A Java library for accessing FIDO U2F USB tokens for app registration, challenge signing and signature verification.
This library is based on hid4java for USB HID access and it is ported from u2f and u2fcli
Check out the slides by Alexei Czeskis (Google) which provides an overview of how an U2F token can make your service more secure. Flowcharts of Registration and Authentication and a real example should make you more confident before integrating the library.