Help Center/ IoT Device Access/ Getting Started/ Quick Device Access/ Sample Code for Bidirectional Communications/ Quick Experience Based on Java Sample Code
Updated on 2024-03-28 GMT+08:00
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Quick Experience Based on Java Sample Code

Overview

This section describes how to connect a device to Huawei Cloud IoTDA through MQTTS/MQTT using Java code, implement southbound data reporting and command delivery using platform APIs, and receive messages subscribed by the northbound server using the application-side sample code. Taking a smart street light as an example, the device reports information such as luminance to IoTDA, and an application receives device data pushed by IoTDA.

Prerequisites

  • You have installed JDK 1.8 or later.
  • You have installed IntelliJ IDEA. If you have not installed IntelliJ IDEA, visit the IntelliJ IDEA official website to download and install it.

Uploading a Product Model

A product model is a JSON file that describes device capabilities. It defines basic device properties and message formats for data reporting and command delivery. Defining a product model is to construct an abstract model of a device in the platform to enable the platform to understand the device function.

Procedure

  1. Access the IoTDA service page and click Console.
  2. Choose Products in the navigation pane and click Create Product on the left.

    Figure 1 Creating a product

  3. In the displayed dialog box, set parameters based on your requirements.

    Figure 2 Creating an MQTT product

  4. Download the model file. For details about the development process, see Developing a Product Model Online.
  5. After the product is created, click the product, and then click Import from Local to upload the downloaded model file. The model file does not need to be decompressed, and the package name cannot contain brackets.

    Figure 3 Uploading an MQTT product model

Creating a Device

  1. In the navigation pane, choose Devices > All Devices, and click Individual Register.

  2. In the displayed dialog box, configure the parameters by referring to the following figure (select the created product), and click OK. If you do not specify Secret, a secret will be automatically generated by the platform. In this example, the secret is automatically generated.

  3. After the device is created, save the device ID and secret, which will be used for device connection.

Importing Sample Code

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

  3. Select the Java demo downloaded in 1 and click Next.

  4. Import the sample code.

Establishing a Connection

To connect a device or gateway to the platform, upload the device information to bind the device or gateway to the platform.
  1. Before establishing a connection, modify the following parameters: 
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    // MQTT connection address of IoTDA
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 = "yourDeviceID"; // device_id obtained during device registration
static String secret = "yourSecret";     // secret obtained during device registration
    • serverIp indicates the address used by devices to access IoTDA using MQTT. For details about how to obtain the address, see Obtaining Resources.
    • device_id and secret indicate the device ID and secret, which can be obtained after the device is registered.
  2. After the preceding information is modified, run the program. The device is displayed as online on the platform.

Reporting Properties

A device reports its properties to IoTDA. (The sample code implements scheduled reporting. You can view the data reported by the device in IoTDA by referring to Viewing Reported Data.)

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// Report JSON data. service_id must be the same as that defined in the product model.
String jsonMsg = "{\"services\":[{\"service_id\":\"BasicData\",\"properties\":{\"luminance\":32},\"eventTime\":null}]}";
  • The message body jsonMsg is assembled in JSON format, and service_id must be the same as that defined in the product model. properties indicates a device property.
  • luminance indicates the street light brightness.
  • eventTime indicates the UTC time when the device reports data. If this parameter is not specified, the system time is used by default.

After a device or gateway is connected to the platform, you can call publish(String topic,MqttMessage message) of MqttAsyncClient to report device properties to the platform.

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, see Device Reporting Properties.

If no latest reported data is displayed on the device details page, modify the services and properties in the product model to ensure that the services and properties reported by the device are consistent with those in the product model. If they are inconsistent, the data reported by the device is not available on the historical data page. Alternatively, delete all services on the Model Definition page.

Delivering a Command

  1. In the navigation pane, choose API Explorer.

  2. Locate the row that contains the device command. For details about the delivered parameters, see the figure (consistent with those in the product model). Then, click Debug to send the command.

    • service_id indicates the service ID, for example, BasicData.
    • command_name indicates the command name, for example, lightControl.
    • paras indicates a delivered parameter, for example, {"switch":"ON"}.

    You can view the received commands on the device. (The sample code has implemented the subscription to the command receiving topic.)

Obtaining Data Reported by a Device from the Cloud

The following uses AMQP as an example to describe how to obtain data reported by a device to the cloud.

  1. Obtain the Java AMQP access demo.
  2. Log in to the console, choose Rules > Data Forwarding, and click Create Rule to create a data forwarding rule.

    Figure 4 Creating a data forwarding rule

  3. On the Set Forwarding Data page, configure parameters, and click Create Rule.

    Parameter

    Description

    Rule Name

    Customize a rule name.

    Description

    Describe the rule.

    Data Source

    Select Device property.

    Trigger

    Select Device property reported.

    Resource Space

    Select All resource spaces.

  4. Set the forwarding target. Note that you need to click Preset Access Credential to download the file.

    Parameter

    Description

    Forwarding Target

    Select AMQP message queue.

    Access Credential

    Click Preset Access Credential and save the downloaded file, which includes access_key and access_code.

    Message Queue

    DefaultQueue is selected by default.

  5. Click Enable Rule.

  6. Modify the parameters in the AMQP sample code obtained in 1.

    • yourAccessKey: access key of the access credential. For details about how to obtain it, see 4.
    • yourAccessCode: access code of the access credential. For details about how to obtain it, see 4.
    • yourAMQPUrl: AMQP domain name. You can log in to the console, choose Overview, and click Access Addresses to obtain the domain name, as shown in the following figure.

    • yourQueue: queue name. Use the default queue DefaultQueue.

  7. AMQP data is received successfully.

Additional Information

For more development guides, see Using IoT Device SDKs for Access and Using MQTT Demos for Access.