What is Reactive Programming?

Reactive Programming is an asynchronous, non-blocking programming paradigm where:

• Data is treated as a stream of events.
• The system reacts to emitted data, errors, or completion signals.
• It’s designed for scalability and efficient resource usage, especially in I/O-heavy applications.

Core principles (Reactive Manifesto):

1. Responsive – Respond to requests quickly.
2. Resilient – Stay responsive under failure.
3. Elastic – Adapt to changing load.
4. Message-driven – Use asynchronous message passing.

In Java/Spring:

• Implemented via Project Reactor (Mono and Flux).
• Used in Spring WebFlux.

Thread-per-request Model (Traditional)

How it works (Spring MVC style):

• Every incoming HTTP request is assigned its own thread from a pool.
• The thread blocks while waiting for I/O (e.g., database query, API call).
• Thread pool size limits scalability — if all threads are blocked, requests wait.

Problems: