I am not a Clojure programmer, and am pretty skeptical of LISPs and FP more generally, but i have to say that transducers are pretty great. The descriptions of them, and the way the interface is expressed, are a bit off-putting, but once you grok them they're actually simple and useful.

They occupy the same space as Java's streams, but manage to do the same stuff with a smaller, more generic, more extensible interface, that can do more stuff (eg intermediate stages get told when input is finished). I'm jealous.

EDIT: IIUC, in Java terms, Clojure's "reducing functions" are like Collector, and a transducer is a function which takes a Collector and returns another one. There is then a little bit of top-level sugar so you can give a sequence of transducers, terminating in a concrete reducing function, and get back a reducing function which itself feeds things through the chain of reducing functions built by the transducers. You could probably replicate this in Java, but it might be too clunky even for Java programmers.