Imperative vs. Reactive API in Spring Boot

In Spring Boot, APIs can be built using two main programming paradigms: Imperative and Reactive. While both approaches can achieve similar goals, the way they handle execution, data flow, and system resources differs significantly.

Imperative API

The imperative model is synchronous and blocking. When a request is made, the thread that handles the request waits for the task to complete before moving on to the next task. This is the traditional way of writing Java applications. It’s easier to reason about but can lead to thread exhaustion under high load.

Key Features:

• Synchronous: Operations are performed in sequence.
• Blocking: Threads wait for the current task to complete.
• Thread-per-request: Each request occupies a thread until completion.
• Simpler: Easier to debug and understand.

Reactive API

The reactive model, on the other hand, is asynchronous and non-blocking. Spring WebFlux, introduced in Spring 5, provides tools to build reactive APIs using the reactive streams specification. Reactive APIs are highly scalable, as they don’t block threads while waiting for resources (e.g., database responses), making them suitable for high-throughput, low-latency applications.

Key Features:

• Asynchronous: Operations are performed independently of the main thread.
• Non-blocking: Threads are not held up while waiting for external resources.
• Event-driven: Built around the concept of events (data streams).
• Scalable: Better performance under high load.

Example: Building a Reactive API with Spring WebFlux and MongoDB

Below is an example of a Reactive API using Spring WebFlux and MongoDB. It demonstrates how to create a repository, service, and controller using reactive programming principles.

1. Dependency Configuration (pom.xml)

Ensure the following dependencies are included in your pom.xml: