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Reactive Applications with Spring WebFlux Framework (Udemy.com)

Creating a Secure, Reactive and non-blocking REST API with Spring WebFlux

Created by: Sergey Kargopolov

Last updated June 2026

Our take

Based on the ratings of 387 students, a sample of their written reviews and the syllabus, as the course stood in June 2026. No course pays to be reviewed.

Sergey Kargopolov's course is a build-along for Java developers who already know a little Spring. It runs about 11.4 hours across 150 lectures and grows one REST API through the presentation, data and service layers, then adds pagination and error handling. Security takes a big share of the syllabus: password encryption, login, JWT creation and validation, and method-level annotations. The last stretch covers server-sent events, WebClient and testing at the web, service and data layers.

Reviewers like the pace. They describe a calm voice, short videos and explanations that say why each step is taken, not just what to type. One called it straight to the point with no fluff. The complaints are mild. Two say concepts get repeated, one found the database authentication flow confusing without a diagram, and two wanted more theory on reactive design. One reviewer missed a side-by-side performance comparison with blocking code, and another simply found it hard going. Of 387 reviews, 252 are five stars and only two are one star.

The course was last updated in June 2026, so the tooling should not feel stale. It is a practical pick for Java developers who know basic Spring and want a secured, tested WebFlux API to follow step by step. If your goal is to understand reactive streams in depth, you will probably want a second, more theoretical resource alongside it.

Best forJava developers with some Spring who want WebFlux and JWT security taught through one secured API build.
Skip it ifYou want deep reactive theory, design approaches or performance comparisons against blocking code.

Pros

  • Short videos with a calm voice that explains why each step is taken
  • Full security path: login, JWT generation and validation, method-level annotations
  • Tests covered for the web, service and data layers, plus WebClient and SSE
  • Updated in June 2026, with source code provided to follow along

Cons

  • Light on reactive theory and design; some reviewers wanted far more depth
  • Some concepts are repeated, and one student found the database authentication flow confusing
  • No coding exercises, and only two quizzes across the whole course
This is very useful course to learn this new Reactive programming paradigm. Here, it is concisely and clearly explained. No fluff, no unnecessary theory, all straight to the point!!
Zwakele Mgabhi, a student

Tagged All Levels, but it assumes basic Java and some Spring, so it suits beginners to WebFlux, not to Java.

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What you will learn

  • What Reactive Programming is
  • Architecture of Reactive Spring Boot application
  • Create Reactive Spring Boot application
  • Write and read from a database in reactive/non-blocking way
  • Use Spring Security in reactive Spring WebFlux application
  • Implement user authentication in reactive application
  • Implement JWT authentication in reactive application
  • Create and validate JSON Web Tokens(JWT)
  • Use method-level security annotations
  • Write Spring Security Expressions(SpEL)

Course content

21 sections · 150 lectures · 11 hours of video 2 quizzes, 18 articles

  1. 1Introduction 1 free preview1 lecture · 2 min
  2. 2Introduction to traditional(Blocking) Applications3 lectures · 1 quiz · 13 min
  3. 3Introduction to Reactive Programming 1 free preview7 lectures · 1 quiz · 36 min
  4. 4Creating a Reactive Spring Boot application project 2 free previews6 lectures · 29 min
  5. 5Presentation layer: Accept HTTP request and return HTTP response 1 free preview12 lectures · 1.1 hours
  6. 6Data layer: Working with a database4 lectures · 15 min
  7. 7Service layer: Business logic7 lectures · 34 min
  8. 8List all users. Pagination in Reactive Spring WebFlux REST application.5 lectures · 19 min
  9. 9Error Handling in Reactive Spring WebFlux applications7 lectures · 31 min
  10. 10Unprotected API endpoints - Security Security in Reactive WebFlux.4 lectures · 12 min

Who it is for

The instructor says it suits

  • Java developers interested in learning how to create reactive applications with Spring Framework

What you need before you start

  • Basic knowledge of Java
  • Basic familiarity with Spring Framework

How it compares

Against the other 518 rated Udemy courses in Software Development on CourseDuck:

  • Rating4.6 out of 5higher than 62% of them
  • Reviews387#255 of 519 by number of reviews
  • Length11.4 hourslonger than 73% of them
  • Last updatedJune 2026more recently than 78% of them

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Course Description

In this video course you will learn how to create Reactive and Non-blocking applications with Spring WebFlux framework.


