection is established, the device becomes online.

   

   If the connection fails, the onFailure function executes backoff reconnection. The example code is as follows:

   @Override
   public void onFailure(IMqttToken iMqttToken, Throwable throwable) {
       System.out.println("Mqtt connect fail.");
   
       // Backoff reconnection
       int lowBound = (int) (defaultBackoff * 0.8);
       int highBound = (int) (defaultBackoff * 1.2);
       long randomBackOff = random.nextInt(highBound - lowBound);
       long backOffWithJitter = (int) (Math.pow(2.0, (double) retryTimes)) * (randomBackOff + lowBound);
       long waitTImeUntilNextRetry = (int) (minBackoff + backOffWithJitter) > maxBackoff ? maxBackoff : (minBackoff + backOffWithJitter);
       System.out.println("----  " + waitTImeUntilNextRetry);
       try {
           Thread.sleep(waitTImeUntilNextRetry);
           } catch (InterruptedException e) {
               System.out.println("sleep failed, the reason is" + e.getMessage().toString());
           }
           retryTimes++;
           MqttDemo.this.connect(true);
   }

Subscribing to a Topic for Receiving Commands

Only devices that subscribe to a specific topic can receive messages about the topic released by the MQTT broker. Learn about preset topics of the platform in Topic Definition. For details about the API information, see Delivering a Command.

1
2

// Subscribe to a topic for receiving commands.
client.subscribe(getCmdRequestTopic(), qosLevel, null, new IMqttActionListener();

1
2
3

public static String getCmdRequestTopic() {
    return "$oc/devices/" + deviceId + "/sys/commands/#";
}

Reporting Properties

Devices can report their properties to the platform. For details, see Reporting Device Properties.

1
2
3
4

// ReportJSON data. service_id must be the same as that defined in the product model.
String jsonMsg = "{\"services\": [{\"service_id\": \"Temperature\",\"properties\": {\"value\": 57}},{\"service_id\": \"Battery\",\"properties\": {\"level\": 80}}]}";
MqttMessage message = new MqttMessage(jsonMsg.getBytes());
client.publish(getRreportTopic(), message, qosLevel, new IMqttActionListener();

Viewing Reported Data

After the main method is called, you can view the reported device property data on the device details page. For details about the API information, see Reporting Device Properties.

If no latest data is displayed on the device details page, modify the services and properties in the product model to ensure that the reported services and properties are the same as those defined in the product model. Alternatively, go to the Products > Model Definition page and delete all services.

Related Resources

You can refer to the MQTT API Reference to connect MQTT devices to the platform. You can also use MQTT.fx to experience device access and verify whether devices can interact with the platform and publish or subscribe to messages.