The dll (from C sources) and jar-file (from java sources) must be built separately. Checkout from https://gitlab.ost.ch/tech/inf/public/libusb-java. More detailed information for the maintainers can be reached under https://wiki.bu.ost.ch/inf/libusbjava/start (for internal usage only).
Source code is under /LibusbJava_C.
g++ -shared -o libLibusbJava-"VERSION".so -fPIC LibusbJava.cpp -I"/usr/lib/jvm/java-"JAVA-VERSION"-openjdk-"ARCHITECTURE"/include" -I"/usr/lib/jvm/java-"JAVA-VERSION"-openjdk-"ARCHITECTURE"/include/linux" -I"./" -std=c++0x
Source code is under /LibusbJava_Java.
$javah ch.ntb.inf.libusb.Libusb
Copy new header file to LibusbJava_C.