Spring WebFlux Hello World Example

The Spring Web Flux provides different applications to developers to develop asynchronous, non-blocking web applications by using Mono, Flux, and other classes. In this article, we will be learning to write a basic Hello World program in Spring WenFlux.

Project Creation:

• Open STS (Spring Tool Suite) and then select New Project.
• After that, we will be redirected to a project creation screen, in Select Project Category like maven or gradle, choose any (Here we will be using Gradle).
• Then provide the project name, package name, and other details.
• Then select dependencies.
• Now click on finish.

Project Folder Structure:

Project Dependencies:

In this project, we have used below dependencies and the project category is gradle.

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-webflux'
    developmentOnly 'org.springframework.boot:spring-boot-devtools'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
    testImplementation 'io.projectreactor:reactor-test'
}

Hello World Program in Spring WebFlux

Here, we have provided a basic example for printing Hello World by using @RestController.

• For this, in main package, we have created one Java class named as HelloWorldController.
• After that, we have created one @GetMapping end point with name hello.
• The @GetMapping is used for creating API End points.
• While open with browser, this return output as Hello, World!.

HelloWorldController class:

Java

package com.app;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import reactor.core.publisher.Mono;

@RestController
public class HelloWorldController {

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

Main Class:

This is a main class of the project.

Java

package com.app;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class HelloWorldApplication {
    // Main Method
    public static void main(String[] args) {
        SpringApplication.run(HelloWorldApplication.class, args);
    }
}

After successfully running this project as Spring Boot App, open any browser then type below API End Point URL:

http://localhost:8080/hello

Output:

Below we can see the output in browser.

Explanation of the above Program:

• First, we have created one class in main package of project.
• The class name is HelloWorldController.
• After this, we have created one Get Mapping by using @GetMapping with parameter /hello.
• Next, we run this project as Spring Boot Application.
• After running, open browser then type the Get mapping URL that is provided in the above.
• Once hit that API end point, we got the expected output that is visible in the output screen.