Java Webservice and Polymorphism

Question

Let's say i have the following strucutre

public class Mammal
{
    @WebMethod
    public ArrayList<Mammal> getAll(){ return null; }
    @WebMethod
    public String speak(){ return "Unable to speak"; }
    @WebMethod
    public Mammal me(){ return this; } 
}

@WebService
public class Human extends Mammal
{
    @WebMethod
    public ArrayList<Human> getAll(){ /* code to return all humans as ArrayList<Human> */ }
    @WebMethod
    public String speak() { return "Hai!"; }
    @WebMethod(operationName="GetHuman")
    public Human me(){ return this; }
}

Now If you see the Mammal me() and Human me() are overided natuarlly and this works perfectly and the WSDL is generated as it should be because that i add the operationName="".

So far so good, now the method returning an ArrayList does not work. Somehow it says that ArrayList can't override ArrayList which in my opinion should be possible?

Now I found a work-around for this and the result looks as followed

In the Mammal class I have this instead: public ArrayList getAll(){ return null; }

And i leave the Humna-class untouched, now this works.

However! This makes it Impossible to extending a Human and overriding the method from a new sub-class, so I am back at square one again.

How do I solve this?

Let's say I want to access the Webservice from a C# application then i want the method to have a return type of List Human or List Whatever-extended-Mammal, Without having to type-cast on the other side!

Answer 1

What if you try real array instead of collection? I don't think that web service frameworks work well with generics.

EDIT: Something like that:

public class Mammal
{

    @WebMethod
    public Mammal[] getAll() { return null; }

    ...

}

@WebService
public class Human extends Mammal
{

    @WebMethod
    public Human[] getAll() { return null; }

    ...

}

Answer 2

Your code example should not compile even without the web service related annotations. List<Human> is NOT a subtype of List<Mammal>. However, if you use List<? extends Mammal> in your base class, then everything should work just fine.

public class Mammal
{
    @WebMethod
    public List<? extends Mammal> getAll() { return null; }
}

public class Human extends Mammal {
    @WebMethod
    public List<Human> getAll() { return null; }
}

If you want to extend Human even further, then you would have to use

public class Human extends Mammal {
    @WebMethod
    public List<? extends Human> getAll() { return null; }
}