错误java.lang.NumberFormatException: For input string: ""

exception javax.servlet.ServletException: java.lang.NumberFormatException: For input string: ""
org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:535)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:433)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.yufeng.utils.EncodingFilter.doFilter(EncodingFilter.java:24)root cause java.lang.NumberFormatException: For input string: ""
java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
java.lang.Integer.parseInt(Integer.java:468)
java.lang.Integer.parseInt(Integer.java:497)
org.yufeng.struts.action.ArticleAction.admin_add_article(ArticleAction.java:463)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:270)
org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:187)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.yufeng.utils.EncodingFilter.doFilter(EncodingFilter.java:24)
我在用jsp编程做一个Struts+Spring+Hibernate文档管理系统，以上错误是在执行上传文件时出现的，具体情况：在admin_add_article.jsp中填写文档信息，点击该页面上传按钮跳转至do_upload.jsp显示上传信息，就是在点击“上传”按钮之后do_upload.jsp无法显示并出现以上错误。
                                 admin_add_article.jsp
<%@ page contentType="text/html;charset=UTF-8"  import="java.util.*,com.jspsmart.upload.*" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<html>
<head>
<title>文章资源管理</title>
<meta http-equiv="Content-Type" content="text/html;charset=gb2312">
<meta http-equiv="Content-Language" Content="zh-CN">
<meta name="Keywords" Content="">
<meta name="Description" Content="">
<link type="text/css" rel="stylesheet" href="/yf_article/Style/Style.css">
<Script Language="JavaScript" src="Include/Function.js"></Script>
<Script Language="JavaScript" src="Include/PopText.js"></Script>
<Script Language="JavaScript" src="Include/jquery.js"></Script>
<Script Language="JavaScript" src="Include/verify.js"></Script>
<Script Language="JavaScript">
function addar(){
if(document.Admin_Article.ar_name.value==""){
alert("文章标题不能为空！");
return false;
}
}
</script>
</head>
<body bgcolor="#FFFFFF" leftMargin="10" topmargin="10">
<form name="Admin_Article" method="post"
action="article.do?method=admin_add_article&ar_id=${article.ar_id }"
onSubmit="return addar();">
<table align="center" border="0" cellpadding="0" cellspacing="1" width="600"
height="100" bgcolor="#CEEFE7"> <tr>
<td width="600" height="28" background="Images/Admin_T_Bg1.gif"
align="center" colspan="4">
<font class="BlackS12"><b>文 章 详 细 信 息</b> </font>
</td>
</tr>
<tr>
<td width="600" height="10" bgcolor="#FFFFFF" colspan="4"></td>
</tr>
<tr>
<td width="80" height="28" bgcolor="#FFFFFF" align="center">
<font class="BlackS12">文章标题</font>
</td>
<td width="518" height="28" bgcolor="#FFFFFF" colspan="3">
&nbsp;
<input type="text" name="ar_name" onFocus=""
value="${article.ar_name }" Maxlength="100"
style="width: 383; background-color: #EAFBF5; color: ;"
class="Admin_Select">
&nbsp; &nbsp;
</td>
</tr>
               //   此处有文章其它信息的设置的代码，应该与此帖问题无关，在此省略
                                <tr>
<td width="80" height="28" bgcolor="#FFFFFF" align="center">
<font class="BlackS12">上传文件</font>
</td> <td width="518" height="28" bgcolor="#FFFFFF" colspan="3">
&nbsp;
<FORM METHOD="POST" ACTION="do_upload.jsp" ENCTYPE="multipart/form-data">
                         <table width="75%" border="1" align="center">
                          <tr> 
                           <td><div align="center"> 
                            <input type="FILE" name="FILE1" size="30">
                           </div></td>
                          </tr>
                          <tr> 
                           <td><div align="center">
                            <input type="submit" name="Submit" value="上传">
                           </div></td>
                          </tr>
                         </table>
                        </FORM>
   </td>
      </tr>
<%

out.println("<TR><TD>文件路径（FilePath）</TD><TD>"+getServletContext().getRealPath("/")+"</TD></TR>");
 %>      


<tr>
<td width="80" height="38" bgcolor="#FFFFFF">
<input type="hidden" name="GuComm" value="ArAdSa">
</td>
<td width="518" height="38" bgcolor="#FFFFFF" colspan="3">
<input type="hidden" name="type" value="${type }">
&nbsp;
<c:choose>
<c:when test="${type==1}">
<input type="submit" value="" class="Admin_Button_Add">
&nbsp;
</c:when>
</c:choose>
<input type="reset" value="" name="Admin_Button_Reset"
class="Admin_Button_Reset">
&nbsp;
</td>
</tr>
</table>
</form>
<br>
</body>
</html>
                                            do_upload.jsp
<%@ page contentType="text/html; charset=gb2312" language="java" import="java.util.*,com.jspsmart.upload.*" errorPage="" %>
<html>
<head>
<title>文件上传处理页面</title>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
</head>
<body>
<p align="center">
<%
// 新建一个SmartUpload对象
SmartUpload su = new SmartUpload();
// 上传初始化
su.initialize(pageContext);
// 设定上传限制
// 1.限制每个上传文件的最大长度。
 //su.setMaxFileSize(40000);
// 2.限制总上传数据的长度。
 su.setTotalMaxFileSize(150000);
// 3.设定允许上传的文件（通过扩展名限制）,仅允许doc,txt文件。
 //su.setAllowedFilesList("doc,txt");
// 4.设定禁止上传的文件（通过扩展名限制）,禁止上传带有exe,bat,jsp,htm,html扩展名的文件和没有扩展名的文件。
 //su.setDeniedFilesList("exe,bat,jsp,htm,html,,");
// 上传文件
su.upload();
// 将上传文件全部保存到指定目录
int count = su.save("/upload");
out.println(count+"个文件上传成功！<br>");
// 逐一提取上传文件信息，同时可保存文件。
for (int i=0;i<su.getFiles().getCount();i++)
{
com.jspsmart.upload.File file = su.getFiles().getFile(i);
// 若文件表单中的文件选项没有选择文件则继续
if (file.isMissing()) continue;
// 显示当前文件信息
out.println("<TABLE BORDER=1>");
out.println("<TR><TD>表单项名（FieldName）</TD><TD>"+file.getFieldName()+"</TD></TR>");
out.println("<TR><TD>文件长度（Size）</TD><TD>"+file.getSize()+"</TD></TR>");
out.println("<TR><TD>文件名（FileName）</TD><TD>"+file.getFileName()+"</TD></TR>");
out.println("<TR><TD>文件扩展名（FileExt）</TD><TD>" +file.getFileExt()+"</TD></TR>");
out.println("<TR><TD>文件全名（FilePathName）</TD><TD>"+file.getFilePathName()+"</TD></TR>");
out.println("</TABLE><BR>");
}
%>
</p>
<a href="admin_add_article.jsp">返回</a>
</body>
</html>
刚开始学jsp，恳请大家指点迷津！谢谢