Controller层 
查询总用户数
    @RequestMapping(value = "/findTotalUsers.do",method = RequestMethod.GET)
    public @ResponseBody Long findTotalUsers(){
        ModelAndView modelAndView = new ModelAndView();
        Long sum = personService.findTotalUsers();
        System.out.println(sum+"....................................");
        modelAndView.addObject("sum",sum);
        return sum;
    }

Service层
public Long findTotalUsers() {
        return personDao.findTotalUsers();
    }

Dao层
public Long findTotalUsers() {
        String hql = "select count(*) from Person";
        return (Long) this.getSessionFactory().getCurrentSession().createQuery(hql).uniqueResult();
    }

ajax代码
<script src="../js/jquery-1.8.3.min.js" type="text/javascript"></script>
    <script type="text/javascript">
        $(document).ready(
                function ajaxRePost(url,params){
                    var message = "";
                    var options={
                        type:"GET",url:"${pageContext.request.contextPath}/person/findTotalUsers.do",data:{},async:false,success:function (msg) {
                            message=msg;
                        }
                    };
                    $.ajax(options);
                    alert(message);
//                    debugger;
                    $("#count").text(message);
                    return message;
                }
        )

    </script>