How to setup log4net

• Create a new .NET Framework console project. This can be applied to .NET Core

• Install log4net Nuget package.

install-package log4net

• Set up the main class.

  // Import log4net classes.
  using log4net;
  using log4net.Config;
  public static class Program
  {
      // Define a static logger variable so that it references the
      // Logger instance named "Program".
      private static readonly ILog log = LogManager.GetLogger(typeof(Program));
      public static void Main(string[] args)
      {
          // Set up an XmlConfigurator to use log4net XML configuration file
          XmlConfigurator.Configure(new FileInfo("log4net.config"));
          log.Info("Entering application.");
      }
  }

• Create log4net.config file at root level of the project and set "copy to output directory" as "copy as newer".
• Add configuration content to log4net.config.

Rolling file appender

<?xml version="1.0" encoding="utf-8" ?>
<log4net>
    <!--
         Roll log files on a date period and within a date period on file size.
         For each day only the last 10 files of 1MB will be kept.
         We can't keep a file on date/time boundaries, more details https://issues.apache.org/jira/browse/LOG4NET-27
         This problem is fixed by creating a cron job to delete log files and keep some latest days/months.
     -->
    <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
        <!-- The location of the logging file which is relative to the application base directory -->
        <!-- You will find a log file in bin/Debug/logs folder -->
        <file value="logs/" />
        <appendToFile value="true" />
        <rollingStyle value="Composite" />
        <!-- Define the date pattern as a file name and create a log file for each day-->
        <!-- For more format https://docs.microsoft.com/en-us/dotnet/standard/base-types/custom-date-and-time-format-strings -->
        <!--<datePattern value="yyyy-MM-dd-HH-mm-ss.'log'" /> create a new file every second, useful for debugging  -->
        <datePattern value="yyyy-MM-dd.'log'" />
        <!--
            Set to true to always logs to log.txt and then renames the rolling file when appropriate.
            It makes the active log file super obvious.
        -->
        <staticLogFileName value="false"/>
        <maxSizeRollBackups value="10" />
        <maximumFileSize value="1MB" />
        <layout type="log4net.Layout.PatternLayout">
        <!-- https://logging.apache.org/log4net/log4net-1.2.13/release/sdk/log4net.Layout.PatternLayout.html -->
            <conversionPattern value="%date{yyyy-mm-yy HH:mm:ss:fff} [%-5level] line:%line method:%method - %message%newline" />
        </layout>
    </appender>
    <root>
        <!-- To log all message levels -->
        <level value="all" />
        <appender-ref ref="RollingLogFileAppender" />
    </root>
</log4net>

Example file structure of the project

• Project folder
  • ProjectName.csproj
  • Program.cs
  • log4net.config
  • packages.config

Logging level

โดย logging message จะถูกแบ่งออกเป็น 6 ระดับ เรียงตามความสำคัญมากสูง ไปต่ำสุด

• FATAL Highest Very severe error events that will presumably lead the application to abort.
• ERROR Error events that might still allow the application to continue running.
• WARN Potentially harmful situations which still allow the application to continue running.
• INFO Informational messages that highlight the progress of the application at coarse-grained level.
• DEBUG Fine-grained informational events that are most useful to debug an application.
• TRACE Lowest Finest-grained informational events.