.NET Core 3.0之深入源码理解Configuration(二)

原创
2019/06/21 08:00
阅读数 0

文件型配置基本内容

上一篇文章讨论了Configuration的几个核心对象,本文继续讨论Configuration中关于文件型配置的相关内容。相比较而言,文件型配置的使用场景更加广泛,用户自定义配置扩展也可以基于文件型配置进行扩展。如果需要查看上一篇文章,可以点击移步

.NET Core文件型配置中我们提供了三种主要的实现,分别是JSON、XML、INI,请查看下图

由图可知,这三种配置的实现方式是一样的,当然了其他的配置比如命令行配置、环境变量配置等也是大同小异,理解了改配置类型的实现方式,后面我们再扩展基于Consul或者ZK的实现,就非常简单了。

文件型配置的抽象扩展

文件型配置的抽象扩展位于Microsoft.Extensions.Configuration.FileExtensions组件中,该扩展是一个基础实现。不过其命名空间是Microsoft.Extensions.Configuration,而Micros oft.Extensions.Configuration扩建本身又是整个.NET Core Configuration的基础实现。将File扩展独立于外部,体验了.NET Core的模块化设计。

FileConfigurationSource

Configuration.FileExtensions组件中,FileConfigurationSource是继承于IConfigurationSource的一个抽象类,包含了一个IConfigurationProvider类型的抽象方法,如下所示

   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);

该抽象类中还包括了几个比较重要的参数,分别用于配置性行为、文件内容访问以及异常处理。

string Path:文件的路径

bool Optional:标识加载的文件是否是可选的

bool ReloadOnChange:如果文件发生修改,是否重新加载配置源

int ReloadDelay:加载延迟,单位是毫秒,默认是250毫秒

IFileProvider FileProvider:用于获取文件内容

Action<FileLoadExceptionContext> OnLoadException:文件加载异常处理

该类对FileProvider有特殊处理,就是如果没有提供FileProvider实例,则会基于绝对路径,在最近的现有目录中创建物理文件提供程序。源码如下,

   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

该类是继承于ConfigurationProvider的抽象类,是从文件系统加载配置的基类,同时还继承了IDisposable,其抽象方法是Load方法,用于从当前的Provider中以Stream方式加载数据

   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);

该类还重写了ConfigurationProvider的Load方法,并对文件加载中的异常做了处理,Data属性在前文有提到过,此处不再做其他说明。方法源码如下所示:

   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?,通过注释,我们可以知道OnReload()方法可能会在新版中发生变化
  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:  }

另外它还有一个特殊方法,就是参数类型为FileConfigurationSource的构造函数,其主要功能是监控文件,并在FileConfigurationSource.ReloadDelay设置的时间里重新加载文件并返回一个IDisposable类型的值,以下是该构造函数的源码:

   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

该类是一个静态类,其提供了的多个扩展方法,主要基于

  • IConfigurationBuilder

  • IFileProvider

  • Action<FileLoadExceptionContext>

包括主要用于设置或获取IFileProvider对象,前文有介绍过,是存储于字典之中,需要注意的是,在Get的时候如果字典中并不存在IFileProvider对象,则会实例化一个PhysicalFileProvider对象出来,该类位于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:  }

为指定路径的物理文件设置文件型Provider,该方法同样基于PhysicalFileProvider,并返回IConfigurationBuilder对象

   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:  }

以及异常处理,可以看到其异常处理也会存放于字典中,如果字典中找不到,就会返回空,这个地方如果直接使用,需要注意空指针问题。

   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:  }

该类还有两个静态私有变量,指定了文件Provider的Key以及文件加载异常处理Key。

   1:  private static string FileProviderKey = "FileProvider";
   2:  private static string FileLoadExceptionHandlerKey = "FileLoadExceptionHandler";

总结

文件型配置还依赖于.NET Core的其他组件Microsoft.Extensions.FileProviders和Microsoft.Extensions.Primitives。

FileProviders组件提供了文件处理的一般方法,Primitives组件提供了监控机制,同时还包括两个比较重要的结构体StringValues和StringSegment,本文暂时不做讨论,有兴趣的朋友,可以自行查看该组件源码。


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