The only thing I have done with Java is navigate the source definitions of methods, using this alias for deps.edn projects https://practicalli.github.io/spacemacs/navigating-code/java-definitions.html Let me know if there are any example projects that would be useful to try out

Oh and of course there is auto-completion for java methods in clojure-mode, although I havent tested how extensive this is. Seems to work for most of the methods I call (eg. java.util.UUID/randomUUID)