介紹
.Net 6為我們帶來的一種全新的載入程式啟動的方式。與之前的拆分成Program.cs和Startup不同，整個引導啟動程式碼都在Program.cs中。
WebApplicationBuilder builder = WebApplication.CreateBuilder(args);在上篇文章中，我簡要描述瞭如何使用 WebApplication和WebApplicationBuilder配置 ASP.NET Core 應用程式。在這篇文章中，我們來深入看下程式碼.
正文
我們示例程式的第一步是執行WebApplicationBuilder builder = WebApplication.CreateBuilder(args);建立一個WebApplicationBuilder例項。
從命令列中分配Args引數，並將選項物件傳遞給WebApplicationBuilder建構函式的WebApplicationOptions
/// <summary>
/// Initializes a new instance of the <see cref="WebApplicationBuilder"/> class with preconfigured defaults.
/// </summary>
/// <param name="args">Command line arguments</param>
/// <returns>The <see cref="WebApplicationBuilder"/>.</returns>
public static WebApplicationBuilder CreateBuilder(string[] args) =>
new(new() { Args = args });
WebApplicationOptions和WebApplicationBuilder後面在講
internal WebApplicationBuilder(WebApplicationOptions options, Action<IHostBuilder>? configureDefaults = null)
/// <summary>
/// Options for configuing the behavior for <see cref="WebApplication.CreateBuilder(WebApplicationOptions)"/>.
/// </summary>
public class WebApplicationOptions
{
/// <summary>
/// The command line arguments.
/// </summary>
public string[]? Args { get; init; }
/// <summary>
/// The environment name.
/// </summary>
public string? EnvironmentName { get; init; }
/// <summary>
/// The application name.
/// </summary>
public string? ApplicationName { get; init; }
/// <summary>
/// The content root path.
/// </summary>
public string? ContentRootPath { get; init; }
/// <summary>
/// The web root path.
/// </summary>
public string? WebRootPath { get; init; }
}
WebApplicationBuilder由一堆只讀屬性和一個方法組成Build()，該方法建立了一個WebApplication. 我刪除了部分講解用不到的程式碼。
如果您熟悉 ASP.NET Core，那麼其中許多屬性都使用以前版本中的常見型別
- IWebHostEnvironment: 用於檢索環境
- IServiceCollection: 用於向 DI 容器註冊服務。
- ConfigurationManager: 用於新增新配置和檢索配置值。我在之前的文章有講
- ILoggingBuilder: 用於註冊額外的日誌提供程式
在WebHost和Host性質很有趣，因為它們暴露出新的型別，ConfigureWebHostBuilder和ConfigureHostBuilder。這些型別分別實現IWebHostBuilder和IHostBuilder。
公開IWebHostBuilder和IHostBuilder介面對於允許從.NET 6 之前的應用程式遷移到新的最小託管，我們如何將的lambda風格配置IHostBuilder與命令式風格的WebApplicationBuilder協調起來，這就是ConfigureHostBuilder和ConfigureWebHostBuilder與一些內部沿來IHostBuilder實現。
public sealed class WebApplicationBuilder
{
private const string EndpointRouteBuilderKey = "__EndpointRouteBuilder";
private readonly HostBuilder _hostBuilder = new();
private readonly BootstrapHostBuilder _bootstrapHostBuilder;
private readonly WebApplicationServiceCollection _services = new();
private readonly List<KeyValuePair<string, string>> _hostConfigurationValues;
private WebApplication? _builtApplication;
/// <summary>
/// Provides information about the web hosting environment an application is running.
/// </summary>
public IWebHostEnvironment Environment { get; }
/// <summary>
/// A collection of services for the application to compose. This is useful for adding user provided or framework provided services.
/// </summary>
public IServiceCollection Services { get; }
/// <summary>
/// A collection of configuration providers for the application to compose. This is useful for adding new configuration sources and providers.
/// </summary>
public ConfigurationManager Configuration { get; }
/// <summary>
/// A collection of logging providers for the application to compose. This is useful for adding new logging providers.
/// </summary>
public ILoggingBuilder Logging { get; }
/// <summary>
/// An <see cref="IWebHostBuilder"/> for configuring server specific properties, but not building.
/// To build after configuration, call <see cref="Build"/>.
/// </summary>
public ConfigureWebHostBuilder WebHost { get; }
/// <summary>
/// An <see cref="IHostBuilder"/> for configuring host specific properties, but not building.
/// To build after configuration, call <see cref="Build"/>.
