.Net Core使用NLog记录日志

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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"> 
<extensions>
<add assembly="NLog.Web.AspNetCore"/>
</extensions> 
<targets>

<target name="allFile" xsi:type="File" fileName="logs\nlog-all-${shortdate}.log"
layout="${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}" /> 
<target name="ownFile" xsi:type="File" fileName="logs\nlog-own-${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>

<logger name="*" minlevel="Trace" writeTo="allFile" />

<logger name="HiP.*" minlevel="Trace" writeTo="ownFile" /> 
 </rules>
</nlog>

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();
}