ASP.NET实现文件上传

protected void Button4_Click(object sender, EventArgs e)
    {
        string fullname = this.FileUpload4.PostedFile.FileName;
        string filename = fullname.Substring(fullname.LastIndexOf("//") + 1);
        string type = fullname.Substring(fullname.LastIndexOf(".")+1);
        if (type == "jpg" || type == "gif" || type == "bmp")
        {
            this.FileUpload4.PostedFile.SaveAs(Server.MapPath("Upload") + "//" + filename);
        }
        else
        {
            Response.Write("<script language='java-script'>alert('你上传的文件格式不正确!')</script>");
        }
    }
说明：FileUpload为.NET中提供的控件；