Check if null attribute present in Optional and return String Java Stream API

Question

I have the following

class Person
  private String firstName;
  private String familyName;

  // Setters and Getters

And I have the following method

public String getFullName(Optional<Person> persons) {
  return persons
           .map(person -> (person.getFirstName() + " " + person.getFamilyName())).orElse("Invalid");
}

I just want to check if either first or last name is null, display "Invalid" for that person. I was thinking to add a method for validation but I am sure there is an easier way I cannot think about.

Passing Optional as a parameter is not a good idea. instead, having Optional<String> for the method would be better. something like this: Optional<String> getFullName(Person person) { if (person.getFamilyName() == null && person.getFirstName() == null) return Optional.empty(); return Optional.of(person.getFirstName() + " " + person.getFamilyName()); } — Hadi
– Hadi, Commented Apr 3, 2020 at 19:16
@HadiJ Good point. Also thought about that after answering the question. The developers cannot get used to the original purpose of Optional, being a safe way to return a nullable value. Having Optional as a method parameter is kinda violating this principle. — ETO
– ETO, Commented Apr 3, 2020 at 19:26

Youcef LAIDANI · Accepted Answer · 2020-04-03 16:54:52Z

4

You are looking to Optional::filter, before the map:

return persons
        .filter(person -> person.getFamilyName() != null && person.getFirstName() != null)
        .map(person -> person.getFirstName() + " " + person.getFamilyName())
        .orElse("Invalid");

Which mean, if the family and first names are not null then create your concatination, otherwise return an Invalid message, or you can even throw an exception by using orElseThrow

answered Apr 3, 2020 at 16:54

Youcef LAIDANI

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Comments

Andronicus · Accepted Answer · 2020-04-03 16:53:17Z

1

You can use filter for that:

public String getFullName(Optional<Person> persons) {
  return persons
           .filter(person -> Objects.nonNull(person.getFirstName()) && Objects.nonNull(person.getFamilyName()))
           .map(person -> (person.getFirstName() + " " + person.getFamilyName())).orElse("Invalid");
}

answered Apr 3, 2020 at 16:53

Andronicus

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ETO · Accepted Answer · 2020-04-03 19:22:59Z

1

Another functional approach.

First create a predicate builder method for required field validation:

public static <T, F> Predicate<T> hasRequiredValue(Function<T, F> fieldGetter) {
    return fieldGetter.andThen(Objects::nonNull)::apply;
}

And modify the getFullName a little bit:

public Optional<String> getFullName(Person person) {
    return Optional.ofNullable(person)
                   .filter(hasRequiredValue(Person::getFamilyName))
                   .filter(hasRequiredValue(Person::getFirstName))
                   .map(p -> p.getFirstName() + " " + p.getFamilyName());
}

Then use it as follows:

Person person = ...
String fullName = getFullName(person).orElse("Invalid");

edited Apr 3, 2020 at 19:22

answered Apr 3, 2020 at 19:15

ETO

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