Project Reactor is a Java library for composing reactive data pipelines. Instead of waiting for an entire batch before passing it on, a pipeline can pass along data as it becomes available—like newspapers delivered each day rather than all at year’s end. Its operations may run on the same thread or different threads; a pipeline does not guarantee either. section 11.0 section 11.2
Reactor implements Reactive Streams and supplies a functional API for joining its parts: a Publisher emits data, a Subscriber receives it, and a Processor can receive data and publish results. This model underpins Spring’s reactive programming model. section 11.1.1
Start with Reactor’s two Publisher types:
- Flux represents zero, one, or many items, potentially without an end. section 11.2
- Mono is optimized for no more than one item. section 11.2
Mono.just("Craig")
.map(n -> n.toUpperCase())
.map(cn -> "Hello, " + cn + "!")
.subscribe(System.out::println);
A greeting pipeline starts with Mono.just(), transforms the value with two map() calls, and prints the result through subscribe(). Each transformation produces another Mono. section 11.2
To try a pipeline in a Spring Boot project, add reactor-core to the build; add reactor-test for tests. Spring Boot manages their versions. Outside Spring Boot, configure Reactor’s BOM for dependency management. section 11.2.2
<dependency> <groupId>io.projectreactor</groupId> <artifactId>reactor-core</artifactId> </dependency>
This Maven dependency adds the Reactor library needed for Mono and Flux pipelines. section 11.2.2
