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

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.

You are looking to [Optional::filter][1], 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
[1]: https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html#filter-java.util.function.Predicate-

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");
}

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");