The caching is to avoid looking up the resource method and scanning its annotations on every Jersey event. Not to avoid looking up the corresponding metric. I have looked in Jersey code before, but by no means an expert, so it is possible even that is not the most important saving but seemed prudent at the time. 

Again, I don't know at this point if I should apply your code review comments to my own PR or let @cab222  apply them to this one.

Cheers.