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 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.

│   ├───java
│   │   └───com
│   │       └───zetcode
│   │           │   Application.java
│   │           └───controller
│   │                   MyController.java
│   └───resources
│           application.properties

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 {

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.


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;

public class MyController {

    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;

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.


My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

List all Spring Boot tutorials.