在页面中检测上传文件类型：

<script language=”javascript” type =”text/javascript”>
        function CheckImg(FileUpload)
        {
           var   e=document.getElementById(“fulFile”); 
         var mime=FileUpload.value;
            mime=mime.toLowerCase().substr(mime.lastIndexOf(“.”));
         if(mime!=”.jpg”)
         {  
               e.outerHTML=e.outerHTML;
         alert(“仅支持JPG格式”);
         }
}
</script>
//在页面中的调用
<asp:FileUpload  οnchange=”CheckImg(this)” ID=”fulFile” runat=”server” Style=”z-index: 100; left: 30px; position: absolute;top: 61px” />

 后台代码：

protected void Button1_Click(object sender, EventArgs e)
    {
        if (FulFile .HasFile )
        {
            try
            {

                 HttpPostedFile postedFile = this.FulFile.PostedFile; //得到要上传文件
                //存储文件
                //FulFile.SaveAs(“C://” + FulFile.FileName);
                //string s = System.Web.HttpContext.Current.Request.MapPath(“file/”);//返回file文件夹所在的物理路径

                //保存文件到文件夹，地址是当前页面的同一级目录下的file文件夹中
                FulFile.SaveAs(System .Web.HttpContext.Current .Request .MapPath (“file/”)
                    +FulFile .FileName);
                //显示上传文件的具体信息
                Label1.Text = “上传的文件名是” + FulFile.FileName + “<br/>”
                    + “上传的文件大小是” + FulFile.PostedFile.ContentLength + “KB<br/>”
                    + “文件的扩展名是” + Path.GetExtension(FulFile .FileName)+”<br/>”
                    + “文件类型是” + FulFile.PostedFile.ContentType;
            }
            catch (Exception ex)
            {
                Label1.Text = ex.Message;
            }
        }
        else
        {
            Label1.ForeColor = System.Drawing.Color.Red;
            Label1.Text = “没有找到文件”;
        }
    }