一、安装NuGet包

二、添加配置

// log4net日志
 builder.Logging.AddLog4Net("CfgFile/log4net.config");

三、配置log4net.config文件

<?xml version="1.0" encoding="utf-8"?>
<log4net>
	<!-- Define some output appenders -->
	<appender name="rollingAppender" type="log4net.Appender.RollingFileAppender">
		<!--    value="logs/log.log"-->
		<file value="logs/" />
		<!--追加日志内容-->
		<appendToFile value="true" />

		<!--防止多线程时不能写Log,官方说线程非安全-->
		<lockingModel type="log4net.Appender.FileAppender+MinimalLock" />

		<!--可以为:Once|Size|Date|Composite-->
		<!--Composite为Size和Date的组合-->
		<rollingStyle value="Composite" />

		<!--当备份文件时,为文件名加的后缀-->
		<datePattern value="yyyyMMdd/&quot;log.log&quot;" />

		<!--日志最大个数,都是最新的-->
		<!--rollingStyle节点为Size时,只能有value个日志-->
		<!--rollingStyle节点为Composite时,每天有value个日志-->
		<maxSizeRollBackups value="20" />

		<!--可用的单位:KB|MB|GB-->
		<maximumFileSize value="3MB" />

		<!--置为true,当前最新日志文件名永远为file节中的名字-->
		<staticLogFileName value="false" />

		<!--输出级别在INFO和ERROR之间的日志-->
		<filter type="log4net.Filter.LevelRangeFilter">
			<param name="LevelMin" value="ALL" />
			<param name="LevelMax" value="FATAL" />
		</filter>
		<layout type="log4net.Layout.PatternLayout">
			<conversionPattern value="%date [%thread] %-5level %logger - %message%newline"/>
		</layout>
	</appender>
	<!-- error日志 -->
	<appender name="errorAppender" type="log4net.Appender.RollingFileAppender">
		<file value="logs/" />
		<appendToFile value="true" />
		<lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
		<rollingStyle value="Composite" />
		<datePattern value="yyyyMMdd/&quot;error.log&quot;" />
		<maxSizeRollBackups value="20" />
		<maximumFileSize value="3MB" />
		<staticLogFileName value="false" />
		<filter type="log4net.Filter.LevelRangeFilter">
			<param name="LevelMin" value="ERROR" />
			<param name="LevelMax" value="ERROR" />
		</filter>
		<layout type="log4net.Layout.PatternLayout">
			<conversionPattern value="%date [%thread] %-5level %logger - %message%newline"/>
		</layout>
	</appender>
	<root>

		<!--控制级别，由低到高: ALL|DEBUG|INFO|WARN|ERROR|FATAL|OFF-->
		<!--OFF:0-->
		<!--FATAL:FATAL-->
		<!--ERROR: ERROR,FATAL-->
		<!--WARN: WARN,ERROR,FATAL-->
		<!--INFO: INFO,WARN,ERROR,FATAL-->
		<!--DEBUG: INFO,WARN,ERROR,FATAL-->
		<!--ALL: DEBUG,INFO,WARN,ERROR,FATAL-->
		<priority value="ALL"/>

		<level value="INFO"/>
		<!--使用上面配置的那个规则-->
		<appender-ref ref="rollingAppender" />
		<appender-ref ref="errorAppender" />
	</root>
</log4net>

四、记录日志

private readonly ILogger<WeatherForecastController> _logger;
/// <summary>
/// 构造函数
/// </summary>
/// <param name="logger"></param>
public WeatherForecastController(ILogger<WeatherForecastController> logger)
{
	_logger = logger;
    _logger.LogInformation($"{this.GetType()},info,接口访问Info");
    _logger.LogDebug($"{this.GetType()},debugger,接口访问Debugger");
    _logger.LogWarning($"{this.GetType()},warning,接口访Warning");
    _logger.LogError($"{this.GetType()},error,接口访问Error");
}

五、查看日志文件