Lambda expression and Optional how to return String value

user_689876 0
Viewed 4304

I'd like to get an Optional value, I have something like this:

Optional<String> value =

Optional.ofNullable(MyObject.getPeople())
    .ifPresent(people -> people                                                                    
        .stream()                                                                    
        .filter(person -> person.getName().equals("test1"))
        .findFirst()
        .map(person -> person.getId()));

person.getId() should return a string, I tried this but it didn't work, getting incompatible types: void cannot be converted to java.util.Optional

Optional<String> value =

Optional.ofNullable(MyObject.getPeople())
    .ifPresent(people -> people                                                                    
        .stream()                                                                    
        .filter(person -> person.getName().equals("test1"))
        .findFirst()
        .map(person -> person.getId()))
        .orElse(null);

Any idea? Thanks

java-stream java-8 collections lambda java
3 Answers

Optional.ifPresent takes a Consumer - so you cannot return anything from it. Use Optional.map.

Optional.ofNullable(MyObject.getPeople())
    .map(people -> people                                                                    
        .stream()                                                                    
        .filter(person -> person.getName().equals("test1"))
        .findFirst()
        .map(person -> person.getId()))
    .orElse(null);

A better one would be to use flatmap and not return a null at the end (It is not recommended to assign null to an Optional variable)

Optional.ofNullable(MyObject.getPeople())
    .flatmap(people -> people                                                                    
        .stream()                                                                    
        .filter(person -> person.getName().equals("test1"))
        .findFirst()
        .map(person -> person.getId()));

Note: Your first statement is also a bit weird. If MyObject.getPeople returns a collection, then there is no need to wrap it with an Optional (unless the return value could be null - but again, it is recommended not to return null when the return type is a Collection).

user_44057570

Assuming people is a Collection, the first use of Optional is not needed. You may do it like so,

Optional<String> value = MyObject.getPeople().stream()
    .filter(person -> person.getName().equals("test1"))
    .findFirst().map(person -> person.getId());

If there exists a value it will return it, otherwise it will return an empty Optional.

user_41085900

Actually you don't need a nested lambda for that. Return Collections.emptyList() on orElse instead.

Optional<String> value = Optional.ofNullable(MyObject.getPeople())
            .orElse(Collections.emptyList())
            .stream()
            .filter(person -> person.getName().equals("test"))
            .findFirst()
            .map(Person::getId);
user_105846050
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