Polymorphism in jackson annotations: @JsonTypeInfo usage

Question

I would like to know if @JsonTypeInfo annotation can be used for interfaces. I have set of classes which should be serialized and deserialized.

Here is what I'm trying to do. I have two implementation classes Sub1, Sub2 implementing MyInt. Some of the model classes have the interface reference for the implementation types. I would like to deserialize the objects based on polymorphism

@JsonTypeInfo(use=JsonTypeInfo.Id.NAME, include=As.WRAPPER_OBJECT) @JsonSubTypes({     @Type(name="sub1", value=Sub1.class),      @Type(name="sub2", value=Sub2.class)}) public interface MyInt{ }  @JsonTypeName("sub1") public Sub1 implements MyInt{ }  @JsonTypeName("sub2") public Sub2 implements MyInt{ } 

I get the following JsonMappingException:

Unexpected token (END_OBJECT), expected FIELD_NAME: need JSON String that contains type id

Answer 1

@JsonSubTypes.Type must have a value and a name like this,

@JsonTypeInfo(use=JsonTypeInfo.Id.NAME, include=As.WRAPPER_OBJECT, property="type") @JsonSubTypes({            @JsonSubTypes.Type(value=Dog.class, name="dog"),     @JsonSubTypes.Type(value=Cat.class, name="cat")        })  

In the subclass, use @JsonTypeName("dog") to say the name.
The values dog and cat will be set in the property named type.

Answer 2

Yes it can be used both for abstract classes and interfaces.

Consider following code example

Suppose we have an enum , interface and classes

enum VehicleType {     CAR,     PLANE }  interface Vehicle {     VehicleType getVehicleType();     String getName(); }   @NoArgsConstructor @Getter @Setter class Car implements Vehicle {     private boolean sunRoof;     private String name;      @Override     public VehicleType getVehicleType() {         return VehicleType.Car;     } }  @NoArgsConstructor @Getter @Setter class Plane implements Vehicle {     private double wingspan;     private String name;      @Override     public VehicleType getVehicleType() {         return VehicleType.Plane;     } } 

If we try to deserialize this json into List<Vehicle>

[   {"sunRoof":false,"name":"Ferrari","vehicleType":"CAR"},    {"wingspan":19.25,"name":"Boeing 750","vehicleType":"PLANE"} ] 

then we will get error

abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information 

To solve this just add following JsonSubTypes and JsonTypeInfo annotations to the interface, as shown below

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME,         property = "vehicleType") @JsonSubTypes({         @JsonSubTypes.Type(value = Car.class, name = "CAR"),         @JsonSubTypes.Type(value = Plane.class, name = "PLANE") }) interface Vehicle {     VehicleType getVehicleType();     String getName(); } 

With this the deserialization will work with interface and you will get a List<Vehicle> back

You can check out the code here - https://github.com/chatterjeesunit/java-playground/blob/master/src/main/java/com/play/util/jackson/PolymorphicDeserialization.java