To simplify things and help our users to be more productive, we have archived the current forum and focus our efforts on helping developers on Stack Overflow. You can post new questions on Stack Overflow or join our Discord channel.
Currently, Vaadin does not communicate the focused component back to the server.
However, since Vaadin 6.2, it is possible to get information about some focus changes by registering a FocusListener (and maybe also a BlurListener) on components that implement the interface FocusNotifier, including the many of the common types of fields used in forms.
If this is a common need in your application, you could even consider subclassing Form and implementing automatic focus tracking for such components within it.