Kafka streams and windowing to keep count over a time window

Question

I'm new to Stackoverflow, so forgive me if the question is badly asked. Any help/inspiration is much appreciated!

I'm using Kafka streams to filter incoming data to my database. The incoming messages looks like {"ID":"X","time":"HH:MM"} and a few other parameters, irrelevant in this case. I managed to get a java application running that reads from a topic and prints out the incoming messages. Now what I want to do is to use KTables(?) to group incoming messages with the same ID and then use a session window to group the table in time-slots. I want a time window of X minutes continuously running on the time axis.

The first thing is of course to get a KTable running to count incoming messages with the same ID. What I would like to do should result in something like this:

ID       Count
X          1
Y          3
Z          1

that keeps getting updated continuously, so messages with an outdated timestamp is removed from the table.

I'm not a hundred percent sure, but I think what I want is KTables and not KStreams, am I right? And how do I achieve the Sliding Window if this is the proper way of achieving my desired results?

This is the code I use right now. It only reads from a topic and prints the incoming messages.

private static List<String> printEvent(String o) {
    System.out.println(o);
    return Arrays.asList(o);
}

final StreamsBuilder builder = new StreamsBuilder();
    builder.<String, String>stream(srcTopic)
    .flatMapValues(value -> printEvent(value));

I would like to know what I have to add to achieve my desired output stated above, and where I put it in my code.

Thanks in advance for the help!

Answer 1

Yes you need Ktable and sliding window, i also recommend you look on watermark feature , to handle late delivery message. Example

KTable<Windowed<Key>, Value> oneMinuteWindowed = yourKStream

.groupByKey()

.reduce(/*your adder*/, TimeWindows.of(60*1000, 60*1000), "store1m");
        //where your adder can be as simple as (val, agg) -> agg + val
        //for primitive types or as complex as you need