概述

我們都知道asp.net core配置信息的讀取離不開IConfigurationSource和IConfigurationProvider這兩個類，ConfigurationSource可以提供一個ConfigurationProvider，然后去讀取信息。究竟他們之間有著怎樣的千絲萬縷，我們一起來看看源碼。

首先我們來建立一個.net core控制臺項目，來運行以下代碼：

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

短短幾行 代碼看起來很簡單，就是用來讀取appsettings.json文件中的配置信息。然而我們今天想搞清楚其背后運行的原理，要花點時間。

首先、我們根據代碼ConfigurationBuilder configBuilder = new ConfigurationBuilder();知道創建了一個configBuilder對象；

其次，configBuilder.SetBasePath(Directory.GetCurrentDirectory()) 該代碼的調用我們也能大概見名知義，獲取當前的目錄；

接下來，重點來了，configBuilder.AddJsonFile("appsettings.json")的實現究竟是怎樣的？我們來看下源碼的實現：

f12進去后源碼如下：

/// <summary>Extension methods for adding <see cref="T:Microsoft.Extensions.Configuration.Json.JsonConfigurationProvider" />.</summary>public static class JsonConfigurationExtensions{/// <summary>Adds the JSON configuration provider at <paramref name="path" /> to <paramref name="builder" />.</summary>/// <param name="builder">The <see cref="T:Microsoft.Extensions.Configuration.IConfigurationBuilder" /> to add to.</param>/// <param name="path">Path relative to the base path stored in/// <see cref="P:Microsoft.Extensions.Configuration.IConfigurationBuilder.Properties" /> of <paramref name="builder" />.</param>/// <returns>The <see cref="T:Microsoft.Extensions.Configuration.IConfigurationBuilder" />.</returns>public static IConfigurationBuilder AddJsonFile(this IConfigurationBuilder builder,string path){return builder.AddJsonFile((IFileProvider) null, path, false, false);} }

緊接著f12再看實現的源碼，依然在JsonConfigurationExtensions這個擴展類里面：

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<JsonConfigurationSource>) (s =>{s.FileProvider = provider;s.Path = path;s.Optional = optional;s.ReloadOnChange = reloadOnChange;s.ResolveFileProvider();}));}

這時候有沒有發現builder.AddJsonFile((Action<JsonConfigurationSource>)這個方法里面出現了一個關鍵的信息點：JsonConfigurationSource (JsonConfigurationSource 繼承抽象類FileConfigurationSource,而FileConfigurationSource：IConfigurationSource) 。關系如下圖：

?看完上面這個關系圖后，我們緊接著上面builder.AddJsonFile()的實現源碼繼續f12往下,源碼如下：

//該代碼依然在JsonConfigurationExtensions類里面public static IConfigurationBuilder AddJsonFile(this IConfigurationBuilder builder,Action<JsonConfigurationSource> configureSource){return ConfigurationExtensions.Add<JsonConfigurationSource>(builder, (Action<M0>) configureSource);}

我們看到上面的擴展方法實現是ConfigurationExtensions.Add...,再往下看實現：

public static class ConfigurationExtensions{/// <summary>Adds a new configuration source.</summary>/// <param name="builder">The <see cref="T:Microsoft.Extensions.Configuration.IConfigurationBuilder" /> to add to.</param>/// <param name="configureSource">Configures the source secrets.</param>/// <typeparam name="TSource" />/// <returns>The <see cref="T:Microsoft.Extensions.Configuration.IConfigurationBuilder" />.</returns>public static IConfigurationBuilder Add<TSource>(this IConfigurationBuilder builder,Action<TSource> configureSource)where TSource : IConfigurationSource, new(){TSource source = new TSource();if (configureSource != null)configureSource(source);return builder.Add((IConfigurationSource) source);} }

到這里我們看到了其實就是IConfigurationBuilder調用了Add方法，添加了一個數據源（JsonConfigurationSource），至于JsonConfigurationSource類里面做了什么，我們看下實現。

public class JsonConfigurationSource : FileConfigurationSource{/// <summary>Builds the <see cref="T:Microsoft.Extensions.Configuration.Json.JsonConfigurationProvider" /> for this source.</summary>/// <param name="builder">The <see cref="T:Microsoft.Extensions.Configuration.IConfigurationBuilder" />.</param>/// <returns>A <see cref="T:Microsoft.Extensions.Configuration.Json.JsonConfigurationProvider" /></returns>public override IConfigurationProvider Build(IConfigurationBuilder builder){this.EnsureDefaults(builder);return (IConfigurationProvider) new JsonConfigurationProvider(this);}}

JsonConfigurationSource類面的Build方法提供了一個JsonConfigurationProvider類，這里再貼下JsonConfigurationProvider類里面的代碼：

/// <summary>A JSON file based <see cref="T:Microsoft.Extensions.Configuration.FileConfigurationProvider" />.</summary>public class JsonConfigurationProvider : FileConfigurationProvider{/// <summary>Initializes a new instance with the specified source.</summary>/// <param name="source">The source settings.</param>public JsonConfigurationProvider(JsonConfigurationSource source): base((FileConfigurationSource) source){}/// <summary>Loads the JSON data from a stream.</summary>/// <param name="stream">The stream to read.</param>public virtual void Load(Stream stream){try{this.set_Data(JsonConfigurationFileParser.Parse(stream));}catch (JsonException ex){throw new FormatException(SR.Error_JSONParseError, (Exception) ex);}}}

