code: public static void show(DateRange dateRange, IResponseCallback<DateRange> callback) {
          Map<String, Object> args = new HashMap<>();
          args.put("dateRange", dateRange);
          Window dlg = (Window) PageUtil.createPage(DialogConstants.RESOURCE_PREFIX + "dateRangeDialog.fsp", null, args)
                  .get(0);
          dlg.modal((event) -> {
              callback.onComplete((DateRange) dlg.getAttribute("result"));
          }
docs: Displays the date range dialog.
  
  @param dateRange The initial date range.
  @param callback Callback for returning a date range reflecting the inputs from the dialog.
  This will be null if the input is cancelled or if an unexpected error occurs.