Servlet.service() for servlet default threw exception   java.lang.IllegalArgumentException: Can not find a java.io.InputStream with the name [imageStream] 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.best.top.validate.TopInterceptor.intercept(TopInterceptor.java:47)   at com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:224)   at com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:223)   at com.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)   at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:221)   at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:50)   at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:504)   at org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:419)  

if (inputStream == null) {   // Find the inputstream from the invocation variable stack  inputStream = (InputStream) invocation.getStack().findValue(conditionalParse(inputName, invocation));   }   if (inputStream == null) {   String msg = ("Can not find a java.io.InputStream with the name [" + inputName + "] in the invocation stack. " +   "Check the <param name=\"inputName\"> tag specified for this action.");   LOG.error(msg);   throw new IllegalArgumentException(msg);   }  

InputStream in=ServletActionContext.getServletContext().getResourceAsStream(realPath);
System.out.println(in);

<a href="fileDownload.action?fileName=<s:property value ="imageName" />">下载此图片</a>

<!-- 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>

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;
}