.net core mvc启动顺序以及主要部件2

原文:.net core mvc启动顺序以及主要部件2

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：

 public IWebHost Build()
         {
             if (!_webHostBuilt)
             {
                 _webHostBuilt = true;
                 AggregateException hostingStartupErrors;
                 IServiceCollection serviceCollection = BuildCommonServices(out hostingStartupErrors);
                 IServiceCollection serviceCollection2 = serviceCollection.Clone();
                 IServiceProvider hostingServiceProvider = _003CBuild_003Eg__GetProviderFromFactory_007C13_0(serviceCollection);
                 if (!_options.SuppressStatusMessages)
                 {
                     if (Environment.GetEnvironmentVariable("Hosting:Environment") != null)
                     {
                         Console.WriteLine("The environment variable 'Hosting:Environment' is obsolete and has been replaced with 'ASPNETCORE_ENVIRONMENT'");
                     }
                     if (Environment.GetEnvironmentVariable("ASPNET_ENV") != null)
                     {
                         Console.WriteLine("The environment variable 'ASPNET_ENV' is obsolete and has been replaced with 'ASPNETCORE_ENVIRONMENT'");
                     }
                     if (Environment.GetEnvironmentVariable("ASPNETCORE_SERVER.URLS") != null)
                     {
                         Console.WriteLine("The environment variable 'ASPNETCORE_SERVER.URLS' is obsolete and has been replaced with 'ASPNETCORE_URLS'");
                     }
                 }
                 AddApplicationServices(serviceCollection2, hostingServiceProvider);
                 WebHost webHost = new WebHost(serviceCollection2, hostingServiceProvider, _options, _config, hostingStartupErrors);
                 try
                 {
                     webHost.Initialize();
                     ILogger<WebHost> requiredService = webHost.Services.GetRequiredService<ILogger<WebHost>>();
                     foreach (IGrouping<string, string> item in from g in _options.GetFinalHostingStartupAssemblies().GroupBy((string a) => a, StringComparer.OrdinalIgnoreCase)
                                                                where g.Count() >
                                                                select g)
                     {
                         requiredService.LogWarning($"The assembly {item} was specified multiple times. Hosting startup assemblies should only be specified once.");
                     }
                     return webHost;
                 }
                 catch
                 {
                     webHost.Dispose();
                     throw;
                 }
             }
             throw new InvalidOperationException(Resources.WebHostBuilder_SingleInstance);
         }

