I've been playing with jni.h and D. I think I've got a fully working jni.d and I have the start of a nicer D wrapper around it with djvm.d.
https://github.com/jamesmahler/djvm There is an example usage in the README.md. There's also why I'd do such a thing in there. I'm not sure if anyone else would be interested in this. I'm open to help and merge requests if anyone wants to join in. In the short term, I still have several low level things to wrap with the more D interfaces. In the longer term, I want to have D interfaces around JDBC.