spring整合dwr上传文件报错 求解?报错

10:11:07,356 WARN  [directwebremoting.dwrp.BaseCallHandler] Exception while processing batch
java.lang.NullPointerException
at org.directwebremoting.dwrp.Batch.<init>(Batch.java:62)
at org.directwebremoting.dwrp.CallBatch.<init>(CallBatch.java:46)
at org.directwebremoting.dwrp.BaseCallHandler.handle(BaseCallHandler.java:74)
at org.directwebremoting.servlet.UrlProcessor.handle(UrlProcessor.java:120)
at org.directwebremoting.servlet.DwrServlet.doPost(DwrServlet.java:141)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:88)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.orm.hibernate4.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:119)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1822)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)

dwr.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 3.0//EN" "http://getahead.org/dwr/dwr30.dtd">

<dwr>
  <allow>
    <!-- intro - for the test on index.html -->
    <create creator="spring" javascript="attachmentService" >
      <param name="beanName" value="attachmentService"/>
      <include method="upload" />
    </create> 
    
    
     <!-- 声明异常转换器 -->
	<convert converter="exception" match="java.lang.Exception"/>
    <convert converter="bean" match="java.lang.StackTraceElement"/>

  </allow>
</dwr>

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
  <filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <filter>
    <filter-name>OpenSessionInViewFilter</filter-name>
    <filter-class>org.springframework.orm.hibernate4.support.OpenSessionInViewFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>OpenSessionInViewFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <servlet>
    <servlet-name>CheckCodeServlet</servlet-name>
    <servlet-class>cn.guhai.cms.servlet.CheckCodeServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>CheckCodeServlet</servlet-name>
    <url-pattern>/CheckCodeServlet</url-pattern>
  </servlet-mapping>
  <filter>
    <filter-name>struts2</filter-name>
    <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>struts2</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>INCLUDE</dispatcher>
  </filter-mapping>
  
   <display-name>DWR (Direct Web Remoting)</display-name>
  <description>A Simple Demo DWR</description>

  <listener>
    <listener-class>org.directwebremoting.servlet.DwrListener</listener-class>
  </listener>
  
  <servlet>
    <servlet-name>dwr-invoker</servlet-name>   
    <servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class>
	 
    <init-param>
      <param-name>debug</param-name>
      <param-value>true</param-value>
    </init-param>
    <!-- 以下注释掉的暂时为解决dwr上传文件报错设置，目前没有效果 -->    
  <!--   <init-param>
             <param-name>crossDomainSessionSecurity</param-name>
             <param-value>false</param-value>
      </init-param>
      <init-param>
            <param-name>allowScriptTagRemoting</param-name>
            <param-value>true</param-value>
      </init-param>
     -->
     
<!--  <load-on-startup>1</load-on-startup> -->
  </servlet>
   
  <servlet-mapping>
    <servlet-name>dwr-invoker</servlet-name>
    <url-pattern>/dwr/*</url-pattern>
  </servlet-mapping>
  
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext-*.xml</param-value>
  </context-param>
  
 
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

Dwr调用方法upload

public String upload(InputStream is,String fileName){
 //String name = FilenameUtils.getName(fileName);
 System.out.println(fileName);
 return fileName;
 }