.net core mvc启动顺序以及主要部件2

概述前一篇提到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

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                    {14                         Console.Writeline("The environment variable ‘Hosting:Environment‘ is obsolete and has been replaced with ‘ASPNETCORE_ENVIRONMENT‘");15                     }16                     if (Environment.GetEnvironmentvariable("ASPNET_ENV") != null)17                     {18                         Console.Writeline("The environment variable ‘ASPNET_ENV‘ is obsolete and has been replaced with ‘ASPNETCORE_ENVIRONMENT‘");19                     }20                     if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                    {22                         Console.Writeline("The environment variable ‘ASPNETCORE_SERVER.URLS‘ is obsolete and has been replaced with ‘ASPNETCORE_URLS‘");23                     }24                 }25                 Add@R_301_968@s(serviceCollection2,hostingServiceProvIDer);26                 WebHost webHost = new WebHost(serviceCollection2,hostingServiceProvIDer,_options,_config,hostingStartupErrors);27                 try28                 {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() > 133                                                                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                 catch40                 {41                     webHost.dispose();42                     throw;43                 }44             }45             throw new InvalIDOperationException(Resources.WebHostBuilder_SingleInstance);46         }

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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                     try11                     {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                 try57                 {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                     else64                     {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>)delegate76                     {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         }

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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

@H_502_787@

 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                 else11                 {12                     services.AddSingleton(typeof(IStartup),delegate (IServiceProvIDer sp)13                     {14                         IHostingEnvironment requiredService = sp.GetrequiredService<IHostingEnvironment>();15                         return new ConventionBasedStartup(StartupLoader.LoadMethods(sp,requiredService.Environmentname));16                     });17                 }18             });19         }

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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

总结

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