關于JsonConfigurationProvider里面的Load就是去讀取信息的實現，至于Load的具體實現我們不再深究。我們回到最初的控制臺configBuilder.Build()，看看其的實現：

public class ConfigurationBuilder : IConfigurationBuilder{/// <summary>Returns the sources used to obtain configuration values.</summary>public IList<IConfigurationSource> Sources { get; } = (IList<IConfigurationSource>) new List<IConfigurationSource>();/// <summary>Gets a key/value collection that can be used to share data between the <see cref="T:Microsoft.Extensions.Configuration.IConfigurationBuilder" />/// and the registered <see cref="T:Microsoft.Extensions.Configuration.IConfigurationProvider" />s.</summary>public IDictionary<string, object> Properties { get; } = (IDictionary<string, object>) new Dictionary<string, object>();/// <summary>Adds a new configuration source.</summary>/// <param name="source">The configuration source to add.</param>/// <returns>The same <see cref="T:Microsoft.Extensions.Configuration.IConfigurationBuilder" />.</returns>public IConfigurationBuilder Add(IConfigurationSource source){if (source == null)throw new ArgumentNullException(nameof (source));this.Sources.Add(source);return (IConfigurationBuilder) this;}/// <summary>Builds an <see cref="T:Microsoft.Extensions.Configuration.IConfiguration" /> with keys and values from the set of providers registered in/// <see cref="P:Microsoft.Extensions.Configuration.ConfigurationBuilder.Sources" />.</summary>/// <returns>An <see cref="T:Microsoft.Extensions.Configuration.IConfigurationRoot" /> with keys and values from the registered providers.</returns>public IConfigurationRoot Build(){List<IConfigurationProvider> configurationProviderList = new List<IConfigurationProvider>();foreach (IConfigurationSource source in (IEnumerable<IConfigurationSource>) this.Sources){IConfigurationProvider configurationProvider = source.Build((IConfigurationBuilder) this);configurationProviderList.Add(configurationProvider);}return (IConfigurationRoot) new ConfigurationRoot((IList<IConfigurationProvider>) configurationProviderList);}}

看到這個源碼的時候有沒有種豁然開朗的感覺，前面我們說到IConfigurationBuilder調用了Add方法添加一個數據源，并沒說添加了一個數據源存在了哪里，到底有什么用處，現在在上面ConfigurationBuilder類里面看到存在了Sources 集合里面。然后configBuilder.Build()

去調用的時候遍歷數據源（Sources ）集合，緊接著source (IConfigurationSource)調用了Build方法構建了一個configurationProvider對象存到configurationProviderList集合里面，最后在返回一個ConfigurationRoot對象的構造函數里面傳遞了configurationProviderList集合去執行。

貼上ConfigurationRoot的源碼：

public class ConfigurationRoot : IConfigurationRoot, IConfiguration, IDisposable{private readonly IList<IConfigurationProvider> _providers;private readonly IList<IDisposable> _changeTokenRegistrations;/// <summary>Initializes a Configuration root with a list of providers.</summary>/// <param name="providers">The <see cref="T:Microsoft.Extensions.Configuration.IConfigurationProvider" />s for this configuration.</param>public ConfigurationRoot(IList<IConfigurationProvider> providers){if (providers == null)throw new ArgumentNullException(nameof (providers));this._providers = providers;this._changeTokenRegistrations = (IList<IDisposable>) new List<IDisposable>(providers.Count);foreach (IConfigurationProvider provider in (IEnumerable<IConfigurationProvider>) providers){IConfigurationProvider p = provider;p.Load();this._changeTokenRegistrations.Add(ChangeToken.OnChange((Func<IChangeToken>) (() => p.GetReloadToken()), (Action) (() => this.RaiseChanged())));}} }public class ConfigurationRoot : IConfigurationRoot, IConfiguration, IDisposable{private readonly IList<IConfigurationProvider> _providers;private readonly IList<IDisposable> _changeTokenRegistrations;/// <summary>Initializes a Configuration root with a list of providers.</summary>/// <param name="providers">The <see cref="T:Microsoft.Extensions.Configuration.IConfigurationProvider" />s for this configuration.</param>public ConfigurationRoot(IList<IConfigurationProvider> providers){if (providers == null)throw new ArgumentNullException(nameof (providers));this._providers = providers;this._changeTokenRegistrations = (IList<IDisposable>) new List<IDisposable>(providers.Count);foreach (IConfigurationProvider provider in (IEnumerable<IConfigurationProvider>) providers){IConfigurationProvider p = provider;p.Load();this._changeTokenRegistrations.Add(ChangeToken.OnChange((Func<IChangeToken>) (() => p.GetReloadToken()), (Action) (() => this.RaiseChanged())));}} }

看到沒，最后providers去調用了load方法。

結語

就上面的控制臺代碼來說IConfigurationSource對應的實現是JsonConfigurationSource；IConfigurationProvider，抽象類ConfigurationProvider對應的實現為JsonConfigurationProvider。如果我們要換成別的文件格式呢？比如ini,怎樣自定義配置源呢？大家可以先想想，其實也很簡單，下次跟大家分享。

最后說真的，.netCore源碼真的特別優秀，很值得花一番時間去看看！從其中可以學到許多架構知識！

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