Update UI element at one particular client from BG-thread

Hi all,
I’m new to VAADIN and have a simple, but I guess, common problem.

I have to update a kind of alarm text box with some notification text on a particular client from a
background thread. The backgound thread gets its orders by a UserId-String, so does not know
anything about windows or sessions.

Now how to find the correct client to get the notification box and update it ?

My idea was to catch and store Application- objects along with some clientID Strings in a static global
hashMap e.g. Hashmap <String,Application> .

The hashmap is filled at application.init() with a <UserID, Application-object> pair and removed at
windowClose(CloseEvent e) Event. By having a reference to the application object, I can reference
the Updater/Refresher- plugin and start a refresh action as outlined in the famous '“Updating UI from another thread” - thread by Artur Signel.

Is that a suitable way to go ?

Any comment or hint/link - if this item is already discussed - is highly welcome !
I read the various threads about background thread updating but could not find a discussion about this.