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要了解程序的运行原理,就要先知道程序的进入点及生命周期。以往ASP.NET MVC的启动方式,是继承 HttpApplication 作为网站开始的进入点,而ASP.NET Core 改变了网站的启动方式,变得比较像是 Console Application。
本篇将介绍ASP.NET Core 的程序生命周期 (Application Lifetime) 及捕捉 Application 停止启动事件。
.NET Core 把 Web 及 Console 项目都处理成一样的启动方式,默认以 Program.cs 的 Program.Main
作为程序入口,再从程序入口把 ASP.NET Core 网站实例化。个人觉得比ASP.NET MVC 继承 HttpApplication
的方式简洁许多。
通过 .NET Core CLI 创建的 Program.cs 內容大致如下:
Program.cs
using System; using System.Collections.Generic; using System.IO; using System.Linq; using System.Threading.Tasks; using Microsoft.AspNetCore; using Microsoft.AspNetCore.Hosting; using Microsoft.Extensions.Configuration; using Microsoft.Extensions.Logging; namespace MyWebsite { public class Program { public static void Main(string[] args) { BuildWebHost(args).Run(); } public static IWebHost BuildWebHost(string[] args) => WebHost.CreateDefaultBuilder(args) .UseStartup<Startup>() .Build(); } }
Program.Main
通过 BuildWebHost 方法取得 WebHost 后,再运行 WebHost;WebHost 就是 ASP.NET Core 的网站实例。
当网站启动后,WebHost会实例化 UseStartup 设置的Startup类,并且调用以下两个方法:
通过 .NET Core CLI生成的Startup.cs 内容大致如下:
Startup.cs
using System; using System.Collections.Generic; using System.Linq; using System.Threading.Tasks; using Microsoft.AspNetCore.Builder; using Microsoft.AspNetCore.Hosting; using Microsoft.AspNetCore.Http; using Microsoft.Extensions.DependencyInjection; namespace MyWebsite { public class Startup { // This method gets called by the runtime. Use this method to add services to the container. // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940 public void ConfigureServices(IServiceCollection services) { } // This method gets called by the runtime. Use this method to configure the HTTP request pipeline. public void Configure(IApplicationBuilder app, IHostingEnvironment env) { if (env.IsDevelopment()) { app.UseDeveloperExceptionPage(); } app.Run(async (context) => { await context.Response.WriteAsync("Hello World!"); }); } } }
Configure
方法的参数并不固定,参数的实例都是从 WebHost 注入进来,可依需求增减需要的参数。对 WebHost 来说 Startup.cs 并不是必要存在的功能。
可以试着把 Startup.cs 中的两个方法,都改成在 WebHost Builder 设置,变成启动的前置准备。如下:
Program.cs
using System; using System.Collections.Generic; using System.IO; using System.Linq; using System.Threading.Tasks; using Microsoft.AspNetCore; using Microsoft.AspNetCore.Hosting; using Microsoft.Extensions.Configuration; using Microsoft.Extensions.Logging; using Microsoft.AspNetCore.Builder; using Microsoft.AspNetCore.Http; using Microsoft.Extensions.DependencyInjection; namespace MyWebsite { public class Program { public static void Main(string[] args) { BuildWebHost(args).Run(); } public static IWebHost BuildWebHost(string[] args) => WebHost.CreateDefaultBuilder(args) .ConfigureServices(services => { // ... }) .Configure(app => { app.Run(async (context) => { await context.Response.WriteAsync("Hello World!"); }); }) .Build(); } }
把 ConfigureServices
及 Configure
都改到 WebHost Builder 注册,网站的执行结果是一样的。
两者之间最大的不同就是调用的时间点不同。
但
Configure
无法使用除了IApplicationBuilder
以外的参数。
因为在 WebHost 实例化前,自己都还没被实例化,怎么可能会有有对象能注入给Configure
。
除了程序进入点外,WebHost的启动和停止也是网站事件很重要一环,ASP.NET Core不像ASP.NET MVC用继承的方式捕捉启动及停止事件,而是透过Startup.Configure
注入IApplicationLifetime
来补捉Application启动停止事件。
IApplicationLifetime
有三个注册监听事件及终止网站事件可以触发。如下:
public interface IApplicationLifetime { CancellationToken ApplicationStarted { get; } CancellationToken ApplicationStopping { get; } CancellationToken ApplicationStopped { get; } void StopApplication(); }
通过Console输出执行的过程,示例如下:
Program.cs
using System; using System.Collections.Generic; using System.IO; using System.Linq; using System.Threading.Tasks; using Microsoft.AspNetCore; using Microsoft.AspNetCore.Hosting; using Microsoft.Extensions.Configuration; using Microsoft.Extensions.Logging; using Microsoft.AspNetCore.Builder; using Microsoft.AspNetCore.Http; using Microsoft.Extensions.DependencyInjection; namespace MyWebsite { public class Program { public static void Main(string[] args) { Output("Application - Start"); var webHost = BuildWebHost(args); Output("Run WebHost"); webHost.Run(); Output("Application - End"); } public static IWebHost BuildWebHost(string[] args) { Output("Create WebHost Builder"); var webHostBuilder = WebHost.CreateDefaultBuilder(args) .ConfigureServices(services => { Output("webHostBuilder.ConfigureServices - Called"); }) .Configure(app => { Output("webHostBuilder.Configure - Called"); }) .UseStartup<Startup>(); Output("Build WebHost"); var webHost = webHostBuilder.Build(); return webHost; } public static void Output(string message) { Console.WriteLine($"[{DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss")}] {message}"); } } }
Startup.cs
using System; using System.Collections.Generic; using System.Linq; using System.Threading; using System.Threading.Tasks; using Microsoft.AspNetCore.Builder; using Microsoft.AspNetCore.Hosting; using Microsoft.AspNetCore.Http; using Microsoft.Extensions.DependencyInjection; namespace MyWebsite { public class Startup { public Startup() { Program.Output("Startup Constructor - Called"); } // This method gets called by the runtime. Use this method to add services to the container. // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940 public void ConfigureServices(IServiceCollection services) { Program.Output("Startup.ConfigureServices - Called"); } // This method gets called by the runtime. Use this method to configure the HTTP request pipeline. public void Configure(IApplicationBuilder app, IApplicationLifetime appLifetime) { appLifetime.ApplicationStarted.Register(() => { Program.Output("ApplicationLifetime - Started"); }); appLifetime.ApplicationStopping.Register(() => { Program.Output("ApplicationLifetime - Stopping"); }); appLifetime.ApplicationStopped.Register(() => { Thread.Sleep(5 * 1000); Program.Output("ApplicationLifetime - Stopped"); }); app.Run(async (context) => { await context.Response.WriteAsync("Hello World!"); }); // For trigger stop WebHost var thread = new Thread(new ThreadStart(() => { Thread.Sleep(5 * 1000); Program.Output("Trigger stop WebHost"); appLifetime.StopApplication(); })); thread.Start(); Program.Output("Startup.Configure - Called"); } } }
输出内容少了webHostBuilder.Configure - Called,因为Configure
只能有一个,后注册的Configure
会把之前注册的覆盖掉。
程序执行流程如下:
Application startup in ASP.NET Core
Hosting in ASP.NET Core
老司机发车啦:https://github.com/SnailDev/SnailDev.NETCore2Learning
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