关于Asp.net core配置信息读取的源码分析梳理

概述

我们都知道asp.net core配置信息的读取离不开IConfigurationSource和IConfigurationProvider这两个类，ConfigurationSource可以提供一个ConfigurationProvider，然后去读取信息。究竟他们之间有着怎样的千丝万缕，我们一起来看看源码。

首先我们来建立一个.net core控制台项目，来运行以下代码：

 class Program
    {
        static void Main(string[] args)
        {
            ConfigurationBuilder configBuilder = new ConfigurationBuilder();
            configBuilder.SetBasePath(Directory.GetCurrentDirectory())   
                   .AddJsonFile("appsettings.json");
            var configFile = configBuilder.Build();

            Console.ReadKey();
        }
    }

短短几行 代码看起来很简单，就是用来读取appsettings.json文件中的配置信息。然而我们今天想搞清楚其背后运行的原理，要花点时间。

首先、我们根据代码ConfigurationBuilder configBuilder = new ConfigurationBuilder();知道创建了一个configBuilder对象；

其次，configBuilder.SetBasePath(Directory.GetCurrentDirectory()) 该代码的调用我们也能大概见名知义，获取当前的目录；

接下来，重点来了，configBuilder.AddJsonFile("appsettings.json")的实现究竟是怎样的？我们来看下源码的实现：

f12进去后源码如下：

/// 
Extension methods for adding .
  public static class JsonConfigurationExtensions
  {
    /// 
Adds the JSON configuration provider at  to .
    /// The  to add to.
    /// Path relative to the base path stored in
    ///  of .
    /// The .
    public static IConfigurationBuilder AddJsonFile(
      this IConfigurationBuilder builder,
      string path)
    {
      return builder.AddJsonFile((IFileProvider) null, path, false, false);
    }
}

紧接着f12再看实现的源码，依然在JsonConfigurationExtensions这个扩展类里面：

    public static IConfigurationBuilder AddJsonFile(
      this IConfigurationBuilder builder,
      IFileProvider provider,
      string path,
      bool optional,
      bool reloadOnChange)
    {
      if (builder == null)
        throw new ArgumentNullException(nameof (builder));
      if (string.IsNullOrEmpty(path))
        throw new ArgumentException(SR.Error_InvalidFilePath, nameof (path));
      return builder.AddJsonFile((Action) (s =>
      {
        s.FileProvider = provider;
        s.Path = path;
        s.Optional = optional;
        s.ReloadOnChange = reloadOnChange;
        s.ResolveFileProvider();
      }));
    }

这时候有没有发现builder.AddJsonFile((Action)这个方法里面出现了一个关键的信息点：JsonConfigurationSource (JsonConfigurationSource 继承抽象类FileConfigurationSource,而FileConfigurationSource：IConfigurationSource) 。 关系如下图：

 看完上面这个关系图后，我们紧接着上面builder.AddJsonFile()的实现源码继续f12往下,源码如下：

  
//该代码依然在JsonConfigurationExtensions类里面
public static IConfigurationBuilder AddJsonFile(
      this IConfigurationBuilder builder,
      Action configureSource)
    {
      return ConfigurationExtensions.Add(builder, (Action) configureSource);
    }

我们看到上面的扩展方法实现是ConfigurationExtensions.Add...,再往下看实现：

public static class ConfigurationExtensions
  {
    /// 
Adds a new configuration source.
    /// The  to add to.
    /// Configures the source secrets.
    /// 
    /// The .
    public static IConfigurationBuilder Add(
      this IConfigurationBuilder builder,
      Action configureSource)
      where TSource : IConfigurationSource, new()
    {
      TSource source = new TSource();
      if (configureSource != null)
        configureSource(source);
      return builder.Add((IConfigurationSource) source);
    }
}

到这里我们看到了其实就是IConfigurationBuilder调用了Add方法，添加了一个数据源（JsonConfigurationSource），至于JsonConfigurationSource类里面做了什么，我们看下实现。

  public class JsonConfigurationSource : FileConfigurationSource
  {
    /// 
Builds the  for this source.
    /// The .
    /// A 
    public override IConfigurationProvider Build(IConfigurationBuilder builder)
    {
      this.EnsureDefaults(builder);
      return (IConfigurationProvider) new JsonConfigurationProvider(this);
    }
  }

