ASP.NET Core[源碼分析篇] - Startup
應用啟動的重要類 - Startup
在ASP.NET Core - 從Program和Startup開始這篇文章裡面，我們知道了Startup這個類的重要性，它主要負責了：
配置應用需要的服務（服務注冊，ConfigureServices方法）。
建立應用的請求處理處理管道（Configure方法）。
在源碼分析之前補充一點，雖然我們一般是按約定把這個類名定義成了Startup，但是在真正應用中，我們不是必須要命名為Startup的，這隻是一個抽象概念，我們可以命名其他的類名，隻需要在UseStartup/UseStartup中顯式注冊這個啟動類即可，系統會把這個啟動類注冊為單例，例如：
複制代碼
public class Program
{
public static void Main(string[] args)
{
BuildWebHost(args).Run();
}
public static IWebHost BuildWebHost(string[] args) =>
WebHost.CreateDefaultBuilder(args)
.UseStartup<YourStartupClass>()
.Build(); }
public class YourStartupClass
public void ConfigureService(IServiceCollection services)
{
}
public void Configure(IApplicationBuilder app)
{
} Startup是如何被注冊進來的？
從前面我們可以看到Startup是在UseStartup方法裡面被引用進來，我們先看一下UseStartup是如何把Startup類注冊進來的
/// Specify the startup type to be used by the web host.
/// <param name="hostBuilder">The <see cref="T:Microsoft.AspNetCore.Hosting.IWebHostBuilder" /> to configure.</param>
/// <param name="startupType">The <see cref="T:System.Type" /> to be used.</param>
/// <returns>The <see cref="T:Microsoft.AspNetCore.Hosting.IWebHostBuilder" />.</returns>
public static IWebHostBuilder UseStartup(this IWebHostBuilder hostBuilder,Type startupType)
{
string name = startupType.GetTypeInfo().Assembly.GetName().Name;
return hostBuilder.UseSetting(WebHostDefaults.ApplicationKey, name).ConfigureServices((Action<IServiceCollection>) (services =>
{
if (typeof (IStartup).GetTypeInfo().IsAssignableFrom(startupType.GetTypeInfo()))
ServiceCollectionServiceExtensions.AddSingleton(services, typeof (IStartup), startupType);
else
ServiceCollectionServiceExtensions.AddSingleton(services, typeof (IStartup), (Func<IServiceProvider, object>) (sp =>
{
IHostingEnvironment requiredService = sp.GetRequiredService<IHostingEnvironment>();
return (object) new ConventionBasedStartup(StartupLoader.LoadMethods(sp, startupType, requiredService.EnvironmentName));
}));
}));
}
/// <summary>Specify the startup type to be used by the web host.</summary>
/// <param name="hostBuilder">The <see cref="T:Microsoft.AspNetCore.Hosting.IWebHostBuilder" /> to configure.</param>
/// <typeparam name="TStartup">The type containing the startup methods for the application.</typeparam>
/// <returns>The <see cref="T:Microsoft.AspNetCore.Hosting.IWebHostBuilder" />.</returns>
public static IWebHostBuilder UseStartup<TStartup>(this IWebHostBuilder hostBuilder)
where TStartup : class
{
return hostBuilder.UseStartup(typeof (TStartup));
} _configureServicesDelegates
從上面代碼我們可以看出，這裡主要是調用了WebHostBuilder的ConfigureServices方法，我們看一下ConfigureServices做了什麼
public IWebHostBuilder ConfigureServices( Action configureServices)
{
if (configureServices == null)
throw new ArgumentNullException(nameof (configureServices));
return this.ConfigureServices((Action<WebHostBuilderContext, IServiceCollection>) ((_, services) => configureServices(services)));
}
/// <summary>
/// Adds a delegate for configuring additional services for the host or web application. This may be called
/// multiple times.