/// </summary>
public ConfigureHostBuilder Host { get; }
/// <summary>
/// Builds the <see cref="WebApplication"/>.
/// </summary>
/// <returns>A configured <see cref="WebApplication"/>.</returns>
public WebApplication Build()
{
// Wire up the host configuration here. We don't try to preserve the configuration
// source itself here since we don't support mutating the host values after creating the builder.
_hostBuilder.ConfigureHostConfiguration(builder =>
{
builder.AddInMemoryCollection(_hostConfigurationValues);
});
var chainedConfigSource = new TrackingChainedConfigurationSource(Configuration);
// Wire up the application configuration by copying the already built configuration providers over to final configuration builder.
// We wrap the existing provider in a configuration source to avoid re-bulding the already added configuration sources.
_hostBuilder.ConfigureAppConfiguration(builder =>
{
builder.Add(chainedConfigSource);
foreach (var (key, value) in ((IConfigurationBuilder)Configuration).Properties)
{
builder.Properties[key] = value;
}
});
// This needs to go here to avoid adding the IHostedService that boots the server twice (the GenericWebHostService).
// Copy the services that were added via WebApplicationBuilder.Services into the final IServiceCollection
_hostBuilder.ConfigureServices((context, services) =>
{
// We've only added services configured by the GenericWebHostBuilder and WebHost.ConfigureWebDefaults
// at this point. HostBuilder news up a new ServiceCollection in HostBuilder.Build() we haven't seen
// until now, so we cannot clear these services even though some are redundant because
// we called ConfigureWebHostDefaults on both the _deferredHostBuilder and _hostBuilder.
foreach (var s in _services)
{
services.Add(s);
}
// Add the hosted services that were initially added last
// this makes sure any hosted services that are added run after the initial set
// of hosted services. This means hosted services run before the web host starts.
foreach (var s in _services.HostedServices)
{
services.Add(s);
}
// Clear the hosted services list out
_services.HostedServices.Clear();
// Add any services to the user visible service collection so that they are observable
// just in case users capture the Services property. Orchard does this to get a "blueprint"
// of the service collection
// Drop the reference to the existing collection and set the inner collection
// to the new one. This allows code that has references to the service collection to still function.
_services.InnerCollection = services;
var hostBuilderProviders = ((IConfigurationRoot)context.Configuration).Providers;
if (!hostBuilderProviders.Contains(chainedConfigSource.BuiltProvider))
{
// Something removed the _hostBuilder's TrackingChainedConfigurationSource pointing back to the ConfigurationManager.
// This is likely a test using WebApplicationFactory. Replicate the effect by clearing the ConfingurationManager sources.
((IConfigurationBuilder)Configuration).Sources.Clear();
}
// Make builder.Configuration match the final configuration. To do that, we add the additional
// providers in the inner _hostBuilders's Configuration to the ConfigurationManager.
foreach (var provider in hostBuilderProviders)
{
if (!ReferenceEquals(provider, chainedConfigSource.BuiltProvider))
{
((IConfigurationBuilder)Configuration).Add(new ConfigurationProviderSource(provider));
}
}
});
// Run the other callbacks on the final host builder
Host.RunDeferredCallbacks(_hostBuilder);
_builtApplication = new WebApplication(_hostBuilder.Build());
// Mark the service collection as read-only to prevent future modifications
_services.IsReadOnly = true;
// Resolve both the _hostBuilder's Configuration and builder.Configuration to mark both as resolved within the
// service provider ensuring both will be properly disposed with the provider.
