<interceptor-ref name="fileUploadStack">
                <!-- 大小 -->        
                <param name="fileUpload.maximumSize">10000000</param>
                <param name="fileUpload.allowedExtensions">.ppt,.pptx,.doc,.docx,.xls,.xlsx</param>
                <param name="fileUpload.allowedTypes">application/vnd.ms-powerpoint,application/msword,application/excel,application/vnd.ms-excel</param>
                <param name="fileUpload.useActionMessageBundle">true</param>
            </interceptor-ref>

以上是单纯的上传大小控制，但是当文件大于系统默认大小时，不会把自定义的国际化错误提示返回到页面。

需要在struts.xml文件内添加

    <constant name="struts.multipart.maxSize" value="10000000" />

用来修改系统默认最大上线