Yes, there were lots of last minute Java changes due to folks coming in and saying it wasn’t working for them. I am able to build on Linux and was also able to get macOS without issue when I was testing it.
Yes, we now use CMake’s Java support (as I’ve said multiple times). We used to make custom commands for compiling each .java file and then creating the jar ourselves with add_custom_command. Now we just tell CMake to make the jar file. If something goes wrong after that, it is a CMake problem, not a VTK problem. I suspect that VS doesn’t support Java, but the rest seems like CMake should be making noise that it doesn’t have the tools to actually make the jar and erroring.