public static <T> T unmarshal(Class<T> clz, File file) throws JAXBException {
    Unmarshaller u = _jaxbContexts.get(clz).createUnmarshaller();

    return clz.cast(u.unmarshal(file));
  }
Manages Action definitions read from XML files
ambari-server/src/main/java/org/apache/ambari/server/customactions/ActionDefinitionManager.java