Python微信订餐小程序课程视频
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Python实战量化交易理财系统
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Minimal API仅仅是在基于IHost/IHostBuilder的服务承载系统上作了小小的封装而已，它利用WebApplication和WebApplicationBuilder这两个类型提供了更加简洁的API，同时提供了与现有API的兼容。要成分理解Minimal API的实现原理，得先对服务承载系统有基本的理解，对此不了解的可以参阅《服务承载模型[上篇]》、《[服务承载模型下篇]》、《承载服务启动流程[上篇]》和《承载服务启动流程[下篇]》。对于本篇提供的模拟代码，可以从这里下载。
一、基础模型
二、WebApplication
三、WebApplication的构建 1. BootstrapHostBuilder 2. ConfigureHostBuilder 3. ConfigureWebHostBuilder 4. WebApplicationBuilder
四、 工厂方法
一、基础模型
对于由WebApplication和WebApplicationBuilder构建的承载模型，我们没有必要了解其实现的每一个细节，知道其大致的设计和实现原理就可以了，所以本节会采用最简洁的代码模拟这两个类型的实现。如图1所示，代表承载应用的WebApplication对象是对一个IHost对象的封装，而且该类型自身也实现了IHost接口， WebApplication对象其实还是作为一个IHost对象被启动的。作为构建这的WebApplicationBuilder则是对一个IHostBuilder对象的封装，它对WebApplication对象的构建体现在利用封装的IHostBuilder对象构建一个对应的IHost对象，最终利用后者将WebApplication对象创建出来。
图17-8 完整的请求处理管道
二、WebApplication
WebApplication类型不仅仅实现了IHost接口，还同时实现IApplicationBuilder接口，所以中间件可以直接注册到这个对象上的。该类型还实现了IEndpointRouteBuilder接口，所以我们还能利用它进行路由注册，我们在20章才会涉及到路由，所以我们现在先忽略针对该接口的实现。下面的代码模拟WebApplication类型的实现。如代码片段所示，WebApplication的构造函数定义了一个IHost类型的参数，它利用这个对象完成了对IHost接口所有成员的实现，针对IApplicationBuilder接口成员的实现则利用创建的ApplicationBuilder对象来完成。WebApplication还提供了一个BuildRequestDelegate方法利用这个ApplicationBuilder对象完成了对中间件管道的构建。
public class WebApplication : **IApplicationBuilder, IHost**
{
private readonly IHost \_host;
private readonly ApplicationBuilder \_app;
public WebApplication(IHost host)
{
\_host = host;
\_app = new ApplicationBuilder(host.Services);
}
IServiceProvider IHost.Services => \_host.Services;
Task IHost.StartAsync(CancellationToken cancellationToken) => \_host.StartAsync(cancellationToken);
Task IHost.StopAsync(CancellationToken cancellationToken) => \_host.StopAsync(cancellationToken);
IServiceProvider IApplicationBuilder.ApplicationServices { get => \_app.ApplicationServices; set => \_app.ApplicationServices = value; }
IFeatureCollection IApplicationBuilder.ServerFeatures => \_app.ServerFeatures;
IDictionary<string, object?> IApplicationBuilder.Properties => \_app.Properties;
RequestDelegate IApplicationBuilder.Build() => \_app.Build();
IApplicationBuilder IApplicationBuilder.New() => \_app.New();
IApplicationBuilder IApplicationBuilder.Use(Func middleware) => \_app.Use(middleware);
void IDisposable.Dispose() => \_host.Dispose();
public IServiceProvider Services => \_host.Services;
internal RequestDelegate BuildRequestDelegate() => \_app.Build();
...
}
WebApplication额外定义了如下的RunAsync和Run方法，它们分别以异步和同步方式启动承载的应用。调用这两个方法的时候可以指定监听地址，指定的地址被添加到IServerAddressesFeature特性中，而服务器正式利用这个特性来提供监听地址的。
public class WebApplication : IApplicationBuilder, IHost
{
private readonly IHost \_host;
public ICollection<string> Urls => \_host.Services.GetRequiredService().Features.Get()?.Addresses ?? throw new InvalidOperationException("IServerAddressesFeature is not found.");
public Task RunAsync(string? url = null)
{
Listen(url);
return HostingAbstractionsHostExtensions.RunAsync(this);
}
public void Run(string? url = null)
{
Listen(url);
HostingAbstractionsHostExtensions.Run(this);
}
private void Listen(string? url)
{
if (url is not null)
{
var addresses = \_host.Services.GetRequiredService().Features.Get()?.Addresses ?? throw new InvalidOperationException("IServerAddressesFeature is not found.");
addresses.Clear();
addresses.Add(url);
}
}
...
