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.NET Core 3.0之深入源码理解Configuration(二)

程序员文章站 2022-05-21 20:19:18
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 ......
 

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。

.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。

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