Spring WebFlux

Spring WebFlux is Spring Framework's reactive web framework for building high-concurrency, non-blocking web applications. Unlike traditional Spring MVC (which allocates one thread per request), WebFlux uses async streams to handle thousands of concurrent connections with a small, fixed pool of threads. It's built on Project Reactor, which provides Mono and Flux abstractions for composing asynchronous operations. WebFlux is ideal for APIs with high concurrency (mobile apps, real-time applications, IoT), microservices, and systems where thread count is a bottleneck. Cloud-native and microservice architectures demand high-concurrency frameworks. Traditional blocking frameworks (Spring MVC) don't scale well beyond a few thousand requests; WebFlux scales to millions. Teams using WebFlux reduce server costs, improve latency, and handle traffic spikes gracefully. WebFlux engineers command competitive salaries ($150-220k USD senior) because they solve hard problems: concurrency, streaming, backpressure, and distributed systems. It's becoming the standard for modern Java backends.