Grab generic interfaces of a class by Class#getGenericInterfaces() which you then in turn check if it's a ParameterizedType and then grab the actual type arguments accordingly. .

Get_Concrete_Type_of_Generic.java

// Interface
public interface FooBar<T> {
  // ...
}

// Impl Class
public class BarFoo implements FooBar<Person> {
  // ...
}

// Logic to Grab Generic Interfaces & Args of Class
Type[] genericInterfaces = BarFoo.class.getGenericInterfaces();
for (Type genericInterface : genericInterfaces) {
    if (genericInterface instanceof ParameterizedType) {
        Type[] genericTypes = ((ParameterizedType) genericInterface).getActualTypeArguments();
        for (Type genericType : genericTypes) {
            System.out.println("Generic type: " + genericType);
        }
    }
}