code: public String preview() {
      OqlBuilder<Menu> query = OqlBuilder.from(Menu.class, "menu");
      populateConditions(query);
      query.orderBy("menu.indexno asc");
      put("menus", entityDao.search(query));
  
      query.clearOrders();
      query.select("max(length(menu.indexno)/2)");
      List<?> rs = entityDao.search(query);
      put("depth", rs.get(0));
      return forward();
    }
docs: 打印预览功能列表