How to display notifications in the application?

Question

Notifications

The rest server is being written in spring. Tell me how best to implement the following thing:
for example, there are 3 users, user 1 started reading another 2, and since user 3 is subscribed to 1, he immediately receives a notification about this action. And the same with the rest: user 1 did some action -> all the necessary users were notified.
So how can this be done, what experience do you have in this case?
-Do I need to do something at the level of the base itself?
I suppose this is done on the service layer, and if the client is only for android, then you need to use GCM (google cloud messaging)?

Answer 1

I'm a developer of https://PushAll.ru , you can use our service, especially since it's free. Android apps, Google Chrome add-on, android and chrome web push are available. telegram bot, soon there will be a full iOS version, support for firefox and safari.

Answer 2

Push notifications can be used to notify mobile clients. If you search Google, you will find thousands of services. If your application has a WEB-muzzle, and the user interacts with it, and notifications should be in the same place, then you can look towards WebSockets, since, again, there are thousands of articles about it in Google.