/// <summary>
    /// Response.AddHeader实现下载
    /// </summary>
    /// <param name="filePath">完整的文件路径</param>
    /// <param name="fileName">文件名</param>
    private void DownFile(string filePath, string fileName)
     {
         FileInfo fileInfo = new FileInfo(filePath);
         Response.Clear();
         Response.ClearContent();
         Response.ClearHeaders();
         Response.AddHeader("Content-Disposition", "attachment;filename=" + System.Web.HttpUtility.UrlEncode(Request.ContentEncoding.GetBytes(fileName))););
         Response.AddHeader("Content-Length", fileInfo.Length.ToString());
         Response.AddHeader("Content-Transfer-Encoding", "binary");
         Response.ContentType = "application/octet-stream";
         Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");
         Response.WriteFile(fileInfo.FullName);
         Response.Flush();
         Response.End();
     }

====================================================

response.addheader "pragma","no-cache" 是不要网页存于缓存之中。



相当于<meta http-equiv="pragma" content="no-cache">

addheader 是发送给浏览器 HTTP 头信息

服务器端：
<%
Response.Buffer = True
Response.ExpiresAbsolute = Now() - 1
Response.Expires = 0
Response.CacheControl = "no-cache"
%>  
客户端：
用客户端代码使浏览器不再缓存Web页面：       
     <html>        
     <head>        
     <meta http-equiv="Expires" CONTENT="0">        
     <meta http-equiv="Cache-Control" CONTENT="no-cache">        
     <meta http-equiv="Pragma" CONTENT="no-cache">        
     </head>     
     　　 如果使用上面的方法强制浏览器不再缓存Web页面，必须注意以下几点：        
     只有在使用安全连接时“Pragma: no-cache”才防止浏览器缓存页面。对于不受安全保护的页面，“Pragma: no-cache”被视为与“Expires: -1”相同，此时浏览器仍旧缓存页面，但把页面标记为立即过期。  
     但是在IE 4或5中，“Cache-Control”META HTTP-EQUIV标记将被忽略，不起作用。