求教uploadify3.1的formdata问题

求教uploadify3.1的formdata问题,我想传个额外的值给服务器 ，为什么服务器接不到呢？jQuery("#uploadify").uploadify({
 swf: '${pageContext.request.contextPath}/plugin/upload/uploadify.swf',
 method:"post",
 uploader: "${pageContext.request.contextPath}/UpLoad",
 fileTypeExts :"*.doc;*.gif;*.docx",
 fileTypeDesc:"上传文件过大",
 multi :true,
 buttonText:"选择文件",
 fileDataName:"uploadify",
 cancelImage: "${pageContext.request.contextPath}/plugin/upload/cancel.png",
  queueID: "divUpload",
   auto: false,
    fileSizeLimit:"5MB",
    'formData': {'myValue':'333'},
    onUploadSuccess:function(file,data,response){
     $("#fileList").append(data);
    }
});
}); <div id="divUpload">
  
  </div>
<input type="file" id="uploadify" name="uploadify" value="浏览"/> 
<a href="javascript:$('#uploadify').uploadify('upload','*');">上传</a>