log4net 有四种主要的组件，分别是Logger（记录器）, Repository（库）, Appender（附着器）以及 Layout（布局）.

第一步：Log4net的安装

Install-Package log4net

第二步：Log4net的配置

log4net.config

注意：将log4net.config的属性“复制到输出目录”设置为“始终复制”

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
  </configSections>

  <log4net>
    <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
      <!--日志路径-->
      <param name= "File" value= "D:\App_Log\"/>
      <!--是否是向文件中追加日志-->
      <param name= "AppendToFile" value= "true"/>
      <!--log保留天数-->
      <param name= "MaxSizeRollBackups" value= "10"/>
      <!--日志文件名是否是固定不变的-->
      <param name= "StaticLogFileName" value= "false"/>
      <!--日志文件名格式为:2008-08-31.log-->
      <param name= "DatePattern" value= "yyyy-MM-dd".log""/>
      <!--日志根据日期滚动-->
      <param name= "RollingStyle" value= "Date"/>
      <layout type="log4net.Layout.PatternLayout">
        <param name="ConversionPattern" value="%d [%t] %-5p %c - %m%n %loggername" />
      </layout>
    </appender>

    <!-- 控制台前台显示日志 -->
    <appender name="ColoredConsoleAppender" type="log4net.Appender.ColoredConsoleAppender">
      <mapping>
        <level value="ERROR" />
        <foreColor value="Red, HighIntensity" />
      </mapping>
      <mapping>
        <level value="Info" />
        <foreColor value="Green" />
      </mapping>
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%n%date{HH:mm:ss,fff} [%-5level] %m" />
      </layout>

      <filter type="log4net.Filter.LevelRangeFilter">
        <param name="LevelMin" value="Info" />
        <param name="LevelMax" value="Fatal" />
      </filter>
    </appender>

    <root>
      <!--(高) OFF > FATAL > ERROR > WARN > INFO > DEBUG > ALL (低) -->
      <level value="all" />
      <appender-ref ref="ColoredConsoleAppender"/>
      <appender-ref ref="RollingLogFileAppender"/>
    </root>
  </log4net>
</configuration>

第三步：调用

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

using log4net;
using log4net.Config;

namespace Log4net
{
    class Program
    {
        static void Main(string[] args)
        {
            InitLog4Net();

            var logger = LogManager.GetLogger(typeof(Program));

            logger.Info("消息");
            logger.Warn("警告");
            logger.Error("异常");
            logger.Fatal("错误");

            Console.ReadLine();
        }

        private static void InitLog4Net()
        {
            var logCfg = new FileInfo(AppDomain.CurrentDomain.BaseDirectory + "log4net.config");
            XmlConfigurator.ConfigureAndWatch(logCfg);
        }
    }
}