}
三、WebApplication的构建
要创建一个WebApplication对象，只需要提供一个对应的IHost对象即可。IHost对象是通过IHostBuilder对象构建的，所以WebApplicationBuilder需要一个IHostBuilder对象，具体来说是一个HostBuilder对象。我们针对WebApplicationBuilder对象所作的一切设置最终都需要转移到这个HostBuilder对象上才能生效。为了提供更加简洁的API，WebApplicationBuilder类型提供了一系列的属性。比如它利用Serrvices属性提供了可以直接进行服务注册的IServiceCollection集合，利用Environment属性提供了表示当前承载环境的IWebHostEnvironment对象，利用Configuration属性提供的ConfigurationManager对象不仅可以作为IConfigurationBuilder对象帮助我们完成对配置系统的一切设置，它自身也可以作为IConfiguration对象为我们提供配置。
WebApplicationBuilder还定义了Host和WebHost属性，对应类型为ConfigureHostBuilder和ConfigureWebHostBuilder，它们分别实现了IHostBuilder和IWebHostBuilder接口，其目的是为了复用IHostBuilder和IWebHostBuilder接口承载的API（主要是扩展方法）。为了会尽可能使用现有方法对IHostBuilder对象进行初始化设置，它还使用了一个实现了IHostBuilder接口的BootstrapHostBuilder类型。有这些对象组成了WebApplicationBuilder针对HostBuilder的构建模型。如图2所示，WebApplicationBuilder的所有工作都是为了构建它封装的HostBuilder对象。
当WebApplicationBuilder初始化的时候，它除了会创建这个HostBuilder对象，还会创建存储服务注册的IServiceCollection对象，以及用来对配置进行设置的ConfigurationManager对象。接下来它会创建一个BootstrapHostBuilder对象，并将它参数调用相应的方法（比如ConfigureWebHostDefaults方法）将初始化设置收集起来，收集的服务注册和针对配置系统的设置分别转移到创建的IServiceCollection和ConfigurationManager对象中，其他设置直接应用到封装的HostBuilder对象上。
图2 HostBuilder构建模型
WebApplicationBuilder在此之后会创建出代表承载环境的IWebHostEnvironment对象，并对Environment属性进行初始化。在得到表示承载上下文的WebHostBuilderContext对象之后，上述的ConfigureHostBuilder和ConfigureWebHostBuilder对象被创建出来，并赋值给Host和WebHost属性。与BootstrapHostBuilder作用类似，我们利用这两个对象所作的设置最终都会转移到上述的三个对象中。当WebApplicationBuilder进行WebApplication对象构建的时候，IServiceCollection对象存储的服务注册和ConfigurationManager对象承载配置最终转移到HostBuilder对象上。此时再利用后者构建出对应的IHost对象，代表承载应用的WebApplication对象最终由该对象构建出来。
1. BootstrapHostBuilder
如下所示的是我们模拟的BootstrapHostBuilder类型的定义。正如上面所说，这个它的作用是收集初始化IHostBuilder对象提供的设置并将它们分别应用到指定的IServiceCollection、ConfigurationManager和IHostBuilder对象上。这一使命体现在BootstrapHostBuilder的Apply方法上，该方法还通过一个输出参数返回创建的HostBuilderContext上下文。
public class BootstrapHostBuilder : IHostBuilder
{
private readonly List> \_configureHostConfigurations = new();
private readonly List> \_configureAppConfigurations = new();
private readonly List> \_configureServices = new();
private readonly List> \_others = new();
public IDictionary<object, object> Properties { get; } = new Dictionary<object, object>();
public IHost Build() => throw new NotImplementedException();
public IHostBuilder ConfigureHostConfiguration(Action configureDelegate)
{
\_configureHostConfigurations.Add(configureDelegate);
return this;
}
public IHostBuilder ConfigureAppConfiguration(Action configureDelegate)
{
\_configureAppConfigurations.Add(configureDelegate);
return this;
}
public IHostBuilder ConfigureServices(Action configureDelegate)
{
\_configureServices.Add(configureDelegate);
return this;
}
public IHostBuilder UseServiceProviderFactory(IServiceProviderFactory factory)
{
\_others.Add(builder => builder.UseServiceProviderFactory(factory));
return this;
}
public IHostBuilder UseServiceProviderFactory(Func> factory)
{
\_others.Add(builder => builder.UseServiceProviderFactory(factory));
return this;
}
public IHostBuilder ConfigureContainer(Action configureDelegate)
{
\_others.Add(builder => builder.ConfigureContainer(configureDelegate));
return this;
}
