webwork2上传，是不是有bug啊？大侠们都来看看吧~送分了

页面：<%@ taglib prefix="ww" uri="/webwork" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head><title>index</title></head><body id="page-home">
<ww:form name="fileform" action="/test/upload.action" method="POST" enctype="multipart/form-data"><ww:token/>
      <ww:file name="file"></ww:file>
      <ww:submit></ww:submit>
  </ww:form>
</body>
</html>
xwork.xml:<!DOCTYPE xwork PUBLIC "-//OpenSymphony Group//XWork 1.1.1//EN" "http://www.opensymphony.com/xwork/xwork-1.1.1.dtd"><xwork>
<include file="webwork-default.xml" /> <package name="default" extends="webwork-default">
<interceptors>
<interceptor name="fileUpload"
class="com.opensymphony.webwork.interceptor.FileUploadInterceptor">
<param name="allowedTypes">
image/jpeg/jpg/bmp/txt
</param>
<param name="maximumSize">10000000</param>
</interceptor>
<interceptor-stack name="conairStack">
<interceptor-ref name="exception" />
<interceptor-ref name="alias" />
<interceptor-ref name="servlet-config" />
<interceptor-ref name="prepare" />
<interceptor-ref name="i18n" />
<interceptor-ref name="chain" />
<interceptor-ref name="model-driven" />
<interceptor-ref name="fileUpload" />
<interceptor-ref name="static-params" />
<interceptor-ref name="params" />
<interceptor-ref name="validation">
<param name="excludeMethods">
input,back,cancel,browse
</param>
</interceptor-ref>
</interceptor-stack>
</interceptors>
<default-interceptor-ref name="conairStack" />

</package>
<include file="/com/upload/test.xml" />
</xwork>
test.xml:<!DOCTYPE xwork PUBLIC "-//OpenSymphony Group//XWork 1.1.1//EN" "http://www.opensymphony.com/xwork/xwork-1.1.1.dtd"><xwork>
<package name="test" namespace="/test" extends="default">

<action name="upload" class="com.upload.UploadAction">
<result name="index">/index.jsp</result>

</action>
</package>
</xwork>
webwork.properties:webwork.configuration.xml.reload=true
webwork.custom.i18n.resources=application
webwork.devMode=false
webwork.i18n.encoding=UTF-8
webwork.i18n.reload=true
webwork.locale=zh_CNwebwork.multipart.parser=jakarta
webwork.multipart.saveDir=E:/temp
webwork.multipart.maxSize=10000000
Action如下:package com.upload;import java.io.File;import javax.servlet.ServletContext;import com.opensymphony.webwork.ServletActionContext;
import com.opensymphony.xwork.ActionSupport;public class UploadAction extends ActionSupport {
private File file;
    private String contentType;
    private String filename;
    
public File getFile() {
return file;
} public void setFile(File file) {
this.file = file;
}
    
    private ServletContext d;     public void setUploadContentType(String contentType) {
       this.contentType = contentType;
    }    public void setUploadFileName(String filename) {
       this.filename = filename;
    } public String execute() throws Exception {
// TODO Auto-generated method stub
this.addActionMessage("上传成功！");
d = ServletActionContext.getServletContext(); 
String path=d.getRealPath("/");//取得根目录///我又把它重新的放到别一个位置， 

File target = new File(path+"asd.txt"); 
        if (target.exists()) { 
            target.delete(); 
        }else{ 
            target.mkdir(); 
        }
        file.renameTo(target);//这里的file总是为null
return "index";
}
}就是搞不懂为什么file对象总是为null的？？？是不是webwork里有bug啊？？？请大侠们再一次申出你们宝贵的手吧！~谢谢了~~~