.NET Core 3.0之深入源码理解Configuration(一)

原创
2019/06/21 08:00
阅读数 0

Configuration总体介绍

微软在.NET Core里设计出了全新的配置体系,并以非常灵活、可扩展的方式实现。从其源码来看,其运行机制大致是,根据其Source,创建一个Builder实例,并会向其添加Provider,在我们使用配置信息的时候,会从内存中获取相应的Provider实例。

.NET Core采用了统一的调用方式来加载不同类型的配置信息,并通过统一的抽象接口IConfigurationSource对配置源进行管理,这也是刚刚所说的灵活。而其扩展性就是我们可以自己自定义新的Provider实例,而不会改变其原来的调用方式。接下来的文章将会基于Consul,扩展一个新的Provider实例。

在ASP.NET Core 中,我们的应用配置是基于IConfigurationProvider的键值对。我们先看一下思维导图:

基于上图,我们可以看到主要有键值对有多种,分别是:

 环境变量

命令行参数

各种形式的配置文件

内存对象

用户自定义扩展源 

核心对象

在介绍.NET Core配置功能之前,先简要说明一下Microsoft.Extensions.Configuration.Abstractions,该组件抽象了.NET Core的配置功能,并对自定义扩展制定了新的标准。以下介绍的四个核心对象全部来自于该组件。

IConfiguration

该接口表示一组键/值应用程序配置属性,应用程序使用配置时的入口对象,.NET Core对其有多种扩展,其派生类包括位于统一类库的IConfigurationSection,以及Microsoft.Extensions.Configuration类库中的ConfigurationRoot、ConfigurationSection、IConfigurationRoot。我们可以通过DI获取IConfiguration实例。

它主要有以下三个方法:

  • GetChildren():获取直接子配置子节

  • GetReloadToken():返回一个IChangeToken,可用于确定何时重新加载配置

  • GetSection(String):获取指定键的子节点

我们来看一下源码:

   1:  /// <summary>
   2:      /// Represents a set of key/value application configuration properties.
   3:      /// </summary>
   4:      public interface IConfiguration
   5:      {
   6:          /// <summary>
   7:          /// Gets or sets a configuration value.
   8:          /// </summary>
   9:          /// <param name="key">The configuration key.</param>
  10:          /// <returns>The configuration value.</returns>
  11:          string this[string key] { get; set; }
  12:   
  13:          /// <summary>
  14:          /// Gets a configuration sub-section with the specified key.
  15:          /// </summary>
  16:          /// <param name="key">The key of the configuration section.</param>
  17:          /// <returns>The <see cref="IConfigurationSection"/>.</returns>
  18:          /// <remarks>
  19:          ///     This method will never return <c>null</c>. If no matching sub-section is found with the specified key,
  20:          ///     an empty <see cref="IConfigurationSection"/> will be returned.
  21:          /// </remarks>
  22:          IConfigurationSection GetSection(string key);
  23:   
  24:          /// <summary>
  25:          /// Gets the immediate descendant configuration sub-sections.
  26:          /// </summary>
  27:          /// <returns>The configuration sub-sections.</returns>
  28:          IEnumerable<IConfigurationSection> GetChildren();
  29:   
  30:          /// <summary>
  31:          /// Returns a <see cref="IChangeToken"/> that can be used to observe when this configuration is reloaded.
  32:          /// </summary>
  33:          /// <returns>A <see cref="IChangeToken"/>.</returns>
  34:          IChangeToken GetReloadToken();
  35:      }

通常我们要求配置文件要有足够的灵活性,尤其是我们所扩展的配置信息存放在了其他服务器,当修改的时候我们很需要一套监控功能,以及时灵活的应对配置信息的修改。现在.NET Core为我们提供了这样一个功能,我们只需要自定义少量代码即可完成配置信息的同步。这个方法就是GetReloadToken(),其返回值是IChangeToken。此处对配置信息的同步只做一个引子,后面的文章会详细说明。

由于ConfigurationRoot、ConfigurationSection聚集于IConfiguration接口,此处也对这两个类进行讨论,方便我们对.NET Core的配置功能有个更加形象的印象。这两个接口,本质上就是.NET Core关于配置信息的读取方式。

XML是使用比较广泛的一种数据结构,我们在配置XML时,一般会使用根节点、父节点、子节点之类的术语,此处也一样。

ConfigurationRoot是配置的根节点,也实现了IConfigurationRoot,此接口只有一个方法,其主要功能就是实现对配置信息的重新加载,另外还包括一个IConfigurationProvider类型的集合属性。其源码如下

