What’s the Difference Between @Async and Spring WebFlux?

Both help you do things asynchronously in Spring — but they’re not the same.

@Async:

• Works in traditional Spring MVC.

• Runs the method on a new thread, using a thread pool.

• Still uses blocking I/O — threads wait for things like DB calls or file access.

• Best for simple background tasks like sending emails or logging.

Easy to use, but not great for handling lots of users or real-time data.

WebFlux:

• Uses reactive programming (Mono, Flux).

• Built for non-blocking, event-driven apps.

• Doesn’t need a new thread per request — super efficient under high load.

• Supports backpressure (lets slow consumers avoid being overwhelmed).

Great for APIs, streaming data, or apps that handle lots of users at once.