Spring / Spring Webflux Interview questions

What does "Nothing happens until you subscribe" mean?

Reactive streams are lazy. Both Mono and Flux are just blueprints of an execution plan. Data doesn't start moving, and computations (like DB calls or API requests) don't trigger until a .subscribe() call is made.

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What is Reactive Programming? What is Spring Webflux? Is Spring WebClient thread safe? Is Spring RestTemplate deprecated? What are the benefits of using Spring Webflux? What is bodyToMono? Difference between Mono and Flux. How to handle errors in Spring WebFlux? Difference between Spring MVC @async and Spring Webflux? What is Reactor netty? What are router functions? What does Mono.defer() do? When should we choose Reactor over RxJava? How to handle an exception in a Spring Webflux based application? What is bodyToFlux? Disadvantages of Using Reactive Streams. Difference between the Web client and Web Test Client? Can we use SpringMvc and webflux together? What are the main components of Spring Webflux? What is the Flux API? What is a Publisher? Explain its main interfaces. Explain the difference between hot publishers and cold publishers. Explain throttling. What is Backpressure and how does it relate to Flux? Can you use a Flux to represent a single result? Why would you use Mono instead? What does "Nothing happens until you subscribe" mean? How do you convert a Flux into a Mono>? What is the difference between flatMap, concatMap, and switchMap? How do you handle errors in a Mono/Flux pipeline? When should you use Schedulers.boundedElastic()? Difference between Mono.just() and Mono.defer(). Difference between Mono.fromCallable and Mono.fromRunnable. Difference between Project Reactor and WebFlux.

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