.NET Core 3.0之深刻源碼理解Configuration(二)

 

文件型配置基本內容

上一篇文章討論了Configuration的幾個核心對象，本文繼續討論Configuration中關於文件型配置的相關內容。相比較而言，文件型配置的使用場景更加普遍，用戶自定義配置擴展也能夠基於文件型配置進行擴展。若是須要查看上一篇文章，能夠點擊移步。

.NET Core文件型配置中咱們提供了三種主要的實現，分別是JSON、XML、INI，請查看下圖

由圖可知，這三種配置的實現方式是同樣的，固然了其餘的配置好比命令行配置、環境變量配置等也是大同小異，理解了改配置類型的實現方式，後面咱們再擴展基於Consul或者ZK的實現，就很是簡單了。

文件型配置的抽象擴展

文件型配置的抽象擴展位於Microsoft.Extensions.Configuration.FileExtensions組件中，該擴展是一個基礎實現。不過其命名空間是Microsoft.Extensions.Configuration，而Micros oft.Extensions.Configuration擴建自己又是整個.NET Core Configuration的基礎實現。將File擴展獨立於外部，體驗了.NET Core的模塊化設計。

FileConfigurationSource

Configuration.FileExtensions組件中，FileConfigurationSource是繼承於IConfigurationSource的一個抽象類，包含了一個IConfigurationProvider類型的抽象方法，以下所示

   1:  /// <summary>

   2:  /// Builds the <see cref="IConfigurationProvider"/> for this source.

   3:  /// </summary>

   4:  /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>

   5:  /// <returns>A <see cref="IConfigurationProvider"/></returns>

   6:  public abstract IConfigurationProvider Build(IConfigurationBuilder builder);

該抽象類中還包括了幾個比較重要的參數，分別用於配置性行爲、文件內容訪問以及異常處理。

string Path：文件的路徑

bool Optional：標識加載的文件是不是可選的

bool ReloadOnChange：若是文件發生修改，是否從新加載配置源

int ReloadDelay：加載延遲，單位是毫秒，默認是250毫秒

IFileProvider FileProvider：用於獲取文件內容

Action<FileLoadExceptionContext> OnLoadException：文件加載異常處理

該類對FileProvider有特殊處理，就是若是沒有提供FileProvider實例，則會基於絕對路徑，在最近的現有目錄中建立物理文件提供程序。源碼以下，

   1:  /// <summary>

   2:  /// If no file provider has been set, for absolute Path, this will creates a physical file provider 

   3:  /// for the nearest existing directory.

   4:  /// </summary>

   5:  public void ResolveFileProvider()

   6:  {

   7:      if (FileProvider == null && 

   8:          !string.IsNullOrEmpty(Path) &&

   9:          System.IO.Path.IsPathRooted(Path))

  10:      {

  11:      

var directory = System.IO.Path.GetDirectoryName(Path);

  12:          var pathToFile = System.IO.Path.GetFileName(Path);

  13:          while (!string.IsNullOrEmpty(directory) && !Directory.Exists(directory))

  14:          {

  15:              pathToFile = System.IO.Path.Combine(System.IO.Path.GetFileName(directory), pathToFile);

  16:              directory = System.IO.Path.GetDirectoryName(directory);

  17:          }

  18:          if (Directory.Exists(directory))

  19:          {

  20:              FileProvider = new PhysicalFileProvider(directory);

  21:              Path = pathToFile;

  22:          }

  23:      }

  24:  }

FileConfigurationProvider

該類是繼承於ConfigurationProvider的抽象類，是從文件系統加載配置的基類，同時還繼承了IDisposable，其抽象方法是Load方法，用於從當前的Provider中以Stream方式加載數據

   1:  /// <summary>

   2:  /// Loads this provider's data from a stream.

