Handling nulls with Optional

Let's imagine following situation:
We have some 3rd party code (or legacy one that you can't change at the moment) that fetches objects representing people based on some parameter. This could look as following:

	public interface PersonService {
	Person getByName(String name);
	}
	public class Person {
	private final String name;
	private final int age;
	private final Address address;
	// ...
	}
	public class Address {
	private final String street;
	private final String city;
	// ...
	}

view raw PersonLegacy.java hosted with ❤ by GitHub

Our task is to retrieve city in which specific person lives for further processing. We don't have any guarantee over data consistency, so we need to handle it on our own.

Task seems to be simple, how can we achieve this?
One solution could look something like:

	public class CityRetriever {
	private final PersonService personService;
	public String retrieveCity(String name) {
	Person person = personService.getByName(name);
	if (person != null) {
	Address address = person.getAddress();
	if (address != null) {
	if (address.getCity() != null) {
	return address.getCity();
	}
	}
	}
	return null;
	}
	}

view raw CityRetriever.java hosted with ❤ by GitHub

As you can see above it's quite ugly. Multiple nested if statements don't look nice. What is more, returning null is not a good practice.

What can we do to get rid of the ifs and indicate that city might not be present?

We can use Optional type:

	public class CityRetrieverWithOptional {
	private final PersonService personService;
	public Optional<String> retrieveCity(String name) {
	return Optional.ofNullable(personService.getByName(name))
	.map(Person::getAddress)
	.map(Address::getCity);
	}
	}

view raw CityRetrieverWithOptional.java hosted with ❤ by GitHub

map methods take care of handling null and we're returning Optional to indicate that value might not be there.
Instead of returning Optional we could consider null object

The whole project (with the tests checking the solution) can be found on github