NLog is a flexible and free logging platform for various .NET platforms, including .NET standard. NLog makes it easy to write to several targets. (database, file, console) and change the logging configuration on-the-fly.

• 官网：https://nlog-project.org
• 开源地址：https://github.com/NLog/NLog

最佳实践

控制台项目

在项目中添加组件包

Install-Package Microsoft.Extensions.Configuration.Json
Install-Package NLog
Install-Package NLog.Extensions.Logging

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*"
}

<?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="Warn"
      internalLogFile="internal-nlog.txt">

  <!-- define various log targets -->
  <targets>
    <!-- write logs to file -->
    <target xsi:type="File" name="allfile" fileName="nlog-all-${shortdate}.log"
                 layout="${longdate}|${logger}|${uppercase:${level}}|${message} ${exception}" />


    <target xsi:type="File" name="ownFile-web" fileName="nlog-own-${shortdate}.log"
             layout="${longdate}|${logger}|${uppercase:${level}}|  ${message} ${exception}" />

    <target xsi:type="Null" name="blackhole" />
  </targets>

  <rules>
    <!--All logs, including from Microsoft-->
    <logger name="*" minlevel="Trace" writeTo="allfile" />

    <!--Skip Microsoft logs and so log only own logs-->
    <logger name="Microsoft.*" minlevel="Trace" writeTo="blackhole" final="true" />
    <logger name="*" minlevel="Trace" writeTo="ownFile-web" />
  </rules>
</nlog>

添加一个类Runner.cs。

using Microsoft.Extensions.Logging;

namespace ConsoleDemo
{
    public class Runner
    {
        private readonly ILogger<Runner> _logger;

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

        public void DoAction(string name)
        {
            _logger.LogDebug(20, "Doing hard work! {Action}", name);
        }
    }
}

通过注入的方式调用。

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using NLog;
using NLog.Extensions.Logging;
using System;

namespace ConsoleDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            var logger = LogManager.GetCurrentClassLogger();

            try
            {
                var config = new ConfigurationBuilder().SetBasePath(System.IO.Directory.GetCurrentDirectory())
                                                       .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                                                       .Build();
                var servicesProvider = BuildDi(config);

                using (servicesProvider as IDisposable)
                {
                    var runner = servicesProvider.GetRequiredService<Runner>();
                    runner.DoAction("Action1");

                    Console.WriteLine("Press ANY key to exit");
                    Console.ReadKey();
                }

            }
            catch (Exception ex)
            {
                // NLog: catch any exception and log it.
                logger.Error(ex, "Stopped program because of exception");
                throw;
            }
            finally
            {
                LogManager.Shutdown();
            }
        }

        private static IServiceProvider BuildDi(IConfiguration config)
        {
            return new ServiceCollection()
               .AddTransient<Runner>() // Runner is the custom class
               .AddLogging(loggingBuilder =>
               {
                   // configure Logging with NLog
                   loggingBuilder.ClearProviders();
                   loggingBuilder.SetMinimumLevel(Microsoft.Extensions.Logging.LogLevel.Trace);
                   loggingBuilder.AddNLog(config);
               })
               .BuildServiceProvider();
        }
    }
}

运行项目，项目根目录下会多出两个日志文件。

AspNetCore项目

在项目中添加组件包

Install-Package NLog
Install-Package NLog.Web.AspNetCore

{
  "Logging": {
    "LogLevel": {
      "Default": "Trace",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*"
}

<?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="Warn"
      internalLogFile="internal-nlog.txt">

  <!-- define various log targets -->
  <targets>
    <!-- write logs to file -->
    <target xsi:type="File" name="allfile" fileName="nlog-all-${shortdate}.log"
                 layout="${longdate}|${logger}|${uppercase:${level}}|${message} ${exception}" />


    <target xsi:type="File" name="ownFile-web" fileName="nlog-own-${shortdate}.log"
             layout="${longdate}|${logger}|${uppercase:${level}}|  ${message} ${exception}" />

    <target xsi:type="Null" name="blackhole" />
  </targets>

  <rules>
    <!--All logs, including from Microsoft-->
    <logger name="*" minlevel="Trace" writeTo="allfile" />

    <!--Skip Microsoft logs and so log only own logs-->
    <logger name="Microsoft.*" minlevel="Trace" writeTo="blackhole" final="true" />
    <logger name="*" minlevel="Trace" writeTo="ownFile-web" />
  </rules>
</nlog>

在Program.cs中使用NLog。

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using NLog.Web;
using System;

namespace WebDemo
{
    public class Program
    {
        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 exception)
            {
                //NLog: catch setup errors
                logger.Error(exception, "Stopped program because of exception");
                throw;
            }
            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)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                })
                .ConfigureLogging(logging =>
                {
                    logging.ClearProviders();
                    logging.SetMinimumLevel(LogLevel.Trace);
                }).UseNLog();  // NLog: Setup NLog for Dependency injection
    }
}

一切准备就绪，在任意地方写日志。

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;

namespace WebDemo.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 ILogger<WeatherForecastController> _logger;

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


        [HttpGet]
        public IEnumerable<WeatherForecast> Get()
        {
            _logger.LogInformation("Hello, this is a Weather api!");

            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();
        }
    }
}

调用上面api，查看日志文件。

更多用法，请查看官方wiki文档：https://github.com/NLog/NLog/wiki