spring webclient: retry with backoff on specific error

Question

i'd like to retry the request 3 times after waiting 10sec when response is 5xx. but i don't see a method that I can use. On object

WebClient.builder()
                .baseUrl("...").build().post()
                .retrieve().bodyToMono(...)

i can see methods:

retrying on condition with retry count but no delay

.retry(3, {it is WebClientResponseException && it.statusCode.is5xxServerError} )

retrying with backoff and number of times but no condition

.retryBackoff 

there is also a retryWhen but i'm not sure how to use it

Answer 1

With reactor-extra you could do it like:

.retryWhen(Retry.onlyIf(this::is5xxServerError)
        .fixedBackoff(Duration.ofSeconds(10))
        .retryMax(3))

private boolean is5xxServerError(RetryContext<Object> retryContext) {
    return retryContext.exception() instanceof WebClientResponseException &&
            ((WebClientResponseException) retryContext.exception()).getStatusCode().is5xxServerError();
}

Update: With new API the same solution will be:

    .retryWhen(Retry.fixedDelay(3, Duration.ofSeconds(10))
            .filter(this::is5xxServerError));

//...

private boolean is5xxServerError(Throwable throwable) {
    return throwable instanceof WebClientResponseException &&
            ((WebClientResponseException) throwable).getStatusCode().is5xxServerError();
}

Answer 2

You can do this taking the following approach:

• Use the exchange() method to obtain the response without an exception, and then throw a specific (custom) exception on a 5xx response (this differs from retrieve() which will always throw WebClientResponseException with either a 4xx or 5xx status);
• Intercept this specific exception in your retry logic;
• Use reactor-extra - it contains a nice way to use retryWhen() for more complex & specific retries. You can then specify a random backoff retry that starts after 10 seconds, goes up to an arbitrary time and tries a maximum of 3 times. (Or you can use the other available methods to pick a different strategy of course.)

For example:

//...webclient
.exchange()
.flatMap(clientResponse -> {
    if (clientResponse.statusCode().is5xxServerError()) {
        return Mono.error(new ServerErrorException());
    } else {
        //Any further processing
    }
}).retryWhen(
    Retry.anyOf(ServerErrorException.class)
       .randomBackoff(Duration.ofSeconds(10), Duration.ofHours(1))
       .maxRetries(3)
    )
);

Answer 3

the retryWhen with Retry.anyOf and Retry.onlyIf are deprecated I assume. I found this approach useful, and it allows us to process and throw a User defined exception.

for example :

retryWhen(Retry.backoff(3, Duration.of(2, ChronoUnit.SECONDS))
                        .filter(error -> error instanceof UserDefinedException/AnyOtherException)
                        .onRetryExhaustedThrow((retryBackoffSpec, retrySignal) ->
                                new UserDefinedException(retrySignal.failure().getMessage())))