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浅析Asp.Net Core框架IConfiguration配置


目录

  • 一、建造者模式(Builder Pattern)
  • 二、核心接口与配置存储本质
  • 三、简易QueryString配置源实现
  • 四、宿主配置与应用配置
  • 五、文件配置源配置更新原理

一、建造者模式

为什么提建造者模式?在阅读.NET Core源码时,时常碰到IHostBuilder,IConfigurationBuilder,ILoggerBuilder等诸如此类带Builder名称的类/接口,起初专研时那是一头愣。知识不够,勤奋来凑,在了解到Builder模式后终于理解,明白这些Builder类是用来构建相对应类的对象,用完即毁别无他用。理解建造者模式,有助于阅读源码时发现核心接口/类,将文件分类,直指堡垒。详细建造者模式可参阅此篇文章:磁悬浮快线

二、核心接口与配置存储本质

在.NET Core中读取配置是通过IConfiguration接口,它存在于Microsoft.Extensions.Configuration.Abstractions项目中,如下图:
浅析Asp.Net Core框架IConfiguration配置

IConfiguration:配置访问接口
IConfigurationProvider:配置提供者接口
IConfigurationSource:配置源接口
IConfigurationRoot:配置根接口,继承IConfiguration,维护着IConfigurationProvider集合及重新加载配置
IConfigurationBuilder:IConfigurationRoot接口实例的构造者接口

1.服务容器中IConfiguration实例注册(ConfigurationRoot)

/// <summary> /// Represents the root of an <see cref="IConfiguration"/> hierarchy. => 配置根路径 /// </summary> public interface IConfigurationRoot : IConfiguration { 	/// <summary> 	/// Force the configuration values to be reloaded from the underlying <see cref="IConfigurationProvider"/>s. => 从配置源重新加载配置 	/// </summary> 	void Reload();  	/// <summary> 	/// The <see cref="IConfigurationProvider"/>s for this configuration. => 依赖的配置源集合 	/// </summary> 	IEnumerable<IConfigurationProvider> Providers { get; } } 

IConfigurationRoot(继承IConfiguration)维护着一个IConfigurationProvider集合列表,也就是我们的配置源。IConfiguration实例的创建并非通过new()方式,而是由IConfigurationBuilder来构建,实现了按需加载配置源,是建造者模式的充分体现。IConfigurationBuilder上的所有操作如:

HostBuilder.ConfigureAppConfiguration((context, builder) => { 	builder.AddCommandLine(args);   // 命令行配置源 	builder.AddEnvironmentVariables();   // 环境配置源 	builder.AddJsonFile("demo.json");   // json文件配置源 	builder.AddInMemoryCollection();  // 内存配置源 	// ... }) 

皆是为IConfigurationRoot.Providers做准备,最后通过Build()方法生成ConfigurationRoot实例注册到服务容器

public class HostBuilder : IHostBuilder { 	private HostBuilderContext _hostBuilderContext; 	// 配置构建 委托 	private List<Action<HostBuilderContext, IConfigurationBuilder>> _configureAppConfigActions = new List<Action<HostBuilderContext, IConfigurationBuilder>>(); 	private IConfiguration _appConfiguration; 	private void BuildAppConfiguration() 	{ 		IConfigurationBuilder configBuilder = new ConfigurationBuilder();  		foreach (Action<HostBuilderContext, IConfigurationBuilder> buildAction in _configureAppConfigActions) 		{ 			buildAction(_hostBuilderContext, configBuilder); 		} 		_appConfiguration = configBuilder.Build(); // 调用Build()创建IConfiguration 实例 ConfigurationRoot 		_hostBuilderContext.Configuration = _appConfiguration; 	} 	private void CreateServiceProvider() 	{ 		var services = new ServiceCollection(); 		// register configuration as factory to make it dispose with the service provider 		services.AddSingleton(_ => _appConfiguration);  // 注册 IConfiguration - 单例 	} } 

2.IConfiguration/IConfigurationSection读取配置与配置储存本质
程序中我们会通过如下方式获取配置值(当然还有绑定IOptions)

IConfiguration[“key”]
IConfiguration.GetSection(“key”).Value

而IConfiguration注册的实例是ConfigurationRoot,代码如下,其索引器实现竟是倒序遍历配置源,获取配置值。原来当我们通过IConfiguration获取配置时,其实就是倒序遍历IConfigurationBuilder加载进来的配置源。

public class ConfigurationRoot : IConfigurationRoot, IDisposable { 	private readonly IList<IConfigurationProvider> _providers; 	public IEnumerable<IConfigurationProvider> Providers => _providers; 	public string this[string key] 	{ 		get 		{ 			// 倒序遍历配置源,获取到配置 就返回,这也是配置覆盖的根本原因,后添加的相同配置会覆盖前面的 			for (int i = _providers.Count - 1; i >= 0; i--) 			{ 				IConfigurationProvider provider = _providers[i];  				if (provider.TryGet(key, out string value)) 				{ 					return value; 				} 			}  			return null; 		} 	} } 

