求教,文件上传进度条有关问题

求教,文件上传进度条问题
我使用的apache commons，但是上传后，前面一直阻塞，进度条不动，一直到最后上传完，进度条跳到100%。请各位大侠帮忙看看，谢谢
jsp部分：
<script>
        var timeid;
        function callback(){
                //alert(123);
                $.ajax({
                        type:"post",  
                        url:"progress",//响应文件上传进度的servlet
                        success:function(msg){
                                //alert(msg);
                                value = msg;
                                if(value<100){
                                        document.getElementById("xxx").innerHTML="已上传："+msg;//显示读取百分比   
                                }
                                else if(value==100){
                                        window.clearInterval(timeid);
                                        document.getElementById("xxx").innerHTML="已上传："+msg;//显示读取百分比   
                                }
                        }
                });
        }
        function submitForm(){
                timeid = window.setInterval("callback()", 10);
                $('#ff').form('submit');
        }
</script>
<form id="ff" method="post" action="UpFile" enctype="multipart/form-data">
                    <table>
                            <tr>
                                    <td>导入路径:</td>
                                    <td>
                                            <select class="easyui-combobox" name="language" >
                                            <option value="1">123</option>
                                            <option value="2">456</option>
                                            <option value="3">789</option>