Singletons factory using generics and reflection

OrderDBManager, UserDBManager, ProductDBManager extend DBManager. I'm trying to create a singletons DBManager Factory to get instances of different DBManager type classes.

But I have a problem using generics to return an instance of exact DBManager type class user wants. Right now it only works for DBManager itself. I would appreciate your help!

public class DBManagerFactory {

     private static final Map<String, DBManager> instances = new HashMap<>();

     private static final String DB_MANAGER_PACKAGE_NAME = "ua.Test.db.";

     public static DBManager getInstance(Class<? extends DBManager> dbManagerClass) {
            String dbManagerClassName = dbManagerClass.getSimpleName();
            DBManager dbManager = instances.get(dbManagerClassName);

            if(dbManager == null){
                Class clazz = Class.forName(DB_MANAGER_PACKAGE_NAME + dbManagerClassName);
                dbManager = (DBManager)clazz.newInstance();
                instances.put(dbManagerClassName, dbManager);    
            }
            return dbManager;                                             
     }}