[ASP.net Core] 加入log4net作logger

之前寫過文章利用.net 及Java 寫紀錄, 現在則會示範在.net Core 中利用log4net 進行記錄.

1. 安裝log4net.
   在Package Management Console 中, 輸入以下指令.

   Install-Package log4net

2. 設定log4net.
   建立XML 檔, 命名為log4net.config, 並輸入以下設定.

   <?xml version="1.0" encoding="utf-8" ?>
   <configuration>
     <log4net>
       <appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
         <file value="C:\log\log4net" />
         <appendToFile value="true" />
         <rollingStyle value="Composite" />
         <datePattern value="_yyyy-MM-dd.lo\g" />
         <maximumFileSize value="5MB" />
         <maxSizeRollBackups value="15" />
         <staticLogFileName value="false" />
         <PreserveLogFileNameExtension value="true" />
         <layout type="log4net.Layout.PatternLayout">
           <conversionPattern value="%date [%thread] %level %logger - %message%newline" />
         </layout>
       </appender>
       <root>
         <appender-ref ref="RollingFileAppender" />
       </root>
     </log4net>
   </configuration>

3. 建立Logger
   因為Log4net 本身沒有implement ILogger, 加上雙方的log level 不同, 因此需要自行處理.
   建立class file 並命名為log4netLogger.cs, 並輸入以下代碼.

   public class Log4netLogger : ILogger
       {
           private readonly ILog _log;
   
           public Log4netLogger(string name, FileInfo fileInfo)
           {
               var repository = LogManager.CreateRepository(
                       Assembly.GetEntryAssembly(),
                       typeof(log4net.Repository.Hierarchy.Hierarchy)
                   );
               XmlConfigurator.Configure(repository, fileInfo);
               _log = LogManager.GetLogger(repository.Name, name);
           }
   
           public IDisposable BeginScope<TState>(TState state)
           {
               return null;
           }
   
           public bool IsEnabled(LogLevel logLevel)
           {
               switch (logLevel)
               {
                   case LogLevel.Critical: return _log.IsFatalEnabled;
                   case LogLevel.Debug:
                   case LogLevel.Trace: return _log.IsDebugEnabled;
                   case LogLevel.Error: return _log.IsErrorEnabled;
                   case LogLevel.Information: return _log.IsInfoEnabled;
                   case LogLevel.Warning: return _log.IsWarnEnabled;
                   default: 
                       throw new ArgumentOutOfRangeException(nameof(logLevel));
               }
           }
   
           public void Log<TState>(LogLevel logLevel, EventId eventId, TState state,
               Exception exception, Func<TState, Exception, string> formatter)
           {
               if (!IsEnabled(logLevel))
               {
                   return;
               }
               if (formatter == null)
               {
                   throw new ArgumentNullException(nameof(formatter));
               }
               string message = null;
               if (null != formatter)
               {
                   message = formatter(state, exception);
               }
               if (!string.IsNullOrEmpty(message) || exception != null)
               {
                   switch (logLevel)
                   {
                       case LogLevel.Critical: _log.Fatal(message); break;
                       case LogLevel.Debug:
                       case LogLevel.Trace: _log.Debug(message); break;
                       case LogLevel.Error: _log.Error(message); break;
                       case LogLevel.Information: _log.Info(message); break;
                       case LogLevel.Warning: _log.Warn(message); break;
                       default: 
                           _log.Warn($"Unknown log level {logLevel}.\r\n{message}"); 
                           break;
                   }
               }
           }
       }

4. 建立Provider.
   因為在.net core 中, ILogger 是透過Factory Pattern 產生, 而其factory 是ILoggerProvider, 所以須要implement 它.
   建立class file 並命名為Log4netProvider.cs, 並輸入以下代碼.

   public class Log4netProvider : ILoggerProvider
       {
           private readonly FileInfo _fileInfo;
   
           public Log4netProvider(string log4netConfigFile)
           {
               _fileInfo = new FileInfo(log4netConfigFile);
           }
   
           public ILogger CreateLogger(string name)
           {
               return new Log4netLogger(name, _fileInfo);
           }
   
           public void Dispose()
           {
           }
       }

5. 加入logger 到Webhost 中.
   在program.cs 中修改CreateWebHostBuilder method chain 如下.

   public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
               WebHost.CreateDefaultBuilder(args)
               .ConfigureLogging(logging=> {
                   logging.AddProvider(new Log4netProvider(@"log4net.config"));
               })
               .ConfigureAppConfiguration((builderContext, config) =>
               {
                   config.AddEnvironmentVariables();
               })
               .UseStartup<Startup>();

6. 測試.
   按F5 執行程式, 當見到有記錄檔產生及資料寫入, 代表測試成功.
   

雖然log4net 可以透過database 儲存, 但現在其AdoNetAppender仍未支援.net Core, 所以並沒有用作實戰使用. 但仍將建立紀錄留記, 示範中會利用SQL server 存儲記錄.

1. 建立Table.
   於SQL Server Management Studio 中執行以下指令.

   CREATE TABLE [dbo].[Log](
     [Id] [bigint] IDENTITY(1,1) NOT NULL,
     [Date] [datetime2] NOT NULL,
     [Thread] [varchar](255) NOT NULL,
     [Level] [varchar](50) NOT NULL,
     [Logger] [varchar](255) NOT NULL,
     [Message] [varchar](max) NOT NULL,
     [Exception] [varchar](max) NULL
   ) ON [PRIMARY]
   GO

2. 加入AdoNetAppender.
   修改log4net.config, 並加入以下設定.

   <?xml version="1.0" encoding="utf-8" ?>
   <configuration>
     <log4net>
     <appender name="AdoNetAppender" type="log4net.Appender.AdoNetAppender">
    <bufferSize value="1" />
         <connectionType value="System.Data.SqlClient.SqlConnection,System.Data,Version=4.0.0.0,Culture=neutral,PublicKeyToken=b77a5c561934e089" />
         <connectionString value="<<Connection String Here>>" />
         <commandText value="INSERT INTO Log ([Date],[Thread],[Level],[Logger],[Message],[Exception]) VALUES (@log_date, @thread, @log_level, @logger, @message, @exception)" />
         <parameter>
           <parameterName value="@log_date" />
           <dbType value="DateTime" />
           <layout type="log4net.Layout.RawTimeStampLayout" />
         </parameter>
         <parameter>
           <parameterName value="@thread" />
           <dbType value="String" />
           <size value="255" />
           <layout type="log4net.Layout.PatternLayout">
             <conversionPattern value="%thread" />
           </layout>
         </parameter>
         <parameter>
           <parameterName value="@log_level" />
           <dbType value="String" />
           <size value="50" />
           <layout type="log4net.Layout.PatternLayout">
             <conversionPattern value="%level" />
           </layout>
         </parameter>
         <parameter>
           <parameterName value="@logger" />
           <dbType value="String" />
           <size value="255" />
           <layout type="log4net.Layout.PatternLayout">
             <conversionPattern value="%logger" />
           </layout>
         </parameter>
         <parameter>
           <parameterName value="@message" />
           <dbType value="String" />
           <size value="4000" />
           <layout type="log4net.Layout.PatternLayout">
             <conversionPattern value="%message" />
           </layout>
         </parameter>
         <parameter>
           <parameterName value="@exception" />
           <dbType value="String" />
           <size value="2000" />
           <layout type="log4net.Layout.ExceptionLayout" />
         </parameter>
       </appender>
       <root>
         <appender-ref ref="AdoNetAppender" />
       </root>
     </log4net>
   </configuration>