code: private List<?> loadDataFromXmlFile() {
          logger.entering();
          Preconditions.checkArgument(resource.getCls() != null, "Please provide a valid type.");
          List<?> returned;
  
          try {
              JAXBContext context = JAXBContext.newInstance(Wrapper.class, resource.getCls());
              Unmarshaller unmarshaller = context.createUnmarshaller();
              StreamSource xmlStreamSource = new StreamSource(resource.getInputStream());
              Wrapper<?> wrapper = unmarshaller.unmarshal(xmlStreamSource, Wrapper.class).getValue();
              returned = wrapper.getList();
          } catch (JAXBException excp) {
              logger.exiting(excp.getMessage());
              throw new DataProviderException("Error unmarshalling XML file.", excp);
          }
  
          logger.exiting(returned);
          return returned;
      }
docs: Generates a list of the declared type after parsing the XML file.
  
  @return A {@link List} of object of declared type {@link XmlFileSystemResource#getCls()}.