code: protected static String getFileName(Appender app) {
  
          String result = null;
          Method getFileName;
          try {
              getFileName = app.getClass().getDeclaredMethod("getFileName", (Class<?>[])null);
  
              result = (String)getFileName.invoke(app, (Object[])null);
          } catch (Exception e) {
              LOG.warn(e.getLocalizedMessage(), e);
          }
          return result;
      }
docs: Returns the file name or <code>null</code> associated with the given appender.<p>
  
  @param app the appender
  
  @return the file name