浅讲.Net 6 之 WebApplicationBuilder
介绍
.Net 6为我们带来的一种全新的引导程序启动的方式。与之前的拆分成Program.cs和Startup不同，整个引导启动代码都在Program.cs中。
WebApplicationBuilder builder = WebApplication.CreateBuilder(args);在上篇文章中，我简要描述了如何使用 WebApplication和WebApplicationBuilder配置 ASP.NET Core 应用程序。在这篇文章中，我们来深入看下代码.
正文
我们示例程序的第一步是执行WebApplicationBuilder builder = WebApplication.CreateBuilder(args);创建一个WebApplicationBuilder实例。
从命令行中分配Args参数，并将选项对象传递给WebApplicationBuilder构造函数的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后面在讲
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由一堆只读属性和一个方法组成Build()，该方法创建了一个WebApplication. 我删除了部分讲解用不到的代码。
如果您熟悉 ASP.NET Core，那么其中许多属性都使用以前版本中的常见类型
- IWebHostEnvironment: 用于检索环境
- IServiceCollection: 用于向 DI 容器注册服务。
- ConfigurationManager: 用于添加新配置和检索配置值。我在之前的文章有讲
- ILoggingBuilder: 用于注册额外的日志提供程序
在WebHost和Host性质很有趣，因为它们暴露出新的类型，ConfigureWebHostBuilder和ConfigureHostBuilder。这些类型分别实现IWebHostBuilder和IHostBuilder。
公开IWebHostBuilder和IHostBuilder接口对于允许从.NET 6 之前的应用程序迁移到新的最小托管，我们如何将的lambda风格配置IHostBuilder与命令式风格的WebApplicationBuilder协调起来，这就是ConfigureHostBuilder和ConfigureWebHostBuilder与一些内部沿来IHostBuilder实现。
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实现IHostBuilder和ISupportsConfigureWebHost，但 ISupportsConfigureWebHost 的实现是假的什么意思呢？
这意味着虽然以下代码可以编译,但是会在运行时抛出异常。
WebApplicationBuilder builder = WebApplication.CreateBuilder(args);
builder.Host.ConfigureWebHost(webBuilder =>
{
webBuilder.UseStartup<Startup>();
});
ConfigureServices()，该方法Action<>使用IServiceCollection从WebApplicationBuilder. 所以以下两个调用在功能上是相同的：
后一种方法显然不值得在正常实践中使用，但仍然可以使用依赖于这种方法的现有代码,
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>());
并非所有委托ConfigureHostBuilder都立即传递给运行中的方法。例如UseServiceProviderFactory()保存在列表中，稍后在调用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我们看内部的BootstrapHostBuilder,它记录了IHostBuilder收到的所有调用。例如ConfigureHostConfiguration()和ConfigureServices()，
这与ConfigureHostBuilder立即执行提供的委托相比，BootstrapHostBuilder的保存将委托提供给稍后执行的列表。这类似于泛型的HostBuilder工作方式。但请注意，这BootstrapHostBuilder调用Build()会引发异常
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构造函数
最后我们来看WebApplicationBuilder构造函数，注释都给大家翻译了
internal WebApplicationBuilder(WebApplicationOptions options, Action<IHostBuilder>? configureDefaults = null)
{
Services = _services;
var args = options.Args;
//尽早运行方法配置通用和web主机默认值，以从appsettings.json填充配置
//要预填充的环境变量（以DOTNET和ASPNETCORE为前缀）和其他可能的默认源
//正确的默认值。
_bootstrapHostBuilder = new BootstrapHostBuilder(Services, _hostBuilder.Properties);
//不要在这里指定参数，因为我们希望稍后应用它们，以便
//可以覆盖ConfigureWebHostDefaults指定的默认值
_bootstrapHostBuilder.ConfigureDefaults(args: null);
// This is for testing purposes
configureDefaults?.Invoke(_bootstrapHostBuilder);
//我们上次在这里指定了命令行，因为我们跳过了对ConfigureDefaults的调用中的命令行。
//args可以包含主机和应用程序设置，因此我们要确保
//我们适当地订购这些配置提供程序，而不复制它们
if (args is { Length: > 0 })
{
_bootstrapHostBuilder.ConfigureAppConfiguration(config =>
{
config.AddCommandLine(args);
});
}
// ....
}
// 自ConfigureWebHostDefaults覆盖特定于主机的设置（应用程序名称）以来，上次将参数应用于主机配置。
_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这玩意到底在干嘛。只要能看明白下面代码就好了，调用BootstrapHostBuilder.RunDefaultCallbacks()，
它以正确的顺序运行我们迄今为止积累的所有存储的回调，以构建HostBuilderContext. 该HostBuilderContext则是用来最终设定的剩余性能WebApplicationBuilder。
完成特定于应用程序的配置后，在由我们手动调用Build()创建一个WebApplication实例。
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()
该Build()方法不是非常复杂，首先是将配置的配置源复制到_hostBuilder的ConfigurationBuilder实现中。调用此方法时，builder它最初为空，因此这将填充由默认构建器扩展方法添加的所有源，以及您随后配置的额外源。
// 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;
}
});
接下来，是一样的事情IServiceCollection，将它们从_services实例复制到_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));
}
}
});
接下来运行我们在ConfigureHostBuilder属性中收集的任何回调
// Run the other callbacks on the final host builder
Host.RunDeferredCallbacks(_hostBuilder);
最后我们调用_hostBuilder.Build()构建Host实例，并将其传递给 的新实例WebApplication。调用_hostBuilder.Build()是调用所有注册回调的地方。
_builtApplication = new WebApplication(_hostBuilder.Build());
最后，为了保持一切一致ConfigurationManager实例被清除，并链接到存储在WebApplication. 此外IServiceCollectiononWebApplicationBuilder被标记为只读，因此在调用后尝试添加服务WebApplicationBuilder将抛出一个InvalidOperationException. 最后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;
差不多就是这样.
结语
作者第一次解读源码，该讲解可能有些罗里吧嗦乱七八糟，直接看文章也可能看不懂，推荐大家打开源码对比阅读，我也在整理整理思绪争取下一篇好一些。
最后欢迎各位读者关注我的博客， https://github.com/MrChuJiu/Dppt/tree/master/src 欢迎大家Star
联系作者：加群：867095512 @MrChuJiu
