Quickstart: Control a device connected to an IoT hub (Java)

IoT Hub is an Azure service that enables you to ingest high volumes of telemetry from your IoT devices into the cloud and manage your devices from the cloud. In this quickstart, you use a direct method to control a simulated device connected to your IoT hub. You can use direct methods to remotely change the behavior of a device connected to your IoT hub.

The quickstart uses two pre-written Java applications:

  • A simulated device application that responds to direct methods called from a back-end application. To receive the direct method calls, this application connects to a device-specific endpoint on your IoT hub.
  • A back-end application that calls the direct methods on the simulated device. To call a direct method on a device, this application connects to service-side endpoint on your IoT hub.

Open Azure Cloud Shell

Azure Cloud Shell is a free, interactive shell that you can use to run the steps in this article. Common Azure tools are preinstalled and configured in Cloud Shell for you to use with your account. Just select the Copy button to copy the code, paste it in Cloud Shell, and then press Enter to run it. There are a few ways to open Cloud Shell:

Select Try It in the upper-right corner of a code block. Cloud Shell in this article
Open Cloud Shell in your browser. https://shell.azure.com/bash
Select the Cloud Shell button on the menu in the upper-right corner of the Azure portal. Cloud Shell in the portal

If you don’t have an Azure subscription, create a free account before you begin.

Prerequisites

The two sample applications you run in this quickstart are written using Java. You need Java SE 8 or later on your development machine.

You can download Java for multiple platforms from Oracle.

You can verify the current version of Java on your development machine using the following command:

java --version

To build the samples, you need to install Maven 3. You can download Maven for multiple platforms from Apache Maven.

You can verify the current version of Maven on your development machine using the following command:

mvn --version

If you haven't already done so, download the sample Java project from https://github.com/Azure-Samples/azure-iot-samples-java/archive/master.zip and extract the ZIP archive.

Create an IoT hub

If you completed the previous Quickstart: Send telemetry from a device to an IoT hub, you can skip this step.

The first step is to use the Azure portal to create an IoT hub in your subscription. The IoT hub enables you to ingest high volumes of telemetry into the cloud from many devices. The hub then enables one or more back-end services running in the cloud to read and process that telemetry.

  1. Sign in to the Azure portal.

  2. Select Create a resource > Internet of Things > IoT Hub.

    Select to install IoT Hub

  3. In the IoT hub pane, enter the following information for your IoT hub:

    • Subscription: Choose the subscription that you want to use to create this IoT hub.
    • Resource group: Create a resource group to contain the IoT hub or use an existing one. By putting all related resources in a group together, such as TestResources, you can manage them all together. For example, deleting the resource group deletes all resources contained in that group. For more information, see Use resource groups to manage your Azure resources.
    • Region: Select the closest location to your devices.
    • Name: Create a unique name for your IoT hub. If the name you enter is available, a green check mark appears.

    Important

    The IoT hub will be publicly discoverable as a DNS endpoint, so make sure to avoid any sensitive information while naming it.

    IoT Hub basics window

  4. Select Next: Size and scale to continue creating your IoT hub.

  5. Choose your Pricing and scale tier. For this article, select the F1 - Free tier if it's still available on your subscription. For more information, see the Pricing and scale tier.

    IoT Hub size and scale window

  6. Select Review + create.

  7. Review your IoT hub information, then click Create. Your IoT hub might take a few minutes to create. You can monitor the progress in the Notifications pane.

Register a device

If you completed the previous Quickstart: Send telemetry from a device to an IoT hub, you can skip this step.

A device must be registered with your IoT hub before it can connect. In this quickstart, you use the Azure CLI to register a simulated device.

  1. Add the IoT Hub CLI extension and create the device identity. Replace {YourIoTHubName} with the name you chose for your IoT hub:

    az extension add --name azure-cli-iot-ext
    az iot hub device-identity create --hub-name {YourIoTHubName} --device-id MyJavaDevice
    

    If you choose a different name for your device, update the device name in the sample applications before you run them.

