In today’s high-data-flow environment, we need the kind of responsiveness and scalability that reactive systems provide. However, reactive systems require specialized development resources and personnel to realize their potential fully. The spring boot WebFlux framework and Project Reactor are designed to address today’s businesses’ reactive requirements.

In this article, we will show you how to build a Java application using WebFlux and discuss how it compares to and differs from other technologies in the reactive stack.

What is a Reactive System?

Systems built using the reactive architectural pattern place a premium on adaptability, scalability, and low coupling between its many parts. They are also built with redundancy and fault tolerance in mind so that the rest of the system will continue to function normally if one component fails.

Reactive systems focus on the following:

1. Reactiveness

The most important property of reactive systems is their ability to react instantly to any input from the user. Proponents of spring boot reactive say that the system’s responsiveness improves the quality of data collecting and the user experience.

2. Resilience

System failures may be prevented if reactive systems are built with resilience. Reactive systems plan for future component failure by creating loosely linked systems that can continue functioning even if some portions cease functioning.

3. Scalability

Reactive systems should be able to expand or contract in response to changes in demand. Many reactive systems use predictive scaling to foresee and prepare for future changes. 

To effectively apply elasticity, bottlenecks must be eliminated, and systems must be designed to share or replicate individual components as needed.

4. Message-driven communication

Thanks to message-driven communication, all parts of a reactive system are loosely connected and have clear divisions of responsibility. Explicit message passing is required to allow your system to communicate across these boundaries. Failures are sent to other parts of the system, and workflow is distributed to the most competent parts with the assistance of these messages.

The ability of reactive systems to perform numerous unblocked calls simultaneously distinguishes them from other web architectures. Because each web application component may complete its task without waiting for another component, reactive systems improve performance and responsiveness.

Reactive systems improve speed, user experience, and error handling by using loosely linked, unblocked components when you hire a dedicated Java developer.

What is Project Reactor?

Pivotal’s Project Reactor is a Spring-based framework. It uses the Reactive Streams standard as its primary reactive API design to build Java applications.

The parallels between a Stream and a Flux (or its single-element cousin, Mono) are immediately apparent to anybody acquainted with Java 8 Streams. The Stream API does not provide back-pressure, but Fluxes and Monos, the primary competitors, do.

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The primary benefit of Reactor is that you have complete command over how information is sent. You may utilize a complete push method without back-pressure, depending on the subscriber’s ability to request more data when it’s ready to analyze it or buffer some results on the publisher’s side.

What is Spring WebFlux?

Spring WebFlux is an annotation-based, non-blocking web framework based on Project Reactor that facilitates the development of HTTP-level reactive applications. WebFlux applies functional programming to the web layer without using declarative controllers or Request Mappings through a new router functions capability.

WebFlux has Reactor as a mandatory import requirement. With the release of Spring 5, the option to use the reactive Java spring boot WebFlux framework instead of Spring MVC became available.

Non-blocking threads are a kind of concurrent thread that does not wait for other activities to finish before completing their own. The Reactive Stream API is a standardized application programming interface that provides non-blocking, asynchronous stream processing facilities.

When data is processed asynchronously, the app’s usual functionality is not interrupted while the user waits for the data to finish being processed by the Java development company.

WebFlux abandons Spring MVC’s thread-per-request architecture to facilitate reactive, scalable applications in favor of a multi-Event Loop non-blocking model. WebFlux is an integral element of a reactive stack, and it now supports widely used servers like Netty, Undertow, and Servlet 3.1+ containers.

Salient Features of Spring WebFlux

Router functions

In place of the conventional Spring MVC @RequestMapping and @Controller annotations, Router Function provides a functional alternative. Requests may be directed to appropriate functions using this mechanism.


public class ProductController {


public List<Product> productlisting() {

return ps.findAll();



Instead of constructing a whole router function from scratch, you can use RouterFunctions.route() to generate routes. Because they are just Spring beans, routes may be defined in any configuration class.

Potential unintended consequences of request mapping’s several steps are avoided by using router functions to simplify the process into a linear chain of routers and handlers. Because of this, reactive programming may be implemented in functional languages.


