.net core mvc啟動順序以及主要部件2

前一篇提到WebHost.CreateDefaultBuilder(args)方法創建了WebHostBuilder實例，WebHostBuilder實例有三個主要功能 1、構建了IConfiguration實例和基礎環境配置，2、構建了IServiceCollection服務，也就是依賴註入的容器 ...

前一篇提到WebHost.CreateDefaultBuilder(args)方法創建了WebHostBuilder實例，WebHostBuilder實例有三個主要功能 1、構建了IConfiguration實例和基礎環境配置，2、構建了IServiceCollection服務，也就是依賴註入的容器，3、創建了webhost實例，這個webhost就是我們的接收請求的第一個管道，其中暴露出來的主要方法Build，請看源代碼：

 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14                         Console.WriteLine("The environment variable 'Hosting:Environment' is obsolete and has been replaced with 'ASPNETCORE_ENVIRONMENT'");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18                         Console.WriteLine("The environment variable 'ASPNET_ENV' is obsolete and has been replaced with 'ASPNETCORE_ENVIRONMENT'");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22                         Console.WriteLine("The environment variable 'ASPNETCORE_SERVER.URLS' is obsolete and has been replaced with 'ASPNETCORE_URLS'");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         }

View Code

這個方法中有幾個筆記重要的部分，下麵我給標記一下

調用BuildCommonServices私有方法主要是註入一些程式所需的基礎組件，請看源代碼：

 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         }

View Code

這個方法中其中就包含了註入IConfiguration的代碼和構建IServiceCollection容器的代碼，當然還有一些其他的主要中間件註入啊IApplicationBuilderFactory，包括HttpContextFactory等等都在這個方法裡面被IServiceCollection容器管理，具體請看下圖

這裡講清楚之後，我們直接進入UseStartup方法中，這個方法是註入了Startup的實例，請看主要源代碼

 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         }