ASP.NET上传图片的简单方法

private void Button1_Click(object sender, System.EventArgs e)
{
string filename = "";
if (File1.PostedFile.ContentLength != 0)
{ 
string fn = File1.PostedFile.FileName;
filename =getRandomFilename();
filename += fn.Substring(fn.LastIndexOf("."));
if((fn.Substring(fn.LastIndexOf(".")+1).ToLower()=="jpg")||(fn.Substring(fn.LastIndexOf(".")+1).ToLower()=="gif"))
{
File1.PostedFile.SaveAs(Server.MapPath("file") + "/" + filename);
}
else
{
Response.Write("<script language='javascript'>alert('"+fn.Substring(fn.LastIndexOf(".")+1).ToLower()+"请选择格式为“jpg”或“gif”的图片或格式为“swf”的flash')</script>");
return;
}
Response.Write("<script language='javascript'>alert('上传成功')</script>");
}
else
{
Response.Write("<script language='javascript'>alert('没有图片')</script>");
return;
}
}

static public string getRandomFilename()
{
System.Random rand = new System.Random();
DateTime now = DateTime.Now;
string str = "";
str += now.Year.ToString();
//str += now.Year.ToString().Substring(now.Year.ToString().LastIndexOf("0")+1).Trim();
str += now.Month.ToString();
str += now.Day.ToString();
str += now.Hour.ToString();
str += now.Minute.ToString();
str += now.Second.ToString();
str += rand.Next(0, 1000);
return str; 
}