Most fingerprint reader are USB, so you will hardly find a pure Java
SDK. Now some manufacturer might have a Java SDK that you can get/buy
from them. But what you are asking is not really possible today:
fingerprint reader manufacturers didn't define any standard protocol to
interface their hardware (but there are standard fingerprint formats, to
represent the fingerprint themselves, not the communication to the device).
Unless you find a fingerprint reader with Serial connector or Network
card, I doubt you will be able to connect the device without the
manufacturer help (or reverse engineering of the USB port communication)
There are some Java API for the USB communication, but I don't know much
about it.

Good luck.