Thanks for sharing your experience, David!
On 2025-11-17 15:08, David Alayachew wrote:
Hello @core-libs-dev <mailto:[email protected]>,
This is a follow up of one of my previous experience reports, a little
over a year ago.
https://mail.openjdk.org/pipermail/core-libs-dev/2024-August/127293.html
Just wanted to report more of my positive experiences with Gatherers,
specifically with a custom Gatherer that @Viktor Klang
<mailto:[email protected]> made for me called windowBy. Here is
the implementation below.
<TR> Gatherer<TR, ?, List<TR>> windowBy(Predicate<TR>
includeInCurrentWindow) {
class State {
ArrayList<TR> window;
boolean integrate(TR element, Gatherer.Downstream<? super
List<TR>> downstream) {
if (window != null && !includeInCurrentWindow.test(element)) {
var result = Collections.unmodifiableList(window);
window = null;
if (!downstream.push(result))
return false;
}
if (window == null)
window = new ArrayList<>();
return window.add(element);
}
void finish(Gatherer.Downstream<? super List<TR>> downstream) {
if (window != null) {
var result = Collections.unmodifiableList(window);
window = null;
downstream.push(result);
}
}
}
return Gatherer.<TR, State, List<TR>>ofSequential(State::new,
State::integrate, State::finish);
}
Clean and simple.
Anyways, as for my experience report, a found a brand new way to use
this custom Gatherer -- event coalescing.
Sometimes, if consecutive events being streamed are of the same type,
then to reduce computation, you might be able to avoid doing more work
by grouping together the potential duplicates, then handling them
separately in a coalescing path. I'd much rather solve that problem
than a caching problem lol.
Anyways, here are the 2 examples where it served me well.
1. Network Request Coalescing.
1. When checking the availability of certain networks, I am now
able to save some bandwidth by combining multiple, consecutive
requests within a certain time to a certain network. And since
I am definitely bandwidth bound, that helps. Nothing I
couldn't do before, but keeping it within Streams allowed me
to avoid ripping out my old solution when it stopped being a
good fit. I wish I could share the code, but it's not my right
to share it.
2. Path-Finding Algorithm -- Clustering
1. This one is still a work in progress, so I may be speaking
prematurely here. But I was so impressed that this is working
thus far. Long story short, I am building a path-finding
algorithm where, if a set of points are close enough together,
then they can be serviced as a group, and thus, lower the
total weight of servicing those nodes, as opposed to servicing
them individually. Again, not done yet, so I might be jumping
the gun, but it worked so well for me out of the box, that I
thought it was worth sharing.
Hopefully this bumps up windowBy on the triage list of potential
pre-built gatherers to add to the standard library. And thanks again
to Viktor and friends for putting this Gatherers library together --
it's a great addition!
Thank you all for your time and consideration!
David Alayachew
--
Cheers,
√
Viktor Klang
Software Architect, Java Platform Group
Oracle
