struts2文件下载出现Can not find a java.io.InputStream with the name的错误

今天在用struts2就行文件下载时出现如下错误：

Servlet.service()forservletdefaultthrewexception
 java.lang.IllegalArgumentException:Cannotfindajava.io.InputStreamwiththename[imageStream]intheinvocationstack.Checkthe<paramname="inputName">tagspecifiedforthisaction.
 atorg.apache.struts2.dispatcher.StreamResult.doExecute(StreamResult.java:189)
 atorg.apache.struts2.dispatcher.StrutsResultSupport.execute(StrutsResultSupport.java:178)
 atcom.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:348)
 atcom.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:253)
 atcom.best.top.validate.TopInterceptor.intercept(TopInterceptor.java:47)
 atcom.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:224)
 atcom.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:223)
 atcom.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)
 atcom.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:221)
 atorg.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:50)
 atorg.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:504)
 atorg.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:419)

说实话这个提示真有误导人的嫌疑，刚开始还以为是名称不对，估计一般人看到这个提示都这样想。然后查看StreamResult的源代码才发现是因为InputStream为null的缘故，汗一个。看下源码：

if(inputStream==null){
 //Findtheinputstreamfromtheinvocationvariablestack
inputStream=(InputStream)invocation.getStack().findValue(conditionalParse(inputName,invocation));
}

 if(inputStream==null){
 Stringmsg=("Cannotfindajava.io.InputStreamwiththename["+inputName+"]intheinvocationstack."+
 "Checkthe<paramname=\"inputName\">tagspecifiedforthisaction.");
LOG.error(msg);
 thrownewIllegalArgumentException(msg);
}

大家如果也碰到此类问题,直接打印
InputStream in=ServletActionContext.getServletContext().getResourceAsStream(realPath);
System.out.println(in);

如果打印为NULL的话,恭喜您,问题得以解决,问题的原因是这个流的realPath路径错误,

还没明白的往下看

怪呀,我的配置应该没错呀
页面上:
<a href="fileDownload.action?fileName=<s:property value ="imageName" />">下载此图片</a>
struts.xml中
----------------------------------------------------------
<!-- 文件下载，支持中文附件名 -->
<action name="fileDownload"
class="com.test.action.filedown.FileDownloadAction">
<result name="success" type="stream">
<!-- 动态文件下载的，事先并不知道未来的文件类型，那么我们可以把它的值设置成为：application/octet-stream;charset=ISO8859-1 ，注意一定要加入charset，否则某些时候会导致下载的文件出错； -->
<param name="contentType">
application/octet-stream;charset=ISO8859-1
</param>
<param name="contentDisposition">
attachment;filename="${downloadFileName}"
</param>
<!-- 使用经过转码的文件名作为下载文件名，downloadFileName属性
对应action类中的方法 getDownloadFileName() 其中特殊的代码就是${downloadFileName}，它的效果相当于运行的时候将action对象的属性的取值动态的填充在${}中间的部分，我们可以认为它等价于＋action. getDownloadFileName()。 -->
<param name="inputName">inputStream</param>
<param name="bufferSize">4096</param>
</result>
</action>
----------------------------------------------------------
action中
----------------------------------------------------------
private String fileName;// 初始的通过param指定的文件名属性 set get

/** 文件名 转换编码 防止中文乱码*/
public String getDownloadFileName() {
String fileName=ServletActionContext.getRequest().getParameter("fileName");
String downFileName = fileName;
try {
downFileName = new String(downFileName.getBytes(), "ISO8859-1");
} catch (Exception e) {
e.printStackTrace();
}
return downFileName;
}
//下载的流
public InputStream getInputStream() {
String name=this.getDownloadFileName();
//String realPath=ServletActionContext.getServletContext().getRealPath("/uploadImages")+ "/"+name; 路径错误
String realPath="/uploadImages/"+name;
InputStream in=ServletActionContext.getServletContext().getResourceAsStream(realPath);
if(null==in){
System.out.println("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.检查action中文件下载路径是否正确.");
}
return ServletActionContext.getServletContext().getResourceAsStream(realPath);
}

@Override
public String execute() throws Exception {
return SUCCESS;
}