1. ติดตั้ง Package ผ่าน NuGet
2. สร้างไฟล์ log4net.config
3. บอก log4net ให้โหลดไฟล์คอนฟิก

• How to use Log4Net with ASP.NET Core for logging | dotnetthoughts
• Does Log4Net Work With .NET 6? – Loupe (onloupe.com)

1.ติดตั้ง Package ผ่าน NuGet

• NuGet Gallery | log4net 2.0.13

PM> Install-Package log4net -Version 2.0.13

• NuGet Gallery | log4net 2.0.15

PM> NuGet\Install-Package log4net -Version 2.0.15

> dotnet add package log4net --version 2.0.15

2.สร้างไฟล์ log4net.config

สร้างไฟล์ log4net.config ไว้เก็บค่า config เกี่ยวกับ log4net

<?xml version="1.0" encoding="utf-8" ?>
<log4net>
  <appender name="console" type="log4net.Appender.ConsoleAppender">
    <layout type="log4net.Layout.PatternLayout">
      <conversionPattern value="%date %level - %message%newline" />
    </layout>
  </appender>
  <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
    <lockingModel type="log4net.Appender.FileAppender+MinimalLock"/>
    <file value="log/" />
    <datePattern value="yyyy-MM-dd.'log'"/>
    <staticLogFileName value="false"/>
    <appendToFile value="true"/>
    <rollingStyle value="Date"/>
    <maxSizeRollBackups value="100"/>
    <maximumFileSize value="15MB"/>
    <encoding value="UTF-8"/>
    <layout type="log4net.Layout.PatternLayout">
      <param name="ConversionPattern" value="%-5p%d{ yyyy-MM-dd HH:mm:ss} - %m  %n" />
    </layout>
  </appender>
  <root>
    <level value="ALL"/>
    <appender-ref ref="console" />
    <appender-ref ref="RollingLogFileAppender"/>
  </root>
</log4net>

หรือ

<?xml version="1.0" encoding="utf-8" ?>
<log4net>
  <root>
    <level value="All" />
    <appender-ref ref="console" />
    <appender-ref ref="file" />
  </root>
  <appender name="console" type="log4net.Appender.ConsoleAppender">
    <layout type="log4net.Layout.PatternLayout">
      <conversionPattern value="%date %level %method - %message%newline" />
    </layout>
  </appender>
  <appender name="file" type="log4net.Appender.RollingFileAppender">
    <lockingModel type="log4net.Appender.FileAppender+MinimalLock"/>
    <file value="logs/" />
    <datePattern value="yyMMdd'_C5.log'" />
    <staticLogFileName value="false" />
    <appendToFile value="true" />
    <rollingStyle value="Composite" />
    <maxSizeRollBackups value="10" />
    <maximumFileSize value="10MB" />
    <encoding value="UTF-8"/>
    <layout type="log4net.Layout.PatternLayout">
      <param name="ConversionPattern" value="%-5p%d{ HH:mm:ss} li:%line - [%method] %m  %n" />
    </layout>
  </appender>
</log4net>

และที่ “Copy to Output Directory” ให้เลือกเป็น “Copy if newer”

3.บอก log4net ให้โหลดไฟล์คอนฟิก

.NET 5 แก้ไขไฟล์ Program.cs

using System.IO;
using System.Reflection;
using System.Xml;

namespace ConsoleApp5
{
    class Program
    {
        public static readonly log4net.ILog log = log4net.LogManager.GetLogger(typeof(Program));
        static void Main()
        {
            XmlDocument log4netConfig = new XmlDocument();
            log4netConfig.Load(File.OpenRead("log4net.config"));
            var repo = log4net.LogManager.CreateRepository(Assembly.GetEntryAssembly(),
                       typeof(log4net.Repository.Hierarchy.Hierarchy));
            log4net.Config.XmlConfigurator.Configure(repo, log4netConfig["log4net"]);

            log.Info("Hello World!");
        }
    }
}

.NET 6 แก้ไขไฟล์ Program.cs

using System.Reflection;
using System.Xml;

namespace ConsoleApp6;

class Program
{
    public static readonly log4net.ILog log = log4net.LogManager.GetLogger(typeof(Program));

    static void Main()
    {
        XmlDocument log4netConfig = new XmlDocument();
        log4netConfig.Load(File.OpenRead("log4net.config"));
        var repo = log4net.LogManager.CreateRepository(Assembly.GetEntryAssembly(),
                   typeof(log4net.Repository.Hierarchy.Hierarchy));
        log4net.Config.XmlConfigurator.Configure(repo, log4netConfig["log4net"]);

        log.Info("Hello World!");
    }
}

.NET 6 new program style

// See https://aka.ms/new-console-template for more information

using System.Reflection;
using System.Xml;

log4net.ILog log = log4net.LogManager.GetLogger(typeof(Program));

XmlDocument log4netConfig = new XmlDocument();
log4netConfig.Load(File.OpenRead("log4net.config"));
var repo = log4net.LogManager.CreateRepository(Assembly.GetEntryAssembly(),
           typeof(log4net.Repository.Hierarchy.Hierarchy));
log4net.Config.XmlConfigurator.Configure(repo, log4netConfig["log4net"]);
log.Info("Hello World!");