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Kotlin Spring WebFlux Annotation-Based RestAPIs - with SpringBoot 2

loizenai profile image loizenai ・2 min read

Kotlin Spring WebFlux Annotation-Based RestAPIs - with SpringBoot 2

Reactive programming is about non-blocking applications. And Spring Framework 5 includes a new spring-webflux module, supports Reactive Streams for communicating backpressure across async components and libraries. So in the tutorial, JavaSampleApproach will guide you through the steps for creating a Kotlin Spring WebFlux Annotation-Based RestAPIs with SpringBoot 2.

Related posts:

I. Technologies

– Java: 1.8
– Maven: 3.5.2
– Spring Tool Suite: Version 3.9.0.RELEASE
– Spring Boot: 2.0.0.M7

  • Kotlin 1.1.61 – Spring Boot Starter Webflux
  • Postman client

    II. Spring WebFlux

    Spring Framework 5.0 supports WebFlux with fully asynchronous and non-blocking and does NOT require the Servlet API(Unlike Spring MVC).

Spring WebFlux supports 2 distinct programming models:
– Annotation-based with @RestController
– Functional with Java 8 lambda style

In the tutorial, we will introduce WebFlux with Annotation-based and Kotlin language.
For starting with WebFlux, SpringBoot supports a collection dependency: spring-boot-starter-webflux.

Kotlin sample code:

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

class RestControllerAPIs {

    fun getAll(): Flux {
        return Flux.fromIterable(ArrayList(custStores.values));
    fun getCustomer(@PathVariable id: Long): Mono {
        return Mono.justOrEmpty(custStores.get(id))

reactor.core.publisher.Flux: is a standard Publisher representing a reactive sequence of 0..N items, optionally terminated by either a success signal or an error.
reactor.core.publisher.Mono: Mono is a specialized Publisher that emits at most single-valued-or-empty result.

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