  2. Run the following command to get the device connection string for the device you just registered:

    az iot hub device-identity show-connection-string --hub-name {YourIoTHubName} --device-id MyJavaDevice --output table
    

    Make a note of the device connection string, which looks like Hostname=...=. You use this value later in the quickstart.

Retrieve the service connection string

You also need your IoT hub service connection string to enable the back-end application to connect to the hub and retrieve the messages. The following command retrieves the service connection string for your IoT hub:

az iot hub show-connection-string --hub-name {YourIoTHubName} --output table

Make a note of the service connection string, which looks like Hostname=...=. You use this value later in the quickstart.

Listen for direct method calls

The simulated device application connects to a device-specific endpoint on your IoT hub, sends simulated telemetry, and listens for direct method calls from your hub. In this quickstart, the direct method call from the hub tells the device to change the interval at which it sends telemetry. The simulated device sends an acknowledgement back to your hub after it executes the direct method.

  1. In a terminal window, navigate to the root folder of the sample Java project. Then navigate to the iot-hub\Quickstarts\simulated-device-2 folder.

  2. Open the src/main/java/com/microsoft/docs/iothub/samples/SimulatedDevice.java file in a text editor of your choice.

    Replace the value of the connString variable with the device connection string you made a note of previously. Then save your changes to SimulatedDevice.java file.

  3. In the terminal window, run the following commands to install the required libraries and build the simulated device application:

    mvn clean package
    
  4. In the terminal window, run the following commands to run the simulated device application:

    java -jar target/simulated-device-2-1.0.0-with-deps.jar
    

    The following screenshot shows the output as the simulated device application sends telemetry to your IoT hub:

    Run the simulated device

Call the direct method

The back-end application connects to a service-side endpoint on your IoT Hub. The application makes direct method calls to a device through your IoT hub and listens for acknowledgements. An IoT Hub back-end application typically runs in the cloud.

  1. In another terminal window, navigate to the root folder of the sample Java project. Then navigate to the iot-hub\Quickstarts\back-end-application folder.

  2. Open the src/main/java/com/microsoft/docs/iothub/samples/BackEndApplication.java file in a text editor of your choice.

    Replace the value of the iotHubConnectionString variable with the service connection string you made a note of previously. Then save your changes to the BackEndApplication.java file.

  3. In the terminal window, run the following commands to install the required libraries and build the back-end application:

    mvn clean package
    
  4. In the terminal window, run the following commands to run the back-end application:

    java -jar target/back-end-application-1.0.0-with-deps.jar
    

    The following screenshot shows the output as the application makes a direct method call to the device and receives an acknowledgement:

    Run the back-end application

    After you run the back-end application, you see a message in the console window running the simulated device, and the rate at which it sends messages changes:

    Change in simulated client

Clean up resources

If you will be continuing to the next recommended article, you can keep the resources you've already created and reuse them.

Otherwise, you can delete the Azure resources created in this article to avoid charges.

Important

Deleting a resource group is irreversible. The resource group and all the resources contained in it are permanently deleted. Make sure that you do not accidentally delete the wrong resource group or resources. If you created the IoT Hub inside an existing resource group that contains resources you want to keep, only delete the IoT Hub resource itself instead of deleting the resource group.

To delete a resource group by name:

  1. Sign in to the Azure portal and click Resource groups.

  2. In the Filter by name... textbox, type the name of the resource group containing your IoT Hub.

  3. To the right of your resource group in the result list, click ... then Delete resource group.

    Delete

  4. You will be asked to confirm the deletion of the resource group. Type the name of your resource group again to confirm, and then click Delete. After a few moments, the resource group and all of its contained resources are deleted.

Next steps

In this quickstart, you've called a direct method on a device from a back-end application, and responded to the direct method call in a simulated device application.

To learn how to route device-to-cloud messages to different destinations in the cloud, continue to the next tutorial.