How you would use Spring WebFlux to consume data from an external service in a non-blocking manner and process this data reactively within your Spring Boot application.

Question

Accepted Answer

Spring WebFlux consumes external data non-blockingly using WebClient, whose responses are handled as reactive Mono/Flux streams so the calling thread is never blocked waiting on I/O.

Key Points:
• WebClient.get().uri(...).retrieve() issues the call without blocking the current thread.
• bodyToMono() is used for a single expected object; bodyToFlux() is used for a stream of multiple items.
• Operators like map(), filter(), and flatMap() transform the data reactively as it arrives, without waiting for the entire response to complete first.
• Backpressure is handled automatically by the reactive streams implementation, preventing a fast producer from overwhelming a slow consumer.
• The whole chain stays non-blocking end to end only if downstream code also avoids blocking calls (e.g. no .block() in request-handling paths).

Example:
Fetching a stream of stock price updates with WebClient returns a Flux that the application can filter for a specific symbol and map into a display format as each update arrives, without ever pausing the thread to wait.

Code Example:
```
public Flux streamPrices(String symbol) {
    return webClient.get()
            .uri("/prices/stream")
            .retrieve()
            .bodyToFlux(PriceUpdate.class)
            .filter(p -> p.getSymbol().equals(symbol));
}
```

Interview Tip:
A concise interview answer is:

"I'd use WebClient's non-blocking get().retrieve() and map the response into a Mono or Flux depending on whether I expect one item or a stream. From there, operators like map and filter let me process the data reactively as it arrives, keeping the whole pipeline non-blocking end to end."