internal void Apply(IHostBuilder hostBuilder, ConfigurationManager configuration, IServiceCollection services, out HostBuilderContext builderContext)
{
// 初始化针对宿主的配置
var hostConfiguration = new ConfigurationManager();
\_configureHostConfigurations.ForEach(it => it(hostConfiguration));
// 创建承载环境
var environment = new HostingEnvironment()
{
ApplicationName = hostConfiguration[HostDefaults.ApplicationKey],
EnvironmentName = hostConfiguration[HostDefaults.EnvironmentKey] ?? Environments.Production,
ContentRootPath = HostingPathResolver.ResolvePath(hostConfiguration[HostDefaults.ContentRootKey])
};
environment.ContentRootFileProvider = new PhysicalFileProvider(environment.ContentRootPath);
// 创建HostBuilderContext上下文
var hostContext = new HostBuilderContext(Properties)
{
Configuration = hostConfiguration,
HostingEnvironment = environment,
};
// 将针对宿主的配置添加到ConfigurationManager中
configuration.AddConfiguration(hostConfiguration, true);
// 初始化针对应用的配置
\_configureAppConfigurations.ForEach(it => it(hostContext, configuration));
// 收集服务注册
\_configureServices.ForEach(it => it(hostContext, services));
// 将针对依赖注入容器的设置应用到指定的IHostBuilder对象上
\_others.ForEach(it => it(hostBuilder));
// 将自定义属性转移到指定的IHostBuilder对象上
foreach (var kv in Properties)
{
hostBuilder.Properties[kv.Key] = kv.Value;
}
builderContext = hostContext;
}
}除了Build方法，IHostBuilder接口中定义的所有方法的参数都是委托，所以实现的这些方法将提供的委托收集起来。在Apply方法中，我们通过执行这些委托对象，将初始化设置应用到指定的IServiceCollection、ConfigurationManager和IHostBuilder对象上，并根据初始化宿主配置构建出代表承载环境的HostingEnvironment对象。该方法最后根据承载环境结合配置将HostBuilderContext上下文创建出来，并以输出参数的形式返回。
internal static class HostingPathResolver
{
public static string ResolvePath(string? contentRootPath) => ResolvePath(contentRootPath, .BaseDirectory);
public static string ResolvePath(string? contentRootPath, string basePath) => string.IsNullOrEmpty(contentRootPath)
? Path.GetFullPath(basePath): Path.IsPathRooted(contentRootPath)? Path.GetFullPath(contentRootPath)
: Path.GetFullPath(Path.Combine(Path.GetFullPath(basePath), contentRootPath));
}
2. ConfigureHostBuilder
ConfigureHostBuilder是在应用了BootstrapHostBuilder收集的初始化设置之后创建的，在创建该对象时提供了HostBuilderContext上下文， ConfigurationManager和IServiceCollection对象。提供的服务注册直接添加到IServiceCollection对象中，针对配置的设置已经应用到ConfigurationManager对象，直接针对IHostBuilder对象的设置则利用_configureActions字段暂存起来。
public class ConfigureHostBuilder : IHostBuilder
{
private readonly ConfigurationManager \_configuration;
private readonly IServiceCollection \_services;
private readonly HostBuilderContext \_context;
private readonly List> \_configureActions = new();
internal ConfigureHostBuilder(HostBuilderContext context, ConfigurationManager configuration, IServiceCollection services)
{
\_configuration = configuration;
\_services = services;
\_context = context;
}
public IDictionary<object, object> Properties => \_context.Properties;
public IHost Build() => throw new NotImplementedException();
public IHostBuilder ConfigureAppConfiguration(Action configureDelegate)
=> Configure(() => configureDelegate(\_context, \_configuration));
public IHostBuilder ConfigureHostConfiguration(Action configureDelegate)
{
var applicationName = \_configuration[HostDefaults.ApplicationKey];