   3:  /// </summary>

   4:  /// <param name="stream">The stream to read.</param>

   5:  public abstract void Load(Stream stream);

該類還重寫了ConfigurationProvider的Load方法，並對文件加載中的異常作了處理，Data屬性在前文有提到過，此處再也不作其餘說明。方法源碼以下所示：

   1:  private void Load(bool reload)

   2:  {

   3:      var file = Source.FileProvider?.GetFileInfo(Source.Path);

   4:      if (file == null || !file.Exists)

   5:      {

   6:          if (Source.Optional || reload) // Always optional on reload

   7:          {

   8:              Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);

   9:          }

  10:          else

  11:          {

  12:              var error = new StringBuilder($"The configuration file '{Source.Path}' was not found and is not optional.");

  13:              if (!string.IsNullOrEmpty(file?.PhysicalPath))

  14:              {

  15:                  error.Append($" The physical path is '{file.PhysicalPath}'.");

  16:              }

  17:              HandleException(new FileNotFoundException(error.ToString()));

  18:          }

  19:      }

  20:      else

  21:      {

  22:          // Always create new Data on reload to drop old keys

  23:          if (reload)

  24:          {

  25:              Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);

  26:          }

  27:          using (var stream = file.CreateReadStream())

  28:          {

  29:              try

  30:              {

  31:                  Load(stream);

  32:              }

  33:              catch (Exception e)

  34:              {

  35:                  HandleException(e);

  36:              }

  37:          }

  38:      }

  39:      // REVIEW: Should we raise this in the base as well / instead?，經過註釋，咱們能夠知道OnReload()方法可能會在新版中發生變化

  40:      OnReload();

  41:  }

  42:   

  43:  /// <summary>

  44:  /// Loads the contents of the file at <see cref="Path"/>.

  45:  /// </summary>

  46:  /// <exception cref="FileNotFoundException">If Optional is <c>false</c> on the source and a

  47:  /// file does not exist at specified Path.</exception>

  48:  public override void Load()

  49:  {

  50:      Load(reload: false);

  51:  }

另外它還有一個特殊方法，就是參數類型爲FileConfigurationSource的構造函數，其主要功能是監控文件，並在FileConfigurationSource.ReloadDelay設置的時間裏從新加載文件並返回一個IDisposable類型的值，如下是該構造函數的源碼：

   1:  /// <summary>

   2:  /// Initializes a new instance with the specified source.

   3:  /// </summary>

   4:  /// <param name="source">The source settings.</param>

   5:  public FileConfigurationProvider(FileConfigurationSource source)

   6:  {

   7:      if (source == null)

   8:      {

   9:          throw new ArgumentNullException(nameof(source));

  10:      }

  11:      Source = source;

  12:   

  13:      if (Source.ReloadOnChange && Source.FileProvider != null)

  14:      {

  15:          _changeTokenRegistration = ChangeToken.OnChange(

  16:              () => Source.FileProvider.Watch(Source.Path),

  17:              () => {

  18:                  Thread.Sleep(Source.ReloadDelay);

  19:                  Load(reload: true);

  20:              });

  21:      }

  22:  }

FileConfigurationExtensions

該類是一個靜態類，其提供了的多個擴展方法，主要基於

• IConfigurationBuilder
• IFileProvider
• Action<FileLoadExceptionContext>

包括主要用於設置或獲取IFileProvider對象，前文有介紹過，是存儲於字典之中，須要注意的是，在Get的時候若是字典中並不存在IFileProvider對象，則會實例化一個PhysicalFileProvider對象出來，該類位於Microsoft.Extensions.FileProviders.PhysicalFileProvider

   1:  /// <summary>

   2:  /// Sets the default <see cref="IFileProvider"/> to be used for file-based providers.

   3:  /// </summary>

   4:  /// <param name="builder">The <see cref="IConfigurationBuilder"/> to add to.</param>

   5:  /// <param name="fileProvider">The default file provider instance.</param>

   6:  /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>

   7:  public static IConfigurationBuilder SetFileProvider(this IConfigurationBuilder builder, IFileProvider fileProvider)

   8:  {

   9:      if (builder == null)

  10:      {

  11:          throw new ArgumentNullException(nameof(builder));

  12:      }

  13:   

  14:      builder.Properties[FileProviderKey] = fileProvider ?? throw new ArgumentNullException(nameof(fileProvider));

  15:      return builder;

  16:  }

  17:   

  18:  /// <summary>

  19:  /// Gets the default <see cref="IFileProvider"/> to be used for file-based providers.

