在MVC專案下建立Log類別

public class LogWriter<T> where T : Enum
{
    /// <summary>路徑</summary>
    private static string Path = "C:\\LogFile";
    /// <summary>檔案名稱</summary>
    private static string Name = "Log";
    /// <summary>篩選內容</summary>
    private static T AllowType;

    /// <summary>
    /// 設定路徑和名稱
    /// </summary>
    /// <param name="NewPath">路徑</param>
    /// <param name="NewName">名稱</param>
    /// <param name="NewAllowType">篩選的列舉</param>
    public static void SetPathAndName(string NewPath, string NewName, T NewAllowType)
    {
        Path = NewPath;
        Name = NewName;
        AllowType = NewAllowType;
    }
    
    /// <summary>
    /// 更換新的允許
    /// </summary>
    /// <param name="NewAllowType">新允許</param>
    public void ChangeAllow(T NewAllowType)
    {
        AllowType = NewAllowType;
    }

    /// <summary>產生Log檔</summary>
    public static void CreateLogger()
    {
        //如果此路徑沒有資料夾
        if (!Directory.Exists(Path))
        {
            //新增資料夾
            Directory.CreateDirectory(Path);
        }
        WriteLog("=======================================");
        WriteLog("程式啟動 : " + DateTime.Now.ToString());
        WriteLog("=======================================");
    }
    
    /// <summary>
    /// 寫入Log
    /// </summary>
    /// <param name="log">Log內容</param>
    public static void WriteLog(string log)
    {
        if (!Directory.Exists(Path))
            CreateLogger();
        using (StreamWriter sw = File.AppendText(Path + "\\" + Name))
            sw.WriteLine(log);
    }

    /// <summary>
    /// 寫入Log(複合列舉)
    /// </summary>
    /// <param name="LogType">Log類別</param>
    /// <param name="ClassName">使用GetType的Name或FullName</param>
    /// <param name="MethodName">使用MethodBase.GetCurrentMethod</param>
    /// <param name="Message">Log內容</param>
    /// <returns></returns>
    public static void WriteLogs(T LogType, string ClassName, string MethodName, string Message)
    {
        if (!Directory.Exists(Path))
            CreateLogger();
        List<string> AllowTypeList = new List<string>();
        foreach (T EnumType in Enum.GetValues(typeof(T)))
            if (AllowType.HasFlag(EnumType) && LogType.HasFlag(EnumType))
                AllowTypeList.Add(EnumType.ToString());
                
        using (StreamWriter sw = File.AppendText(Path + "\\" + Name)){
           sw.WriteLine($"[{string.Join("|", AllowTypeList)}] {ClassName}[{MethodName}] {Message}");
        } 
    }
    /// <summary>
    /// 寫入Log(多列舉)
    /// </summary>
    /// <param name="LogType">Log類別</param>
    /// <param name="ClassName">使用GetType的Name或FullName</param>
    /// <param name="MethodName">使用MethodBase.GetCurrentMethod</param>
    /// <param name="Message">Log內容</param>
    /// <returns></returns>
    public static void WriteLogm(T LogType, string ClassName, string MethodName, string Message)
    {
        if (!Directory.Exists(Path))
            CreateLogger();
        foreach (T EnumType in Enum.GetValues(typeof(T)))
            if (LogType.HasFlag(EnumType))
                WriteLog(EnumType, ClassName, MethodName, Message);
    }
    /// <summary>
    /// 寫入Log
    /// </summary>
    /// <param name="LogType">Log類別</param>
    /// <param name="ClassName">使用GetType的Name或FullName</param>
    /// <param name="MethodName">使用MethodBase.GetCurrentMethod</param>
    /// <param name="Message">Log內容</param>
    /// <returns></returns>
    public static void WriteLog(T LogType, string ClassName, string MethodName, string Message)
    {
        if (!AllowType.HasFlag(LogType))
            return;
        WriteLog($"[{LogType}] {ClassName}[{MethodName}] {Message}");
    }
}

建立Log用Enum

public class ConstEnum
{
    /// <summary>Log列舉</summary>
    [Flags]
    public enum ELogType
    {
        #region 介面
        /// <summary>網站</summary>
        WEB = 0x0001,
        /// <summary>核心</summary>
        CORE = 0x0002,
        #endregion

        #region 類型
        /// <summary>訊息</summary>
        INFO = 0x0004,
        /// <summary>警告</summary>
        WARN = 0x0008,
        /// <summary>錯誤</summary>
        ERROR = 0x0010,
        #endregion
    }
}

在應用程式開始和結束的地方加入

namespace WebProjectName
{
    /// <summary>執行端</summary>
    public class MvcApplication : System.Web.HttpApplication
    {
        /// <summary>應用程式開始</summary>
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            //加入路由
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            //封裝JS和CSS檔
            BundleConfig.RegisterBundles(BundleTable.Bundles);
            
            //開啟log記錄
            LogWriter<ELogType>.SetPathAndName("C:\\LogFile", "Log", (ELogType)0xFFFF);
            LogWriter<ELogType>.CreateLogger();
        }

        /// <summary>應用程式結束</summary>
        protected void Application_End()
        {
            LogWriter<ELogType>.WriteLog("============================");
            LogWriter<ELogType>.WriteLog("程式結束Application_End : " + DateTime.Now.ToString());
            LogWriter<ELogType>.WriteLog("============================");
        }

        /// <summary>程式出錯</summary>
        protected void Application_Error()
        {
            Exception ErrorMsg = Server.GetLastError();
            LogWriter<ELogType>.WriteLog($"[Application_Error] Exception:{ErrorMsg.GetType().Name}({ErrorMsg.Message}) \nSource:{ErrorMsg.Source} \nStackTrace:{ErrorMsg.StackTrace}");
        }
    }
}

使用方式

LogWriter.WriteLogs(
    ELogType.WEB | ELogType.WARN,
    GetType().Name,
    MethodBase.GetCurrentMethod().Name, "訊息");