JsonConfigurationSource类面的Build方法提供了一个JsonConfigurationProvider类，这里再贴下JsonConfigurationProvider类里面的代码：

  /// 
A JSON file based .
  public class JsonConfigurationProvider : FileConfigurationProvider
  {
    /// 
Initializes a new instance with the specified source.
    /// The source settings.
    public JsonConfigurationProvider(JsonConfigurationSource source)
      : base((FileConfigurationSource) source)
    {
    }

    /// 
Loads the JSON data from a stream.
    /// The stream to read.
    public virtual void Load(Stream stream)
    {
      try
      {
        this.set_Data(JsonConfigurationFileParser.Parse(stream));
      }
      catch (JsonException ex)
      {
        throw new FormatException(SR.Error_JSONParseError, (Exception) ex);
      }
    }
  }

关于JsonConfigurationProvider里面的Load就是去读取信息的实现，至于Load的具体实现我们不再深究。我们回到最初的控制台configBuilder.Build()，看看其的实现：

  public class ConfigurationBuilder : IConfigurationBuilder
  {
    /// 
Returns the sources used to obtain configuration values.
    public IList Sources { get; } = (IList) new List();

    /// 
Gets a key/value collection that can be used to share data between the 
    /// and the registered s.
    public IDictionary<string, object> Properties { get; } = (IDictionary<string, object>) new Dictionary<string, object>();

    /// 
Adds a new configuration source.
    /// The configuration source to add.
    /// The same .
    public IConfigurationBuilder Add(IConfigurationSource source)
    {
      if (source == null)
        throw new ArgumentNullException(nameof (source));
      this.Sources.Add(source);
      return (IConfigurationBuilder) this;
    }

    /// 
Builds an  with keys and values from the set of providers registered in
    /// .
    /// An  with keys and values from the registered providers.
    public IConfigurationRoot Build()
    {
      List configurationProviderList = new List();
      foreach (IConfigurationSource source in (IEnumerable) this.Sources)
      {
        IConfigurationProvider configurationProvider = source.Build((IConfigurationBuilder) this);
        configurationProviderList.Add(configurationProvider);
      }
      return (IConfigurationRoot) new ConfigurationRoot((IList) configurationProviderList);
    }
  }

看到这个源码的时候有没有种豁然开朗的感觉，前面我们说到IConfigurationBuilder调用了Add方法添加一个数据源，并没说添加了一个数据源存在了哪里，到底有什么用处，现在在上面ConfigurationBuilder类里面看到存在了Sources 集合里面。然后configBuilder.Build()

去调用的时候遍历数据源（Sources ）集合，紧接着source (IConfigurationSource)调用了Build方法构建了一个configurationProvider对象存到configurationProviderList集合里面，最后在返回一个ConfigurationRoot对象的构造函数里面传递了configurationProviderList集合去执行。

贴上ConfigurationRoot的源码：

  public class ConfigurationRoot : IConfigurationRoot, IConfiguration, IDisposable
  {

    private readonly IList _providers;
    private readonly IList _changeTokenRegistrations;

    /// 
Initializes a Configuration root with a list of providers.
    /// The s for this configuration.
    public ConfigurationRoot(IList providers)
    {
      if (providers == null)
        throw new ArgumentNullException(nameof (providers));
      this._providers = providers;
      this._changeTokenRegistrations = (IList) new List(providers.Count);
      foreach (IConfigurationProvider provider in (IEnumerable) providers)
      {
        IConfigurationProvider p = provider;
        p.Load();
        this._changeTokenRegistrations.Add(ChangeToken.OnChange((Func) (() => p.GetReloadToken()), (Action) (() => this.RaiseChanged())));
      }
    }
}

看到没，最后providers去调用了load方法。

结语

就上面的控制台代码来说IConfigurationSource对应的实现是JsonConfigurationSource；IConfigurationProvider，抽象类ConfigurationProvider对应的实现为JsonConfigurationProvider。如果我们要换成别的文件格式呢？比如ini,怎样自定义配置源呢？大家可以先想想，其实也很简单，下次跟大家分享。

最后说真的，.netCore源码真的特别优秀，很值得花一番时间去看看！从其中可以学到许多架构知识！