struts2 Action返回List返回空.该如何处理

private List<ForumPageVo> fList;        @Resource    private ForumService forumService;        private Page page;    private Integer pageNo;    private String pageNoStr;        private Integer f;            public String SerachById(){                page = new Page(50, ForumPageVo.class);        if (!"".equals(pageNoStr) && pageNoStr != null) {            pageNo = Integer.parseInt(pageNoStr);        }        page.setPageNo(pageNo);        page = forumService.findPageBySql(page, forumService.FORUM_BY_ID_SQL, f);        fList = page.getResult();                return "success";    }