前一篇提到WebHost.CreateDefaultBuilder(args)方法创建了WebHostBuilder实例，WebHostBuilder实例有三个主要功能 1、构建了IConfiguration实例和基础环境配置，2、构建了IServiceCollection服务，也就是依赖注入的容器，3、创建了webhost实例，这个webhost就是我们的接收请求的第一个管道，其中暴露出来的主要方法Build，请看源代码：
1 public IWebHost Build()
2 {
3 if (!_webHostBuilt)
4 {
5 _webHostBuilt = true;
6 AggregateException hostingStartupErrors;
7 IServiceCollection serviceCollection = BuildCommonServices(out hostingStartupErrors);
8 IServiceCollection serviceCollection2 = serviceCollection.Clone();
9 IServiceProvider hostingServiceProvider = _003CBuild_003Eg__GetProviderFromFactory_007C13_0(serviceCollection);
10 if (!_options.SuppressStatusMessages)
11 {
12 if (Environment.GetEnvironmentVariable("Hosting:Environment") != null)
13 {
14 Console.WriteLine("The environment variable ‘Hosting:Environment‘ is obsolete and has been replaced with ‘ASPNETCORE_ENVIRONMENT‘");
15 }
16 if (Environment.GetEnvironmentVariable("ASPNET_ENV") != null)
17 {
18 Console.WriteLine("The environment variable ‘ASPNET_ENV‘ is obsolete and has been replaced with ‘ASPNETCORE_ENVIRONMENT‘");
19 }
20 if (Environment.GetEnvironmentVariable("ASPNETCORE_SERVER.URLS") != null)
21 {
22 Console.WriteLine("The environment variable ‘ASPNETCORE_SERVER.URLS‘ is obsolete and has been replaced with ‘ASPNETCORE_URLS‘");
23 }
24 }
25 AddApplicationServices(serviceCollection2, hostingServiceProvider);
26 WebHost webHost = new WebHost(serviceCollection2, hostingServiceProvider, _options, _config, hostingStartupErrors);
27 try
28 {
29 webHost.Initialize();
30 ILogger<WebHost> requiredService = webHost.Services.GetRequiredService<ILogger<WebHost>>();
31 foreach (IGrouping<string, string> item in from g in _options.GetFinalHostingStartupAssemblies().GroupBy((string a) => a, StringComparer.OrdinalIgnoreCase)
32 where g.Count() > 1
33 select g)
34 {
35 requiredService.LogWarning($"The assembly {item} was specified multiple times. Hosting startup assemblies should only be specified once.");
36 }
37 return webHost;
38 }
39 catch
40 {
41 webHost.Dispose();
42 throw;
43 }
44 }
45 throw new InvalidOperationException(Resources.WebHostBuilder_SingleInstance);
46 }
这个方法中有几个笔记重要的部分，下面我给标记一下
调用BuildCommonServices私有方法主要是注入一些程序所需的基础组件，请看源代码：
1 private IServiceCollection BuildCommonServices(out AggregateException hostingStartupErrors)
2 {
3 hostingStartupErrors = null;
4 _options = new WebHostOptions(_config, Assembly.GetEntryAssembly()?.GetName().Name);
5 if (!_options.PreventHostingStartup)
6 {
7 List<Exception> list = new List<Exception>();
8 foreach (string item in _options.GetFinalHostingStartupAssemblies().Distinct(StringComparer.OrdinalIgnoreCase))
9 {
10 try
11 {
12 foreach (HostingStartupAttribute customAttribute in Assembly.Load(new AssemblyName(item)).GetCustomAttributes<HostingStartupAttribute>())
13 {
14 ((IHostingStartup)Activator.CreateInstance(customAttribute.HostingStartupType)).Configure(this);
15 }
16 }
17 catch (Exception innerException)
18 {
19 list.Add(new InvalidOperationException("Startup assembly " + item + " failed to execute. See the inner exception for more details.", innerException));
20 }
21 }
22 if (list.Count > 0)
23 {
24 hostingStartupErrors = new AggregateException(list);
25 }
26 }
27 string contentRootPath = ResolveContentRootPath(_options.ContentRootPath, AppContext.BaseDirectory);
28 _hostingEnvironment.Initialize(contentRootPath, _options);
29 _context.HostingEnvironment = _hostingEnvironment;
30 ServiceCollection serviceCollection = new ServiceCollection();
31 serviceCollection.AddSingleton(_options);
32 ((IServiceCollection)serviceCollection).AddSingleton((IHostingEnvironment)_hostingEnvironment);
33 ((IServiceCollection)serviceCollection).AddSingleton((Microsoft.Extensions.Hosting.IHostingEnvironment)_hostingEnvironment);
34 serviceCollection.AddSingleton(_context);
