datatable服务器翻页，后台代码有运行，但前台不刷新（jquery)

使用datatable，能实现初始化，在点击页码切换时，后台代码也有运行，但前台页面上的表格不刷新，一直显示“处理中”，请问大牛们，是什么原因造成的？js主要代码如下：
    <script type="text/javascript">
    $(document).ready(function() {
            var table1 = $('#sample_1').dataTable( {
                "processing" : true,
                "serverSide": true,
//                "paging" : false, //可以控制自定义显示多少页和下面的页码
                "sPaginationType": "bootstrap_full_number",
                "searching": false,
                "lengthMenu": [ 5, 10, 15, 20 ],
                "pageLength": 5, 
/*     "sAjaxSource": "user/getusers",*/
                "bServerSide": true,
                "bPaginate":true,
                "ajax": {
                    "url":"user/getusers",
                    "type": "POST",
                    "dataSrc":  
                        function(json){
                    
                     for ( var i=0, ien=json.data.length ; i<ien ; i++ ) {
                             json.data[i][0] = '<a href="/message/'+json.data[i][0]+'">View message</a>';
                             alert(json.data[i][0]);
                     }
                           return json.data;
                        }
                },
                "columns": [
                    { "data": "id" },
                    { "data": "username" },
                    { "data": "loginname" },
                    { "data": "password" },
                    { "data": "sex" },
                    { "data": "telephe" },
                    { "data": "email" },
                    { "data": "about" },
                    { "data": "imgurl" }
                ],
                language : {  
                    "sProcessing" : "处理中...",  
                    "sLengthMenu" : "显示 _MENU_ 项结果",  
                    "sZeroRecords" : "没有匹配结果",  
                    "sInfo" : "显示第 _START_ 至 _END_ 项结果，共 _TOTAL_ 项",  
                    "sInfoEmpty" : "显示第 0 至 0 项结果，共 0 项",  
                    "sInfoFiltered" : "(由 _MAX_ 项结果过滤)",  
                    "sInfoPostFix" : "",  
                    "sSearch" : "搜索:",  
                    "sUrl" : "",  
                    "sEmptyTable" : "表中数据为空",  
                    "sLoadingRecords" : "载入中...",  
                    "sInfoThousands" : ",",  
                    "oPaginate" : {  
                    "sFirst" : "首页",  
                    "sPrevious" : "上页",  
                    "sNext" : "下页",  
                    "sLast" : "末页"  
                    },  
                    "oAria" : {  
                    "sSortAscending" : ": 以升序排列此列",  
                    "sSortDescending" : ": 以降序排列此列"  
                    } 
                }
            });
     });  
</script>
后台controller.java代码如下：
@RequestMapping("/getusers")
public void getUserPage(HttpServletRequest request,  HttpServletResponse response)throws Exception{
response.setContentType("application/json;charset=utf-8");
Integer pageNo = Integer.valueOf(request.getParameter("start")) ;
Integer pageLength = Integer.valueOf(request.getParameter("length")) ;

List<User> lists = systemService.findUser(pageNo,pageLength) ;
// List<String> liststr = new ArrayList();
Iterator<User> iter = lists.iterator();
while(iter.hasNext()){
User user = (User)iter.next();

user.setImgurl("<a href=user/update?flag=1&id=" + user.getId()+">打开</a>"); 
}
Integer allRecord = systemService.findCountUser();
PrintWriter pw = response.getWriter();
Map<String,Object> map = new HashMap<String,Object>();
map.put("draw", 1) ;
map.put("recordsTotal", allRecord);  
        map.put("recordsFiltered", allRecord); 
map.put("data", lists) ;
Gson g  = new Gson();
String jsons = g.toJson(map);
pw.write(jsons);
}