How to output result of windowed aggregation only when window is finished? [duplicate]

Answer 1

You can use new feature of KTable KTable.suppress in version 2.1

This method allows you get exactly one final result per window/key for windowed computations.

More about suppres in KIP-328

You can update your implementation with suppress like this:

KTable<Windowed<Long>, Counter> ret = input.groupByKey()
        .windowedBy(TimeWindows.of(Duration.of(10, SECONDS)))
        .aggregate(Counter::new, (k, v, c) -> new Counter(c.count + v.getDimension()))
        .suppress(untilWindowCloses(BufferConfig.unbounded()));

ret.toStream().to("output"); // now stream should flush events to the output topic only when the window closes