Tell about a new concept or technology you recently mastered.

Recently, I mastered the concept of reactive programming in Java using the Reactor project and Spring WebFlux. This allows creating non-blocking, asynchronous applications that scale better under high load.

Instead of the traditional synchronous approach, where a thread waits for an operation to complete, the reactive approach uses data streams (Flux, Mono) that are processed as they arrive, increasing performance and responsiveness.

An example of creating a reactive controller in Spring WebFlux:

@GetMapping("/numbers")
public Flux<Integer> streamNumbers() {
    return Flux.range(1, 10).delayElements(Duration.ofMillis(500));
}

This controller sends numbers from 1 to 10 with a delay, without blocking the server.