"Functional programming"

FunctionalProgramming.java

class FunctionalProgramming {
 
  private static <T> CheckoutModel<Optional<T>> oldHandleObservable(Observable<T> observable, RegisterFailed attempt) {
    final Set<ChkNotificationMessage> errorMessages = new HashSet<>();
    Optional<T> optional = observable
            .doOnError(throwable -> errorMessages.addAll(mapChkAdapterExceptions(throwable, attempt)))
            .onErrorResumeNext(Observable.empty())
            .map(Optional::of)
            .defaultIfEmpty(Optional.empty())
            .toBlocking()
            .single();
    optional.ifPresent(it -> errorMessages.addAll(getMessages(it)));
    return new CheckoutModel<>(optional, errorMessages);
  }
  
  private static <T> Observable<CheckoutModel<Optional<T>>> handleObservable(Observable<T> observable, RegisterFailed attempt) {
    return observable
            .map(it -> new CheckoutModel<>(Optional.of(it), getMessages(it)))
            .onErrorResumeNext(this::handleRedirect) // throw redirect exception
            .onErrorResumeNext(it -> handleOtherThanRedirect(it, attempt));
  }
}