FileUpload1 上传文件类型验证正则表达式

<asp:RegularExpressionValidator  
id="FileUpLoadValidator" runat="server"  
ErrorMessage="Upload Jpegs and Gifs only."  
ValidationExpression="^(([a-zA-Z]:)|(\\{2}\w+)\$?)(\\(\w[\w].*))(.jpg|.JPG|.gif|.GIF)$"  
ControlToValidate="FileUpload1"> 
</asp:RegularExpressionValidator>