35 IConfigurationBuilder configurationBuilder = new ConfigurationBuilder().SetBasePath(_hostingEnvironment.ContentRootPath).AddConfiguration(_config);
36 foreach (Action<WebHostBuilderContext, IConfigurationBuilder> configureAppConfigurationBuilderDelegate in _configureAppConfigurationBuilderDelegates)
37 {
38 configureAppConfigurationBuilderDelegate(_context, configurationBuilder);
39 }
40 IConfigurationRoot configurationRoot = configurationBuilder.Build();
41 ((IServiceCollection)serviceCollection).AddSingleton((IConfiguration)configurationRoot);
42 _context.Configuration = configurationRoot;
43 DiagnosticListener implementationInstance = new DiagnosticListener("Microsoft.AspNetCore");
44 serviceCollection.AddSingleton(implementationInstance);
45 ((IServiceCollection)serviceCollection).AddSingleton((DiagnosticSource)implementationInstance);
46 serviceCollection.AddTransient<IApplicationBuilderFactory, ApplicationBuilderFactory>();
47 serviceCollection.AddTransient<IHttpContextFactory, HttpContextFactory>();
48 serviceCollection.AddScoped<IMiddlewareFactory, MiddlewareFactory>();
49 serviceCollection.AddOptions();
50 serviceCollection.AddLogging();
51 serviceCollection.AddTransient<IStartupFilter, AutoRequestServicesStartupFilter>();
52 serviceCollection.AddTransient<IServiceProviderFactory<IServiceCollection>, DefaultServiceProviderFactory>();
53 serviceCollection.AddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
54 if (!string.IsNullOrEmpty(_options.StartupAssembly))
55 {
56 try
57 {
58 Type startupType = StartupLoader.FindStartupType(_options.StartupAssembly, _hostingEnvironment.EnvironmentName);
59 if (IntrospectionExtensions.GetTypeInfo(typeof(IStartup)).IsAssignableFrom(startupType.GetTypeInfo()))
60 {
61 serviceCollection.AddSingleton(typeof(IStartup), startupType);
62 }
63 else
64 {
65 serviceCollection.AddSingleton(typeof(IStartup), delegate (IServiceProvider sp)
66 {
67 IHostingEnvironment requiredService = sp.GetRequiredService<IHostingEnvironment>();
68 return new ConventionBasedStartup(StartupLoader.LoadMethods(sp, startupType, requiredService.EnvironmentName));
69 });
70 }
71 }
72 catch (Exception source)
73 {
74 ExceptionDispatchInfo capture = ExceptionDispatchInfo.Capture(source);
75 ((IServiceCollection)serviceCollection).AddSingleton((Func<IServiceProvider, IStartup>)delegate
76 {
77 capture.Throw();
78 return null;
79 });
80 }
81 }
82 foreach (Action<WebHostBuilderContext, IServiceCollection> configureServicesDelegate in _configureServicesDelegates)
83 {
84 configureServicesDelegate(_context, serviceCollection);
85 }
86 return serviceCollection;
87 }
这个方法中其中就包含了注入IConfiguration的代码和构建IServiceCollection容器的代码，当然还有一些其他的主要中间件注入啊IApplicationBuilderFactory，包括HttpContextFactory等等都在这个方法里面被IServiceCollection容器管理，具体请看下图
这里讲清楚之后，我们直接进入UseStartup方法中，这个方法是注入了Startup的实例，请看主要源代码
1 public static IWebHostBuilder UseStartup(this IWebHostBuilder hostBuilder, Type startupType)
2 {
3 string name = startupType.GetTypeInfo().Assembly.GetName().Name;
4 return hostBuilder.UseSetting(WebHostDefaults.ApplicationKey, name).ConfigureServices(delegate (IServiceCollection services)
5 {
6 if (IntrospectionExtensions.GetTypeInfo(typeof(IStartup)).IsAssignableFrom(startupType.GetTypeInfo()))
7 {
8 services.AddSingleton(typeof(IStartup), startupType);
9 }
10 else
11 {
12 services.AddSingleton(typeof(IStartup), delegate (IServiceProvider sp)
13 {
14 IHostingEnvironment requiredService = sp.GetRequiredService<IHostingEnvironment>();
15 return new ConventionBasedStartup(StartupLoader.LoadMethods(sp, startupType, requiredService.EnvironmentName));
16 });
17 }
18 });
19 }
上面只是被IServiceCollection所管理 并没有真正起作用，真正调用的是Main方法中的Build().Run()，这里的Build就是上面那个IWebHostBuilder中的主要的构建方法，而Run则是正式启动应用程序和调用Startup中的ConfigureServices方法
请看代码：
分享Program类的过程大致就到这里了
原文地址：https://www.cnblogs.com/lvshunbin/p/11072531.html
时间： 2024-11-12 21:42:07