@Override
  public T get() {
    LOGGER.debug("Getting {} configuration...", configurationCategory.getCategoryName());
    if (instance == null) {
      instance = loadInstance();
    }
    return instance;
  }
Upon receiving this event, the JPA infrastructure has completed initialization and the relevant
data may be retrieved.

@param event the received {@link JpaInitializedEvent}
ambari-server/src/main/java/org/apache/ambari/server/configuration/AmbariServerConfigurationProvider.java