public class Logger
    {
        private static ILog logger;
       static Logger()
        {
            if (logger == null)
            {
                var repository = LogManager.CreateRepository("NETCoreRepository");
                //log4net从log4net.config文件中读取配置信息
                XmlConfigurator.Configure(repository, new FileInfo("log4net.config"));
                logger = LogManager.GetLogger(repository.Name, "Logger");
            }
        }
        public static void Info(string message, Exception exception = null)
        {
            if (exception == null)
                logger.Info(message);
            else
                logger.Info(message, exception);
        }
        public static void Warn(string message, Exception exception = null)
        {
            if (exception == null)
                logger.Warn(message);
            else
                logger.Warn(message, exception);
        }
        public static void Error(string message, Exception exception = null)
        {
            if (exception == null)
                logger.Error(message);
            else
                logger.Error(message, exception);
        }
    }

config配置如下

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <!-- This section contains the log4net configuration settings -->
  <log4net>
    <appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender">
      <layout type="log4net.Layout.PatternLayout" value="%date [%thread] %-5level %logger - %message%newline" />
    </appender>
    <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
      <file value="Log/" />
      <appendToFile value="true" />
      <rollingStyle value="Composite" />
      <staticLogFileName value="false" />
      <datePattern value="yyyyMMdd'.log'" />
      <maxSizeRollBackups value="10" />
      <maximumFileSize value="50MB" />
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date  [%thread]  %-5level  %message%newline" />
      </layout>
    </appender>
    <!-- Setup the root category, add the appenders and set the default level -->
    <root>
      <level value="ALL" />
      <appender-ref ref="ConsoleAppender" />
      <appender-ref ref="RollingLogFileAppender" />
    </root>
  </log4net>
</configuration>

然后，在该调用的地方，直接调用

[Route("api/[controller]/[action]")]
    public class LogController:Controller
    {
        [HttpGet]
        public IActionResult Get(string x)
        {
            Logger.Info("info:" + x);
            Logger.Warn("warn:" + x);
            return Ok(x);
        }
    }

即可在console和file中显示

log4net查看地址：http://logging.apache.org/log4net/release/manual/configuration.html