使用注释的Jackson多态反序列化

Question

Assume we have the following types:

interface Animal {}
class Dog implements Animal {...}
class Cat implements Animal {...}
class Zoo {
    private String animalType;
    private Animal animal;
    ...
}

Having that Cat and Dog have different properties, how can we deserialize Zoo object to appropriate Animal subtype based on animalType string which is always present in json ? I know how to do that with custom deserialization but i can't find the way to do the same using Jackson annotations . This would be possible if animalType property resides in Cat or Dog but in my case its location is in Zoo .

Any idea ?

Answer 1

You can annotate the animal field in Zoo with JsonTypeInfo to specify which subtype you want Dog or Cat per the animalType field also in Zoo . The tricky bit is to specify that the specific type of Animal will come from a property outside of Animal in the JSON ie an EXTERNAL_PROPERTY

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXTERNAL_PROPERTY, property = "animalType")
@JsonSubTypes({
        @JsonSubTypes.Type(value = Cat.class, name = "cat"),
        @JsonSubTypes.Type(value = Dog.class, name = "dog")
})
private Animal animal;