<"1.0""conn" connectionString="Data Source=localhost;Initial Catalog=helloworld;Integrated Security=True"/>
 </connectionStrings>
 <appSettings>
 <add key="app_key" value="helloworld" />
 <add key="app_secret" value="1234567890abcdef" />
 </appSettings>
</configuration>

{
 "connectionStrings": {
 "conn": "Data Source=localhost;Initial Catalog=helloworld;Integrated Security=True"
 }
 "appSettings": {
 "app_key": "helloworld",
 "app_secret": "1234567890abcdef"
 }
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
//修改为
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)

loggerFactory.AddNLog();
app.AddNLogWeb();
loggerFactory.ConfigureNLog(“nlog.config”);

<"1.0" encoding="utf-8""http://www.nlog-project.org/schemas/NLog.xsd"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 <targets>
  <target xsi:type="File" name="logfile" fileName="${basedir}/logs/${shortdate}.log" keepFileOpen="false" layout="${longdate}|${callsite:fileName=True}|${uppercase:${level}}|${message} ${exception}" />
  <target xsi:type="File" name="debugfile" fileName="${basedir}/logs/${shortdate}_debug.log" keepFileOpen="false" layout="${longdate}|${callsite:fileName=True}|${uppercase:${level}}|${message} ${exception}" />
 <target xsi:type="File" name="errfile" fileName="${basedir}/logs/${shortdate}_error.log" keepFileOpen="false" layout="${longdate}|${callsite:fileName=True}|${uppercase:${level}}|${message} ${exception}" />
 </targets>
 <rules>
 <logger name="*" level="Debug" writeTo="debugfile" />
  <logger name="*" level="Error" writeTo="errfile" />
 <logger name="*" minlevel="Trace" writeTo="logfile" />
 </rules>
</nlog>

using System;
using System.IO;
using Microsoft.Extensions.Configuration;
using NLog.Extensions.Logging;
using NLog.Web;
public class Program
{
 public static IConfigurationRoot Configuration { get; set; }
 public static NLog.Logger log = NLog.LogManager.GetCurrentClassLogger();
 public static void ConfigAndLog()
 {
  var builder = new ConfigurationBuilder()
   .SetBasePath(Directory.GetCurrentDirectory())
   .AddJsonFile("appsettings.json");
  Configuration = builder.Build();
  string app_key = Configuration["appSettings:app_key"];
  string coon = Configuration["connectionStrings:conn"];
  log.Debug("数据库连接为：" + conn);
  return;
 }
}