[JackMorgan]

I wanted something like this, so I made this library that checks annotations at run time rather than compile time.

https://github.com/steveshogren/deft

Right now it only checks maps for a set of keys, the idea longer term is to add in other types of "type" checking.

I haven't yet tied into the built-in annotations, just because those didn't appear to check anything but valid Java types. If it is possible, I would be really interested in seeing how.