4:Startup:掌握ASP.NET Core的启动过程-.NET Core开发实战
.NET Core开发实战前文传送门:
04 | Startup:掌握ASP.NET Core的启动过程
新建一个 ASP.NET Core Web 应用程序
选择 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 函数中
CreateHostBuilder 方法返回了一个 IHostBuilder
它是应用程序启动的核心接口
IHostBuilder 接口有六个方法:

主要关注以下三个:
- ConfigureAppConfiguration
- ConfigureHostConfiguration
- ConfigureServices
接下来,我们添加一些代码演示整个应用程序的启动过程:
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>(); });
接着,在 Startup 的三个方法中添加一些代码
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"); ...
启动程序查看输出:
ConfigureWebHostDefaults ConfigureHostConfiguration ConfigureAppConfiguration ConfigureServices Startup Startup.ConfigureServices Startup.Configure
调整一下委托的注册顺序
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"); });
会得到不同的结果
ConfigureWebHostDefaults ConfigureHostConfiguration ConfigureAppConfiguration Startup Startup.ConfigureServices ConfigureServices Startup.Configure
本质上,如果查看源码会发现,委托注册进去之后,实际上是按照一定的顺序来执行的:
1、ConfigureWebHostDefaults
这个阶段注册了应用程序必要的几个组件,比如配置的组件、容器组件
2、ConfigureHostConfiguration
用于配置应用程序启动时必要的配置,比如应用程序启动时所需要监听的端口,URL 地址
在这个过程可以嵌入一些自己配置的内容,注入到配置的框架中
3、ConfigureAppConfiguration
用于嵌入自己的配置文件,供应用程序读取,这些配置将会在后续的应用程序执行过程中间每个组件读取
4、ConfigureServices, ConfigureLogging, Startup, Startup.ConfigureServices
用于往容器里注入应用的组件
5、Startup.Configure
用于注入中间件,处理 HttpContext 整个请求过程
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(); }); }
在整个启动的过程中,Startup 这个类不是必要的,只是让代码结构更加合理
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"); }) ; }
启动程序查看输出:
ConfigureWebHostDefaults ConfigureHostConfiguration ConfigureAppConfiguration webBuilder.ConfigureServices ConfigureServices webBuilder.Configure
服务注册一般放在 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(); }
中间件的注册一般放在 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(); }); }

原文出处:微信公众号【DotNet NB】,作者【郑子铭】
原文链接:https://mp.weixin.qq.com/s/mEPAEPsRzKE4an49-mvjRw
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