<action name="upload" class="action.MulUpload">
            <!-- 设置文件的类型 -->
            <interceptor-ref name="fileUpload">
                <param name="allowedTypes">image/JPEG,image/JPG</param>               
            </interceptor-ref>
            <interceptor-ref name="defaultStack"/>
            
            <result name="input">/mulFile.jsp</result>
            <result name="success">/success.jsp</result>
        </action>

irefox与IE的区别(不加以区分的话，可能会上传失败)
1. firefox:  image/jpeg image/bmp image/gif image/png 
2.IE:  image/pjpeg image/bmp image/gif image/x-png