Or a Clojure PersistentHashMap behind an Atom. That's the idiomatic way to do caching in Clojure. It would work just fine in regular Java, and you could wrap

Or a Clojure PersistentHashMap behind an Atom. That's the idiomatic way to do caching in Clojure. It would work just fine in regular Java, and you could wrap the Atom in a class that converts the usual java.util.Map methods to their equivalent Atom/PersistentHashMap operations and completely hides the fact that you're using (a non-transactional) part of the Clojure persistence framework. You don't even need Lisp! (Like any Java programmer, you will need wrist braces in a few years, though.)