Accepting Notifications
For a newspaper subscription, your house is like the callback URL. When the paper arrives, you can take any action you wish in response, from reading the paper to lining a birdcage with it. The callback URL you provide will receive a POST notification JSON object, allowing your service to take some action when the subscribed event has happened.
Google expects your service to respond with a 200 HTTP code within 10 seconds. This is a pretty standard requirement for web-service callbacks. If you need to execute a long-running job, you can put it in a task queue to be executed asynchronously.
Let’s dig into the steps required to accept notifications; we’ll craft a callback servlet that accepts notifications for the PIN menu ...
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