原文:.NET Core 3.0之深入源码理解Configuration(一)
Configuration总体介绍
微软在.NET Core里设计出了全新的配置体系,并以非常灵活、可扩展的方式实现。从其源码来看,其运行机制大致是,根据其Source,创建一个Builder实例,并会向其添加Provider,在我们使用配置信息的时候,会从内存中获取相应的Provider实例。
.NET Core采用了统一的调用方式来加载不同类型的配置信息,并通过统一的抽象接口IConfigurationSource对配置源进行管理,这也是刚刚所说的灵活。而其扩展性就是我们可以自己自定义新的Provider实例,而不会改变其原来的调用方式。接下来的文章将会基于Consul,扩展一个新的Provider实例。
在ASP.NET Core 中,我们的应用配置是基于IConfigurationProvider的键值对。 我们先看一下思维导图:
基于上图,我们可以看到主要有键值对源有多种,分别是:
环境变量
命令行参数
各种形式的配置文件
内存对象
用户自定义扩展源
核心对象
在介绍.NET Core配置功能之前,先简要说明一下Microsoft.Extensions.Configuration.Abstractions,该组件抽象了.NET Core的配置功能,并对自定义扩展制定了新的标准。以下介绍的四个核心对象全部来自于该组件。
IConfiguration
该接口表示一组键/值应用程序配置属性,应用程序使用配置时的入口对象,.NET Core对其有多种扩展,其派生类包括位于统一类库的IConfigurationSection,以及Microsoft.Extensions.Configuration类库中的ConfigurationRoot、ConfigurationSection、IConfigurationRoot。我们可以通过DI获取IConfiguration实例。
它主要有以下三个方法:
- GetChildren():获取直接子配置子节
- GetReloadToken():返回一个IChangeToken,可用于确定何时重新加载配置
- GetSection(String):获取指定键的子节点
我们来看一下源码:
1: /// <summary>
2: /// Represents a set of key/value application configuration properties.
3: /// </summary>
4: public interface IConfiguration
5: {
6: /// <summary>
7: /// Gets or sets a configuration value.
8: /// </summary>
9: /// <param name="key">The configuration key.</param>
10: /// <returns>The configuration value.</returns>
11: string this[string key] { get; set; }
12:
13: /// <summary>
14: /// Gets a configuration sub-section with the specified key.
15: /// </summary>
16: /// <param name="key">The key of the configuration section.</param>
17: /// <returns>The <see cref="IConfigurationSection"/>.</returns>
18: /// <remarks>
19: /// This method will never return <c>null</c>. If no matching sub-section is found with the specified key,
20: /// an empty <see cref="IConfigurationSection"/> will be returned.
21: /// </remarks>
22: IConfigurationSection GetSection(string key);
23:
24: /// <summary>
25: /// Gets the immediate descendant configuration sub-sections.
26: /// </summary>
27: /// <returns>The configuration sub-sections.</returns>
28: IEnumerable<IConfigurationSection> GetChildren();
29:
30: /// <summary>
31: /// Returns a <see cref="IChangeToken"/> that can be used to observe when this configuration is reloaded.
32: /// </summary>
33: /// <returns>A <see cref="IChangeToken"/>.</returns>
34: IChangeToken GetReloadToken();
35: }
通常我们要求配置文件要有足够的灵活性,尤其是我们所扩展的配置信息存放在了其他服务器,当修改的时候我们很需要一套监控功能,以及时灵活的应对配置信息的修改。现在.NET Core为我们提供了这样一个功能,我们只需要自定义少量代码即可完成配置信息的同步。这个方法就是GetReloadToken(),其返回值是IChangeToken。此处对配置信息的同步只做一个引子,后面的文章会详细说明。
由于ConfigurationRoot、ConfigurationSection聚集于IConfiguration接口,此处也对这两个类进行讨论,方便我们对.NET Core的配置功能有个更加形象的印象。这两个接口,本质上就是.NET Core关于配置信息的读取方式。
XML是使用比较广泛的一种数据结构,我们在配置XML时,一般会使用根节点、父节点、子节点之类的术语,此处也一样。
ConfigurationRoot是配置的根节点,也实现了IConfigurationRoot,此接口只有一个方法,其主要功能就是实现对配置信息的重新加载,另外还包括一个IConfigurationProvider类型的集合属性。其源码如下
1: /// <summary>
2: /// Represents the root of an <see cref="IConfiguration"/> hierarchy.