   1:  /// <summary>
   2:  /// Represents the root of an <see cref="IConfiguration"/> hierarchy.
   3:  /// </summary>
   4:  public interface IConfigurationRoot : IConfiguration
   5:  {
   6:      /// <summary>
   7:      /// Force the configuration values to be reloaded from the underlying <see cref="IConfigurationProvider"/>s.
   8:      /// </summary>
   9:      void Reload();
  10:   
  11:      /// <summary>
  12:      /// The <see cref="IConfigurationProvider"/>s for this configuration.
  13:      /// </summary>
  14:      IEnumerable<IConfigurationProvider> Providers { get; }
  15:  }

下面是ConfigurationRoot关于Reload()方法的实现

   1:  /// <summary>
   2:  /// Force the configuration values to be reloaded from the underlying sources.
   3:  /// </summary>
   4:  public void Reload()
   5:  {
   6:      foreach (var provider in _providers)
   7:      {
   8:          provider.Load();
   9:      }
  10:   
  11:      RaiseChanged();
  12:  }

通过源码我们知道,如果调用了Reload()方法,所有类型的Provider都会重新加载。

前面有ConfigurationRoot表示配置的根节点,那么ConfigurationSection则表示非跟节点,毕竟父节点、子节点都是相对,所以此处使用非根节点。ConfigurationSection继承于IConfigurationSection,该接口只有三个只读属性,分别表示配置信息的Key、Value以及路径信息,需要指出的是,此处的路径信息主要指从根节点到当前节点的路径,以表示当前节点的位置,类似于A:B:C可以表示节点C的位置,其中A、B、C都是ConfigurationSection的Key。以下是ConfigurationSection的源码

   1:  /// <summary>
   2:  /// Represents a section of application configuration values.
   3:  /// </summary>
   4:  public interface IConfigurationSection : IConfiguration
   5:  {
   6:      /// <summary>
   7:      /// Gets the key this section occupies in its parent.
   8:      /// </summary>
   9:      string Key { get; }
  10:   
  11:      /// <summary>
  12:      /// Gets the full path to this section within the <see cref="IConfiguration"/>.
  13:      /// </summary>
  14:      string Path { get; }
  15:   
  16:      /// <summary>
  17:      /// Gets or sets the section value.
  18:      /// </summary>
  19:      string Value { get; set; }
  20:  }

IConfigurationBuilder

该接口主要用于创建IConfigurationProvider,其派生类包括Microsoft.Extensions.Configuration.ConfigurationBuilder。其成员包括

两个只读属性:

  • Properties:获取可用于在IConfigurationBuilder之间共享数据的键/值集合

  • Sources:该属性用于缓存不同的配置源,以用于相对应的Provider的创建

两个方法:

  • Add(IConfigurationSource source):新增IConfigurationSource,并添加到属性中Sources中

  • Build():该方法遍历Sources属性,并调用IConfigurationSource的Build()方法,通过获取Provider集合,最终创建IConfigurationRoot对象

ConfigurationBuilder源码如下

   1:  /// <summary>
   2:      /// Used to build key/value based configuration settings for use in an application.
   3:      /// </summary>
   4:      public class ConfigurationBuilder : IConfigurationBuilder
   5:      {
   6:          /// <summary>
   7:          /// Returns the sources used to obtain configuration values.
   8:          /// </summary>
   9:          public IList<IConfigurationSource> Sources { get; } = new List<IConfigurationSource>();
  10:   
  11:          /// <summary>
  12:          /// Gets a key/value collection that can be used to share data between the <see cref="IConfigurationBuilder"/>
  13:          /// and the registered <see cref="IConfigurationProvider"/>s.
  14:          /// </summary>
  15:          public IDictionary<string, object> Properties { get; } = new Dictionary<string, object>();
  16:   
  17:          /// <summary>
  18:          /// Adds a new configuration source.
  19:          /// </summary>
  20:          /// <param name="source">The configuration source to add.</param>
  21:          /// <returns>The same <see cref="IConfigurationBuilder"/>.</returns>
  22:          public IConfigurationBuilder Add(IConfigurationSource source)
  23:          {
  24:              if (source == null)
  25:              {
  26:                  throw new ArgumentNullException(nameof(source));
  27:              }
  28:   
  29:              Sources.Add(source);
  30:              return this;
  31:          }
  32:   
  33:          /// <summary>
  34:          /// Builds an <see cref="IConfiguration"/> with keys and values from the set of providers registered in
  35:          /// <see cref="Sources"/>.
  36:          /// </summary>
  37:          /// <returns>An <see cref="IConfigurationRoot"/> with keys and values from the registered providers.</returns>
  38:          public IConfigurationRoot Build()
  39:          {
  40:              var providers = new List<IConfigurationProvider>();
  41:              foreach (var source in Sources)
  42:              {
  43:                  var provider = source.Build(this);
  44:                  providers.Add(provider);
  45:              }
  46:              return new ConfigurationRoot(providers);
  47:          }
  48:      }

