1. Overview

Reactive programming is a programming paradigm emphasizing the principles of asynchronous data streams and non-blocking operations. The key objective is to build applications that can handle multiple concurrent events and process them in real-time.

Traditionally, in imperative programming, we execute code sequentially, one instruction at a time. However, in reactive programming, we can process multiple events concurrently, which enables us to create more responsive and scalable applications.

This tutorial will cover Hibernate Reactive programming, including the basics, its differences from traditional imperative programming, and a step-by-step guide on using Hibernate Reactive with Spring Boot.

2. What Is Hibernate Reactive?

Reactive Hibernate is an extension of the Hibernate ORM framework, widely used for mapping object-oriented programming models to relational databases. This extension incorporates reactive programming concepts into Hibernate, enabling Java applications to interact with relational databases more efficiently and responsively. By integrating reactive principles such as non-blocking I/O and asynchronous data processing, Reactive Hibernate allows developers to create highly scalable and responsive database interactions within their Java applications.

Hibernate Reactive extends the popular Hibernate ORM framework to support reactive programming paradigms. This extension enables developers to build reactive applications capable of handling large datasets and high traffic loads. One significant benefit of Hibernate Reactive is its ability to facilitate asynchronous database access, ensuring the application can handle multiple requests concurrently without creating a bottleneck.

3. What Makes It Special

In traditional database interactions, when a program sends a request to the database, it has to wait for the response before moving on to the next task. This waiting time can add up, especially in applications heavily relying on the database. Hibernate Reactive introduces a new approach where database interactions are handled asynchronously.

This means that instead of waiting for each database operation to finish before moving forward, the program can carry out other tasks at the same time while waiting for the database response.

This concept is similar to being able to continue shopping while the cashier processes the payment. Hibernate Reactive significantly improves applications’ overall efficiency, performance, resource utilization, and responsiveness by allowing programs to perform other tasks while waiting for database responses.

This is particularly important in scenarios such as high-traffic e-commerce websites, where applications must handle many concurrent users or execute multiple database operations simultaneously.

In such cases, Hibernate Reactive’s capability to continue with other tasks while waiting for database responses can greatly enhance the application’s performance and user experience. Hibernate Reactive provides developers with the tools to build highly scalable and responsive applications. It enables these applications to handle heavy database workloads without sacrificing performance. This demonstrates the potential of Hibernate Reactive in the hands of skilled developers. Explaining these points helps to understand how Hibernate Reactive differs from traditional database interactions and why it is beneficial for creating modern Java applications. However, it’s important to note that Hibernate Reactive may not be suitable for all use cases, especially those that require strict transactional consistency or have complex data access patterns.

4. Maven Dependency

Before we start, we need to add the Hibernate Reactive Core and Reactive Relational Database Connectivity (R2DBC) dependencies to the pom.xml file:


5. Add Reactive Repository

In traditional Spring Data, repositories handle database interactions synchronously. Reactive repositories perform these operations asynchronously, making them more responsive.

5.1. Entities

Entities are the same as the traditional entities used in traditional applications:

public class Product {
    private Long id;
    private String name;

5.2. Reactive Repository Interfaces

Reactive repositories are specialized interfaces that extend R2dbcRepository, which is designed to support reactive programming with relational databases(R2DBC). These repositories in Hibernate offer a range of methods tailored for asynchronous operations, including save, find, update, and delete. This asynchronous approach allows for non-blocking interactions with the database, making it well-suited for high-concurrency and high-throughput applications:

public interface ProductRepository extends R2dbcRepository<Product, Long> {

Reactive repositories return reactive types such as Mono (for single results) or Flux (for multiple results), allowing for the handling of asynchronous database interactions.

6. Add Reactive Service

In Spring Boot, reactive services are designed to handle business logic asynchronously by leveraging reactive programming principles, promoting increased application responsiveness and scalability. In contrast to traditional Spring applications, where service classes execute business logic synchronously, reactive applications have service methods that return reactive types to manage asynchronous operations effectively. This approach allows for more efficient resource utilization and improved handling of concurrent requests :

public class ProductService {
    private final ProductRepository productRepository;
    public ProductService(ProductRepository productRepository) {
        this.productRepository = productRepository;

    public Flux<Product> findAll() {
        return productRepository.findAll();

    public Mono<Product> save(Product product) {
        return productRepository.save(product);

like Repositories, Services methods return reactive types like Mono or Flux, allowing them to perform asynchronous operations without blocking the application.

7. Unit Testing

Reactive unit testing is an essential practice in software development, focusing on testing individual application components in isolation to ensure their proper functioning. Specifically in reactive applications, unit tests play a crucial role in verifying the behavior of reactive components such as controllers, services, and repositories. Regarding reactive services, unit tests are important for ensuring that service methods exhibit the expected behavior, including managing asynchronous operations and correctly handling error conditions. These tests help to guarantee the reliability and effectiveness of the reactive components within the application:

public class ProductServiceUnitTest {
    private ProductService productService;

    private ProductRepository productRepository;
    void setUp() {
          .then(productRepository.save(new Product(1L, "Product 1", "Category 1", 10.0)))
          .then(productRepository.save(new Product(2L, "Product 2", "Category 2", 15.0)))
          .then(productRepository.save(new Product(3L, "Product 3", "Category 3", 20.0)))

    void testSave() {
        Product newProduct = new Product(4L, "Product 4", "Category 4", 24.0);

          .assertNext(product -> {
              assertEquals("Product 4", product.getName());

    void testFindAll() {

8. Conclusion

In this tutorial, We covered the fundamentals of building reactive applications using Hibernate Reactive and Spring Boot. We also discussed the benefits and how to define and implement reactive components. We also addressed unit testing for reactive components, emphasizing the ability to create modern, efficient, and scalable applications. As always, the source code for this tutorial is available over on GitHub.

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