_ = _builtApplication.Services.GetService<IEnumerable<IConfiguration>>();
return _builtApplication;
}
private void ConfigureApplication(WebHostBuilderContext context, IApplicationBuilder app)
{
Debug.Assert(_builtApplication is not null);
// UseRouting called before WebApplication such as in a StartupFilter
// lets remove the property and reset it at the end so we don't mess with the routes in the filter
if (app.Properties.TryGetValue(EndpointRouteBuilderKey, out var priorRouteBuilder))
{
app.Properties.Remove(EndpointRouteBuilderKey);
}
if (context.HostingEnvironment.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
// Wrap the entire destination pipeline in UseRouting() and UseEndpoints(), essentially:
// destination.UseRouting()
// destination.Run(source)
// destination.UseEndpoints()
// Set the route builder so that UseRouting will use the WebApplication as the IEndpointRouteBuilder for route matching
app.Properties.Add(WebApplication.GlobalEndpointRouteBuilderKey, _builtApplication);
// Only call UseRouting() if there are endpoints configured and UseRouting() wasn't called on the global route builder already
if (_builtApplication.DataSources.Count > 0)
{
// If this is set, someone called UseRouting() when a global route builder was already set
if (!_builtApplication.Properties.TryGetValue(EndpointRouteBuilderKey, out var localRouteBuilder))
{
app.UseRouting();
}
else
{
// UseEndpoints will be looking for the RouteBuilder so make sure it's set
app.Properties[EndpointRouteBuilderKey] = localRouteBuilder;
}
}
// Wire the source pipeline to run in the destination pipeline
app.Use(next =>
{
_builtApplication.Run(next);
return _builtApplication.BuildRequestDelegate();
});
if (_builtApplication.DataSources.Count > 0)
{
// We don't know if user code called UseEndpoints(), so we will call it just in case, UseEndpoints() will ignore duplicate DataSources
app.UseEndpoints(_ => { });
}
// Copy the properties to the destination app builder
foreach (var item in _builtApplication.Properties)
{
app.Properties[item.Key] = item.Value;
}
// Remove the route builder to clean up the properties, we're done adding routes to the pipeline
app.Properties.Remove(WebApplication.GlobalEndpointRouteBuilderKey);
// reset route builder if it existed, this is needed for StartupFilters
if (priorRouteBuilder is not null)
{
app.Properties[EndpointRouteBuilderKey] = priorRouteBuilder;
}
}
private sealed class LoggingBuilder : ILoggingBuilder
{
public LoggingBuilder(IServiceCollection services)
{
Services = services;
}
public IServiceCollection Services { get; }
}
}
ConfigureHostBuilder
public sealed class ConfigureHostBuilder : IHostBuilder, ISupportsConfigureWebHost
IHostBuilder ISupportsConfigureWebHost.ConfigureWebHost(Action<IWebHostBuilder> configure, Action<WebHostBuilderOptions> configureOptions)
{
throw new NotSupportedException("ConfigureWebHost() is not supported by WebApplicationBuilder.Host. Use the WebApplication returned by WebApplicationBuilder.Build() instead.");
}
ConfigureHostBuilder實現IHostBuilder和ISupportsConfigureWebHost，但 ISupportsConfigureWebHost 的實現是假的什麼意思呢？
這意味著雖然以下程式碼可以編譯,但是會在執行時丟擲異常。
WebApplicationBuilder builder = WebApplication.CreateBuilder(args);
builder.Host.ConfigureWebHost(webBuilder =>
{
webBuilder.UseStartup<Startup>();
});
ConfigureServices()，該方法Action<>使用IServiceCollection從WebApplicationBuilder. 所以以下兩個呼叫在功能上是相同的：
後一種方法顯然不值得在正常實踐中使用，但仍然可以使用依賴於這種方法的現有程式碼,
public IHostBuilder ConfigureAppConfiguration(Action<HostBuilderContext, IConfigurationBuilder> configureDelegate)
{
// Run these immediately so that they are observable by the imperative code
configureDelegate(_context, _configuration);
return this;
}
public IHostBuilder ConfigureServices(Action<HostBuilderContext, IServiceCollection> configureDelegate)
{
// Run these immediately so that they are observable by the imperative code
configureDelegate(_context, _services);
return this;
}
builder.Services.AddSingleton<MyImplementation>();
builder.Host.ConfigureServices((ctx, services) => services.AddSingleton<MyImplementation>());
並非所有委託ConfigureHostBuilder都立即傳遞給執行中的方法。例如UseServiceProviderFactory()儲存在列表中，稍後在呼叫WebApplicationBuilder.Build()
public IHostBuilder UseServiceProviderFactory<TContainerBuilder>(IServiceProviderFactory<TContainerBuilder> factory) where TContainerBuilder : notnull
{
if (factory is null)
{
throw new ArgumentNullException(nameof(factory));
}
_operations.Add(b => b.UseServiceProviderFactory(factory));
return this;
}
BootstrapHostBuilder
回到ConfigureHostBuilder我們看內部的BootstrapHostBuilder,它記錄了IHostBuilder收到的所有呼叫。例如ConfigureHostConfiguration()和ConfigureServices()，
這與ConfigureHostBuilder立即執行提供的委託相比，BootstrapHostBuilder的儲存將委託提供給稍後執行的列表。這類似於泛型的HostBuilder工作方式。但請注意，這BootstrapHostBuilder呼叫Build()會引發異常
internal class BootstrapHostBuilder : IHostBuilder
{
private readonly IServiceCollection _services;
private readonly List<Action<IConfigurationBuilder>> _configureHostActions = new();
private readonly List<Action<HostBuilderContext, IConfigurationBuilder>> _configureAppActions = new();
private readonly List<Action<HostBuilderContext, IServiceCollection>> _configureServicesActions = new();
public IHost Build()
{
// HostingHostBuilderExtensions.ConfigureDefaults should never call this.
