04 | Startup：掌握ASP.NET Core的啟動(dòng)過程

新建一個(gè) ASP.NET Core Web 應(yīng)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(shù)中

CreateHostBuilder 方法返回了一個(gè) IHostBuilder

它是應(yīng)用程序啟動(dòng)的核心接口

IHostBuilder 接口有六個(gè)方法：

主要關(guān)注以下三個(gè)：

• ConfigureAppConfiguration

• ConfigureHostConfiguration

• ConfigureServices

接下來，我們添加一些代碼演示整個(gè)應(yīng)用程序的啟動(dòng)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(gè)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(dòng)程序查看輸出：

ConfigureWebHostDefaults ConfigureHostConfiguration ConfigureAppConfiguration ConfigureServices Startup Startup.ConfigureServices Startup.Configure

調(diào)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(huì)得到不同的結(jié)果

ConfigureWebHostDefaults ConfigureHostConfiguration ConfigureAppConfiguration Startup Startup.ConfigureServices ConfigureServices Startup.Configure

本質(zhì)上，如果查看源碼會(huì)發(fā)現(xiàn)，委托注冊進(jìn)去之后，實(shí)際上是按照一定的順序來執(zhí)行的：

1、ConfigureWebHostDefaults

這個(gè)階段注冊了應(yīng)用程序必要的幾個(gè)組件，比如配置的組件、容器組件

2、ConfigureHostConfiguration

用于配置應(yīng)用程序啟動(dòng)時(shí)必要的配置，比如應(yīng)用程序啟動(dòng)時(shí)所需要監(jiān)聽的端口，URL 地址

在這個(gè)過程可以嵌入一些自己配置的內(nèi)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(yīng)用程序讀取，這些配置將會(huì)在后續(xù)的應(yīng)用程序執(zhí)行過程中間每個(gè)組件讀取

4、ConfigureServices, ConfigureLogging, Startup, Startup.ConfigureServices

用于往容器里注入應(yīng)用的組件

5、Startup.Configure

用于注入中間件，處理 HttpContext 整個(gè)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(gè)啟動(dòng)的過程中，Startup 這個(gè)類不是必要的，只是讓代碼結(jié)構(gòu)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(dòng)程序查看輸出：

ConfigureWebHostDefaults ConfigureHostConfiguration ConfigureAppConfiguration webBuilder.ConfigureServices ConfigureServices webBuilder.Configure

服務(wù)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(jié)

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