Detection whether a Vaadin UI/Window has been activated again


I open a Lotus Notes document with a Link in my Vaadin Application.
In the Lotus Notes Document some updates will be done in my database.
When I activate my Vaadin Web application again (return to the browser tab of my Vaadin app.),
I need to show the database updates immediately in my vaadin application.

Is there a way to check whether the Vaadin application (or Browser-Tab) is activated again?
If it’s possible with Javascript, how to start then the server side check to my database?

Thanks very much for any help.