throw new InvalidOperationException();
}
public IHostBuilder ConfigureHostConfiguration(Action<IConfigurationBuilder> configureDelegate)
{
_configureHostActions.Add(configureDelegate ?? throw new ArgumentNullException(nameof(configureDelegate)));
return this;
}
public IHostBuilder ConfigureServices(Action<HostBuilderContext, IServiceCollection> configureDelegate)
{
// HostingHostBuilderExtensions.ConfigureDefaults calls this via ConfigureLogging
_configureServicesActions.Add(configureDelegate ?? throw new ArgumentNullException(nameof(configureDelegate)));
return this;
}
// .....
}
WebApplicationBuilder建構函式
最後我們來看WebApplicationBuilder建構函式，註釋都給大家翻譯了
internal WebApplicationBuilder(WebApplicationOptions options, Action<IHostBuilder>? configureDefaults = null)
{
Services = _services;
var args = options.Args;
//儘早執行方法配置通用和web主機預設值，以從appsettings.json填充配置
//要預填充的環境變數（以DOTNET和ASPNETCORE為字首）和其他可能的預設源
//正確的預設值。
_bootstrapHostBuilder = new BootstrapHostBuilder(Services, _hostBuilder.Properties);
//不要在這裡指定引數，因為我們希望稍後應用它們，以便
//可以覆蓋ConfigureWebHostDefaults指定的預設值
_bootstrapHostBuilder.ConfigureDefaults(args: null);
// This is for testing purposes
configureDefaults?.Invoke(_bootstrapHostBuilder);
//我們上次在這裡指定了命令列，因為我們跳過了對ConfigureDefaults的呼叫中的命令列。
//args可以包含主機和應用程式設定，因此我們要確保
//我們適當地訂購這些配置提供程式，而不復制它們
if (args is { Length: > 0 })
{
_bootstrapHostBuilder.ConfigureAppConfiguration(config =>
{
config.AddCommandLine(args);
});
}
// ....
}
// 自ConfigureWebHostDefaults覆蓋特定於主機的設定（應用程式名稱）以來，上次將引數應用於主機配置。
_bootstrapHostBuilder.ConfigureHostConfiguration(config =>
{
if (args is { Length: > 0 })
{
config.AddCommandLine(args);
}
// Apply the options after the args
options.ApplyHostConfiguration(config);
});
到此你可能都非常疑惑這玩意到底在幹嘛。只要能看明白下面程式碼就好了，呼叫BootstrapHostBuilder.RunDefaultCallbacks()，
它以正確的順序執行我們迄今為止積累的所有儲存的回撥，以構建HostBuilderContext. 該HostBuilderContext則是用來最終設定的剩餘效能WebApplicationBuilder。
完成特定於應用程式的配置後，在由我們手動呼叫Build()建立一個WebApplication例項。
Configuration = new();
// Collect the hosted services separately since we want those to run after the user's hosted services
_services.TrackHostedServices = true;
// This is the application configuration
var (hostContext, hostConfiguration) = _bootstrapHostBuilder.RunDefaultCallbacks(Configuration, _hostBuilder);
// Stop tracking here
_services.TrackHostedServices = false;
// Capture the host configuration values here. We capture the values so that
// changes to the host configuration have no effect on the final application. The
// host configuration is immutable at this point.
_hostConfigurationValues = new(hostConfiguration.AsEnumerable());
// Grab the WebHostBuilderContext from the property bag to use in the ConfigureWebHostBuilder
var webHostContext = (WebHostBuilderContext)hostContext.Properties[typeof(WebHostBuilderContext)];
// Grab the IWebHostEnvironment from the webHostContext. This also matches the instance in the IServiceCollection.
