Well, that stdio thing is actually what I love about Hacker Rank :)
I don't think the boilerplate code is a problem, if you use a reasonable language. Racket is a pleasure to use over there, Clojure slightly less so but wouldn't call it irritating...
I just wind up getting irritated having to rewrite the same code all the time. Some popular languages will generally come with a pre-filled template with the I/O already covered, but quite a lot of the FP stuff didn't.
But yeah, I've seen some Java solutions on HR...