.Net Core使用NLog记录日志

　　参见：https://github.com/NLog/NLog.Web/wiki/Getting-started-with-ASP.NET-Core-2

补充：

　　如在本地能写log，但是发布到IIS无法写log，请注意引用程序池的账号，默认的“ApplicationPoolIdentity”应该是没有权限的，将其改为“LocalSystem”即可。

大致步骤：

• Nuget中引用NLog及NLog.Web.AspNetCore 4.5+
• 创建nlog.config文件，部分修改：

  <?xml version="1.0" encoding="utf-8" ?>
  <nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        autoReload="true"
        internalLogLevel="info"
        internalLogFile="logs\internal-nlog.log">
  
    <!-- enable asp.net core layout renderers -->
    <extensions>
      <add assembly="NLog.Web.AspNetCore"/>
    </extensions>
  
    <!-- the targets to write to -->
    <targets>
      <!-- write logs to file  -->
      <target name="allFile" xsi:type="File" fileName="logs\nlog-all-${shortdate}.log"
              layout="${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}" />
  
      <!-- another file log, only own logs. Uses some ASP.NET core renderers -->
      <target name="ownFile" xsi:type="File" fileName="logs\nlog-own-${shortdate}.log"
              layout="${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}" />
  
      <target name="blackHole" xsi:type="Null"  />
  
    </targets>
  
    <!-- rules to map from logger name to target -->
    <rules>
      <!--All logs, including from Microsoft-->
      <logger name="*" minlevel="Trace" writeTo="allFile" />
      <!--Own logs-->
      <logger name="HiP.*" minlevel="Trace" writeTo="ownFile" />
  
      <!--Skip non-critical Microsoft logs and so log only own logs-->
      <!--<logger name="Microsoft.*" maxLevel="Info" writeTo="blackHole" final="true" />-->
  
    </rules>
  </nlog>
  <!--LogLevel="Trace|Debug|Info|Warn|Error|Fatal"-->

• 右键nlog.config，属性，生成操作设为“内容”，复制到输出目录为“始终复制”
• Program.cs中：

  public static void Main(string[] args)
          {
              var logger = NLog.Web.NLogBuilder.ConfigureNLog("nlog.config").GetCurrentClassLogger();
              try
              {
                  logger.Debug("init main");
  
                  CreateHostBuilder(args).Build().Run();
              }
              catch (Exception ex)
              {
                  //NLog: catch setup errors
                  logger.Error(ex, "Stopped program because of exception");
                  throw ex;
              }
              finally
              {
                  // Ensure to flush and stop internal timers/threads before application-exit (Avoid segmentation fault on Linux)
                  NLog.LogManager.Shutdown();
              }
  
          }
  
          public static IHostBuilder CreateHostBuilder(string[] args) =>
              Host.CreateDefaultBuilder(args)
               .UseServiceProviderFactory(new AutofacServiceProviderFactory())    //会调用Startup中的ConfigureContainer方法
               .ConfigureWebHostDefaults(webBuilder =>
               {
                   webBuilder
                     .UseStartup<Startup>()
                     .UseUrls("http://localhost:8080")
                     //这里是配置log的
                     .ConfigureLogging((hostingContext, builder) =>
                     {
                         builder.ClearProviders();
                         //builder.SetMinimumLevel(LogLevel.Warning); //使用Nlogs的配置
                         //builder.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
                         //builder.AddConsole();
                         //builder.AddDebug();
                     })
                     .UseNLog();    // NLog: setup NLog for Dependency injection. 3.0中这样添加
               });
      }

• 配置appsettings.json。注意在配置中的设置将覆盖代码中的SetMinimumLevel属性。所以要么删除“Default”使用代码中的配置，要么就要设置正确。

  {
      "Logging": {
          "LogLevel": {
              "Default": "Trace",
              "Microsoft": "Information"
          }
      }
  }

  注意：如你有多个环境，注意appsetings.Development.json的配置。

• 使用：

using Microsoft.Extensions.Logging;

public class HomeController : Controller
{
    private readonly ILogger<HomeController> _logger;

    public HomeController(ILogger<HomeController> logger)
    {
        _logger = logger;
    }

    public IActionResult Index()
    {
        _logger.LogInformation("Index page says hello");
        return View();
    }

• 结果查看。如你的配置与我一致，则在项目的logs文件夹会存在internal-nlog.txt文件。在bin\Debug\netcoreappXX\logs目录下会以日期存在输出日志。