Polymorphism in XStream serialization and deserialization

Question

I have these classes:

@XStreamAlias("person")
public class PersonConfig {

    private AnimalConfig animalConfig;

}

public interface AnimalConfig {}

@XStreamAlias("dog");
public class DogConfig extend AnimalConfig {}

@XStreamAlias("cat");
public class CatConfig extend AnimalConfig {}

And I would like to be able to deserialize this xml with the classes above:

<person>
    <dog/>
<person>

As well as deserialize this xml too, with the same classes:

<person>
    <cat/>
<person>

So that in both cases, the PersonConfig's field animalConfig is filled. In the first XML with a DogConfig instance and in the second XML with a CatConfig instance.

Is this possible by adding some annotation to make this work?

Answer 1

It seems XStream does not allow you to do it easily.

Your question is similar to this one, asking for managing something like a xsd:choice with XStream.

If you don't necessarily need to use XStream, JAXB will allow you to do it easily :

@XmlRootElement(name="person")
public class PersonConfig {

    private AnimalConfig animalConfig;

    @XmlElementRefs({
        @XmlElementRef(name="cat", type=CatConfig.class),
        @XmlElementRef(name="dog", type=DogConfig.class)
    })
    public AnimalConfig getAnimalConfig() {
        return animalConfig;
    }

    public void setAnimalConfig(AnimalConfig animalConfig) {
        this.animalConfig = animalConfig;
    }
}

After some researches, listing all available classes for your property can be avoided if you choose to use the XmlAdapter. In Blaise Doughan link, the example uses an abstract class, not an interface.

Edit :

As Blaise Doughan said in its comment, @XmlElementRef is better suited for this purpose. Code has been updated accordingly.