和之前的ASP.NET MVC中的使用LOG4NET的方法有些不同，这里先记录一下，使用步骤如下 ：

1. 建立 ASP.NET CORE项目中，NUGET中搜索log4net后下载安装

2. 根目录建立 log4net.config文件，内容如下：

<?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="FileAppender" type="log4net.Appender.FileAppender">
      <file value="log-file.log" />
      <appendToFile value="true" />
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %message%newline" />
      </layout>
    </appender>-->

<appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
      <file value="logfile/" />
      <appendToFile value="true" />
      <rollingStyle value="Composite" />
      <staticLogFileName value="false" />
      <datePattern value="yyyyMMdd'.log'" />
      <maxSizeRollBackups value="10" />
      <maximumFileSize value="1MB" />
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %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="FileAppender" />
      <appender-ref ref="RollingLogFileAppender" />
    </root>

</log4net>
</configuration>

3. Startup.cs文件中的Startup方法和ConfigureServices方法里的AddMvc代码改下，核心代码如下，记得引用相应的命名空间：

//log4net日志
        public static ILoggerRepository repository { get; set; }

public Startup(IConfiguration configuration)
        {
            Configuration = configuration;

//加载log4net日志配置文件
            repository = LogManager.CreateRepository("NETCoreRepository");
            XmlConfigurator.Configure(repository, new FileInfo("log4net.config"));
        }

public IConfiguration Configuration { get; }

// This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {

services.AddMvc(options =>
            {
                options.Filters.Add<Models.HttpGlobalExceptionFilter>(); //加入全局异常类
            });
        }

4. Models文件夹中建立 HttpGlobalExceptionFilter.cs 类，用于全局异常后记录到日志中，内容代码如下 ：

using log4net;
using Microsoft.AspNetCore.Mvc.Filters;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace WebApplication1.Models
{
    /// <summary>
    /// 全局异常类
    /// </summary>
    public class HttpGlobalExceptionFilter : IExceptionFilter
    {
        private ILog log = LogManager.GetLogger(Startup.repository.Name, typeof(HttpGlobalExceptionFilter));
        public void OnException(ExceptionContext context)
        {
            log.Error(context.Exception);
        }
    }
}

5. 下面是控制器的代码，有异常会自动记录下来，用那个log也能手工记录日志信息

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;
using log4net;
using Microsoft.AspNetCore.Mvc;
using WebApplication1.Models;

namespace WebApplication1.Controllers
{
    public class HomeController : Controller
    {
        private ILog log = LogManager.GetLogger(Startup.repository.Name, typeof(HttpGlobalExceptionFilter));
        public IActionResult Index()
        {
            throw new Exception("牛腩自定义异常！！！");  //有异常则会记录到logfile文件夹中
            return View();
        }

public IActionResult About()
        {
            ViewData["Message"] = "Your application description page.";
            log.Info("打开about页面了！！！"); //普通的记录日志
            return View();
        }
 
    }
}