Getting started with Java contributions: Extending the SonyAudio Binding to support more features

I have a Sony HT-ZF9. It’s detected and supported by the SonyAudio binding, but not all of the features that I’d like to use are exposed. I can “manually” control those features using JSON requests via curl (and therefore by the exec binding), but as the Sony binding seems to be a sensible place to put the code, I’d like to look at extending the binding. FWIW I’m only really interested in setting “night” and “voice” modes as I don’t think the developer API exposes the Subwoofer volume control.

I’ve found the OpenHAB contributing guide, but after that I’m lost. I’m at least familiar-ish with Github and FOSS development ideals, but the Eclipse Smarthome Extensions repo is pretty vast. I’ve found the section org.eclipse.smarthome.binding.sonyaudio in what I would guess is an Eclipse (?) Java repo, but I’m not a Java programmer (I used to do a bit of C/C++), and my attempts to open the repo result in Eclipse saying things like “This project won’t build…”.

So, where does one start? Is there a CI service which I can create to test my commits? What does a usual Java development environment even look like these days? (I’m a Unix greybeard, and vim+Make used to be my tools).