Totally depends on what you want to do. You need to know a few basic stream/reader concepts to do any I/O, and of course you'll need to know more if you want t

Totally depends on what you want to do. You need to know a few basic stream/reader concepts to do any I/O, and of course you'll need to know more if you want to use some Java libraries; most of it is easy to pick up as you go. But you can do a lot with pure Clojure.