I read a lot of articles like JCR vs Apache Sling and I'm confused about what to use. Some authors advise to use JCR API like more performance optimized and the rest are on the side of Apache Sling because it's faster to write and far more readable and maintainable in the long run. And I had some questions:
I think Maciej Matuszewski exhausted this subject enough in his presentation JCR, Sling or AEM? Which API should I use and when?.
In most of the cases, it is recommended to use Apache Sling as a higher API whereas JCR is required when performance needs to be taken into account. It is then important however to know the border between these two scenarios.
Maciej notices it is around 1ms difference for opening the regular AEM page without taking any caching into account. Taking care of the performance is totally unnecessary in that case. We should instead focus on writing code that is readable, understandable, reduced to the minimum and reusing already existing APIs, frameworks, util classes that are covered already by proper unit tests and peer reviewed, rather than reinventing the wheel from the beginning. Base on that, we should also prefer AEM layer over Sling layer.
From my experience, I would say that JCR should be utilized in few scenarios, mainly when traversing of a large amount of data of CRX database and it cannot be achieved by any searching API.
So that the difference is like between using C# or C++ as a programming language for computer games development - in some of the cases it is enough to stay higher API for development convenience however for some cases it is required to get lower and start using C++ pointers.
However, the most important thing is to not mix both abstract layers in your implementation.