How can I implement a vtable COM interface in java?

In the old days, I'd use the Microsft JVM, which had built in java-COM interop. What's the equivalent for a modern JRE?

Answers to a similar SO question proposed JACOB. I've looked at JACOB, but that is based on IDispatch, and is aimed at controlling Automation serers. The COM interfaces I need are custom vtable (extend IUnknown), e.g. IPersistStream, IOleWindow, IContextMenu etc.

For my use case, I could implement all the COM specifics in JNI, and have the JNI layer call corresponding interfaces in java. But I'm hoping for a less painful solution.

It's for an open source project, so open source alternatives are preferred.