First above all I suggest you read about the JSF request process lifecycle and understand all phases as soon a request is produced until de page is rendered.
I suggest you also read about the MVC model, wich is where it is based jsf.
That said, when in the client (browser) a component is selected (has the focus) the server does not know anything about this, becuase have not been a request to the server.
One solution to know the component that has the focus in the server is using ajax, you can make a partial request for all components you want when any component has the focus.
If you're using JSF 2.0 you can do it like this:
All the component's between the <f:ajax> and </f:ajax> make a partial request for the onfocus event and call the method especified by the listener attribute
And the method for the listener
I hope this can help you to solve your problem, sorry for my English.