Sorry you've been fighting this. We're actively working on the documentation as well as improving the setup workflows for Actions which should alleviate lots of this pain.

Those one line snippets are likely going to be taken down, most systems are too complicated for those to work. It looks nice for a couple package systems but that Maven one is obviously flawed.

I'd be happy to help you dig through whatever you're trying to do; I'm @clarkbw on twitter. I'd also love another set of eyes on the changes to the setup-java action, specifically getting Maven authentication to work well.

https://github.com/actions/setup-java/pull/29

(I'm the PM heading up the Packages project at GitHub)