In libguestfs 1.21.3 you can now use the libguestfs event API from Java (or JRuby). For example to display progress bars, capture log messages, or do full libvirt authentication.
This effectively completes the Java bindings for libguestfs — as far as I’m aware you can now do anything from Java that you could do from C.

Congrats.
Nit picky, but would look nice if naming convention was more Java friendly.
e.g. GuestFS#setEventCallback instead of GuestFS#set_event_callback
Right .. although it is consistent with other libguestfs language bindings, and we think that consistency is more important.
The class names are camel-cased however.