Question about Graph API - changes notification

[ChenguangHe]

Hello, I'm writing a java project to create subscription to online meeting resources. I followed this instruction https://docs.microsoft.com/en-us/graph/webhooks?view=graph-rest-1.0

to construct a new subscription. This is my request:

POST https://graph.microsoft.com/beta/subscriptions
Content-Type: application/JSON
change Type": "created, updated"
"notificationUrl": "https://my.ngrok.url/notificationClient",
"resource": "/communications/onlineMeetings/{meetingID}",
"expirationDateTime": "2016-03-20T11:00:00.0000000Z",
"clientState": "SecretClientState"

And I created a project locally to receive the POST request as follow

@PostMapping(path = "/notificationClient")
public ResponseEntity<String> Notification(@PathParam ("validationToken") String opaqueTokenCreatedByMicrosoftGraph)

I should receive request from Microsoft Graph like this:

Content-Type: text/plain; charset=utf-8 POST https://{notificationUrl}?validationToken={opaqueTokenCreatedByMicrosoftGraph}

However, the validationToken I received is null. Is there anything wrong and how to create a subscription to online meeting resources?

[#2]

@ChenguangHe - Could you please refer this sample?
 Microsoft-Teams-Samples/samples/graph-change-notification at main · OfficeDev/Microsoft-Teams-Sample...

[#3]

@Prasad_Das-MSFT that project is written in nodejs, is there any Java example?
In addition, can't I just use Graph API to achieve it?

[#4]

@ChenguangHe - There is no Java sample available for it. However, this thread discusses about similar issue. Please have a look at once which explains:
validationToken will only send to the webhook at the time of Subscription creation, after that Microsoft start sending the change notifications and there won't be any validationToken send with the change notification. This is done just to ensure that the Notification endpoint is valid/active.
Set up notifications for changes in resource data - Microsoft Graph | Microsoft Docs

[#5]

Hi @Prasad_Das-MSFT, I used the given sample and still have some issues. When I create request of change notification, how can I get clientState, encryptionCertificate and encryptionCertificateId?

[#6]

@ChenguangHe - Please refer this doc: changeNotification resource type - Microsoft Graph v1.0 | Microsoft Docs

[#7]

Problem solved. Thanks.