Retry for Spring @HttpExchange

Question

I'm using Spring-boot-3 @GetExchange with a WebClient, sometimes we hit a following error:

java.lang.IllegalStateException: Timeout on blocking read for 5000000000 NANOSECONDS

What's the best practice, in case of using @GetExchange to instruct the WebClient to retry? There isn't enough documentation for this new annotation.

Answer 1

You need to use ExchangeFilterFunctions that will help you define your retry logic.

    @Bean
    FooClient fooClient() {
        WebClient webClient =WebClient.builder()
            .baseUrl("your_base_url")
            .filter(withRetryableRequests())
            .build();
        HttpServiceProxyFactory factory=HttpServiceProxyFactory
            .builder(WebClientAdapter.forClient(webClient))
            .blockTimeout(Duration.of(HTTP_CLIENT_READ_TIMEOUT, ChronoUnit.SECONDS)) // Configure how long to wait for a response for an HTTP service method with a synchronous (blocking) method signature.By default this is 5 seconds.
            .build();
        return factory.createClient(FooClient.class);
    }

  
    private ExchangeFilterFunction withRetryableRequests() {
        return (request, next) -> next.exchange(request)
                .flatMap(clientResponse -> Mono.just(clientResponse)
                        .filter(response ->  clientResponse.statusCode().isError())
                        .flatMap(response -> clientResponse.createException())
                        .flatMap(Mono::error)
                        .thenReturn(clientResponse))
                .retryWhen(this.retryBackoffSpec());
    }
    
    private RetryBackoffSpec retryBackoffSpec() {
        return Retry.backoff(3, Duration.ofSeconds(2))
                .filter(throwable->throwable instanceof  WebClientResponseException) // here filter on the errors for which you want a retry
                .doBeforeRetry(retrySignal -> log.warn("Retrying request after following exception : {}",  retrySignal.failure().getLocalizedMessage()))
                .onRetryExhaustedThrow((retryBackoffSpec, retrySignal)  -> retrySignal.failure());
    }

[EDIT] For the particular case that you encounter, i.e. the exception

java.lang.IllegalStateException: Timeout on blocking read for 5000000000 NANOSECONDS

the probable cause is that your service is waiting for the answer to the request and after 5 seconds (by default), the service hangs up.

It would be necessary to increase the read timeout of the http client used. I have edited the code accordingly with a comment on the line concerned.