Environment = webHostContext.HostingEnvironment;
Logging = new LoggingBuilder(Services);
Host = new ConfigureHostBuilder(hostContext, Configuration, Services);
WebHost = new ConfigureWebHostBuilder(webHostContext, Configuration, Services);
WebApplicationBuilder.Build()
該Build()方法不是非常複雜，首先是將配置的配置源複製到_hostBuilder的ConfigurationBuilder實現中。呼叫此方法時，builder它最初為空，因此這將填充由預設構建器擴充套件方法新增的所有源，以及您隨後配置的額外源。
// source itself here since we don't support mutating the host values after creating the builder.
_hostBuilder.ConfigureHostConfiguration(builder =>
{
builder.AddInMemoryCollection(_hostConfigurationValues);
});
_hostBuilder.ConfigureAppConfiguration(builder =>
{
builder.Add(chainedConfigSource);
foreach (var (key, value) in ((IConfigurationBuilder)Configuration).Properties)
{
builder.Properties[key] = value;
}
});
接下來，是一樣的事情IServiceCollection，將它們從_services例項複製到_hostBuilder的集合中。
// This needs to go here to avoid adding the IHostedService that boots the server twice (the GenericWebHostService).
// Copy the services that were added via WebApplicationBuilder.Services into the final IServiceCollection
_hostBuilder.ConfigureServices((context, services) =>
{
// We've only added services configured by the GenericWebHostBuilder and WebHost.ConfigureWebDefaults
// at this point. HostBuilder news up a new ServiceCollection in HostBuilder.Build() we haven't seen
// until now, so we cannot clear these services even though some are redundant because
// we called ConfigureWebHostDefaults on both the _deferredHostBuilder and _hostBuilder.
foreach (var s in _services)
{
services.Add(s);
}
// Add the hosted services that were initially added last
// this makes sure any hosted services that are added run after the initial set
// of hosted services. This means hosted services run before the web host starts.
foreach (var s in _services.HostedServices)
{
services.Add(s);
}
// Clear the hosted services list out
_services.HostedServices.Clear();
// Add any services to the user visible service collection so that they are observable
// just in case users capture the Services property. Orchard does this to get a "blueprint"
// of the service collection
// Drop the reference to the existing collection and set the inner collection
// to the new one. This allows code that has references to the service collection to still function.
_services.InnerCollection = services;
var hostBuilderProviders = ((IConfigurationRoot)context.Configuration).Providers;
if (!hostBuilderProviders.Contains(chainedConfigSource.BuiltProvider))
{
// Something removed the _hostBuilder's TrackingChainedConfigurationSource pointing back to the ConfigurationManager.
// This is likely a test using WebApplicationFactory. Replicate the effect by clearing the ConfingurationManager sources.
((IConfigurationBuilder)Configuration).Sources.Clear();
}
// Make builder.Configuration match the final configuration. To do that, we add the additional
// providers in the inner _hostBuilders's Configuration to the ConfigurationManager.
foreach (var provider in hostBuilderProviders)
{
if (!ReferenceEquals(provider, chainedConfigSource.BuiltProvider))
{
((IConfigurationBuilder)Configuration).Add(new ConfigurationProviderSource(provider));
}
}
});
接下來執行我們在ConfigureHostBuilder屬性中收集的任何回撥
// Run the other callbacks on the final host builder
Host.RunDeferredCallbacks(_hostBuilder);
最後我們呼叫_hostBuilder.Build()構建Host例項，並將其傳遞給 的新例項WebApplication。呼叫_hostBuilder.Build()是呼叫所有註冊回撥的地方。
_builtApplication = new WebApplication(_hostBuilder.Build());
最後，為了保持一切一致ConfigurationManager例項被清除，並連結到儲存在WebApplication. 此外IServiceCollectiononWebApplicationBuilder被標記為只讀，因此在呼叫後嘗試新增服務WebApplicationBuilder將丟擲一個InvalidOperationException. 最後WebApplication返回。
// Mark the service collection as read-only to prevent future modifications
_services.IsReadOnly = true;
// Resolve both the _hostBuilder's Configuration and builder.Configuration to mark both as resolved within the
// service provider ensuring both will be properly disposed with the provider.
_ = _builtApplication.Services.GetService<IEnumerable<IConfiguration>>();
return _builtApplication;
差不多就是這樣.
結語
作者第一次解讀原始碼，該講解可能有些羅裡吧嗦亂七八糟，直接看文章也可能看不懂，推薦大家開啟原始碼對比閱讀，我也在整理整理思緒爭取下一篇好一些。
最後歡迎各位讀者關注我的部落格， https://github.com/MrChuJiu/Dppt/tree/master/src 歡迎大家Star
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