A little used, but legitimate use for JNI would be to provide a Java
API to hardware.
I have no personal experience to back this up, but it seems to me that with hardware like that it would be in everybody best interest to provide the smallest native lump possible, and then provide as much portable code as possible. Code that comes with a device like that is just overhead, it's not the main order of business. If I were designing the interface for that printer (or something similar), I'd be championing Java. It only makes sense.
Greetings.
Albert