When we talk about creating web applications in Java, Spring Framework is a name that comes in mind. which is widely used for building robust and scalable enterprise applications. Spring 5 introduce Spring WebFlux for supporting reactive programming In this comprehensive guide, we will explore what Spring WebFlux is, how it differs from traditional Spring Boot applications, its key features, and when to use it.

Introduction to Spring WebFlux

Spring WebFlux (Reactive spring) is the reactive, high-performance, and non-blocking web framework for building high concurrency web application which is introduced by Spring 5. Its mainly comes for supporting reactive programming in spring. It is part of Reactive Spring and is designed for applications that demand:

• High concurrency
• Low latency
• Streaming data
• Real-time updates
• Better resource utilization

Today, companies building scalable microservices, chat apps, live dashboards, real-time data processing, and streaming platforms prefer WebFlux over traditional Spring Boot (Spring MVC).

What Is Reactive Spring (Reactive Programming)?

Reactive Spring means creating or building software application using Reactive Programming, which focuses on:

• Asynchronous data streams
• Non-blocking execution
• High scalability

Reactive Spring applications can handle thousands of requests using some threads, unlike traditional Spring MVC.

Key features of Spring WebFlux

• Reactive Programming: Spring WebFlux support reactive programming that means its using a non-blocking and asynchronous approach
• Non-blocking I/O: WebFlux uses non-blocking I/O, that means when your application makes a request (for example, to a database or another service), the thread handling that request doesn’t sit idle waiting for the response. It can handle other tasks while waiting.
• Asynchronous Operations: All Operations in WebFlux are execute asynchronously. Your application responds to results as they become available, rather than blocking and waiting.
• Different Concurrency Model: Spring Boot use traditional thread-per-request model but Spring WebFlux efficiently handles multiple concurrent connections using fewer threads through event-loop-style concurrency.

Spring WebFlux vs Spring Boot (Spring MVC) – Full Comparison

1. Architecture Style

Spring WebFlux

• Non-blocking
• Asynchronous
• Event-loop based
• Uses Netty by default

Spring Boot (Spring MVC)

• Blocking
• Synchronous
• Thread-per-request model
• Uses Tomcat by default

2. Performance & Scalability

Spring WebFlux

• Can handle millions of connections
• Lightweight threads
• Ideal for microservices

Spring Boot (Spring MVC)

• Thread gets blocked during DB calls
• Uses many threads → high memory usage

3. Data Handling

Spring WebFlux

• Uses Flux and Mono (reactive types)

Spring Boot (Spring MVC)

• Uses normal Java objects

4. Use Cases

Choose Spring WebFlux for:

• Real-time apps
• Streaming apps
• Chat systems
• Event-driven systems
• High-traffic microservices

Choose Spring MVC for:

• CRUD apps
• Traditional enterprise apps
• Websites, admin dashboards
• Projects with blocking databases

5. Database Support

Spring WebFlux vs Spring Boot (Spring MVC): The Key Differences

Important for Interview Purpose

Spring Boot and Spring WebFlux are not mutually exclusive. Spring WebFlux is a module that you can include within a Spring Boot application.

You choose whether you want to build your web layer using:

• Traditional blocking approach: Using spring-boot-starter-web with Spring MVC.
• Reactive non-blocking approach: Using spring-boot-starter-webflux with Spring WebFlux.

When Should You Use Reactive Spring (WebFlux)?

Reactive Spring (WebFlux) is good for applications with the following characteristics:

• ✔ High Concurrency: Applications that need to handle a large number of connections.
• ✔ Non-blocking Operations: Applications that involve a lot of operations where waiting can be inefficient.
• ✔ Real-time Data Streams: Applications that need to send data to clients in real-time (for example, live dashboards, chat applications).
• ✔ Microservices: In a microservices architecture, where services need to communicating frequently and need to be highly responsive.

Getting Started with Reactive Spring Boot

Using reactive programming principles with Spring WebFlux, You can build web applications that are more flexible and responsive under heavy load. Spring Data also support for reactive data access and its allowing us to interact with databases in a non-blocking manner.

To start using Reactive Spring in a Spring Boot application, Need to follow these steps:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-webflux</artifactId>
</dependency>

implementation 'org.springframework.boot:spring-boot-starter-webflux'

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

import java.time.Duration;
import java.time.LocalTime;

@RestController
public class ReactiveController {

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

    @GetMapping(value = "/stream", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
    public Flux<String> stream() {
        return Flux.interval(Duration.ofSeconds(1))
                   .map(tick -> "Current time: " + LocalTime.now());
    }
}