此处令人感慨颇多,我们最终调用 ConfigurationRoot 的构造函数,究其原因是Provider提供了统一的数据访问方式,不管是基于何种类型的Provider,我们都可以调用其Load()方法加载配置项。此外,IConfigurationBuilder本身有很多的扩展方法来注册数据源,比如AddJsonFile()扩展方法。我们来看一下,我们常见的写法,

   1:  var builder = new ConfigurationBuilder()
   2:   
   3:              .SetBasePath(env.ContentRootPath)
   4:   
   5:              .AddJsonFile("appsettings1.json", false, true)
   6:   
   7:              .AddJsonFile("appsettings2.json", false, true);
   8:   
   9:  Configuration = builder.Build();

IConfigurationSource

该接口表示应用程序配置的键值对。其派生类包括Microsoft.Extensions.Configuration.ChainedConfigurationSource、Microsoft.Extensions.Configuration.Memory.MemoryConfigurationSource。另外该派生类还会在文件类配置场景下依赖Microsoft.Extensions.Configuration.FileExtensions组件。

它是所有配置源的抽象表示,包括JSON、XML、INI、环境变量等等。通过上文我们也知道了,IConfigurationBuilder会注册多个IConfigurationSource实例。它只有一个方法,就是Build()方法,并返回IConfigurationProvider,由此可见,IConfigurationProvider的创建依赖于IConfigurationSource,这也是一一对应的关系。所有不同的源最终都会转化成统一的键值对表示。

以下为

   1:  /// <summary>
   2:  /// Represents a source of configuration key/values for an application.
   3:  /// </summary>
   4:  public interface IConfigurationSource
   5:  {
   6:      /// <summary>
   7:      /// Builds the <see cref="IConfigurationProvider"/> for this source.
   8:      /// </summary>
   9:      /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>
  10:      /// <returns>An <see cref="IConfigurationProvider"/></returns>
  11:      IConfigurationProvider Build(IConfigurationBuilder builder);
  12:  }

以下是MemoryConfigurationSource的源码

   1:  /// <summary>
   2:  /// Represents in-memory data as an <see cref="IConfigurationSource"/>.
   3:  /// </summary>
   4:  public class MemoryConfigurationSource : IConfigurationSource
   5:  {
   6:      /// <summary>
   7:      /// The initial key value configuration pairs.
   8:      /// </summary>
   9:      public IEnumerable<KeyValuePair<string, string>> InitialData { get; set; }
  10:   
  11:      /// <summary>
  12:      /// Builds the <see cref="MemoryConfigurationProvider"/> for this source.
  13:      /// </summary>
  14:      /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>
  15:      /// <returns>A <see cref="MemoryConfigurationProvider"/></returns>
  16:      public IConfigurationProvider Build(IConfigurationBuilder builder)
  17:      {
  18:          return new MemoryConfigurationProvider(this);
  19:      }
  20:  }

IConfigurationProvider

通过上文的介绍,我们可以知道IConfigurationProvider是统一的对外接口,对用户提供配置的查询、重新加载等功能。其派生类包括Microsoft.Extensions.Configuration.ConfigurationProvider、Microsoft.Extensions.Configuration.ChainedConfigurationProvider、Microsoft.Extensions.Configuration.Memory.MemoryConfigurationProvider。另外该派生类还会在文件类配置场景下依赖Microsoft.Extensions.Configuration.FileExtensions组件。

以下是Microsoft.Extensions.Configuration.ConfigurationProvider的源码:

