Log4net 介紹

1、Log4net 是什麼？

Log4net 是 Apache 旗下一個開源的日誌框架的專案，它是Log4j 的一個複製版。Log4net中定義了多種日誌資訊輸出模式。它可以根據需要將日誌輸出到控制檯、文字檔案、windows 日誌事件檢視器中、括資料庫，郵件傳送，以便我們可以根據日誌快速定位線上系統的問題。

2、Log4net 日誌等級

從高到底分別為：OFF > FATAL > ERROR > WARN > INFO > DEBUG > ALL

二、ASP.NET MVC 使用 Log4net 示例

2.1 如何安裝 Log4net Log4net

使用Nuget 安裝 Log4net（工具-NuGet包管理器-程式包管理器控制檯（N））使用管理NuGet程式包功能找到Log4net進行安裝。

2.2 建立 log4net.config 配置檔案 ，並且將該檔案的屬性“複製到輸出目錄”修改為 “始終複製。

log4net.config內容如下：

2.3 新建LogHelper.cs通用日誌類

程式碼如下：

public class LogHelper    {        private ILog _log4Net = null;        private const string DEFAULT_LOGGER_NAME = "Logger";        /// <summary>        /// Prevents a default instance of the <see cref="LogWriter"/> class from being created.        /// </summary>        /// <param name="log4NetInstance">The log4net instance to be used.</param>        private LogHelper(ILog log4NetInstance)        {            _log4Net = log4NetInstance;        }        /// <summary>        /// Gets a logger with the specified configuration name.        /// </summary>        /// <param name="configName">Name of the logger in the configuration.</param>        /// <returns>The logger obtained.</returns>        /// <exception cref="System.Configuration.ConfigurationException">Thrown when no logger with the specified configuration name was found.</exception>        public static LogHelper GetLogger(string configName)        {            var logger = LogManager.GetLogger(configName);            if (logger == null)            {                throw new ArgumentException(string.Format("No logger configuration named '{0}' was found in the configuration.", configName), "configName");            }            return new LogHelper(logger);        }        /// <summary>        /// Gets the default.        /// </summary>        public static LogHelper Default        {            get            {                return GetLogger(DEFAULT_LOGGER_NAME);            }        }        /// <summary>        /// Writes an information level logging message.        /// </summary>        /// <param name="message">The message to be written.</param>        public void WriteInfo(object message)        {            _log4Net.Info(message);        }        /// <summary>        /// Writes a warning level logging message.        /// </summary>        /// <param name="message">The message to be written.</param>        public void WriteWarning(object message)        {            _log4Net.Warn(message);        }        /// <summary>        /// Writes a warning level logging message.        /// </summary>        /// <param name="message">The message to be written.</param>        /// <param name="exception">The exception.</param>        public void WriteWarning(object message, System.Exception exception)        {            _log4Net.Warn(message, exception);        }        /// <summary>        /// Writes the error.        /// </summary>        /// <param name="message">The message to be written.</param>        public void WriteError(object message)        {            _log4Net.Error(message);        }        /// <summary>        /// Writes the error level logging message..        /// </summary>        /// <param name="message">The message to be written.</param>        /// <param name="exception">The exception.</param>        public void WriteError(object message, System.Exception exception)        {            _log4Net.Error(message, exception);        }        /// <summary>        /// Writes the fatal error level logging message..        /// </summary>        /// <param name="message">The message to be written.</param>        public void WriteFatal(object message)        {            _log4Net.Fatal(message);        }        /// <summary>        /// Writes the fatal error level logging message..        /// </summary>        /// <param name="message">The message to be written.</param>        /// <param name="exception">The exception.</param>        public void WriteFatal(object message, System.Exception exception)        {            _log4Net.Fatal(message, exception);        }        public void DeleteLog()        {            string logDirPath = Path.Combine(Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location), "Log");            if (!Directory.Exists(logDirPath)) return;            int days = 30;            foreach (string filePath in Directory.GetFiles(logDirPath))            {                DateTime dt;                DateTime.TryParse(Path.GetFileNameWithoutExtension(filePath).Replace(@"Log\", "").Replace(".", "-"), out dt);                if (dt.AddDays(days).CompareTo(DateTime.Now) < 0)                {                    File.Delete(filePath);                }            }        }    }

2.4 AssemblyInfo.cs 檔案配置log4net.config

特別注意：針對為web專案要載入web專案對應的AssemblyInfo.cs檔案中去，這一點很關鍵要不然就不能輸出日誌檔案

[assembly: log4net.Config.XmlConfigurator(Watch = true, ConfigFileExtension = "config", ConfigFile = @"Configs\log4net.config")]

2.5 自定義日誌異常處理檔案：MyExceptionFileAttribute.cs

用來處理異常記錄日誌檔案，然後可以指定錯誤的跳轉頁面。

public override void OnException(ExceptionContext filterContext) {            base.OnException(filterContext);                   if (!string.IsNullOrWhiteSpace(filterContext.Exception.StackTrace))            {                LogHelper.Default.WriteError(filterContext.Exception.StackTrace);            }                //頁面跳轉到錯誤頁面                        filterContext.HttpContext.Response.Redirect("/Error");        }

2.6 Global.asax新增Log4Net的配置資訊

Application_Start.cs 方法加入下面兩行程式碼：

 // 註冊log4net  log4net.Config.XmlConfigurator.Configure();  // 註冊異常日誌檔案  GlobalFilters.Filters.Add(new MyExceptionFileAttribute());

測試用法

LoginController.cs 程式碼加一個異常

    public ActionResult Index()        {            int a = 0;            int b = 6 / a;            return View();        }

效果展示：

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