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：

  private IServiceCollection BuildCommonServices(out AggregateException hostingStartupErrors)
         {
             hostingStartupErrors = null;
             _options = new WebHostOptions(_config, Assembly.GetEntryAssembly()?.GetName().Name);
             if (!_options.PreventHostingStartup)
             {
                 List<Exception> list = new List<Exception>();
                 foreach (string item in _options.GetFinalHostingStartupAssemblies().Distinct(StringComparer.OrdinalIgnoreCase))
                 {
                     try
                     {
                         foreach (HostingStartupAttribute customAttribute in Assembly.Load(new AssemblyName(item)).GetCustomAttributes<HostingStartupAttribute>())
                         {
                             ((IHostingStartup)Activator.CreateInstance(customAttribute.HostingStartupType)).Configure(this);
                         }
                     }
                     catch (Exception innerException)
                     {
                         list.Add(new InvalidOperationException("Startup assembly " + item + " failed to execute. See the inner exception for more details.", innerException));
                     }
                 }
                 if (list.Count > )
                 {
                     hostingStartupErrors = new AggregateException(list);
                 }
             }
             string contentRootPath = ResolveContentRootPath(_options.ContentRootPath, AppContext.BaseDirectory);
             _hostingEnvironment.Initialize(contentRootPath, _options);
             _context.HostingEnvironment = _hostingEnvironment;
             ServiceCollection serviceCollection = new ServiceCollection();
             serviceCollection.AddSingleton(_options);
             ((IServiceCollection)serviceCollection).AddSingleton((IHostingEnvironment)_hostingEnvironment);
             ((IServiceCollection)serviceCollection).AddSingleton((Microsoft.Extensions.Hosting.IHostingEnvironment)_hostingEnvironment);
             serviceCollection.AddSingleton(_context);
             IConfigurationBuilder configurationBuilder = new ConfigurationBuilder().SetBasePath(_hostingEnvironment.ContentRootPath).AddConfiguration(_config);
             foreach (Action<WebHostBuilderContext, IConfigurationBuilder> configureAppConfigurationBuilderDelegate in _configureAppConfigurationBuilderDelegates)
             {
                 configureAppConfigurationBuilderDelegate(_context, configurationBuilder);
             }
             IConfigurationRoot configurationRoot = configurationBuilder.Build();
             ((IServiceCollection)serviceCollection).AddSingleton((IConfiguration)configurationRoot);
             _context.Configuration = configurationRoot;
             DiagnosticListener implementationInstance = new DiagnosticListener("Microsoft.AspNetCore");
             serviceCollection.AddSingleton(implementationInstance);
             ((IServiceCollection)serviceCollection).AddSingleton((DiagnosticSource)implementationInstance);
             serviceCollection.AddTransient<IApplicationBuilderFactory, ApplicationBuilderFactory>();
             serviceCollection.AddTransient<IHttpContextFactory, HttpContextFactory>();
             serviceCollection.AddScoped<IMiddlewareFactory, MiddlewareFactory>();
             serviceCollection.AddOptions();
             serviceCollection.AddLogging();
             serviceCollection.AddTransient<IStartupFilter, AutoRequestServicesStartupFilter>();
             serviceCollection.AddTransient<IServiceProviderFactory<IServiceCollection>, DefaultServiceProviderFactory>();
             serviceCollection.AddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
             if (!string.IsNullOrEmpty(_options.StartupAssembly))
             {
                 try
                 {
                     Type startupType = StartupLoader.FindStartupType(_options.StartupAssembly, _hostingEnvironment.EnvironmentName);
                     if (IntrospectionExtensions.GetTypeInfo(typeof(IStartup)).IsAssignableFrom(startupType.GetTypeInfo()))
                     {
                         serviceCollection.AddSingleton(typeof(IStartup), startupType);
                     }
                     else
                     {
                         serviceCollection.AddSingleton(typeof(IStartup), delegate (IServiceProvider sp)
                         {
                             IHostingEnvironment requiredService = sp.GetRequiredService<IHostingEnvironment>();
                             return new ConventionBasedStartup(StartupLoader.LoadMethods(sp, startupType, requiredService.EnvironmentName));
                         });
                     }
                 }
                 catch (Exception source)
                 {
                     ExceptionDispatchInfo capture = ExceptionDispatchInfo.Capture(source);
                     ((IServiceCollection)serviceCollection).AddSingleton((Func<IServiceProvider, IStartup>)delegate
                     {
                         capture.Throw();
                         return null;
                     });
                 }
             }
             foreach (Action<WebHostBuilderContext, IServiceCollection> configureServicesDelegate in _configureServicesDelegates)
             {
                 configureServicesDelegate(_context, serviceCollection);
             }
             return serviceCollection;
         }

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

 public static IWebHostBuilder UseStartup(this IWebHostBuilder hostBuilder, Type startupType)
         {
             string name = startupType.GetTypeInfo().Assembly.GetName().Name;
             return hostBuilder.UseSetting(WebHostDefaults.ApplicationKey, name).ConfigureServices(delegate (IServiceCollection services)
             {
                 if (IntrospectionExtensions.GetTypeInfo(typeof(IStartup)).IsAssignableFrom(startupType.GetTypeInfo()))
                 {
                     services.AddSingleton(typeof(IStartup), startupType);
                 }
                 else
                 {
                     services.AddSingleton(typeof(IStartup), delegate (IServiceProvider sp)
                     {
                         IHostingEnvironment requiredService = sp.GetRequiredService<IHostingEnvironment>();
                         return new ConventionBasedStartup(StartupLoader.LoadMethods(sp, startupType, requiredService.EnvironmentName));
                     });
                 }
             });
         }

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