var contentRoot = \_context.HostingEnvironment.ContentRootPath;
var environment = \_configuration[HostDefaults.EnvironmentKey];
configureDelegate(\_configuration);
// 与环境相关的三个配置不允许改变
Validate(applicationName, HostDefaults.ApplicationKey, "Application name cannot be changed.");
Validate(contentRoot, HostDefaults.ContentRootKey, "Content root cannot be changed.");
Validate(environment, HostDefaults.EnvironmentKey, "Environment name cannot be changed.");
return this;
void Validate(string previousValue, string key, string message)
{
if (!string.Equals(previousValue, \_configuration[key], StringComparison.OrdinalIgnoreCase))
{
throw new NotSupportedException(message);
}
}
}
public IHostBuilder ConfigureServices(Action configureDelegate)
=> Configure(() => configureDelegate(\_context, \_services));
public IHostBuilder UseServiceProviderFactory(IServiceProviderFactory factory)
=> Configure(() => \_configureActions.Add(b => b.UseServiceProviderFactory(factory)));
public IHostBuilder UseServiceProviderFactory(Func> factory)
=> Configure(() => \_configureActions.Add(b => b.UseServiceProviderFactory(factory)));
public IHostBuilder ConfigureContainer(Action configureDelegate)
=> Configure(() => \_configureActions.Add(b => b.ConfigureContainer(configureDelegate)));
private IHostBuilder Configure(Action configure)
{
configure();
return this;
}
internal void Apply(IHostBuilder hostBuilder) => \_configureActions.ForEach(op => op(hostBuilder));
}WebApplicationBuilder对象一旦被创建出来后，针对承载环境的配置是不能改变的，所以ConfigureHostBuilder的ConfigureHostConfiguration方法针对此添加了相应的验证。两个UseServiceProviderFactory方法和ConfigureContainer方法针对依赖注入容器的设置最终需要应用到IHostBuilder对象上，所以我们将方法中提供的委托对象利用configureActions字段存起来，并最终利用Apply方法应用到指定的IHostBuilder对象上。
3. ConfigureWebHostBuilder
ConfigureWebHostBuilder同样是在应用了BootstrapHostBuilder提供的初始化设置后创建的，创建该对象时能够提供WebHostBuilderContext上下文和承载配置和服务注册的ConfigurationManager和IServiceCollection对象。由于IWebHostBuilder接口定义的方法只涉及服务注册和针对配置的设置，所以方法提供的委托对象可以直接应用到这两个对象上。
public class ConfigureWebHostBuilder : IWebHostBuilder, ISupportsStartup
{
private readonly WebHostBuilderContext \_builderContext;
private readonly IServiceCollection \_services;
private readonly ConfigurationManager \_configuration;
public ConfigureWebHostBuilder(WebHostBuilderContext builderContext, ConfigurationManager configuration, IServiceCollection services)
{
\_builderContext = builderContext;
\_services = services;
\_configuration = configuration;
}
public IWebHost Build() => throw new NotImplementedException();
public IWebHostBuilder ConfigureAppConfiguration(Action configureDelegate) => Configure(() => configureDelegate(\_builderContext, \_configuration));
public IWebHostBuilder ConfigureServices(Action configureServices) => Configure(() => configureServices(\_services));
public IWebHostBuilder ConfigureServices(Action configureServices) => Configure(() => configureServices(\_builderContext, \_services));
public string? GetSetting(string key) => \_configuration[key];
public IWebHostBuilder UseSetting(string key, string? value) => Configure(() => \_configuration[key] = value);
IWebHostBuilder ISupportsStartup.UseStartup(Type startupType) => throw new NotImplementedException();
