code: public void setMonthDateTimeFormatter(DateTimeFormatter formatter) {
          if (getFormatterMap().get(ViewType.MONTH_VIEW) == null) {
              getFormatterMap().put(ViewType.MONTH_VIEW, formatter);
          } else {
              getFormatterMap().replace(ViewType.MONTH_VIEW, formatter);
          }
      }
docs: Sets the DateTimeFormatter on the Month Label located in the month page.
  Notice that this is also affecting the page that is going to be printed.
  
  @param formatter
  the DateTimeFormatter