Spring Boot Spring Boot WebFlux and Reactive Programming 3

Question 1

Which Reactor operator blocks the reactive pipeline until the Mono or Flux completes, returning the result synchronously?

Accepted Answer

block()

Answer

`block()` subscribes to the publisher and waits (blocking the calling thread) until it emits its terminal signal, returning the value or null.

Question 2

In Spring WebFlux, what is the purpose of `WebTestClient`?

Accepted Answer

A tool for testing reactive WebFlux controllers and endpoints

Answer

`WebTestClient` is a test-focused HTTP client for asserting responses from WebFlux handlers, supporting both mock and live server modes.

Question 3

What does the `switchIfEmpty` operator do in a Reactor pipeline?

Accepted Answer

Subscribes to a fallback publisher when the source completes empty

Answer

`switchIfEmpty` subscribes to an alternate `Publisher` only when the original source completes without emitting any element.

Question 4

Which interface must a class implement to act as a global exception handler in Spring WebFlux?

Accepted Answer

WebExceptionHandler

Answer

`WebExceptionHandler` is the functional interface for handling unhandled exceptions in the WebFlux pipeline, registered as a bean with high priority.

Question 5

How does Spring WebFlux support server-sent events (SSE) in a controller method?

Accepted Answer

By returning Flux> with produces = text/event-stream

Answer

Returning a `Flux>` with `produces = MediaType.TEXT_EVENT_STREAM_VALUE` causes WebFlux to stream SSE events to the client.

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