In my experience Clojure is very callable from Java. For example, Lists and Maps can be passed as normal arguments to clojure functions without conversion step.

In my experience Clojure is very callable from Java. For example, Lists and Maps can be passed as normal arguments to clojure functions without conversion step. This works because Clojure favors abstractions over concretions. For example, instead of a concrete cons cells datastructure, Clojure has the ISeq interface. As far as I can tell, calling clojure from Java introduces no overhead at all. Datomic is a commercial database system developed in Clojure. The peer library is what you use in your client application to query the Datomic server. The peer library is written in Clojure. I expect that means calling Clojure from Java, and including the Clojure runtime jar in a client application, is safe/stable/supported enough to build a business on top of it. I'm still learning though, so take what I said with a grain of salt.