1）Mapper文件代码如下：

@Select("select phone_charge,status,created_time from order_management where " +
                 "user_id =#{userId} and created_time > #{timeLower} order by created_time desc")
List<OrderDO> listByPage(WithdrawQuery withdrawQuery);

2）然后service接受到List后将其转化为了List类型

 List<OrderDO> orderDOs = orderDAO.listByPage(query);
 List<OrderDTO> orderDTOs = ObjectUtils.convertList(orderDOs,OrderDTO.class);

3）为了得到分页的一些信息，将orderDTOs放入到Page对象中

PageInfo page = new PageInfo(orderDOs);

return new AjaxResult<JsonNode>().success(new ObjectMapper().createObjectNode()
       .put("totalCount",page.getTotal())
       .put("pageNum",page.getPageNum())
       .put("pageSize",page.getPageSize())
       .putPOJO("results",orderDTOs));

4）问题出现再上面获得的page.getTotal()不为总数，而等于orderDOs的size数量。
5）Page的构造器的源码如下：

public PageInfo(List<T> list, int navigatePages) {
    super(list);
    this.isFirstPage = false;
    this.isLastPage = false;
    this.hasPreviousPage = false;
    this.hasNextPage = false;
    if (list instanceof Page) {
        Page page = (Page)list;
        this.pageNum = page.getPageNum();
        this.pageSize = page.getPageSize();
        this.pages = page.getPages();
        this.size = page.size();
        if (this.size == 0) {
            this.startRow = 0;
            this.endRow = 0;
        } else {
            this.startRow = page.getStartRow() + 1;
            this.endRow = this.startRow - 1 + this.size;
        }
    } else if (list instanceof Collection) {
        this.pageNum = 1;
        this.pageSize = list.size();
        this.pages = this.pageSize > 0 ? 1 : 0;
        this.size = list.size();
        this.startRow = 0;
        this.endRow = list.size() > 0 ? list.size() - 1 : 0;
    }

    if (list instanceof Collection) {
        this.navigatePages = navigatePages;
        this.calcNavigatepageNums();
        this.calcPage();
        this.judgePageBoudary();
    }

}      

6）上面源码中的if-else可知，如果传进来的集合orderDOs时Page的子类或是子类的子类，则进入条件判断的第1部分。如果不是的话就会进入第2部分（是Collection的子类），这时就会用 list.size()来代替。
7）查看类型发现orderDOs是Page子类的对象，而orderDTOs不是。这或许是因为在Mapper文件中，查询结果直接转化为了Page子类的对象。


8）为了得到正确结果，将PageInfo的构造函数参数从orderDTOs改为orderDOs即可。
PageInfo page = new PageInfo(orderDOs);