ASP.NET Core基础1:应用启动流程
先看下ASP.NET Core的启动代码,如下图:
通过以上代码,我们可以初步得出以下结论:
下面结合源码代详细分析下。
宿主构造器:IWebHostBuilder
看下WebHost的静态方法CreateDefaultBuilder的源码。
/// <summary>
/// Initializes a new instance of the <see cref="WebHostBuilder"/> class with pre-configured defaults.
/// </summary>
/// <remarks>
/// The following defaults are applied to the returned <see cref="WebHostBuilder"/>:
/// use Kestrel as the web server and configure it using the application's configuration providers,
/// set the <see cref="IHostingEnvironment.ContentRootPath"/> to the result of <see cref="Directory.GetCurrentDirectory()"/>,
/// load <see cref="IConfiguration"/> from 'appsettings.json' and 'appsettings.[<see cref="IHostingEnvironment.EnvironmentName"/>].json',
/// load <see cref="IConfiguration"/> from User Secrets when <see cref="IHostingEnvironment.EnvironmentName"/> is 'Development' using the entry assembly,
/// load <see cref="IConfiguration"/> from environment variables,
/// load <see cref="IConfiguration"/> from supplied command line args,
/// configure the <see cref="ILoggerFactory"/> to log to the console and debug output,
/// and enable IIS integration.
/// </remarks>
/// <param name="args">The command line args.</param>
/// <returns>The initialized <see cref="IWebHostBuilder"/>.</returns>
public static IWebHostBuilder CreateDefaultBuilder(string[] args)
{
var builder = new WebHostBuilder(); if (string.IsNullOrEmpty(builder.GetSetting(WebHostDefaults.ContentRootKey)))
{
builder.UseContentRoot(Directory.GetCurrentDirectory());
}
if (args != null)
{
builder.UseConfiguration(new ConfigurationBuilder().AddCommandLine(args).Build());
} builder.UseKestrel((builderContext, options) =>
{
options.Configure(builderContext.Configuration.GetSection("Kestrel"));
})
.ConfigureAppConfiguration((hostingContext, config) =>
{
var env = hostingContext.HostingEnvironment; config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
.AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true); if (env.IsDevelopment())
{
var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
if (appAssembly != null)
{
config.AddUserSecrets(appAssembly, optional: true);
}
} config.AddEnvironmentVariables(); if (args != null)
{
config.AddCommandLine(args);
}
})
.ConfigureLogging((hostingContext, logging) =>
{
logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
logging.AddConsole();
logging.AddDebug();
logging.AddEventSourceLogger();
})
.ConfigureServices((hostingContext, services) =>
{
// Fallback
services.PostConfigure<HostFilteringOptions>(options =>
{
if (options.AllowedHosts == null || options.AllowedHosts.Count == 0)
{
// "AllowedHosts": "localhost;127.0.0.1;[::1]"
var hosts = hostingContext.Configuration["AllowedHosts"]?.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries);
// Fall back to "*" to disable.
options.AllowedHosts = (hosts?.Length > 0 ? hosts : new[] { "*" });
}
});
// Change notification
services.AddSingleton<IOptionsChangeTokenSource<HostFilteringOptions>>(
new ConfigurationChangeTokenSource<HostFilteringOptions>(hostingContext.Configuration)); services.AddTransient<IStartupFilter, HostFilteringStartupFilter>();
})
.UseIIS()
.UseIISIntegration()
.UseDefaultServiceProvider((context, options) =>
{
options.ValidateScopes = context.HostingEnvironment.IsDevelopment();
}); return builder;
}
1,UseContentRoot
指定Web host使用的内容根目录,比如Views。默认为当前应用程序根目录。
2,UseConfiguration
//todo
3,UseKestrel
使用Kestrel作为默认的Web Server。
4,ConfigureAppConfiguration
设置当前应用程序配置。主要是读取 appsettings.json配置文件、开发环境中配置的UserSecrets、添加环境变量和命令行参数 。
5,ConfigureLogging
读取配置文件中的Logging节点,配置日志系统。
6,ConfigureServices
//todo
7,UseIIS
使用IIS中间件。
8,UseIISIntegration
使用IISIntegration中间件。
9,UseDefaultServiceProvider
设置默认的依赖注入容器。
宿主:IWebHost
在ASP.Net Core中定义了IWebHost用来表示Web应用的宿主,并提供了一个默认实现WebHost。宿主的创建是通过调用IWebHostBuilder的Build()方法来完成的。看下源码:
/// <summary>
/// Builds the required services and an <see cref="IWebHost"/> which hosts a web application.
/// </summary>
public IWebHost Build()
{
if (_webHostBuilt)
{
throw new InvalidOperationException(Resources.WebHostBuilder_SingleInstance);
}
_webHostBuilt = true; var hostingServices = BuildCommonServices(out var hostingStartupErrors);
var applicationServices = hostingServices.Clone();
var hostingServiceProvider = GetProviderFromFactory(hostingServices); if (!_options.SuppressStatusMessages)
{
// Warn about deprecated environment variables
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(applicationServices, hostingServiceProvider); var host = new WebHost(
applicationServices,
hostingServiceProvider,
_options,
_config,
hostingStartupErrors);
try
{
host.Initialize(); var logger = host.Services.GetRequiredService<ILogger<WebHost>>(); // Warn about duplicate HostingStartupAssemblies
foreach (var assemblyName in _options.GetFinalHostingStartupAssemblies().GroupBy(a => a, StringComparer.OrdinalIgnoreCase).Where(g => g.Count() > 1))
{
logger.LogWarning($"The assembly {assemblyName} was specified multiple times. Hosting startup assemblies should only be specified once.");
} return host;
}
catch
{
// Dispose the host if there's a failure to initialize, this should clean up
// will dispose services that were constructed until the exception was thrown
host.Dispose();
throw;
} IServiceProvider GetProviderFromFactory(IServiceCollection collection)
{
var provider = collection.BuildServiceProvider();
var factory = provider.GetService<IServiceProviderFactory<IServiceCollection>>(); if (factory != null && !(factory is DefaultServiceProviderFactory))
{
using (provider)
{
return factory.CreateServiceProvider(factory.CreateBuilder(collection));
}
} return provider;
}
}
启动类:Startup
每个ASP.NET Core程序都需要一个启动类,约定命名为:Startup。Startup用于配置服务和配置HTTP请求管道。
namespace HelloNETCoreWebApi
{
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
} public IConfiguration Configuration { get; } // This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
} // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
// The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
app.UseHsts();
} app.UseHttpsRedirection();
app.UseMvc();
}
}
}
Startup必须包含Configure方法, 并选择包含ConfigureServices方法,这两个方法在应用程序启动时调用,该类还可以包含这些方法的特定环境的版本,并且ConfigureServices方法(如果存在)在Configure方法之前调用。
Configure方法主要是配置ASP.NET Core的中间件,相当于我们在ASP.NET中所说的管道,ConfigureServices方法主要是配置依赖注入(DI)。
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