   1:  /// <summary>
   2:  /// Base helper class for implementing an <see cref="IConfigurationProvider"/>
   3:  /// </summary>
   4:  public abstract class ConfigurationProvider : IConfigurationProvider
   5:  {
   6:      private ConfigurationReloadToken _reloadToken = new ConfigurationReloadToken();
   7:   
   8:      /// <summary>
   9:      /// Initializes a new <see cref="IConfigurationProvider"/>
  10:      /// </summary>
  11:      protected ConfigurationProvider()
  12:      {
  13:          Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
  14:      }
  15:   
  16:      /// <summary>
  17:      /// The configuration key value pairs for this provider.
  18:      /// </summary>
  19:      protected IDictionary<string, string> Data { get; set; }
  20:   
  21:      /// <summary>
  22:      /// Attempts to find a value with the given key, returns true if one is found, false otherwise.
  23:      /// </summary>
  24:      /// <param name="key">The key to lookup.</param>
  25:      /// <param name="value">The value found at key if one is found.</param>
  26:      /// <returns>True if key has a value, false otherwise.</returns>
  27:      public virtual bool TryGet(string key, out string value)
  28:          => Data.TryGetValue(key, out value);
  29:   
  30:      /// <summary>
  31:      /// Sets a value for a given key.
  32:      /// </summary>
  33:      /// <param name="key">The configuration key to set.</param>
  34:      /// <param name="value">The value to set.</param>
  35:      public virtual void Set(string key, string value)
  36:          => Data[key] = value;
  37:   
  38:      /// <summary>
  39:      /// Loads (or reloads) the data for this provider.
  40:      /// </summary>
  41:      public virtual void Load()
  42:      { }
  43:  
  44:      /// <summary>
  45:      /// Returns the list of keys that this provider has.
  46:      /// </summary>
  47:      /// <param name="earlierKeys">The earlier keys that other providers contain.</param>
  48:      /// <param name="parentPath">The path for the parent IConfiguration.</param>
  49:      /// <returns>The list of keys for this provider.</returns>
  50:      public virtual IEnumerable<string> GetChildKeys(
  51:          IEnumerable<string> earlierKeys,
  52:          string parentPath)
  53:      {
  54:          var prefix = parentPath == null ? string.Empty : parentPath + ConfigurationPath.KeyDelimiter;
  55:   
  56:          return Data
  57:              .Where(kv => kv.Key.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
  58:              .Select(kv => Segment(kv.Key, prefix.Length))
  59:              .Concat(earlierKeys)
  60:              .OrderBy(k => k, ConfigurationKeyComparer.Instance);
  61:      }
  62:   
  63:      private static string Segment(string key, int prefixLength)
  64:      {
  65:          var indexOf = key.IndexOf(ConfigurationPath.KeyDelimiter, prefixLength, StringComparison.OrdinalIgnoreCase);
  66:          return indexOf < 0 ? key.Substring(prefixLength) : key.Substring(prefixLength, indexOf - prefixLength);
  67:      }
  68:   
  69:      /// <summary>
  70:      /// Returns a <see cref="IChangeToken"/> that can be used to listen when this provider is reloaded.
  71:      /// </summary>
  72:      /// <returns></returns>
  73:      public IChangeToken GetReloadToken()
  74:      {
  75:          return _reloadToken;
  76:      }
  77:   
  78:      /// <summary>
  79:      /// Triggers the reload change token and creates a new one.
  80:      /// </summary>
  81:      protected void OnReload()
  82:      {
  83:          var previousToken = Interlocked.Exchange(ref _reloadToken, new ConfigurationReloadToken());
  84:          previousToken.OnReload();
  85:      }
  86:   
  87:      /// <summary>
  88:      /// Generates a string representing this provider name and relevant details.
  89:      /// </summary>
  90:      /// <returns> The configuration name. </returns>
  91:      public override string ToString() => $"{GetType().Name}";
  92:  }

通过源码,我们可以知道ConfigurationProvider以字典类型缓存了多个Provider对象,有需要的时候,从内存中获取即可,配置的加载通过Load()方法实现,在ConfigurationRoot里我们介绍了其Reload,并且说明其方法是在循环调用ConfigurationProvider的Load方法,但是此处只提供了一个虚方法,其目的是要交给其他具体的Provider,比如环境变量、JSON、XML等,这些具体的Provider可以从相应的配置源中获取配置信息。所有的子节点KEY通过GetChildKeys方法实现,其重新加载方式通过ConfigurationReloadToken实例完成。

另外需要说明一下,在ConfigurationProvider构造函数里,对字典进行了初始化,并同时设置了字典Key不受大小写限制,这是一个需要注意的细节。

Configuration组件结构

通过查看.NET配置功能的源码,所有依赖均基于Microsoft.Extensions.Configuration.Abstractions,在其上有一层实现,即Microsoft.Extensions.Configuration,其内部也多数是抽象实现,并提供了多个虚方法交给其派生组件,比如环境变量、命令行参数、各种文件型配置等,当然各种文件型配置还要依赖Microsoft.Extensions.Configuration.FileExtensions组件。

以下是.NET Core 3.0预览版里的Configuration各个组件的结构图:


本文分享自微信公众号 - DotNet技术平台(DotNetCore_Moments)。
如有侵权,请联系 support@oschina.cn 删除。
本文参与“OSC源创计划”,欢迎正在阅读的你也加入,一起分享。

展开阅读全文
打赏
0
0 收藏
分享
加载中
更多评论
打赏
0 评论
0 收藏
0
分享
返回顶部
顶部