WebFlux’s online client, WebClient, implements the popular RestTemplate reactive web client. An API is a point of entry for synchronous and asynchronous processes and serves as the primary entry point for web requests. Reactive server-to-server communication is WebClient’s primary use case.

Using Maven, you may construct and initialize microservices in Java objects by importing common WebFlux dependencies:





WebClient client = WebClient.create();

Reactive Steam API

The Reactive Stream API is a library of externally-imported functions that facilitates more intelligent stream data flow. The application’s back-pressure and asynchronous processing features guarantee that hardware and software resources are used when you hire a Java developer.


Tomcat, Jetty, and Servlet 3.1+ containers and non-Servlet runtimes like Netty and Undertow are all compatible with WebFlux. WebFlux will automatically utilize Netty, the most popular choice for async and non-blocking designs.

Changing a single setting in your build tools, such as Maven or Gradle, will allow you to switch between various server settings easily. It makes integrating WebFlux into preexisting systems easy and increases WebFlux’s already impressive technological flexibility.

Concurrency Model

WebFlux employs a distinct concurrent programming style from Spring MVC due to its focus on non-blocking design. Spring MVC employs a big thread pool to keep things going in the face of blocking. As a result of the increased number of threads required to run MVC, more hardware resources are required.

Instead of a large thread pool, WebFlux utilizes a tiny one since it never expects you to need to hand off work to escape a blocker. These threads, known as event loop workers, process requests more quickly than Model-View-Controller threads but remain constant in number. WebFlux’s efficient use of computing resources directly results from its constant utilization of active threads.

Get Started with Spring WebFlux

It’s time to put WebFlux into practice to build a Java application. We need to initiate a project first. The Spring Initializr will produce a Maven build that depends on the Spring Reactive Web library.

It will generate a pom.xml file that looks like this:

<?xml version=”1.0″ encoding=”UTF-8″?>

<project xmlns=”″ xmlns:xsi=””







        <relativePath/> <!– lookup parent from repository –>






    <description>Demo project for Spring Boot</description>





























You should now be equipped to go forward. We’ll build a Hello-World app from here on out. Adding a router and a handler will complete our little WebFlux application.


First, we’ll create a router to display our text once at http://localhost:8080/example. It specifies how the user may request the information we’ll describe in the handler.


public class ExampleRouter {


  public RouterFunction<ServerResponse> routeExample (ExampleHandler exampleHandler) {

    return RouterFunctions

        .route(RequestPredicates.GET(“/example”).and(RequestPredicates.accept(MediaType.TEXT_PLAIN)), exampleHandler::hello);




The next step is to implement a listener for the /example route, which will process requests from any user. The router will forward the user to the handler if the requested path is valid. When a user sends a message to us, our handler reads it and redirects them to a page where we may welcome them.


public class ExampleHandler {

  public Mono<ServerResponse> hello(ServerRequest request) {

    return ServerResponse.ok().contentType(MediaType.TEXT_PLAIN)

         .body(BodyInserters.fromObject(“Hello, Spring WebFlux Example!”));



Run the application

Executing the Maven target spring-boot:run will now begin running our application. 

You should now be able to retrieve the following information by using your browser to go to http://localhost:8080/example.


It is dependent, as is the case with most choices concerning software architecture. Are you working on CRUD applications? Then there is no need for it; Spring MVC will do.

Do you manage enormous volumes of streaming data in addition to millions of customers? If this is the case, then reactive frameworks such as Spring WebFlux might reduce the cost of your monthly cloud payment.


Adding the Spring WebFlux module to your project’s dependencies will allow you to create reactive Java apps using Spring Boot. Use reactive types such as Mono or Flux to process input that arrives at different times. Use non-blocking reactive operators to do data transformations and processing.

Annotating your endpoint classes with @RestController and using reactive types for method return types will allow you to build a reactive API in Spring Boot. Use @GetMapping and @PostMapping annotations to route incoming HTTP requests to the appropriate methods. Use operators like onErrorResume and onErrorReturn to respond to errors.

The Spring WebFlux framework is used to construct a reactive application in Spring Boot, facilitating the effective management of concurrent and asynchronous tasks. It achieves great performance and scalability by using non-blocking I/O and event-driven programming. Spring Boot’s reactive applications handle data asynchronously using reactive types, operators, and libraries.