那么配置数据是以什么形式存储的呢?在Microsoft.Extensions.Configuration项目中,提供了一个IConfigurationProvider默认实现存储抽象类ConfigurationProvider,部分代码如下

/// <summary> /// Base helper class for implementing an <see cref="IConfigurationProvider"/> /// </summary> public abstract class ConfigurationProvider : IConfigurationProvider { 	protected ConfigurationProvider() 	{ 		Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase); 	}  	/// <summary> 	/// The configuration key value pairs for this provider. 	/// </summary> 	protected IDictionary<string, string> Data { get; set; }  	public virtual bool TryGet(string key, out string value) 		=> Data.TryGetValue(key, out value); 	/// <summary> 	/// 虚方法,供具体配置源重写,加载配置到 Data中 	/// </summary> 	public virtual void Load() { } } 

从上可知,所有加载到程序中的配置源,其本质还是存储在Provider里面一个类型为IDictionary<string, string> Data属性中。由此推论: 当通过IConfiguration获取配置时,就是通过各个Provider的Data读取!

三、简易QueryString配置源实现

要实现自定义的配置源,只需实现IConfigurationProvider,IConfigurationSource两个接口即可,这里通过一个QueryString格式的简易配置来演示。虫洞隧道
浅析Asp.Net Core框架IConfiguration配置
1.queryString.config数据格式如下

server=localhost&port=3306&datasource=demo&user=root&password=123456&charset=utf8mb4

2.实现IConfigurationSource接口(QueryStringConfiguationSource)

public class QueryStringConfiguationSource : IConfigurationSource { 	public QueryStringConfiguationSource(string path) 	{ 		Path = path; 	} 	/// <summary> 	/// QueryString文件相对路径 	/// </summary> 	public string Path { get; } 	public IConfigurationProvider Build(IConfigurationBuilder builder) 	{ 		return new QueryStringConfigurationProvider(this); 	} } 

3.实现IConfigurationProvider接口(QueryStringConfiguationProvider)

public class QueryStringConfigurationProvider : ConfigurationProvider { 	public QueryStringConfigurationProvider(QueryStringConfiguationSource source) 	{ 		Source = source; 	} 	public QueryStringConfiguationSource Source { get; } 	/// <summary> 	/// 重写Load方法,将自定义的配置解析到 Data 中 	/// </summary> 	public override void Load() 	{ 		// server=localhost&port=3306&datasource=demo&user=root&password=123456&charset=utf8mb4  例子格式 		string queryString = File.ReadAllText(Path.Combine(AppContext.BaseDirectory, Source.Path)); 		string[] arrays = queryString.Split(new[] { "&" }, StringSplitOptions.RemoveEmptyEntries); // & 号分隔  		foreach (var item in arrays) 		{ 			string[] temps = item.Split(new[] { "=" }, StringSplitOptions.RemoveEmptyEntries);  // = 号分隔 			if (temps.Length != 2) continue;  			Data.Add(temps[0], temps[1]); 		} 	} } 

4.IConfigurationBuilder配置源构建

public static class QueryStringConfigurationExtensions { 	/// <summary> 	/// 默认文件名称 queryString.config 	/// </summary> 	/// <param name="builder"></param> 	/// <returns></returns> 	public static IConfigurationBuilder AddQueryStringFile(this IConfigurationBuilder builder) 		=> AddQueryStringFile(builder, "queryString.config"); 	public static IConfigurationBuilder AddQueryStringFile(this IConfigurationBuilder builder, string path) 		=> builder.Add(new QueryStringConfiguationSource(path)); } 

5.Program加载配置源

public static IHostBuilder CreateHostBuilder(string[] args) => 	Host.CreateDefaultBuilder(args) 		.ConfigureAppConfiguration(builder => 		{ 			// 加载QueryString配置源 			builder.AddQueryStringFile();    			//builder.AddQueryStringFile("queryString.config"); 		}) 		.ConfigureWebHostDefaults(webBuilder => 		{ 			webBuilder.UseStartup<Startup>(); 		}); 

至此,自定义QueryString配置源实现完成,便可通过IConfiguration接口获取值,结果如下

IConfiguration[“server”] => localhost
IConfiguration[“datasource”] => demo
IConfiguration[“charset”] => utf8mb4

四、宿主配置与应用配置

.NET Core官方已默认提供了:环境变量、命令行参数,Json、Ini等配置源,不过适用场景却应有不同。不妨可分为两类:一类是宿主配置源,一类是应用配置源
1.宿主配置源
宿主配置源:供IHost宿主启动时使用的配置源。环境变量、命令行参数就可归为这类,以IHostEnvironment为例

/// <summary> /// 提供运行环境相关信息 /// </summary> public interface IHostEnvironment { 	string EnvironmentName { get; set; } 	string ApplicationName { get; set; } 	string ContentRootPath { get; set; } } 

