Reactive

Spring MVC assigns one thread per request. When I/O waits pile up, threads sit idle. WebFlux replaces this with an event loop-based non-blocking model. A summary of the structural differences from MVC, the Reactor pattern, and when to choose which.

Observer cuts coupling through a one-to-many relationship that notifies subscribers of state changes. The Subject just notifies, unaware of who listens. EventEmitter, RxJS, and event-driven architecture all extend from here. It differs from broker-mediated pub/sub.