通过Struts2文件下载时Can not find a java.io.InputStream with the name 异常

异常堆栈信息：

引用:
严重: Can not find a java.io.InputStream with the name [photoStream] in the invocation stack. Check the <param name="inputName"> tag specified for this action.
2008-4-17 17:04:44 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet default threw exception
java.lang.IllegalArgumentException: Can not find a java.io.InputStream with the name [photoStream] in the invocation stack. Check the <param name="inputName"> tag specified for this action.
at org.apache.struts2" onclick="tagshow(event)" class="t_tag">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.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:221)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:86)
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)

可以初步判断为流不存在造成的。

检查Action的相关代码：download.java

复制内容到剪贴板
代码:

public InputStream getPhotoStream() throws Exception {

ServletContext sc = ServletActionContext.getServletContext();
String realpath = sc.getRealPath("/WEB-INF/upload");
String path = realpath + "//" + fileName;
System.out.println("<<<" + this.fileName);
System.out.println(">>>" + path);
return ServletActionContext.getServletContext().getResourceAsStream(path);
}

首先，sc变量是个没充分使用的变量，最后一行又重新去了一次：“ServletActionContext.getServletContext()”。

第二，对ServletContext的getResourceAsStream方法理解有误，该方法不是从本地路径取文件，而是从web application的路径取文件流。

而且在return行前调用ServletActionContext.getServletContext().getResourceAsStream(path)应该可以发现是空指针，比如这样：

复制内容到剪贴板
代码:

System.out.println(">>>"
+ ServletActionContext.getServletContext().getResourceAsStream(
path));
return ServletActionContext.getServletContext().getResourceAsStream(
path);

打印值应该为null，这样就可以定位错误到行了。

我对这部分代码的修改：

复制内容到剪贴板
代码:

return ServletActionContext.getServletContext().getResourceAsStream(
"/WEB-INF/upload/" + this.fileName);