1 string path = Server.MapPath("/Log/Log.txt");
 2 if (File.Exists(path))
 3 {
 4      using (StreamWriter sw = File.AppendText(path))
 5      {
 6          sw.WriteLine("文本内容");
 7          sw.Flush();
 8          sw.Close();
 9       }
10 }
11 else
12 {
13       using (StreamWriter sw = File.CreateText(path))
14       {
15           sw.WriteLine("文本内容");
16           sw.Flush();
17           sw.Close();
18       }
19 }