Set up CI for the extractor.

[rj00a]

Describe the problem related to your feature request.

There is currently no continuous integration for the extractor because it's written in Java and we only have checks for the Rust part of the project. Warnings and style issues can go unnoticed.

What solution would you like?

Set up checks for the Java program like we have for Rust. It should lint for style issues and make sure everything compiles. I don't have any experience with this.

What alternative(s) have you considered?

Leave it as it is because we're lazy or there are too many problems in the code that aren't worth fixing. But I would prefer it if the extractor wasn't totally junk.

Additional context