介绍

NLog是.NET平台下一款日志组件，同时也支持.NET Core。可以直接在项目中安装nuget包使用NLog。

以下示例代码中引用了如下NLog及NLog.Config两个nuget包，其中后者是用来生成NLog的配置文件.

NLog配置

<?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"
      xsi:schemaLocation="http://www.nlog-project.org/schemas/NLog.xsd NLog.xsd"
      autoReload="true"
      throwExceptions="false"
      internalLogLevel="Off" internalLogFile="c:\temp\nlog-internal.log">

  <!-- optional, add some variables
  https://github.com/nlog/NLog/wiki/Configuration-file#variables
  -->
  <variable name="myvar" value="myvalue"/>

  <!--
  See https://github.com/nlog/nlog/wiki/Configuration-file
  for information on customizing logging rules and outputs.
   -->
  <targets>

    <!--
    add your targets here
    See https://github.com/nlog/NLog/wiki/Targets for possible targets.
    See https://github.com/nlog/NLog/wiki/Layout-Renderers for the possible layout renderers.
    -->

    <!--
    Write events to a file with the date in the filename.
    <target xsi:type="File" name="f" fileName="${basedir}/logs/${shortdate}.log"
            layout="${longdate} ${uppercase:${level}} ${message}" />
    -->

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

    <target name="database" xsi:type="Database" dbProvider="MySql.Data.MySqlClient.MySqlConnection, MySql.Data" connectionString="server=127.0.0.1;Database=example;user id=root;password=123456;SslMode=none" >
      <commandText>
        insert into log
        (Application, Logged, Level, Message,Logger, CallSite, Exception)
        values (@Application, @Logged, @Level, @Message,@Logger, @Callsite, @Exception);
      </commandText>
      <parameter name="@application" layout="NLogDemo" />
      <parameter name="@logged" layout="${date}" />
      <parameter name="@level" layout="${level}" />
      <parameter name="@message" layout="${message}" />
      <parameter name="@logger" layout="${logger}" />
      <parameter name="@callSite" layout="${callsite:filename=true}" />
      <parameter name="@exception" layout="${exception:tostring}" />
    </target>
    <target xsi:type="File" name="logfile" fileName="${basedir}/logs/${shortdate}.log"
layout="${longdate} [${uppercase:${level}}] ${newline}    ${message}" />
  </targets>
  <rules>
    <!-- add your logging rules here -->
    <!--
    Write all events with minimal level of Debug (So Debug, Info, Warn, Error and Fatal, but not Trace)  to "f"
    <logger name="*" minlevel="Debug" writeTo="f" />
    -->
    <logger name="Microsoft.*" minlevel="Trace" writeTo="blackhole" final="true" />
    <logger name="NLogDemo.*" minlevel="Info" writeTo="database" />
    <logger name="*" minlevel="Info" maxlevel="Fatal" writeTo="logfile" />
  </rules>
</nlog>

需要记录到数据库可使用以下语句创建表：

CREATE TABLE `log` (
  `Id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `Application` varchar(50) DEFAULT NULL,
  `Logged` datetime DEFAULT NULL,
  `Level` varchar(50) DEFAULT NULL,
  `Message` varchar(512) DEFAULT NULL,
  `Logger` varchar(250) DEFAULT NULL,
  `Callsite` varchar(512) DEFAULT NULL,
  `Exception` varchar(512) DEFAULT NULL,
  PRIMARY KEY (`Id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

说明：以上配置中logfile用于写入文件，database用于写入数据库（本示例中写入MySql）。

控制台示例Demo

引入命名空间using NLog。

示例代码

static void Main(string[] args)
{
    Logger logger = LogManager.GetCurrentClassLogger();
    logger.Trace("Trace Message");
    logger.Debug("Debug Message");
    logger.Info("Info Message");
    logger.Error("Error Message");
    logger.Fatal("Fatal Message");
    Console.WriteLine("Hello World!");
}

.NET Core WebApi示例Dmeo

StartUp.cs配置：

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }

    //使用NLog作为日志记录工具
    loggerFactory.AddNLog();
    //引入Nlog配置文件
    env.ConfigureNLog("Nlog.config");
    app.UseMvc();
}

Program.cs中绑定：

public static IWebHost BuildWebHost(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        .UseNLog()
        .UseStartup<Startup>()
        .Build();

使用方式同上述控制台示例：

private readonly Logger logger = LogManager.GetCurrentClassLogger();
// GET api/values
[HttpGet]
public IEnumerable<string> Get()
{
    logger.Trace("Trace Message");
    logger.Debug("Debug Message");
    logger.Info("Info Message");
    logger.Error("Error Message");
    logger.Fatal("Fatal Message");
    return new string[] { "value1", "value2" };
}

本示例源码地址

Github

参考文章及文档

NLog-Github

日志框架对比 NLog VS Log4net

ASP.NET Core 开发-Logging 使用NLog 写日志文件