This topic describes how to create a server-side subscription of the MNS type. The subscription allows messages about status changes on the devices of a product to be pushed to an MNS queue. Servers receive messages about status changes on devices by monitoring MNS queues.

Prerequisites

Background information

The following figure shows data flows.

Server-side subscription

Create a server-side subscription

In the IoT Platform console, follow these steps to create a server-side subscription of the MNS type and select the types of messages to which you want to subscribe.

  1. Log on to the IoT Platform console.
  2. In the left-side navigation pane, choose Devices > Products. On the Products page, click Create Product to create a product.
  3. Choose Devices > Create Device to add a device in the product.

    When you use a server MNS SDK to provision a device, you must obtain the certificate information of the device.

  4. In the left-side navigation pane, choose Rules > Server-side Subscription. On the Server-side Subscription page, click Create Subscription to create a server-side subscription of the MNS type.
    Note The first time you select MNS in the Subscription Type field, a message prompts you to authorize access. Click Authorize Now to go to the Resource Access Management (RAM) console. Click Confirm Authorization Policy.

    Select Device Status Change Notification. In the product, messages about status changes that occur on all devices will be pushed to an MNS queue.

    Create Subscription

    After you create a server-side subscription, IoT Platform automatically creates a queue in MNS. The queue is used to receive messages from IoT Platform. The format of the queue name is aliyun-iot-${yourProductKey}. When you use an MNS SDK to monitor the messages of a queue, you must specify the name of the queue.

    On the Server-side Subscription page, move the pointer over the icon next to MNS to view the name of a queue.

    Queue name

Use MNS SDK for Java to receive messages

This section uses the MNS Java SDK Demo project as an example.

  1. Visit MNS SDK for Java. On the page that appears, click Download sample to download the aliyun-sdk-mns-samples1.1.8 package, and then decompress the package.
  2. Open Eclipse, click Import Project, and select the aliyun-sdk-mns-samples directory to import.
  3. In the C:\Users\${YourComputerUserName} local directory, create the .aliyun-mns .properties file. Add identity information in the following format to the file. The identity information is used by MNS for authentication.
    mns.accountendpoint=http://$your_accountId.mns.$your_regionId.aliyuncs.com
mns.accesskeyid=$your_accesskeyid
mns.accesskeysecret=$your_accesskeysecret
    Parameter Description
    accountendpoint The endpoint of Message Service. In the MNS console, select the region where the queue resides and click Get Endpoint to view the information.
    accesskeyid The AccessKey ID of your Alibaba Cloud account.

    To create or view your AccessKey pair, follows these steps: Log on to the Alibaba Cloud console. Move the pointer over your profile picture, and click AccessKey to go to the User Management page. On the page, you can create or view your AccessKey pairs.

    accesskeysecret The AccessKey secret of your Alibaba Cloud account. Obtain the AccessKey secret in the same way as the AccessKey ID.
  4. Add the following code to the ComsumerDemo script in the src\main\java\com.aliyun.mns.sample.Queue directory. The code is used to specify the name of the queue that is automatically created by IoT Platform. 
        public static void main(String[] args) {
        CloudAccount account = new CloudAccount(
                ServiceSettings.getMNSAccessKeyId(),
                ServiceSettings.getMNSAccessKeySecret());
                ServiceSettings.getMNSAccountEndpoint());
        MNSClient client = account.getMNSClient(); // Initialize a client

        // Extract messages
        try{
            CloudQueue queue = client.getQueueRef("aliyun-iot-a1eN7La****");//Specify the name of the queue that is automatically created by IoT Platform
            for (int i = 0; i < 10; i++)
            {
                Message popMsg = queue.popMessage(10);  //The timeout for long polling
                if (popMsg ! = null){
                    System.out.println("message handle: " + popMsg.getReceiptHandle());
                    System.out.println("message body: " + popMsg.getMessageBodyAsString()); //Obtain raw messages
                    System.out.println("message id: " + popMsg.getMessageId());
                    System.out.println("message dequeue count:" + popMsg.getDequeueCount());
                    //<<to add your special logic. >>

                    //Delete the messages from the queue
                    queue.deleteMessage(popMsg.getReceiptHandle());
                    System.out.println("delete message successfully.\n");
                }
            }
        }
  5. Run the ComsumerDemo script.

Configure a device SDK

  1. Visit Download device SDKs and select Java SDK.
  2. At the bottom of the Configure a project topic, click Java SDK Demo to download the package, and then decompress the package.
  3. In a Java IDE, select the JavaLinkKitDemo directory to import as a project.
  4. In the device_id file, add certificate information for the device.
    Add certificate information
  5. In the MqttSample script of the src\devicesdk\demo directory, add information of the device, specify the name of your device topic in the publish method.
    MqttSample
  6. Run the MqttSample project to connect the device to IoT Platform.

Verify the results

After you run the device SDK Demo project, a message indicating that the device is online is sent to the MNS queue. The MNS Java SDK Demo project receives the message from the queue and then deletes the message from the queue.

The following figure shows how the MNS Java SDK Demo project receives the message and then deletes the message.

Verify the results