TIL: Creating Periodic Streams with Mutiny in Quarkus

First of all : I wrote this article for myself so that I can refer back to it when I need to

For a demo application, I needed to generate a large number of Kafka messages every second. Instead of using the standard Kafka client, The goal was simple: produce faked messages in continuous batches, without manually managing loops.

In Quarkus, the recommended way to produce messages to Kafka is through Reactive Messaging. According to the documentation, you define a producer method annotated with @Outgoing. This method does not return a single message, but a Multi<T> object, which represents a stream of messages

While exploring the documentation,I discovered that streams can be merged, which makes it possible to create a stream creating every second a batch stream items that generates multiple messages

Here’s the example I used:

ti.createFrom().ticks().every(Duration.ofSeconds(1))
       .onItem()
       .transformToMultiAndMerge(tick ->
               Multi.createFrom().range(0, 100)
                    .map(e -> AircraftMetrics.generate(generateAircraftId()))
       );

In this snippet, ticks().every(Duration.ofSeconds(1)) produces an item every second. Each tick triggers transformToMultiAndMerge, which generates 100 new items via Multi.createFrom().range(0, 100).

Each item is then transformed into a simulated AircraftMetrics object.

The resulting stream emits a batch of 100 messages every second.