今天在用struts2就行文件下载时出现如下错误：

  1. Servlet.service() for servlet default threw exception   
  2. java.lang.IllegalArgumentException: Can not find a java.io.InputStream with the name [imageStream] in the invocation stack. Check the "inputName"> tag specified for this action.   
  3.     at org.apache.struts2.dispatcher.StreamResult.doExecute(StreamResult.java:189)   
  4.     at org.apache.struts2.dispatcher.StrutsResultSupport.execute(StrutsResultSupport.java:178)   
  5.     at com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:348)   
  6.     at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:253)   
  7.     at com.best.top.validate.TopInterceptor.intercept(TopInterceptor.java:47)   
  8.     at com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:224)   
  9.     at com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:223)   
  10.     at com.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)   
  11.     at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:221)   
  12.     at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:50)   
  13.     at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:504)   
  14.     at org.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：

 

  1. if (inputStream == null) {   
  2.                 // Find the inputstream from the invocation variable stack  
  3.                 inputStream = (InputStream) invocation.getStack().findValue(conditionalParse(inputName, invocation));   
  4.             }   
  5.   
  6.             if (inputStream == null) {   
  7.                 String msg = ("Can not find a java.io.InputStream with the name [" + inputName + "] in the invocation stack. " +   
  8.                     "Check the  tag specified for this action.");   
  9.                 LOG.error(msg);   
  10.                 throw new IllegalArgumentException(msg);   
  11.             }  

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:
fileDownload.action?fileName=">下载此图片
struts.xml中
----------------------------------------------------------

       class="com.test.action.filedown.FileDownloadAction">
   
    
    
     application/octet-stream;charset=ISO8859-1
    
    
      attachment;filename="${downloadFileName}"
    
    
     inputStream
     4096
   
  
----------------------------------------------------------
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 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;
}