  20:  /// </summary>

  21:  /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>

  22:  /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>

  23:  public static IFileProvider GetFileProvider(this IConfigurationBuilder builder)

  24:  {

  25:      if (builder == null)

  26:      {

  27:          throw new ArgumentNullException(nameof(builder));

  28:      }

  29:   

  30:      if (builder.Properties.TryGetValue(FileProviderKey, out object provider))

  31:      {

  32:          return provider as IFileProvider;

  33:      }

  34:   

  35:      return new PhysicalFileProvider(AppContext.BaseDirectory ?? string.Empty);

  36:  }

爲指定路徑的物理文件設置文件型Provider，該方法一樣基於PhysicalFileProvider，並返回IConfigurationBuilder對象

   1:  /// <summary>

   2:  /// Sets the FileProvider for file-based providers to a PhysicalFileProvider with the base path.

   3:  /// </summary>

   4:  /// <param name="builder">The <see cref="IConfigurationBuilder"/> to add to.</param>

   5:  /// <param name="basePath">The absolute path of file-based providers.</param>

   6:  /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>

   7:  public static IConfigurationBuilder SetBasePath(this IConfigurationBuilder builder, string basePath)

   8:  {

   9:      if (builder == null)

  10:      {

  11:          throw new ArgumentNullException(nameof(builder));

  12:      }

  13:   

  14:      if (basePath == null)

  15:      {

  16:          throw new ArgumentNullException(nameof(basePath));

  17:      }

  18:   

  19:      return builder.SetFileProvider(new PhysicalFileProvider(basePath));

  20:  }

以及異常處理，能夠看到其異常處理也會存放於字典中，若是字典中找不到，就會返回空，這個地方若是直接使用，須要注意空指針問題。

   1:  /// <summary>

   2:  /// Sets a default action to be invoked for file-based providers when an error occurs.

   3:  /// </summary>

   4:  /// <param name="builder">The <see cref="IConfigurationBuilder"/> to add to.</param>

   5:  /// <param name="handler">The Action to be invoked on a file load exception.</param>

   6:  /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>

   7:  public static IConfigurationBuilder SetFileLoadExceptionHandler(this IConfigurationBuilder builder, Action<FileLoadExceptionContext> handler)

   8:  {

   9:      if (builder == null)

  10:      {

  11:          throw new ArgumentNullException(nameof(builder));

  12:      }

  13:   

  14:      builder.Properties[FileLoadExceptionHandlerKey] = handler;

  15:      return builder;

  16:  }

  17:   

  18:  /// <summary>

  19:  /// Gets the default <see cref="IFileProvider"/> to be used for file-based providers.

  20:  /// </summary>

  21:  /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>

  22:  /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>

  23:  public static Action<FileLoadExceptionContext> GetFileLoadExceptionHandler(this IConfigurationBuilder builder)

  24:  {

  25:      if (builder == null)

  26:      {

  27:          throw new ArgumentNullException(nameof(builder));

  28:      }

  29:   

  30:      if (builder.Properties.TryGetValue(FileLoadExceptionHandlerKey, out object handler))

  31:      {

  32:          return handler as Action<FileLoadExceptionContext>;

  33:      }

  34:      

return null;

  35:  }

該類還有兩個靜態私有變量，指定了文件Provider的Key以及文件加載異常處理Key。

   1:  private static string FileProviderKey = "FileProvider";

   2:  private static string FileLoadExceptionHandlerKey = "FileLoadExceptionHandler";

總結

文件型配置還依賴於.NET Core的其餘組件Microsoft.Extensions.FileProviders和Microsoft.Extensions.Primitives。

FileProviders組件提供了文件處理的通常方法，Primitives組件提供了監控機制，同時還包括兩個比較重要的結構體StringValues和StringSegment，本文暫時不作討論，有興趣的朋友，能夠自行查看該組件源碼。