大家都知道.NET Core现在不再支持原来的web.config配置文件了，取而代之的是json或xml配置文件。官方推荐的项目配置方式是使用appsettings.json配置文件，这对现有一些重度使用web.cofig配置的项目迁移可能是不可接受的。
但是好消息是，我们是可以直接在.NET Core 2.0项目种利用上现有的web.config的。
迁移方法
1.首先在解决方案中引入System.Configuration.ConfigurationManager,只有引入它才可以让我们已有的读取web.config代码起作用.
2. 导入web.config文件到项目根目录，并将名称修改为app.config. 因为.NET Core的项目本质是控制台应用，所以ConfigurationManager的API会去默认读取app.config配置文件，而不是web.config配置文件。
3.去除config中和需要的配置无关的内容，主要是<system.web>,<system.webServer>和<system.codedom>等典型asp.net标签。
移除前：
<?xml version="1.0" encoding="utf-8"?><configuration>
?<configSections>
??<!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
??<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
</configSections>
<connectionStrings>
<add name="DefaultConnection" connectionString="Data Source=(LocalDb)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\aspnet-WebApplication24-20170824065102.mdf;Initial Catalog=aspnet-WebApplication24-20170824065102;Integrated Security=True" ?????providerName="System.Data.SqlClient" />
</connectionStrings> ?<appSettings> ???<add key="webpages:Version" value="3.0.0.0" /> ???<add key="webpages:Enabled" value="false" /> ???<add key="ClientValidationEnabled" value="true" /> ???<add key="UnobtrusiveJavaScriptEnabled" value="true" /> ???<add key="MyKey" value="true"/> ?</appSettings> ?<system.web> ???<compilation debug="true" targetFramework="4.7" /> ???<httpRuntime targetFramework="4.7" /> ???<httpModules> ?????<add name="ApplicationInsightsWebTracking" type="Microsoft.ApplicationInsights.Web.ApplicationInsightsHttpModule, Microsoft.AI.Web" /> ???</httpModules> ?</system.web> ?<runtime> ???<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1"> ?????<dependentAssembly> ???????<assemblyIdentity name="Newtonsoft.Json" culture="neutral" publicKeyToken="30ad4fe6b2a6aeed" /> ???????<bindingRedirect oldVersion="0.0.0.0-6.0.0.0" newVersion="6.0.0.0" /> ?????</dependentAssembly> ?????<dependentAssembly> ???????<assemblyIdentity name="System.Web.Optimization" publicKeyToken="31bf3856ad364e35" /> ???????<bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="1.1.0.0" /> ?????</dependentAssembly> ?????<dependentAssembly> ???????<assemblyIdentity name="WebGrease" publicKeyToken="31bf3856ad364e35" /> ???????<bindingRedirect oldVersion="0.0.0.0-1.5.2.14234" newVersion="1.5.2.14234" /> ?????</dependentAssembly> ?????<dependentAssembly> ???????<assemblyIdentity name="System.Web.Helpers" publicKeyToken="31bf3856ad364e35" /> ???????<bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="3.0.0.0" /> ?????</dependentAssembly> ?????<dependentAssembly> ???????<assemblyIdentity name="System.Web.WebPages" publicKeyToken="31bf3856ad364e35" /> ???????<bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="3.0.0.0" /> ?????</dependentAssembly> ?????<dependentAssembly> ???????<assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" /> ???????<bindingRedirect oldVersion="1.0.0.0-5.2.3.0" newVersion="5.2.3.0" /> ?????</dependentAssembly> ???</assemblyBinding> ?</runtime> ?<system.webServer> ???<validation validateIntegratedModeConfiguration="false" /> ???<modules> ?????<remove name="ApplicationInsightsWebTracking" /> ?????<add name="ApplicationInsightsWebTracking" type="Microsoft.ApplicationInsights.Web.ApplicationInsightsHttpModule, Microsoft.AI.Web" preCondition="managedHandler" /> ???</modules> ?</system.webServer> ?<system.codedom> ???<compilers> ?????<compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:1659;1699;1701" /> ?????<compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:41008 /define:_MYTYPE=\"Web\" /optionInfer+" /> ???</compilers> ?</system.codedom></configuration>
修改后：
<?xml version="1.0" encoding="utf-8"?><configuration> ?<configSections> ???<!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 --> ???<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" /> ?</configSections> ?<connectionStrings> ???<add name="DefaultConnection" connectionString="Data Source=(LocalDb)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\aspnet-WebApplication24-20170824065102.mdf;Initial Catalog=aspnet-WebApplication24-20170824065102;Integrated Security=True" ?????providerName="System.Data.SqlClient" /> ?</connectionStrings> ?<appSettings> ???<add key="webpages:Version" value="3.0.0.0" /> ???<add key="webpages:Enabled" value="false" /> ???<add key="ClientValidationEnabled" value="true" /> ???<add key="UnobtrusiveJavaScriptEnabled" value="true" /> ???<add key="MyKey" value="true"/> ?</appSettings></configuration>
4.测试原ASP.NET代码，查看读取配置值
using System.Configuration;namespace WebConfigTest.Configuration{ ???public class ConfigurationService ???{ ???????public static bool GetConfigValue(string key) ???????{ ???????????var result = false; ??????????var val= ConfigurationManager.AppSettings[key]; ???????????if (val != null) ???????????{ ???????????????result = bool.Parse(val); ???????????} ???????????return result; ???????} ???}}打个断点，看下读取配置值是否正确：
大功告成，读取的配置值完全正确。
大家可以使用这个方法快速迁移现有配置文件和代码过去啦。
.NET Core迁移技巧之web.config配置文件
原文地址：http://www.cnblogs.com/mantgh/p/7425113.html