Parallelization in Java

RxJava can become overly complex and is harder to debug. I had a better experience with reactor, but that was mainly because that was just trying it out, while RxJava was with a large existing project.
I don't know what's the reason you want to use it. For example you can also do parallel progressing in a stream, which might be enough for your use case.

Thanks, both. Let me elaborate on the use case.
Let's say there are API calls being made sequentially but some time can be saved by making those in parallel.
What would best suit in this case?

While completeableFuture fits the purpose as well, I also wanted to start with reactive programming somewhere and this could be one of the places - but again don't want it to be an overkill for this particular use case.