struts2文件下載出現Can not find a java.io.InputStream with the name的錯誤

  今天在用struts2就行文件下載時出現以下錯誤：

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)

說實話這個提示真有誤導人的嫌疑，剛開始還覺得是名稱不對，估計通常人看到這個提示都這樣想。而後查看StreamResult的源代碼才發現是由於InputStream爲null的緣故，汗一個。看下源碼：

 

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);
            }

你們若是也碰到此類問題,直接打印
InputStream in=ServletActionContext.getServletContext().getResourceAsStream(realPath);
System.out.println(in);

若是打印爲NULL的話,恭喜您,問題得以解決,問題的緣由是這個流的realPath路徑錯誤,

 還沒明白的往下看

怪呀,個人配置應該沒錯呀
頁面上:
<a href="fileDownload.action?fileName=<s:property value ="imageName" />">下載此圖片</a>
struts.xml中
----------------------------------------------------------
<!-- 文件下載，支持中文附件名 -->
   <action name="fileDownload"
    class="com.test.action.filedown.FileDownloadAction">
    <result name="success" type="stream">
     <!-- 動態文件下載的，事先並不知道將來的文件類型，那麼咱們能夠把它的值設置成爲：application/octet-stream;charset=ISO8859-1 ，注意必定要加入charset，不然某些時候會致使下載的文件出錯； -->
     <param name="contentType">
     application/octet-stream;charset=ISO8859-1
     </param>
     <param name="contentDisposition">
      attachment;filename="${downloadFileName}"
     </param>
     <!-- 使用通過轉碼的文件名做爲下載文件名，downloadFileName屬性
      對應action類中的方法 getDownloadFileName() 其中特殊的代碼就是${downloadFileName}，它的效果至關於運行的時候將action對象的屬性的取值動態的填充在${}中間的部分，咱們能夠認爲它等價於＋action. getDownloadFileName()。 -->
     <param name="inputName">inputStream</param>
     <param name="bufferSize">4096</param>
    </result>
   </action>
----------------------------------------------------------
action中
----------------------------------------------------------
private String fileName;// 初始的經過param指定的文件名屬性 set get

/** 文件名 轉換編碼 防止中文亂碼*/
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;
}
//下載的流
public InputStream getInputStream() {
   String name=this.getDownloadFileName();
//  String realPath=ServletActionContext.getServletContext().getRealPath("/uploadImages")+ "/"+name; 路徑錯誤
   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.檢查action中文件下載路徑是否正確.");  
   }
   return ServletActionContext.getServletContext().getResourceAsStream(realPath);
}

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