Spring Boot WebFlux
last modified July 21, 2023
Spring Boot WebFlux tutorial shows how to create a simple Spring Boot reactive web application with WebFlux.
WebFlux
WebFlux is a Spring reactive-stack web framework. It was added to Spring 5. It is fully non-blocking, supports reactive streams back pressure, and runs on such servers such as Netty, Undertow, and Servlet 3.1+ containers.
Spring WebFlux is an alternative to the traditional Spring MVC.
Spring WebFlux internally uses Project Reactor and its publisher implementations Flux and Mono. It supports two programming models: a) annotation-based reactive components, b) functional routing and handling.
Reactive programming
Reactive programming is a programming paradigm that is functional, event-based, non-blocking, asynchronous, and centered around data stream processing. The term reactive comes from the fact that we react to changes such as mouse clicks or I/O events.
Reactive applications scale better and are more efficient when we are dealing with lots of streaming data. Reactive applications are non-blocking; they're not using resources waiting for processes to finish.
Reactive applications implement an event-based model where data is pushed to the consumer. The consumer of data, a subscriber, subscribes to the publisher, which publishes asynchronous streams of data.
Spring Reactor
Spring Reactor is a reactive library for building non-blocking applications on the JVM based on the Reactive Streams Specification.
The Reactor Project offers two types of publishers: Mono and
Flux. Flux is a publisher that produces 0 to N values.
Operations that return multiple elements use this type.
Mono is a publisher that produces 0 to 1 value. It is used for
operations that return a single element.
Spring Boot WebFlux example
In the following application we create a simple Spring Boot web application with reactive support.
build.gradle
...
src
├───main
│ ├───java
│ │ └───com
│ │ └───zetcode
│ │ │ Application.java
│ │ └───controller
│ │ MyController.java
│ └───resources
│ application.properties
└───test
└───java
This is the project structure.
plugins {
id 'org.springframework.boot' version '3.1.1'
id 'io.spring.dependency-management' version '1.1.0'
id 'java'
}
group = 'com.zetcode'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'
repositories {
mavenCentral()
}
dependencies {
implementation 'org.springframework.boot:spring-boot-starter-webflux'
}
This is the Gradle build file. The spring-boot-starter-webflux is a
Spring Boot starter for building WebFlux applications using Spring Framework's
Reactive Web support.
spring.main.banner-mode=off
In the application.properties, we turn off the Spring Boot banner.
package com.zetcode.controller;
import org.reactivestreams.Publisher;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import reactor.core.publisher.Mono;
@RestController
public class MyController {
@GetMapping("/")
public Publisher<String> home() {
return Mono.just("Home page");
}
}
We have a simple REST endpoint, which returns a message.
The home method return type is a Publisher.
Mono.just emits the specified string message.
package com.zetcode;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
This code sets up the Spring Boot application.
$ ./gradlew bootRun
We run the application and navigate to localhost:8080.
In this article we have created a simple Spring Boot WebFlux application.