关于上传文件的报错问题

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2010-1-22 9:45:03 org.apache.struts2.dispatcher.StreamResult doExecute
严 重: Can not find a java.io.InputStream with the name [inputStream] in the invocation stack. Check the <param name="inputName"> tag specified for this action.
2010-1-22 9:45:03 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet default threw exception
java.lang.IllegalArgumentException: Can not find a java.io.InputStream with the name [inputStream] in the invocation stack. Check the <param name="inputName"> tag specified for this action.
at org.apache.struts2.dispatcher.StreamResult.doExecute(StreamResult.java:189)
at org.apache.struts2.dispatcher.StrutsResultSupport.execute(StrutsResultSupport.java:178)
at com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:348)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:253)
at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:221)

出现问题的三种情况：
1.struts.xml中<param name="inputName">inputStream</param>和action中的方法名getInputStream()不一致的问题
2.下载目录下没有文件
3,是设置栈顶的值是否正确,注意对象是否是栈顶的值