當(dāng)我們創(chuàng)建好一個新的ASP.NET Core Web應(yīng)用時，系統(tǒng)會使用CreateDefaultBuilder方法，這個方法完成了以下操作：

• use Kestrel as the web server and configure it using the application's configuration providers
• set the ContentRootPath to the result of GetCurrentDirectory()
• load IConfiguration from 'appsettings.json' and 'appsettings.[EnvironmentName].json'
• load IConfiguration from User Secrets when EnvironmentName is 'Development' using the entry assembly,
• load IConfiguration from environment variables
• configure the ILoggerFactory to log to the console and debug output
• and enable IIS integration

如果使用了CreateDefaultBuilder的有參數(shù)版本，則還會通過命令行參數(shù)來初始化IConfiguration。

以上內(nèi)容來源于官方文檔：microsoft.aspnetcore.webhost.createdefaultbuilder