关于fromdata的上传文件问题

<div class="imgDIv"> <label>上传pdf</label> <input id="fileId" type="file" accept="application/pdf" class="imgPic"/> </div>

 var formData = new FormData();
     var file = $("#fileId")[0].files[0];
     formData.append('file', file);
     $.ajax({
         type:'POST',
         url:Feng.ctxPath + "/catalog/add",
         data:formData,
         dataType: "formData",
         cache: false,
         contentType: false,
         processData:false,
         mimeType:"multipart/form-data",
         success:function(data){
             if(data.code==200){
                 layer.msg("保存成功！");
                 window.parent.Catalog.table.refresh();
             }else{
                 layer.msg(data.msg)
             }
         }
     });