code: final DAO loadExternalDAO(String classSimpleName) {
  			ServiceLoader<DAO> daoLoader = ServiceLoader.load(DAO.class, Para.getParaClassLoader());
  			for (DAO dao : daoLoader) {
  				if (dao != null && classSimpleName.equalsIgnoreCase(dao.getClass().getSimpleName())) {
  					return dao;
  				}
  			}
  		return null;
  	}
docs: Scans the classpath for DAO implementations, through the
  {@link ServiceLoader} mechanism and returns one.
  @param classSimpleName the name of the class name to look for and load
  @return a DAO instance if found, or null