Spring WebMVC vs Spring Webflux?

Feature	Spring MVC	Spring WebFlux
Programming model	Synchronous (traditional Java)	Asynchronous (reactive streams)
Controller return	String, ModelAndView, etc.	Mono<T>, Flux<T>
Server container	Tomcat, Jetty, Undertow (Servlet)	Netty (default), or Reactive Jetty
Use case	Simpler apps, low concurrency	High concurrency, streaming, SSE
Gateway support	✅ spring-cloud-starter-gateway-server-webmvc	✅ spring-cloud-starter-gateway-server-webflux

Spring MVC:

@GetMapping("/hello")
public String hello() {
    return "Hello";
}

Spring WebFlux:

@GetMapping("/hello")
public Mono<String> hello() {
    return Mono.just("Hello");
}

Reactive vs Servlet?

Concept	Servlet (Blocking)	Reactive (Non-blocking)
Request model	One thread per request	One thread handles many requests
I/O	Blocking (e.g., InputStream.read())	Non-blocking (e.g., Mono/Flux)
Concurrency	Limited by thread pool	Scales better with fewer threads
Libraries	Uses Tomcat, Jetty, etc.	Uses Netty (no servlet container)
Memory/CPU	Higher resource usage	More efficient under high load
Example use	Traditional CRUD apps, MVC websites	Streaming APIs, high-concurrency APIs