一个上游流馈送多个下游流

I have a general Streams API problem I'd like to solve "efficiently". Suppose I have a (possibly very large, possibly infinite) stream. I want to pre-process it in some way, for example, filtering out some items, and mutating some. Let's assume that this pre-processing is complex, time and compute intensive, so I do not want to do it twice.I have a general Streams API problem I'd like t