Snippet

Non-Blocking WebClient Requests with Timeout and Fallback

Spring WebClient provides a fully reactive and non-blocking alternative to RestTemplate. Combining reactive operators like timeout() and onErrorReturn() prevents thread starvation during slow downstream network calls and supplies reliable fallback values asynchronously.

snippet.java

java

@Service
public class CurrencyConversionService {
 
    private final WebClient webClient;
 
    public CurrencyConversionService(WebClient.Builder builder) {
        this.webClient = builder.baseUrl("https://api.fxrates.example.com").build();
    }
 
    public Mono<BigDecimal> fetchExchangeRate(String currency) {
        return webClient.get()
            .uri("/rates/{currency}", currency)
            .retrieve()
            .bodyToMono(BigDecimal.class)
            .timeout(Duration.ofMillis(1500))
            .onErrorReturn(TimeoutException.class, BigDecimal.ONE);
    }
}

spring

Breakdown

private final WebClient webClient;

Declares the immutable, reactive HTTP client instance.

.bodyToMono(BigDecimal.class)

Decodes the response body asynchronously into a single-element Project Reactor Mono stream.

.timeout(Duration.ofMillis(1500))

Emits a TimeoutException if the remote service does not reply within 1.5 seconds.

.onErrorReturn(TimeoutException.class, BigDecimal.ONE)

Catches the timeout exception and safely defaults to a known base exchange rate.

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Non-Blocking WebClient Requests with Timeout and Fallback

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