04 | Startup：掌握ASP.NET Core的啟動過程

新建一個 ASP.NET Core Web 應用程序

選擇 API

public class Program {public static void Main(string[] args){CreateHostBuilder(args).Build().Run();}public static IHostBuilder CreateHostBuilder(string[] args) =>Host.CreateDefaultBuilder(args).ConfigureWebHostDefaults(webBuilder =>{webBuilder.UseStartup<Startup>();}); }

在 Program.cs 的 Main 函數中

CreateHostBuilder 方法返回了一個 IHostBuilder

它是應用程序啟動的核心接口

IHostBuilder 接口有六個方法：

主要關注以下三個：

• ConfigureAppConfiguration

• ConfigureHostConfiguration

• ConfigureServices

接下來，我們添加一些代碼演示整個應用程序的啟動過程：

public static IHostBuilder CreateHostBuilder(string[] args) =>Host.CreateDefaultBuilder(args).ConfigureAppConfiguration(builder =>{Console.WriteLine("ConfigureAppConfiguration");}).ConfigureServices(service =>{Console.WriteLine("ConfigureServices");}).ConfigureHostConfiguration(builder =>{Console.WriteLine("ConfigureHostConfiguration");}).ConfigureWebHostDefaults(webBuilder =>{Console.WriteLine("ConfigureWebHostDefaults");webBuilder.UseStartup<Startup>();});

接著，在 Startup 的三個方法中添加一些代碼

public Startup(IConfiguration configuration) {Console.WriteLine("Startup");...public void ConfigureServices(IServiceCollection services) {Console.WriteLine("ConfigureServices");...public void Configure(IApplicationBuilder app, IWebHostEnvironment env) {Console.WriteLine("Configure");...

啟動程序查看輸出：

ConfigureWebHostDefaults ConfigureHostConfiguration ConfigureAppConfiguration ConfigureServices Startup Startup.ConfigureServices Startup.Configure

調整一下委托的注冊順序

public static IHostBuilder CreateHostBuilder(string[] args) =>Host.CreateDefaultBuilder(args).ConfigureWebHostDefaults(webBuilder =>{Console.WriteLine("ConfigureWebHostDefaults");webBuilder.UseStartup<Startup>();}).ConfigureServices(service =>{Console.WriteLine("ConfigureServices");}).ConfigureAppConfiguration(builder =>{Console.WriteLine("ConfigureAppConfiguration");}).ConfigureHostConfiguration(builder =>{Console.WriteLine("ConfigureHostConfiguration");});

會得到不同的結果

ConfigureWebHostDefaults ConfigureHostConfiguration ConfigureAppConfiguration Startup Startup.ConfigureServices ConfigureServices Startup.Configure

本質上，如果查看源碼會發現，委托注冊進去之后，實際上是按照一定的順序來執行的：

1、ConfigureWebHostDefaults

這個階段注冊了應用程序必要的幾個組件，比如配置的組件、容器組件

2、ConfigureHostConfiguration

用于配置應用程序啟動時必要的配置，比如應用程序啟動時所需要監聽的端口，URL 地址

在這個過程可以嵌入一些自己配置的內容，注入到配置的框架中

3、ConfigureAppConfiguration

用于嵌入自己的配置文件，供應用程序讀取，這些配置將會在后續的應用程序執行過程中間每個組件讀取

4、ConfigureServices, ConfigureLogging, Startup, Startup.ConfigureServices

用于往容器里注入應用的組件

5、Startup.Configure

用于注入中間件，處理 HttpContext 整個請求過程

public void Configure(IApplicationBuilder app, IWebHostEnvironment env) {Console.WriteLine("Startup.Configure");if (env.IsDevelopment()){app.UseDeveloperExceptionPage();}app.UseHttpsRedirection();app.UseRouting();app.UseAuthorization();app.UseFileServer();app.UseWebSockets();app.UseEndpoints(endpoints =>{endpoints.MapControllers();}); }

在整個啟動的過程中，Startup 這個類不是必要的，只是讓代碼結構更加合理

public static IHostBuilder CreateHostBuilder(string[] args) =>Host.CreateDefaultBuilder(args).ConfigureWebHostDefaults(webBuilder =>{Console.WriteLine("ConfigureWebHostDefaults");//webBuilder.UseStartup<Startup>();webBuilder.ConfigureServices(services =>{Console.WriteLine("webBuilder.ConfigureServices");services.AddControllers();});webBuilder.Configure(app =>{Console.WriteLine("webBuilder.Configure");app.UseHttpsRedirection();app.UseRouting();app.UseAuthorization();app.UseFileServer();app.UseWebSockets();app.UseEndpoints(endpoints =>{endpoints.MapControllers();});});}).ConfigureServices(service =>{Console.WriteLine("ConfigureServices");}).ConfigureAppConfiguration(builder =>{Console.WriteLine("ConfigureAppConfiguration");}).ConfigureHostConfiguration(builder =>{Console.WriteLine("ConfigureHostConfiguration");}); }

啟動程序查看輸出：

ConfigureWebHostDefaults ConfigureHostConfiguration ConfigureAppConfiguration webBuilder.ConfigureServices ConfigureServices webBuilder.Configure

服務注冊一般放在 Startup 的 ConfigureServices，一般是services.AddXXX

public void ConfigureServices(IServiceCollection services) {services.AddMvc();services.AddAuthentication();services.AddAuthorization();Console.WriteLine("Startup.ConfigureServices");services.AddControllers(); }

中間件的注冊一般放在 Startup 的 Configure

public void Configure(IApplicationBuilder app, IWebHostEnvironment env) {Console.WriteLine("Startup.Configure");if (env.IsDevelopment()){app.UseDeveloperExceptionPage();}app.UseHttpsRedirection();app.UseRouting();app.UseAuthorization();app.UseFileServer();app.UseWebSockets();app.UseEndpoints(endpoints =>{endpoints.MapControllers();}); }

總結

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