How to specify concrete type for abstract method param in Jersey/ Jackson?

Question

I am using Jersey and have exposed a resource Resource which implements an Interface . One of the methods from Interface has a parameter a of type A which is an abstract class.

Here is some code for explanation:

//Interface.java
public interface Interface {
    public void setA(A a);
}
//Resource.java
@Path("/hello")
public class Resource implements Interface {
    @POST
    public void setA(A a){ //Here I want to specify AImpl instead of A
        //Code that uses AImpl
    }
}
//A.java
public abstract class A{
    //Some abstract stuff
}
//AImpl.java
public class AImpl extends A{
    //Some concrete stuff
}

This leads to an error:

JsonMappingException: Can not construct instance of A, problem: abstract types can only be instantiated with additional type information

How can this be avoided/ overcome?

One solution would be to make Jersey/Jackson aware that it can use the concrete implementation of A (which is AImpl ) in method setA() of Resource . Is there any annotation that I can use to do that?

Answer 1

Have you considered simply making Interface generic? Something like

public abstract class SuperType {}

public class SubType extends SuperType {}

public interface Resource<T extends SuperType> {
    Response doSomething(T type);
}

@Path("resource")
public class SubTypeResource implements Resource<SubType> {
    @POST
    @Override
    public Response doSomething(SubType type) {
        ...
    } 
}