layui upload上传文件动态传参，后台获取不到值

废话不多说，直接上代码

js:

layui.use('upload', function(){
        var $ = layui.jquery,upload = layui.upload;
        //绑定原始文件域
        upload.render({
            elem: '#test20'
            ,url: "<c:url value='/order/imgUpload.do?proVal=IMG_PATH'/>" 
            ,auto: true
            ,accept: 'file'
            ,exts:"jpg|png|gif|jpeg|bmp"
            ,size:1024
            ,before: function(obj){
                var orderID = $("#orderID").val();
                this.data={"orderID":orderID}//携带动态参数
            }
            ,done: function(res){
                if(res.msg=='ok'){
                    alert('上传成功');
                }else{
                    alert(res.msg);
                }
            }
        });
   });

java:

上传文件的代码我没写，主要写了怎么取这个动态参数的值

@ResponseBody
@RequestMapping("/imgUpload")
public JsonResult imgUpload(
        HttpServletRequest request,HttpServletResponse response,ModelMap map
        ){
    JsonResult json = new JsonResult();
    Integer orderID = null;//订单ID
    
    DiskFileItemFactory factory = new DiskFileItemFactory();
    factory.setSizeThreshold(10240000);
    
    try {
        ServletFileUpload upload = new ServletFileUpload(factory);
        upload.setHeaderEncoding("utf-8");
        @SuppressWarnings("rawtypes")
        List fileList = null;
        try {
            fileList = upload.parseRequest(request);
        } catch (FileUploadException ex) {
            return null;
        }
        @SuppressWarnings("unchecked")
        Iterator<FileItem> it = fileList.iterator();
        
        //取参数
        while (it.hasNext()) {
            FileItem item = it.next();
            if(item.isFormField()&&"orderID".equals(item.getFieldName())){
                orderID = Integer.valueOf(item.getString());
            }
        }


        
        if(orderID==null){
            json.setMsg("参数有误，请刷新重试！");
            return json;
        }
    } catch (Exception e) {
        e.printStackTrace();
        json.setMsg("上传失败");
    }finally{
        factory = null;
    }
    
    return json;
}