.NET Core 下使用 Log4Net 记录日志

Log4Net相信大家都很熟悉了，算是比较主流和著名的日志组件了。

• 官网：http://logging.apache.org
• 开源地址：https://github.com/apache/logging-log4net

最佳实践

在项目中添加组件包

Install-Package log4net 

添加log4net.config文件

<?xml version="1.0" encoding="utf-8" ?> <configuration>   <configSections>     <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>   </configSections>   <log4net debug="false">      <appender name="info" type="log4net.Appender.RollingFileAppender,log4net">       <param name="File" value="log4net/info/" />       <param name="AppendToFile" value="true" />       <param name="MaxSizeRollBackups" value="-1"/>       <param name="MaximumFileSize" value="5MB"/>       <param name="RollingStyle" value="Composite" />       <param name="DatePattern" value="yyyyMMdd\HH&quot;.log&quot;" />       <param name="StaticLogFileName" value="false" />       <layout type="log4net.Layout.PatternLayout,log4net">         <param name="ConversionPattern" value="%n {     &quot;system&quot;: &quot;Meowv.Blog&quot;,     &quot;datetime&quot;: &quot;%d&quot;,     &quot;description&quot;: &quot;%m&quot;,   &quot;level&quot;: &quot;%p&quot;,     &quot;info&quot;: &quot;%exception&quot; }" />       </layout>       <filter type="log4net.Filter.LevelRangeFilter">         <levelMin value="INFO" />         <levelMax value="INFO" />       </filter>     </appender>      <appender name="error" type="log4net.Appender.RollingFileAppender,log4net">       <param name="File" value="log4net/error/" />       <param name="AppendToFile" value="true" />       <param name="MaxSizeRollBackups" value="-1"/>       <param name="MaximumFileSize" value="5MB"/>       <param name="RollingStyle" value="Composite" />       <param name="DatePattern" value="yyyyMMdd\HH&quot;.log&quot;" />       <param name="StaticLogFileName" value="false" />       <layout type="log4net.Layout.PatternLayout,log4net">         <param name="ConversionPattern" value="%n {     &quot;system&quot;: &quot;Meowv.Blog&quot;,     &quot;datetime&quot;: &quot;%d&quot;,     &quot;description&quot;: &quot;%m&quot;,   &quot;level&quot;: &quot;%p&quot;,     &quot;info&quot;: &quot;%exception&quot; }" />       </layout>       <filter type="log4net.Filter.LevelRangeFilter">         <levelMin value="ERROR" />         <levelMax value="ERROR" />       </filter>     </appender>      <root>       <level value="ALL"></level>       <appender-ref ref="info"/>       <appender-ref ref="error"/>     </root>    </log4net>  </configuration> 

控制台项目

using log4net; using log4net.Config; using System; using System.IO; using System.Reflection;  namespace ConsoleAppDemo {     class Program     {         static void Main(string[] args)         {             var log4netRepository = LogManager.GetRepository(Assembly.GetEntryAssembly());             XmlConfigurator.Configure(log4netRepository, new FileInfo("log4net.config"));              ILog log = LogManager.GetLogger(log4netRepository.Name, "NETCorelog4net");              log.Info("NETCorelog4net log");             log.Info("test log");             log.Error("error");             log.Info("linezero");             Console.ReadKey();         }     } } 

AspNetCore项目

新建一个静态类，写一个扩展方法UseLog4Net()，用于log4net初始化。

public static class Log4NetExtensions {     public static IHostBuilder UseLog4Net(this IHostBuilder hostBuilder)     {         var log4netRepository = LogManager.GetRepository(Assembly.GetEntryAssembly());         XmlConfigurator.Configure(log4netRepository, new FileInfo("log4net.config"));          return hostBuilder;     } } 

扩展方法返回IHostBuilder对象，这样可以链式调用，美化代码，然后在Program.cs中使用扩展方法UseLog4Net()。

using Microsoft.AspNetCore.Hosting; using Microsoft.Extensions.Hosting;  namespace WebAppDemo {     public class Program     {         public static void Main(string[] args)         {             CreateHostBuilder(args).Build().Run();         }          public static IHostBuilder CreateHostBuilder(string[] args) =>             Host.CreateDefaultBuilder(args)                 .ConfigureWebHostDefaults(webBuilder =>                 {                     webBuilder.UseStartup<Startup>();                 }).UseLog4Net();     } } 

配置完成，然后在任意地方写入日志即可。

using log4net; using Microsoft.AspNetCore.Mvc; using System; using System.Collections.Generic; using System.Linq;  namespace WebAppDemo.Controllers {     [ApiController]     [Route("[controller]")]     public class WeatherForecastController : ControllerBase     {         private static readonly string[] Summaries = new[]         {             "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"         };          private readonly ILog _log;          public WeatherForecastController()         {             _log = LogManager.GetLogger(typeof(WeatherForecastController));         }          [HttpGet]         public IEnumerable<WeatherForecast> Get()         {             _log.Info("Hello, this is a Weather api!");             _log.Warn("Wran !!!");             _log.Error("Controller Error");              var rng = new Random();             return Enumerable.Range(1, 5).Select(index => new WeatherForecast             {                 Date = DateTime.Now.AddDays(index),                 TemperatureC = rng.Next(-20, 55),                 Summary = Summaries[rng.Next(Summaries.Length)]             })             .ToArray();         }     } }