I thought I would be able to use:

    Component focusOwner = window.getFocusOwner();
    anotherComponent.requestFocusInWindow();
    // do some work
    focusOwner.requestFocusInWindow();

but seems like it is not that straightforward. I'm not expert and
I'm surely missing something.

I'm trying the following: In order to keep the GUI from "freezing"
I'm starting a job in a dedicated thread, but I want to block any
input till the job is done. So I register a mouse and key listener
(which consume all the input events) to the glass pane of my frame
and trigger its visibility. Seems o.k. but it doesn't remove the
focus from text fields and I'm not sure if there are other things
I'm missing.

I've put a self contained test case here:

http://www.geocities.com/stanio/test/FocusTest.java

Try both: focusing the button and the text area before invoking the
"Test" menu item. Note I'm aiming to achieve behavior just like when
one selects an item from the menu - the focus is lost, but right
after "exiting" the menu the focus is returned where it was.