/// </summary>
/// <param name="configureServices">A delegate for configuring the <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" />.</param>
/// <returns>The <see cref="T:Microsoft.AspNetCore.Hosting.IWebHostBuilder" />.</returns>
public IWebHostBuilder ConfigureServices( Action<WebHostBuilderContext, IServiceCollection> configureServices)
{
if (configureServices == null)
throw new ArgumentNullException(nameof (configureServices));
this._configureServicesDelegates.Add(configureServices);
return (IWebHostBuilder) this;
} 這裡主要是把委托添加到_configureServicesDelegates清單裡面，這個_configureServicesDelegates有什麼用呢？這個屬性是一個非常重要的承載角色，在後面的WebHost真正調用Build方法時，我們再詳細講解。
再次看回UseStartup，這裡調用了ConfigureServices并向_configureServicesDelegates注冊了一個委托，我們看一下這個委托的實體，這裡面有兩個分支：
1. Startup實作IStartup接口
直接注冊該Startup為單例。從這裡看出，其實我們的Startup類還有另一種方式實作的，就是直接實作IStartup接口。（其實還有一種是實作StartupBase）
2. Startup沒實作IStartup接口
注冊類型為ConventionBasedStartup的Startup類型
public class ConventionBasedStartup : IStartup
{
private readonly StartupMethods _methods;
public ConventionBasedStartup(StartupMethods methods)
{
this._methods = methods;
}
public void Configure(IApplicationBuilder app)
{
try
{
this._methods.ConfigureDelegate(app);
}
catch (Exception ex)
{
if (ex is TargetInvocationException)
ExceptionDispatchInfo.Capture(ex.InnerException).Throw();
throw;
}
}
public IServiceProvider ConfigureServices(IServiceCollection services)
{
try
{
return this._methods.ConfigureServicesDelegate(services);
}
catch (Exception ex)
{
if (ex is TargetInvocationException)
ExceptionDispatchInfo.Capture(ex.InnerException).Throw();
throw;
}
} }
注意這個ConventionBasedStartup其實也是實作了IStartup接口，ConventionBasedStartup對象是根據一個StartupMethods對象建立的，我們來看一下這個StartupMethods類型的定義
public class StartupMethods
public StartupMethods(object instance,Action<IApplicationBuilder> configure, Func<IServiceCollection, IServiceProvider> configureServices)
{
this.StartupInstance = instance;
this.ConfigureDelegate = configure;
this.ConfigureServicesDelegate = configureServices;
}
public object StartupInstance { get; }
public Func<IServiceCollection, IServiceProvider> ConfigureServicesDelegate { get; }
public Action<IApplicationBuilder> ConfigureDelegate { get; } StartupMethods隻提供兩個注冊服務和中間件的方法，這兩個方法展現在由它的兩個屬性（ConfigureServicesDelegate和ConfigureDelegate）提供的兩個委托對象。
在我們UseStartup代碼裡面，是通過StartupLoader.LoadMethods基于Startup類型擷取到一個StartupMethods
public class StartupLoader
public static StartupMethods LoadMethods(IServiceProvider hostingServiceProvider,Type startupType,string environmentName)
{
ConfigureBuilder configureDelegate = StartupLoader.FindConfigureDelegate(startupType, environmentName);
ConfigureServicesBuilder servicesDelegate = StartupLoader.FindConfigureServicesDelegate(startupType, environmentName);
ConfigureContainerBuilder containerDelegate = StartupLoader.FindConfigureContainerDelegate(startupType, environmentName);
object instance1 = (object) null;
if (!configureDelegate.MethodInfo.IsStatic || servicesDelegate != null && !servicesDelegate.MethodInfo.IsStatic)
instance1 = ActivatorUtilities.GetServiceOrCreateInstance(hostingServiceProvider, startupType);
StartupLoader.ConfigureServicesDelegateBuilder instance2 = (StartupLoader.ConfigureServicesDelegateBuilder) Activator.CreateInstance(typeof (StartupLoader.ConfigureServicesDelegateBuilder<>).MakeGenericType(containerDelegate.MethodInfo != (MethodInfo) null ? containerDelegate.GetContainerType() : typeof (object)), (object) hostingServiceProvider, (object) servicesDelegate, (object) containerDelegate, instance1);
return new StartupMethods(instance1, configureDelegate.Build(instance1), instance2.Build());
}
private static ConfigureBuilder FindConfigureDelegate(Type startupType, string environmentName)
{
return new ConfigureBuilder(StartupLoader.FindMethod(startupType, "Configure{0}", environmentName, typeof (void), true));
}
