一、NLog 简介

   NLog 是一个基于.NET 平台编写的类库，我们可以适应NLog在应用程序中添加极为完善的跟踪代码。

   NLog是一个简单灵活的.NET日志记录类库。通过使用NLog，我们可以在任何一种.NET语言中输出带有上下文的（contextual information）调试诊断信息，根据喜好配置其表现样式之后发送到一个或多个输出目标（target）中。 

二、NLog安装配置

   安装NuGet包：NLog和NLog.Web.AspNetCore 

   并新增 nlog.config文件

<?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">
  <!-- 启用.net core的核心布局渲染器 -->
  <extensions>
    <add assembly="NLog.Web.AspNetCore" />
  </extensions>
  <!-- 写入日志的目标配置 -->
  <targets>
    <!-- 调试  -->
    <target xsi:type="File" name="debug" fileName="logs/debug-${shortdate}.log" layout="${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}" />
    <!-- 警告  -->
    <target xsi:type="File" name="warn" fileName="logs/warn-${shortdate}.log" layout="${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}" />
    <!-- 错误  -->
    <target xsi:type="File" name="error" fileName="logs/error-${shortdate}.log" layout="${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}" />
  </targets>
  <!-- 映射规则 -->
  <rules>
    <!-- 调试  -->
    <logger name="*" minlevel="Trace" maxlevel="Debug" writeTo="debug" />
    <!--跳过不重要的微软日志-->
    <logger name="Microsoft.*" maxlevel="Info" final="true" />
    <!-- 警告  -->
    <logger name="*" minlevel="Info" maxlevel="Warn" writeTo="warn" />
    <!-- 错误  -->
    <logger name="*" minlevel="Error" maxlevel="Fatal" writeTo="error" />
  </rules>
</nlog>

   在Program.cs类中注入

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using NLog.Web;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace NLog.Demo
{
    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>();
                }).UseNLog();
    }
}

三、NLog基本使用

private readonly ILogger<WeatherForecastController> _logger;

public WeatherForecastController(ILogger<WeatherForecastController> logger)
{
    _logger = logger;
}
[HttpGet]
public IEnumerable<WeatherForecast> Get()
 {
    _logger.LogError("错误信息！");
    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();
        }

日志文件输出地址：bin\Debug\netcoreapp3.1\logs\日志文件