IWebHostBuilder ISupportsStartup.UseStartup(Func startupFactory) => throw new NotImplementedException();
IWebHostBuilder ISupportsStartup.Configure(Action configure) => throw new NotImplementedException();
IWebHostBuilder ISupportsStartup.Configure(Action configure) => throw new NotImplementedException();
private IWebHostBuilder Configure(Action configure)
{
configure();
return this;
}
}我们在前面说过，传统承载方式将初始化操作定义在注册的Startup类型的编程方式在Minima API中已经不再被支持了，所以WebApplicationBuilder本不该实现ISupportsStartup接口，但是我们希望用户在采用这种编程方式时得到显式的提醒，所以依然让它实现该接口，并在实现的方法中抛出NotImplementedException类型的异常。
4. WebApplicationBuilder
如下的代码片段模拟了WebApplicationBuilder针对WebApplication的构建。它的构造函数会创建一个BootstrapHostBuilder对象，调用它的ConfigureDefaults和ConfigureWebHostDefaults扩展方法将初始化设置收集起来。ConfigureWebHostDefaults方法会利用提供的Action委托进行中间件的注册，由于中间件的注册被转移到WebApplication对象上，并且它提供了一个BuildRequestDelegate方法返回由注册中间件组成的管道，所以在这里只需调用构建的WebApplication对象（通过_application字段表示，虽然此时尚未创建，但是中间件真正被注册时会被创建出来）的这个方法，并将返回的RequestDelegate对象作为参数调用IApplicationBuilder接口的Run方法将中间件管道注册为请求处理器。
public class WebApplicationBuilder
{
private readonly HostBuilder \_hostBuilder = new HostBuilder();
private WebApplication \_application;
public ConfigurationManager Configuration { get; } = new ConfigurationManager();
public IServiceCollection Services { get; } = new ServiceCollection();
public IWebHostEnvironment Environment { get; }
public ConfigureHostBuilder Host { get; }
public ConfigureWebHostBuilder WebHost { get; }
public ILoggingBuilder Logging { get; }
public WebApplicationBuilder(WebApplicationOptions options)
{
//创建BootstrapHostBuilder并利用它收集初始化过程中设置的配置、服务和针对依赖注入容器的设置
var args = options.Args;
var bootstrap = new BootstrapHostBuilder();
bootstrap
.ConfigureDefaults(null)
**.ConfigureWebHostDefaults(webHostBuilder => webHostBuilder.Configure(app => app.Run(\_application.BuildRequestDelegate())))**
.ConfigureHostConfiguration(config => {
// 添加命令行配置源
if (args?.Any() == true)
{
config.AddCommandLine(args);
}
// 将WebApplicationOptions配置选项转移到配置中
Dictionary<string, string>? settings = null;
if (options.EnvironmentName is not null) (settings ??= new())[HostDefaults.EnvironmentKey] = options.EnvironmentName;
if (options.ApplicationName is not null) (settings ??= new())[HostDefaults.ApplicationKey] = options.ApplicationName;
if (options.ContentRootPath is not null) (settings ??= new())[HostDefaults.ContentRootKey] = options.ContentRootPath;
if (options.WebRootPath is not null) (settings ??= new())[WebHostDefaults.WebRootKey] = options.EnvironmentName;
if (settings != null)
{
config.AddInMemoryCollection(settings);
}
});
// 将BootstrapHostBuilder收集到配置和服务转移到Configuration和Services上
// 将应用到BootstrapHostBuilder上针对依赖注入溶质的设置转移到\_hostBuilder上
// 得到BuilderContext上下文
bootstrap.Apply(\_hostBuilder, Configuration, Services, out var builderContext);
// 如果提供了命令行参数，在Configuration上添加对应配置源
if (options.Args?.Any() == true)
{
Configuration.AddCommandLine(options.Args);
}
// 构建WebHostBuilderContext上下文
// 初始化Host、WebHost和Logging属性
var webHostContext = (WebHostBuilderContext)builderContext.Properties[typeof(WebHostBuilderContext)];
Environment = webHostContext.HostingEnvironment;
