Help Center/ IoT Device Access/ User Guide/ Message Communications/ Custom Topic Communications/ Custom Topics Starting with $oc
Updated on 2024-11-06 GMT+08:00
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Custom Topics Starting with $oc

Process

Figure 1 Communications with custom topics starting with $oc

  1. Product creation: Access the IoTDA service page and click Access Console. Click the target instance card. For details, see Creating a Product.
  2. Topic setting: On the product details page, create a custom topic prefixed with $oc/devices/{device_id}/user/.

    1. Select an MQTT product. On the product details page, click the Topic Management tab, select Custom Topic, and click Add Topic.
      Figure 2 Topic management - Custom topics
    2. In the displayed dialog box, select device operation permissions and enter the topic name.
      Figure 3 Topic management - Adding a custom topic
      Table 1 Parameters

      Parameter

      Description

      Name

      The topic prefix is fixed at $oc/devices/{device_id}/user/. Replace {device_id} with the actual device ID during publishing and subscription. A custom topic must be in a slash-separated format.

      Enter 1 to 64 characters. Use only digits, letters, underscores (_), and slashes (/). The slashes cannot be consecutive.

      NOTE:

      Custom topics do not support custom variables. For example, {type} in $oc/devices/{device_id}/user/setting/{type} is a variable and is not supported.

      Device Operation Permissions

      • Publish: Devices can report messages using this topic. A topic is carried in a device message during data transfer for better classification.

      • Subscribe: Applications can specify a topic to deliver messages to devices.

      • Publish and subscription: Devices can report and receive messages using this topic.

      Description

      Provide a description of the topic.
    3. Click OK. After the topic is added, you can modify or delete it in the custom topic list.

  3. Device creation: Create a device under the product. The created device inherits the custom topics set for the product. For details, see Registering an Individual Device.
  4. Device subscription/publishing: For details about how to publish and subscribe to messages through custom topics, see Using a Custom Topic for Communication.

Java SDK Usage on the Device Side

Devices can integrate the device SDKs provided by Huawei Cloud IoT to quickly connect to Huawei Cloud IoTDA and report messages. The following example uses the Java SDK to connect a device to IoTDA for publishing and subscribing to messages through the custom topic $oc/devices/ + device.getDeviceId() + /user/wpy.

  1. Configure the Maven dependency of the SDK on the device. 
    <dependency>
	<groupId>com.huaweicloud</groupId>
	<artifactId>iot-device-sdk-java</artifactId>
	<version>1.1.4</version>
</dependency>
  2. Configure the SDK and device connection parameters on the device. 
    // Load the CA certificate of the IoT platform. For details about how to obtain the certificate, visit https://support.huaweicloud.com/intl/en-us/devg-iothub/iot_02_1004.html.
URL resource = MessageSample.class.getClassLoader().getResource("ca.jks");
File file = new File(resource.getPath());

// The format is ssl://Domain name:Port number.
// To obtain the domain name, log in to the Huawei Cloud IoTDA console. In the navigation pane, choose Overview and click Access Details in the Instance Information area. Select the access domain name corresponding to port 8883.
String serverUrl = "ssl://localhost:8883";
// Device ID created on the IoT platform
String deviceId = "deviceId";
// Secret corresponding to the device ID
String deviceSecret = "secret";
// Initialize the device connection.
IoTDevice device = new IoTDevice(serverUrl, deviceId, deviceSecret, file);
if (device.init() != 0) {
    return;
}
  3. Report a device message. 
    device.getClient().publishRawMessage(new RawMessage( "$oc/devices/" + device.getDeviceId() + "/user/wpy", "hello", 1), new ActionListener() {
    @Override
    public void onSuccess(Object context) {
        System.out.println("reportDeviceMessage success: ");
    }
    @Override
    public void onFailure(Object context, Throwable var2) {
        System.out.println("reportDeviceMessage fail: " + var2);
    }
});
  4. Subscribe to the topic. 
    device.getClient().subscribeTopic(new RawMessage("$oc/devices/" + device.getDeviceId() + "/user/wpy", new ActionListener() {
    @Override
    public void onSuccess(Object context) {
        System.out.println("subscribeTopic success: ");
    }
    @Override
    public void onFailure(Object context, Throwable var2) {
        System.out.println("subscribeTopic fail: " + var2);
    }
}, 0);