static <T extends Response> RetryRuleWithContent<T> onException(Class<? extends Throwable> exception,
                                                                    Backoff backoff) {
        return RetryRuleWithContent.<T>builder().onException(exception).thenBackoff(backoff);
    }
Returns a newly created a {@link RetryRuleWithContent} that will retry with the specified
{@link Backoff} if an {@link Exception} is raised and that is an instance of the specified
{@code exception}.
core/src/main/java/com/linecorp/armeria/client/retry/RetryRuleWithContent.java