怎么在.Net Core3.0/ 3.1Webapi 中使用Log4net 写日志及读取配置文件的信息

1：安装Log4Net的 NuGet 包：

我们通常之需要安装这一个包即可，其他的主包会自动被添加进来：

insatll-package Microsoft.Extensions.Logging.Log4Net.AspNetCore 3.0.0 （如果不行就直接NuGet可视化安装）！

2：Log4Net的配置文件的内容：

<?xml version="1.0" encoding="utf-8" ?>
<log4net>
  <!-- Define some output appenders -->
  <appender name="rollingAppender" type="log4net.Appender.RollingFileAppender">
    <file value="Errorlog\\log.txt" />

    <!--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,这里可以作为每一天的日志分别存储不同的文件-->
    <datePattern value="yyyyMMdd".txt"" />
    <StaticLogFileName value="false"/>

    <!--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="true" />

    <!--输出级别在INFO和ERROR之间的日志-->
    <filter type="log4net.Filter.LevelRangeFilter">
      <param name="LevelMin" value="DEBUG" />
      <param name="LevelMax" value="FATAL" />
    </filter>

    <layout type="log4net.Layout.PatternLayout">
      <!--日志输出格式：时间  日志类型  日志内容-->
      <conversionPattern value="%date [%thread] %-5level %logger - %message%newline"/>
    </layout>
  </appender>

  <!-- levels: OFF > FATAL > ERROR > WARN > INFO > DEBUG  > ALL -->
  <root>
    <priority value="ALL"/>
    <level value="ALL"/>
    <appender-ref ref="rollingAppender" />
  </root>
</log4net>

3：在StartUp类中新增读取Log4Net的配置文件的代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using WebApp.Filters;

namespace WebApp
{
    using log4net;
    using log4net.Config;
    using log4net.Repository;
    public class Startup
    {
        public static ILoggerRepository repository { get; set; }
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
            repository = LogManager.CreateRepository("rollingAppender");
            XmlConfigurator.Configure(repository, new System.IO.FileInfo(System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "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.AddControllersWithViews();//configure =>         
            //-------全局异常过滤器
            services.AddMvc(c => c.Filters.Add<CustomerExceptionFilterAttribute>());
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
            }
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Student}/{action=Index}/{id?}");
            });
        }
    }
}

　4：Log4Net的文件修改为始终复制：

5：我们在Controller来简单的测试一下，代码如下：

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

namespace WebApp.Controllers
{
    using log4net;
    using Microsoft.Extensions.Configuration;
    public class StudentController : Controller
    {
        private ILog log = LogManager.GetLogger(Startup.repository.Name,typeof(StudentController));

        private IConfiguration config;
        public StudentController(IConfiguration config)
        {
            this.config = config;
        }

        [TypeFilter(typeof(CustomerActionFilterAttribute))]
        [TypeFilter(typeof(CustomerExceptionFilterAttribute))]
        [TypeFilter(typeof(CustomerResourceFilterAttribute))]
        public IActionResult Index()
        {
            string uid = config["mysqlserver:database"];
            string infoName = config["mysqlserver:infos:1:age"];
            log.Info("dsadsadsdsdsaderror");
            log.Error("errorddddddddd");

            int j = 0;
            //    int i = 0 / j;
            ViewBag.uid = uid;
            ViewBag.infoname = infoName;
            ViewBag.Time = $"后台时间是：{ DateTime.Now.ToString()}";
            return View();
        }
    }
}

6：查看效果如下截图：