RFE: allow missing of type id if target value is concrete

@JsonTypeInfo( use = JsonTypeInfo.Id.NAME,  include = JsonTypeInfo.As.PROPERTY, property = "type")
@JsonSubTypes({@JsonSubTypes.Type(value = Dog.class, name = "dog"), @JsonSubTypes.Type(value = Cat.class, name = "cat")})
public abstract class Animal {
    private String sound;

    public String getSound() {
        return sound;
    }

    public void setSound(String sound) {
        this.sound = sound;
    }
}

public class Dog extends Animal {
}

public class Cat extends Animal {
}

public static void main(String[] args) throws IOException {
        Animal animal = new ObjectMapper().readValue("{ \"type\": \"cat\", \"sound\": \"mew\" }", Animal.class); // everything ok
        System.out.println(animal.getSound());

        Cat cat = new ObjectMapper().readValue("{ \"sound\": \"mew\" }", Cat.class); // exception
        System.out.println(cat.getSound()); 
    }
}

Exception:

com.fasterxml.jackson.databind.JsonMappingException: Unexpected token (END_OBJECT), expected FIELD_NAME: missing property 'type' that is to contain type id  (for class Cat)
 at [Source: { "sound": "mew" };

When json is mapped to parent class is ok to send “type” property, but when is mapped to child class, the “type” property must not be required.

[jinmeiliao]

I actually found a way to achieve this. There is a MapperFeature that already exists for this: mapper.configure(MapperFeature.USE_BASE_TYPE_AS_DEFAULT_IMPL, true); this will allow Cat cat = new ObjectMapper().readValue("{ \"sound\": \"mew\" }", Cat.class); to not throw the exception.

[jinmeiliao]

Can I request this feature to be added? If I specifically asked the json string to be parsed into the concrete type Cat cat = new ObjectMapper().readValue("{ \"sound\": \"mew\" }", Cat.class);, it would be nice that I don’t need to include the type info in the json itself.