Since Java 8, the Stream API has been a valuable tool for Java developers. However, our hunt for better solutions has often left us wanting more. Until now, we could only use the standard provided intermediate operations on streams, like map, filter, and flatMap. Enter Java 24's new Stream Gatherers, which allow for adding custom intermediate operations to our streams.

In this session you'll learn what Gatherers are, where they shine, and how you can implement your own. By the end of the session, you'll be fully equipped to use this powerful new feature in your day-to-day work.

Jfokus

Java 24 introduced Stream Gatherers, a generic mechanism for custom intermediate stream operations. The talk covers the five built-in gatherers: windowFixed (fixed-size batching), windowSliding (moving window), scan (cumulative reduction emitting each step), fold (cumulative reduction emitting only the final value), and mapConcurrent (concurrent mapping with order preservation using virtual threads). A practical temperature-sensor data processing scenario motivates each example. The talk also walks through implementing a custom gatherer (zipWithIndex) using the Gatherer interface's initializer, integrator, and finisher components, and recommends starting with Gatherer.ofSequential before adding parallel combiner support.

Level Up Your Java Streams with Gatherers, by Hinse ter Schuur