IHostEnvironment接口提供了当前应用运行环境相关信息,可以通过IsEnvironment()方法判断当前运行环境是Development还是Production、Staging。

public static bool IsEnvironment(this IHostEnvironment hostEnvironment, string environmentName) { 	if (hostEnvironment == null) 	{ 		throw new ArgumentNullException(nameof(hostEnvironment)); 	} 	return string.Equals(hostEnvironment.EnvironmentName, environmentName, StringComparison.OrdinalIgnoreCase); } 

hostEnvironment.EnvironmentName是什么?这就得益于它注册到服务容器时所赋的值:HostBuilder

public class HostBuilder:IHostBuilder { 	private void CreateHostingEnvironment() 	{ 		_hostingEnvironment = new HostingEnvironment() 		{ 			ApplicationName = _hostConfiguration[HostDefaults.ApplicationKey],  // _hostConfiguration 类型是 IConfiguration 			EnvironmentName = _hostConfiguration[HostDefaults.EnvironmentKey] ?? Environments.Production, // 当未配置环境时,默认Production环境,在使用vs开发启动时,lanuchSetting.json 配置了 环境变量:"ASPNETCORE_ENVIRONMENT": "Development" 			ContentRootPath = ResolveContentRootPath(_hostConfiguration[HostDefaults.ContentRootKey], AppContext.BaseDirectory), 		};  		if (string.IsNullOrEmpty(_hostingEnvironment.ApplicationName)) 		{ 			// Note GetEntryAssembly returns null for the net4x console test runner. 			_hostingEnvironment.ApplicationName = Assembly.GetEntryAssembly()?.GetName().Name; 		} 	} } 

由此可见,IHostEnvironment所提供的信息根由仍是从IConfiguration读取,而这些配置正是来自环境变量、命令行参数配置源。
2.应用配置源
应用配置源:供应用业务逻辑使用的配置源。Json、Ini、Xml以及自定义的QueryString等就可归为类。

五、文件配置源配置更新原理

对于文件配置源,.NET Core默认提供了两个抽象类:FileConfigurationSourceFileConfigurationProvider

public abstract class FileConfigurationProvider : ConfigurationProvider, IDisposable { 	private readonly IDisposable _changeTokenRegistration;  	public FileConfigurationProvider(FileConfigurationSource source) 	{ 		if (source == null) 		{ 			throw new ArgumentNullException(nameof(source)); 		} 		Source = source;  		if (Source.ReloadOnChange && Source.FileProvider != null) 		{ 			_changeTokenRegistration = ChangeToken.OnChange(	// 文件改变,重新加载配置 				() => Source.FileProvider.Watch(Source.Path), 				() => 				{ 					Thread.Sleep(Source.ReloadDelay); 					Load(reload: true); 				}); 		} 	}  	/// <summary> 	/// The source settings for this provider. 	/// </summary> 	public FileConfigurationSource Source { get; }   	private void Load(bool reload) 	{ 		IFileInfo file = Source.FileProvider?.GetFileInfo(Source.Path); 		if (file == null || !file.Exists) 		{ 			if (Source.Optional || reload) // Always optional on reload 			{ 				Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);	// Data 被重新创建新的实例赋值了 			} 			else 			{ 				var error = new StringBuilder($"The configuration file '{Source.Path}' was not found and is not optional."); 				if (!string.IsNullOrEmpty(file?.PhysicalPath)) 				{ 					error.Append($" The physical path is '{file.PhysicalPath}'."); 				} 				HandleException(ExceptionDispatchInfo.Capture(new FileNotFoundException(error.ToString()))); 			} 		} 		else 		{ 			// Always create new Data on reload to drop old keys 			if (reload) 			{ 				Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);	// Data 被重新创建新的实例赋值了 			}  			static Stream OpenRead(IFileInfo fileInfo) 			{ 				if (fileInfo.PhysicalPath != null) 				{ 					// The default physical file info assumes asynchronous IO which results in unnecessary overhead 					// especally since the configuration system is synchronous. This uses the same settings 					// and disables async IO. 					return new FileStream( 						fileInfo.PhysicalPath, 						FileMode.Open, 						FileAccess.Read, 						FileShare.ReadWrite, 						bufferSize: 1, 						FileOptions.SequentialScan); 				}  				return fileInfo.CreateReadStream(); 			}  			using Stream stream = OpenRead(file); 			try 			{ 				Load(stream); 			} 			catch (Exception e) 			{ 				HandleException(ExceptionDispatchInfo.Capture(e)); 			} 		} 	}  	public override void Load() 	{ 		Load(reload: false); 	}  	public abstract void Load(Stream stream); } 

所有基于文件配置源(如果要监控配置文件更新,如:appsetting.json)都应实现这个两个抽象类,尽管不懂ChangeToken是个什么东东,只需明白Provider.Data 在文件变更时被重新赋值也未尝不可。

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