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() 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)

 

     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) {
                // 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);
            }

 

需要定义一个方法在action中

   public InputStream getImageStream(){
       return stream; 
   }

谢谢了，解决我的问题了，万分感谢