asp.net fileupload implements upload

protected void Button1_Click(object sender, EventArgs e) 
{ 
string filename = this.DropDownList1.SelectedValue;//最终命名 
if (this.FileUpload1.PostedFile != null) 
{ 
string baseFilename = this.FileUpload1.PostedFile.FileName;//获取上传文件文件名 
int i = baseFilename.LastIndexOf("."); 
string ext = baseFilename.Substring(i);//获取文件的扩展名 
string savePath = Server.MapPath("~/pic/"); 
if (!System.IO.Directory.Exists(savePath)) 
{ 
System.IO.Directory.CreateDirectory(savePath ); 
} 
savePath = savePath + "\\" + filename+ext; 
//Response.Write(ext ); 
if (!ext.Equals(".jpg") && !ext.Equals(".jpeg") && !ext.Equals(".bmp") && !ext.Equals(".gif") && !ext.Equals(".png")) 
{ 
Response.Write("上传文件格式不正确！<a href="\" href="\""upload.aspx\">重新上传</a>"); 
Response.End(); 
} 

FileUpload1.PostedFile.SaveAs( savePath ); 
} 
}