code: @Override
      public void fireAddAppenderEvent(Category logger, Appender appender) {
          if (listeners != null) {
              HierarchyEventListener listener;
              for (Iterator<HierarchyEventListener> it = listeners.iterator(); it
                      .hasNext();) {
                  listener = it.next();
                  listener.addAppenderEvent(logger, appender);
              }
          }
      }
docs: /*
  (non-Javadoc)
  
  @see
  org.apache.log4j.Hierarchy#fireAddAppenderEvent(org.apache.log4j.Category
  , org.apache.log4j.Appender)