asp.net core配置文件加载过程的深入了解

配置文件中程序运行中，担当着不可或缺的角色；通常情况下，使用 visual studio 进行创建项目过程中，项目配置文件会自动生成在项目根目录下，如 appsettings.json，或者是被大家广泛使用的 appsettings.{env.EnvironmentName}.json；配置文件

作为一个入口，可以让我们在不更新代码的情况，对程序进行干预和调整，那么对其加载过程的全面了解就显得非常必要。

何时加载了默认的配置文件

在 Program.cs 文件中，查看以下代码

public class Program { public static void Main(string[] args) { CreateWebHostBuilder(args).Build().Run(); } public static IWebHostBuilder CreateWebHostBuilder(string[] args) => WebHost.CreateDefaultBuilder(args) .UseStartup<Startup>(); }

WebHost.CreateDefaultBuilder 位于程序集 Microsoft.AspNetCore.dll 内，当程序执行 WebHost.CreateDefaultBuilder(args) 的时候，在 CreateDefaultBuilder 方法内部加载了默认的配置文件

代码如下

public static IWebHostBuilder CreateDefaultBuilder(string[] args) { var builder = new WebHostBuilder(); if (string.IsNullOrEmpty(builder.GetSetting(WebHostDefaults.ContentRootKey))) { builder.UseContentRoot(Directory.GetCurrentDirectory()); } if (args != null) { builder.UseConfiguration(new ConfigurationBuilder().AddCommandLine(args).Build()); } builder.UseKestrel((builderContext, options) => { options.Configure(builderContext.Configuration.GetSection("Kestrel")); }) .ConfigureAppConfiguration((hostingContext, config) => { var env = hostingContext.HostingEnvironment; config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true) .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true); if (env.IsDevelopment()) { var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName)); if (appAssembly != null) { config.AddUserSecrets(appAssembly, optional: true); } } config.AddEnvironmentVariables(); if (args != null) { config.AddCommandLine(args); } }) .ConfigureLogging((hostingContext, logging) => { logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging")); logging.AddConsole(); logging.AddDebug(); logging.AddEventSourceLogger(); }) .ConfigureServices((hostingContext, services) => { // Fallback services.PostConfigure<HostFilteringOptions>(options => { if (options.AllowedHosts == null || options.AllowedHosts.Count == 0) { // "AllowedHosts": "localhost;127.0.0.1;[::1]" var hosts = hostingContext.Configuration["AllowedHosts"]?.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries); // Fall back to "*" to disable. options.AllowedHosts = (hosts?.Length > 0 ? hosts : new[] { "*" }); } }); // Change notification services.AddSingleton<IOptionsChangeTokenSource<HostFilteringOptions>>( new ConfigurationChangeTokenSource<HostFilteringOptions>(hostingContext.Configuration)); services.AddTransient<IStartupFilter, HostFilteringStartupFilter>(); }) .UseIIS() .UseIISIntegration() .UseDefaultServiceProvider((context, options) => { options.ValidateScopes = context.HostingEnvironment.IsDevelopment(); }); return builder; }

可以看到，CreateDefaultBuilder 内部还是使用了 IConfigurationBuilder 的实现，且写死了默认配置文件的名字

public static IWebHostBuilder CreateDefaultBuilder(string[] args) { var builder = new WebHostBuilder(); if (string.IsNullOrEmpty(builder.GetSetting(WebHostDefaults.ContentRootKey))) { builder.UseContentRoot(Directory.GetCurrentDirectory()); } if (args != null) { builder.UseConfiguration(new ConfigurationBuilder().AddCommandLine(args).Build()); } builder.UseKestrel((builderContext, options) => { options.Configure(builderContext.Configuration.GetSection("Kestrel")); }) .ConfigureAppConfiguration((hostingContext, config) => { var env = hostingContext.HostingEnvironment; config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true) .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true); if (env.IsDevelopment()) { var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName)); if (appAssembly != null) { config.AddUserSecrets(appAssembly, optional: true); } } config.AddEnvironmentVariables(); if (args != null) { config.AddCommandLine(args); } }) .ConfigureLogging((hostingContext, logging) => { logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging")); logging.AddConsole(); logging.AddDebug(); logging.AddEventSourceLogger(); }) .ConfigureServices((hostingContext, services) => { // Fallback services.PostConfigure<HostFilteringOptions>(options => { if (options.AllowedHosts == null || options.AllowedHosts.Count == 0) { // "AllowedHosts": "localhost;127.0.0.1;[::1]" var hosts = hostingContext.Configuration["AllowedHosts"]?.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries); // Fall back to "*" to disable. options.AllowedHosts = (hosts?.Length > 0 ? hosts : new[] { "*" }); } }); // Change notification services.AddSingleton<IOptionsChangeTokenSource<HostFilteringOptions>>( new ConfigurationChangeTokenSource<HostFilteringOptions>(hostingContext.Configuration)); services.AddTransient<IStartupFilter, HostFilteringStartupFilter>(); }) .UseIIS() .UseIISIntegration() .UseDefaultServiceProvider((context, options) => { options.ValidateScopes = context.HostingEnvironment.IsDevelopment(); }); return builder; }

由于以上代码，我们可以在应用程序根目录下使用 appsettings.json 和 appsettings.{env.EnvironmentName}.json 这种形式的默认配置文件名称

并且，由于 Main 方法默认对配置文件进行了 Build 方法的调用操作

public static void Main(string[] args) { CreateWebHostBuilder(args).Build().Run(); }

我们可以在 Startup.cs 中使用注入的方式获得默认的配置文件对象 IConfigurationRoot/IConfiguration，代码片段

public class Startup { public Startup(IConfiguration configuration) { Configuration = configuration; }

这是为什么呢，因为在 执行 Build 方法的时候，方法内部已经将默认配置文件对象加入了 ServiceCollection 中，代码片段