There are somewhat more involved formal treatments like Welterweight Java [1], which adds some more features, but of course, nowhere near the full set of Java features.
Some of the citations in that paper are also interesting.
I don't think there is a core calculus that specifically incorporates generics as in Java, but I could be wrong. In any case, much of Java's generics flow from theories of parametric polymorphism [2], specifically I believe bounded parametric polymorphism [3].
re: "I don't think there is a core calculus that specifically incorporates generics as in Java": doesn't Featherweight Java [1] already include generics? (Though a simplified version.)
[1] https://www.cis.upenn.edu/~bcpierce/papers/fj-toplas.pdf