Deserialize JSON created using custom getter and unwrapped object using Jackson

This is a follow up question of an answer to Jackson custom getters.

The solution works and creates proper JSON. The problem is deserialization. I have an unwrapped object with some attributes not shown in JSON but instead replaced by a new attribute (e.g. firstname+surname => name).

This is correctly serialized to

{"age":22,"name":"Alex Doe"}

This class can not be edited, so we rely on mixin.

The problem on deserialization is, that PersonSerializer.setFullname() is called before PersonSerializer.setPerson(), probably because attributes are deserialized before subobjects. Which forces me to have a Person-object created when PersonSerializer is created by the ObjectMapper. This Person-object is overwritten when age is deserialized with an Person-object only containing the age:

firstName: null, surname: null, age: 22

I could store fullname in setFullname() and fill it into person when setPerson() is called but this feels incorrect.

What is the proper way to solve this problem?

Code:

public final class Person {

    private String firstName;
    private String surname;
    private int age;

    public Person() {
        super();
    }

    Person(final String firstName, final String surname, final int age) {
        super();
        this.firstName = firstName;
        this.surname = surname;
        this.age = age;
    }
 //getter and setter
}

Serialization helper and mixin based on the answer:

public class PersonSerializer {

    private Person person;

    public PersonSerializer() {
        super();
        person = new Person(); //needed, otherwise NPE in setFullname()
    }

    @JsonUnwrapped
    Person getPerson() {
        return person;
    }

    //customer getter to join firstname and surname
    @JsonGetter("name")
    String fullName() {
        return person.getFirstName() + " " + person.getSurname();
    }

    @JsonSetter("name")
    public void setFullname(final String fullName) {
        final String[] s = fullName.split(" ");
        person.setFirstName(s[0]);
        person.setSurname(s[1]);
    }

    public void setPerson(Person p) {
        person = p;
    }
}

and

abstract class PersonMixin {

    @JsonIgnore String firstName;
    @JsonIgnore String surname;
}

Testcode:

public static void main(String[] args)

        throws JsonProcessingException {

        final ObjectMapper mapper = new ObjectMapper().addMixIn(Person.class, PersonMixin.class);
        mapper.setVisibility(PropertyAccessor.GETTER, JsonAutoDetect.Visibility.ANY);
        final PersonSerializer alex = new PersonSerializer();
        alex.setPerson(new Person("Alex", "Doe", 22));
        final String s = mapper.writeValueAsString(alex);
        out.println(s);

        final Person newAlex = mapper.readValue(s, PersonSerializer.class).getPerson();
        out.println(String.format(
            "firstName: %s, surname: %s, age: %d",
            newAlex.getFirstName(),
            newAlex.getSurname(),
            newAlex.getAge()
        ));
    }

I searched for examples, documentation and StackOverflow but to no avail.