private static void WriteLog(string message)
        {
            try
            {
                string rootPath = AppDomain.CurrentDomain.SetupInformation.ApplicationBase;
                if (!rootPath.EndsWith("\\"))
                {
                    rootPath += "\\";
                }

                string path = rootPath + "Log\\";
                if (!Directory.Exists(path))
                {
                    Directory.CreateDirectory(path);
                }

                string filePath = path + DateTime.Today.ToString("yyyy-mm-dd") + ".txt";

                if (!File.Exists(filePath))
                {
                    File.Create(filePath).Close();    
                }
           
                using (StreamWriter w = File.AppendText(filePath))
                {
                    w.WriteLine("\r\n");
                    w.WriteLine("{0} ", DateTime.Now.ToString(CultureInfo.InvariantCulture));
                    w.WriteLine(message);
                    w.Flush();
                    w.Close();
                }
              
            }
            catch (Exception ex)
            {

            }

        }

参考文章： Error Logging using ASP.NET 2.0

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