Create post merge GitHub actions build for JDK-8, 9, 10, 11, 12, 13, 14, EA

[nikhilnanivadekar]

We should have a post-merge build for all the JDKs to understand the compatibility of the project with various versions of Java else it will be difficult to keep track of compatibility to which JDK version we broke or might break in the future.

[bmvermeer]

You can create github actions to this with all the different JDK's. Is that what you mean? In addition, do you want to keep track non LTS version other than the latest (or latest 2)? I would suggest: 8, 11, (and the latest 2 non LTS), 14 and 15. Maybe you can elaborate a little so I understand better :)

[nikhilnanivadekar]

@bmvermeer I like your idea of latest two versions, LTS and EA. So we should have JDK 8, 11, 14, 15 (latest two versions), and EA. That said, the motivation of this issue is as follows: Currently, the way we run unit tests is we build and test on the same JDK. So, we build on JDK-8 and we run unit tests on JDK-8, build on JDK-EA and run tests on JDK-EA, likewise for other JDKs. But this is not how the release works. For the release we create the jar with only JDK-8 and push that to maven central. In order to guarantee that we test what we produce, we need to have a post-merge set of builds which will create the jar using JDK-8 and then run unit tests using these artifacts.