Save a File on client side pc

Hi everybody,
I have making a program that create a client just by project vaadin 7 (don’t use EntryPoint or DefaultWidgetSet) and I want the client to recive an object from service wich I made already , and the client save the object in pc wich is running the client by enter th url in on of the client’s pc bowser . But I don’t know , how can I do it?
please guide me