.NET Core下使用Log4Net记录日志的方法步骤

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。

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();
  }
 }
}

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