Reactor

Reactor is a reactive programming library for building non-blocking applications on the JVM, implementing the Reactive Streams specification. It provides composable asynchronous sequence APIs—Flux for 0..N elements and Mono for 0..1 elements—enabling efficient, backpressure-ready data streams. It is widely used in reactive systems, particularly with Spring WebFlux for building scalable, event-driven microservices.

Also known as: Project Reactor, Reactor Core, Reactor library, Reactive Streams JVM, Spring Reactor

Why learn Reactor?

Developers should learn Reactor when building high-performance, non-blocking applications that require handling concurrent requests efficiently, such as real-time data processing, microservices, or IoT systems. It is essential for reactive programming in Java and Kotlin, especially within the Spring ecosystem, to manage asynchronous data flows with backpressure and avoid thread-blocking bottlenecks.

Learning Resources

• docs: Reactor Reference Guide
• tutorial: Building Reactive Microservices with Spring WebFlux and Reactor
• tutorial: Reactive Programming with Reactor 3
• book: Reactor in Action
• video: Introduction to Reactive Programming with Reactor