Asp.net Core中使用NLog，并封装成公共的日志方法

1、安装NLog

"NLog.Extensions.Logging": "1.0.0-rtm-alpha4"

2、配置NLog

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
loggerFactory.AddConsole(Configuration.GetSection("Logging"));
loggerFactory.AddDebug();
//配置NLog
            loggerFactory.AddNLog();
env.ConfigureNLog("nlog.config");

app.UseApplicationInsightsRequestTelemetry();

3、nlog.config

<?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"
throwConfigExceptions="true"
internalLogLevel="Debug"
internalLogToTrace="true">

<targets>
<target name="logfile"
xsi:type="File"
fileName="logs/${shortdate}.log"
layout="${longdate} [${level:uppercase=true}] ${callsite:className=true:methodName=true:skipFrames=1} ${message} ${exception} @${callsite:fileName=true:includeSourcePath=true}" />
<target name="console"
xsi:type="ColoredConsole"
layout="${longdate} [${level:uppercase=true}] ${callsite:className=true:methodName=true:skipFrames=1} ${message} ${exception} @${callsite:fileName=true:includeSourcePath=true}"/>
<target xsi:type="Null" name="blackhole" />
</targets>

<rules>
<!-- 除非调试需要，把 .NET Core 程序集的 Debug 输出都屏蔽 Trace -》Debug-》 Information -》Warning-》 Error-》 Critical-->
<logger name="Microsoft.*" minLevel="Trace" writeTo="blackhole" final="true" />
<!-- 除非调试需要，把系统的 Debug 输出都屏蔽 -->
<logger name="System.*" minLevel="Trace" writeTo="blackhole" final="true" />

<logger name="*" minlevel="Debug" writeTo="logfile,console" />
</rules>
</nlog>

NLog的异常等级：Trace -》Debug-》 Information -》Warning-》 Error-》 Critical

注意配置文件中可以移除Microsoft和System开头的组件输出的日志，不然日志会非常多

NLog的更多配置请参考：https://github.com/NLog/NLog/wiki/Callsite-layout-renderer

4、封装成公共方法

using NLog;
using System;
using System.Diagnostics;

namespace UFX.Tools
{
public class LogHelper
{
private static readonly Logger log = LogManager.GetLogger("");
public static void Error(object msg, Exception exp = null)
{
if (exp == null)
log.Error("#" + msg);
else
log.Error("#" + msg + "  " + exp.ToString());
}

public static void Debug(object msg, Exception exp = null)
{
if (exp == null)
log.Debug("#" + msg);
else
log.Debug("#" + msg + "  " + exp.ToString());
}

public static void Info(object msg, Exception exp = null)
{
if (exp == null)
log.Info("#" + msg);
else
log.Info("#" + msg + "  " + exp.ToString());
}

public static void Warn(object msg, Exception exp = null)
{
if (exp == null)
log.Warn("#" + msg);
else
log.Warn("#" + msg + "  " + exp.ToString());
}
}
}

5、其他方法中使用直接LogHelper.Debug("")等即可

但你会发现日志输出的方法中，所有异常都来自Tools.LogHelper，这样就不能准确的返回异常的方法，代码位置了，在.Net Core之前的版本中，我们可以通过StackFrames来找到调用方法，但是.Net Core这个方法不管用了。

好在NLog已经为我们考虑到这个问题了，配置文件中直接可以定义需要打印的方法名称，需要网上寻找的Frame个数

${callsite:className=true:methodName=true:skipFrames=1}

更多配置请参考：https://github.com/NLog/NLog/wiki/Callsite-layout-renderer

using NLog;using System;using System.Diagnostics;
namespace UFX.Tools{ public class LogHelper { private static readonly Logger log = LogManager.GetLogger(""); public static void Error(object msg, Exception exp = null) { if (exp == null) log.Error("#" + msg); else log.Error("#" + msg + " " + exp.ToString()); }
public static void Debug(object msg, Exception exp = null) { if (exp == null) log.Debug("#" + msg); else log.Debug("#" + msg + " " + exp.ToString()); }
public static void Info(object msg, Exception exp = null) { if (exp == null) log.Info("#" + msg); else log.Info("#" + msg + " " + exp.ToString()); }

public static void Warn(object msg, Exception exp = null) { if (exp == null) log.Warn("#" + msg); else log.Warn("#" + msg + " " + exp.ToString()); } }}