Host = new ConfigureHostBuilder(builderContext, Configuration, Services);
WebHost = new ConfigureWebHostBuilder(webHostContext, Configuration, Services);
Logging = new LogginigBuilder(Services);
}
public WebApplication Build()
{
// 将ConfigurationManager的配置转移到\_hostBuilder
\_hostBuilder.ConfigureAppConfiguration(builder =>
{
builder.AddConfiguration(Configuration);
foreach (var kv in ((IConfigurationBuilder)Configuration).Properties)
{
builder.Properties[kv.Key] = kv.Value;
}
});
// 将添加的服务注册转移到\_hostBuilder
\_hostBuilder.ConfigureServices((\_, services) =>
{
foreach (var service in Services)
{
services.Add(service);
}
});
// 将应用到Host属性上的设置转移到\_hostBuilder
Host.Apply(\_hostBuilder);
// 利用\_hostBuilder构建的IHost对象创建WebApplication
return \_application = new WebApplication(\_hostBuilder.Build());
}
}接下来BootstrapHostBuilder的ConfigureHostConfiguration方法被调用，我们利用它将提供的WebApplicationOptions配置选项转移到BootstrapHostBuilder针对宿主的配置上。针对IHostBuilder初始化设置应用到BootstrapHostBuilder对象上之后，我们调用其Apply方法将这些设置分别转移到承载服务注册和配置的IServiceCollection和ConfigurationManager对象，以及封装的HostBuilder对象上。Apply方法利用输出参数提供了HostBuilderContext上下文，我们进一步从中提取出WebHostBuilderContext上下文（GenericWebHostBuilder会将构建的WebHostBuilderContext上下文置于HostBuilderContext对象的属性字典中）。我们利用这个上下文将ConfigureHostBuilder和ConfigureWebHostBuilder对象创建出来，并作为Host和WebHost属性。用于对日志做进一步设置的Logging属性也在这里被初始化，返回的LoggingBuilder对象仅仅是对IServiceCollection对象的简单封装而已。
构建WebApplication对象的Build方法分别调用ConfigureAppConfiguration和ConfigureServices方法将ConfigurationManager和IServiceCollection对象承载的配置和服务注册转移到HostBuilder对象上。它接下来提取出Host属性返回的ConfigureHostBuilder对象，并调用其Apply方法将应用在该对象上针对依赖注入容器的设置转移到HostBuilder对象上。至此所有的设置全部转移到了HostBuilder对象上，我们调用其Build方法构建出对应的IHost对象后，最后利用后者将代码承载应用的WebApplication对象构建出来。我们将这个对象赋值到_application字段上，前面调用ConfigureWebHostDefaults扩展方法提供的委托会将它的BuildRequestDelegate方法构建的中间件管道作为请求处理器。
四、 工厂方法
代表承载应用的WebApplication对象由WebApplicationBuilder构建的，但是我们一般不会通过调用构造函数的方式来创建WebApplicationBuilder对象，这有违“面向接口”编程的原则，所以我们都会使用WebApplication类型提供的静态工厂方法来创建它。WebApplication除了提供了三个用于创建WebApplicationBuilder的CreateBuilder方法重载，还提供了一个直接创建WebApplication对象的Create方法。
public sealed class WebApplication
{
public static WebApplicationBuilder CreateBuilder() => new WebApplicationBuilder(new WebApplicationOptions());
public static WebApplicationBuilder CreateBuilder(string[] args)
{
var options = new WebApplicationOptions();
options.Args = args;
return new WebApplicationBuilder(options);
}
public static WebApplicationBuilder CreateBuilder(WebApplicationOptions options) => new WebApplicationBuilder(options, null);
public static WebApplication Create(string[]? args = null)
{
var options = new WebApplicationOptions();
options.Args = args;
return new WebApplicationBuilder(options).Build();
}
}本节内容通过针对WebApplication和WebApplicationBuilder这两个类型的实现模拟来讲解Minimal API的实现原理。一方面为了让讲解更加清晰，另一方面也出于篇幅的限制，不得不省去很多细枝末节的内容，但是设计思想和实现原理别无二致。上面提供的源代码也不是伪代码，如下所示的就是在“模拟的Minimal API”构建的ASP.NET Core应用，它是可以正常运行的。如果读者朋友们对真实的实现感兴趣，可以将它作为一个“向导”去探寻“真实的Minimal API”。
var app = **App**.WebApplication.Create();
app.Run(httpContext => httpContext.Response.WriteAsync("Hello World!"));
app.Run();
转载请注明：xuhss » ASP.NET Core 6 Minimal API的模拟实现