private static ConfigureContainerBuilder FindConfigureContainerDelegate(Type startupType, string environmentName)
{
return new ConfigureContainerBuilder(StartupLoader.FindMethod(startupType, "Configure{0}Container", environmentName, typeof (void), false));
}
private static ConfigureServicesBuilder FindConfigureServicesDelegate( Type startupType,string environmentName)
{
MethodInfo method = StartupLoader.FindMethod(startupType, "Configure{0}Services", environmentName, typeof (IServiceProvider), false);
if ((object) method == null)
method = StartupLoader.FindMethod(startupType, "Configure{0}Services", environmentName, typeof (void), false);
return new ConfigureServicesBuilder(method);
}
private static MethodInfo FindMethod( Type startupType,string methodName,string environmentName,Type returnType = null, bool required = true)
{
string methodNameWithEnv = string.Format((IFormatProvider) CultureInfo.InvariantCulture, methodName, (object) environmentName);
string methodNameWithNoEnv = string.Format((IFormatProvider) CultureInfo.InvariantCulture, methodName, (object) "");
MethodInfo[] methods = startupType.GetMethods(BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public);
List<MethodInfo> list = ((IEnumerable<MethodInfo>) methods).Where<MethodInfo>((Func<MethodInfo, bool>) (method => method.Name.Equals(methodNameWithEnv, StringComparison.OrdinalIgnoreCase))).ToList<MethodInfo>();
if (list.Count > 1)
throw new InvalidOperationException(string.Format("Having multiple overloads of method '{0}' is not supported.", (object) methodNameWithEnv));
if (list.Count == 0)
{
list = ((IEnumerable<MethodInfo>) methods).Where<MethodInfo>((Func<MethodInfo, bool>) (method => method.Name.Equals(methodNameWithNoEnv, StringComparison.OrdinalIgnoreCase))).ToList<MethodInfo>();
if (list.Count > 1)
throw new InvalidOperationException(string.Format("Having multiple overloads of method '{0}' is not supported.", (object) methodNameWithNoEnv));
}
MethodInfo methodInfo = list.FirstOrDefault<MethodInfo>();
if (methodInfo == (MethodInfo) null)
{
if (required)
throw new InvalidOperationException(string.Format("A public method named '{0}' or '{1}' could not be found in the '{2}' type.", (object) methodNameWithEnv, (object) methodNameWithNoEnv, (object) startupType.FullName));
return (MethodInfo) null;
}
if (!(returnType != (Type) null) || !(methodInfo.ReturnType != returnType))
return methodInfo;
if (required)
throw new InvalidOperationException(string.Format("The '{0}' method in the type '{1}' must have a return type of '{2}'.", (object) methodInfo.Name, (object) startupType.FullName, (object) returnType.Name));
return (MethodInfo) null;
}
這裡面主要是通過反射擷取startupType裡面的Configure和ConfigureServices作為參數指派給StartupMethods的ConfigureDelegate和ConfigureServicesDelegate，這樣一個完整的ConventionBasedStartup類型的startup就被注冊為單例了。
優先級
比較有意思的是，我們可以看到，Startup類中的這兩個方法除了可以命名為ConfigureServices和Configure之外，它們還可以攜帶運作環境名稱，具體采用的格式分别為Configure{EnvironmentName}Services和Configure{EnvironmentName}，後者具有更高的選擇優先級。
注意到FindConfigureServicesDelegate這個方法的實作，一般來說，ConfigureServices/Configure{EnvironmentName}Services這個方法不具有傳回值（傳回類型為void），但是它也可以定義成一個傳回類型為IServiceProvider的方法。如果這個方法傳回一個ServiceProvider對象，後續過程中擷取的所有服務将從這個ServiceProvider中提取。這個傳回的ServiceProvider對我們後續的一個注冊是非常有用的，具體在【ASP.NET Core - 利用Windsor Castle實作通用注冊】這篇文章中提到，我們基于傳回的IServiceProvider進行容器替換進而實作通用注冊，對于沒有傳回值的情況，系統會根據目前注冊的服務建立一個ServiceProvider。
注意到此為止，程式還是沒有執行做一個真正的注冊，因為我們隻是往_configureServicesDelegates添加了委托而已，并沒有執行，這個的執行是在WebHost真正調用Build方法時。
其實CreateDefaultBuilder方法中的其他幾個UseXXX（UserUrl,UseKestrel等）擴充方法也是同樣的道理，把對應需要注冊的Action委托同樣寫入了configureServicesDelegates
總結
上面的這個過程，我們看到其實包含很多隐含的邏輯，這些邏輯的了解，可以提供多種選項讓我們在後面的真正開發中能夠根據自己項目的一個實際情況進行選擇，到此為止，我們現在能看到的最重要的一個點是：_configureServicesDelegates的一個承載作用。
原文位址
https://www.cnblogs.com/lex-wu/p/10782813.html![Docker-compose 進行Doris自動化編排部署[圖]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)