How to use Java reflection to check if ParameterizedType argument extends a specific class

Question

If I have an interface and class that I cannot change that look something like this:

public interface ISport<PlayerType extends IPlayer> {
       String getName();
       List<PlayerType> getPlayers();
}

public class TeamSport<PlayerType extends IPlayer> implements ISport<PlayerType>{  

    // constructor and a bunch of other methods

    @Override
    String getName(){
         return this.name;
    }

    @Override
    List<PlayerType> getPlayers(){
          // returns a maintained players list
    }
}

I am building a set of attributes for an object of any type, using reflection and the getter methods of the object. I need it to perform nesting, though, where it can identify attributes of attributes.

The following method is a simplification of the attribute extraction method (here it just prints the attributes, where in my real code I'm actually doing something with them). There is also a method isGetter, not shown here, which tests that the method name begins with "get" and the method has no arguments and is not a void method.

But I need it to be able to recognize that the return type of getPlayers() is a list of IPlayers, so I can get the attributes of IPlayers.

public static printAttributes(Class sourceClass){
       for(Method method : sourceClass.getMethods()){
           if(isGetter(method)){
               System.out.println(method.getName());
               if(method.getGenericReturnType() instanceof ParameterizedType){
                    for(Type parameterType : type.getActualTypeArguments()){
                         System.out.println("   Child type: "+parameterType;
                         if(parameterType instanceof Class){
                              printAttributes((Class)parameterType));
                         }
                    }
               }
           }
       }
}

Calling this on an instance of TeamSport yields the following:

getName
getPlayers
   Child type: PlayerType

It does not print any IPlayer attributes.

How do I get those IPlayer attributes in my printAttributes method? Can I somehow get IPlayer from the ParameterizedType? Or just check if any ParamaterizedType's arguments extend IPlayer (which is less ideal, but better than what I've got)?

Answer 1

Java generics erase generic type information on compile. You won't be able to get this information at runtime.