Which tool in the Spring Framework allows implementing reactive programming?

In the Spring Framework, the Spring WebFlux project is used to implement reactive programming. It is based on reactive streams and supports asynchronous data processing using libraries such as Reactor (part of the Spring project).

Spring WebFlux allows creating non-blocking, scalable applications using reactive data types, such as Mono and Flux.

Example of a simple controller using WebFlux:

@RestController
public class ReactiveController {

    @GetMapping("/hello")
    public Mono<String> sayHello() {
        return Mono.just("Hello, Reactive World!");
    }
}