This course is perfect for beginners and will start with the basics of Spring WebFlux.


You will learn: 

- What Reactive programming is and how it is different from an imperative programming style,

- The key differences between the traditional, blocking Spring WebMVC and the non-blocking, Reactive Spring WebFlux applications,

- To create reactive RESTful Web Service application that handles different types of HTTP requests,

- Write and read information from a database in a reactive, non-blocking way.


As you progress through the course, you will learn how to:

- Use Spring Security to protect your Spring WebFlux application,

- Implement user login(authentication),

- Generate and use JSON Web Tokens (JWT) for secure communication

- Validate JWT and read token claims,

- Use method-level security annotations to perform authorization.


You will also learn how to add pagination and read database records in smaller chunks to improve performance.


All important concepts are explained using simple, easy-to-follow slides. The source code is provided, so you can download it and follow along with each lesson.


This course also includes helpful quiz questions to test your knowledge as you go. Plus, there is an active Q&A section where you can get answers to all your questions


By the end of this course, you’ll be able to create fast, secure, and scalable Reactive applications with Spring WebFlux.



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Instructor Details

Sergey Kargopolov

I have more than 20 years of experience in building different types of software. I started my career as an Entrepreneur with award-winning web projects and currently, I’m a Full Stack Developer with a passion for teaching beginner programmers to reach their goals and assisting them in the development of their applications.

Follow me on Twitter, LinkedIn or Instagram to stay in touch.

Happy learning!

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Reviews

4.6

387 ratings on Udemy

Select a bar to show only those reviews.Select the bar again to show every rating.

By Cleber B. Luiz on 9/25/2026

This course is excellent. The professor is very didactic and explains everything being implemented in the development process with calmness and clarity, as well as the treatments carried out in the applications and tests, so that the student understands everything that is being done and why. These are not video lessons of the professor just coding, but rather explaining and teaching in the best way possible for comprehension and learning.

By Zwakele Mgabhi on 1/8/2026

This is very useful course to learn this new Reactive programming paradigm. Here, it is concisely and clearly explained. No fluff, no unnecessary theory, all straight to the point!!

By Anonymized User on 11/6/2025

I think you should provide more details how database authentication works by using some flow chart ,it is bit confusing directly code in project.

By Nicola Gioia on 8/13/2025

well structured course for beginner in webflux but with an existing knowledge on Spring framework itself. Sometime some concept are repeated, but basically it seems a good course

By Viachaslau Strelnikau on 7/25/2025

I enjoyed this course. The instructor has a pleasant voice, and the material was presented clearly. The course is well-suited for beginners in reactive development and covers all the essential aspects of the topic. Suggestions for improvement: Include more in-depth theoretical explanations Record videos for the text-based lectures Add quizzes or practical exercises after each topic

By Konstantin on 6/4/2025

Calm voice, good pronounciation, good presentation 10/10, serega keep going, molodec ! Sergey could have repeated some things a little less, and not commented on each of his actions in such detail. However, I highly recommend this course, Sergey did an excellent job and provided high-quality content. Keep going, Serega !

By Anonymized User on 5/28/2025

Very precisely fundamental technical things are explained , I believe anyone can able to get clear understanding how webflux or reactive programming works

By Elwyn Onomor on 3/31/2025

It provided the essential aspects of the framework to get one started and to build upon. However, some area could have been improved with bit more elaboration

By Keshav Kumar Nirala on 1/22/2025

Overall, it's a great. Explanations easy to understand. I would say it is valuable for beginner to medium level students. I missed the Quiz part it was present in starting sections. Things that I think missed in the course: - 1. At the time of explaining any topic (Mono or Flux or Validation etc.) then you can give one easy to understand example that you have done already, but you should also keep in mind that some Realtime complexity example must be included. I mean you should have multiple Mono that results should be combined and based on that another mono will fetch actual data. 2. Lengthy code that needs to be validated and refactored for sonar cube suggestion inside service, ex- Get User api. After fetching user data, it should be validated for email must not empty if it is empty then return the response as email can't be empty. Next validate the address it must contain List of addresses if it is empty return response as address can't be empty and so on.

By Pål Oliver Kristiansen on 1/14/2025

Very nicely paced course. Relatively short, but solid foundations. It uses quite a bit time on the security part though, so if this is important for you, you're in luck.

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Overall Score : 92 / 100