3: /// </summary>
4: public interface IConfigurationRoot : IConfiguration
5: {
6: /// <summary>
7: /// Force the configuration values to be reloaded from the underlying <see cref="IConfigurationProvider"/>s.
8: /// </summary>
9: void Reload();
10:
11: /// <summary>
12: /// The <see cref="IConfigurationProvider"/>s for this configuration.
13: /// </summary>
14: IEnumerable<IConfigurationProvider> Providers { get; }
15: }
下面是ConfigurationRoot关于Reload()方法的实现
1: /// <summary>
2: /// Force the configuration values to be reloaded from the underlying sources.
3: /// </summary>
4: public void Reload()
5: {
6: foreach (var provider in _providers)
7: {
8: provider.Load();
9: }
10:
11: RaiseChanged();
12: }
通过源码我们知道,如果调用了Reload()方法,所有类型的Provider都会重新加载。
前面有ConfigurationRoot表示配置的根节点,那么ConfigurationSection则表示非跟节点,毕竟父节点、子节点都是相对,所以此处使用非根节点。ConfigurationSection继承于IConfigurationSection,该接口只有三个只读属性,分别表示配置信息的Key、Value以及路径信息,需要指出的是,此处的路径信息主要指从根节点到当前节点的路径,以表示当前节点的位置,类似于A:B:C可以表示节点C的位置,其中A、B、C都是ConfigurationSection的Key。以下是ConfigurationSection的源码
1: /// <summary>
2: /// Represents a section of application configuration values.
3: /// </summary>
4: public interface IConfigurationSection : IConfiguration
5: {
6: /// <summary>
7: /// Gets the key this section occupies in its parent.
8: /// </summary>
9: string Key { get; }
10:
11: /// <summary>
12: /// Gets the full path to this section within the <see cref="IConfiguration"/>.
13: /// </summary>
14: string Path { get; }
15:
16: /// <summary>
17: /// Gets or sets the section value.
18: /// </summary>
19: string Value { get; set; }
20: }
IConfigurationBuilder
该接口主要用于创建IConfigurationProvider,其派生类包括Microsoft.Extensions.Configuration.ConfigurationBuilder。其成员包括
两个只读属性:
- Properties:获取可用于在IConfigurationBuilder之间共享数据的键/值集合
- Sources:该属性用于缓存不同的配置源,以用于相对应的Provider的创建
两个方法:
- Add(IConfigurationSource source):新增IConfigurationSource,并添加到属性中Sources中
- Build():该方法遍历Sources属性,并调用IConfigurationSource的Build()方法,通过获取Provider集合,最终创建IConfigurationRoot对象
ConfigurationBuilder源码如下
1: /// <summary>
2: /// Used to build key/value based configuration settings for use in an application.
3: /// </summary>
4: public class ConfigurationBuilder : IConfigurationBuilder
5: {
6: /// <summary>
7: /// Returns the sources used to obtain configuration values.
8: /// </summary>
9: public IList<IConfigurationSource> Sources { get; } = new List<IConfigurationSource>();
10:
11: /// <summary>
12: /// Gets a key/value collection that can be used to share data between the <see cref="IConfigurationBuilder"/>
13: /// and the registered <see cref="IConfigurationProvider"/>s.
14: /// </summary>
15: public IDictionary<string, object> Properties { get; } = new Dictionary<string, object>();
16:
17: /// <summary>
18: /// Adds a new configuration source.
19: /// </summary>
20: /// <param name="source">The configuration source to add.</param>
21: /// <returns>The same <see cref="IConfigurationBuilder"/>.</returns>
22: public IConfigurationBuilder Add(IConfigurationSource source)
23: {
24: if (source == null)
25: {
26: throw new ArgumentNullException(nameof(source));
27: }
28:
29: Sources.Add(source);
30: return this;
31: }
32:
33: /// <summary>
34: /// Builds an <see cref="IConfiguration"/> with keys and values from the set of providers registered in
35: /// <see cref="Sources"/>.
36: /// </summary>
37: /// <returns>An <see cref="IConfigurationRoot"/> with keys and values from the registered providers.</returns>
38: public IConfigurationRoot Build()
39: {
40: var providers = new List<IConfigurationProvider>();
41: foreach (var source in Sources)
42: {
43: var provider = source.Build(this);
44: providers.Add(provider);
45: }
46: return new ConfigurationRoot(providers);
47: }
48: }
此处令人感慨颇多,我们最终调用 ConfigurationRoot 的构造函数,究其原因是Provider提供了统一的数据访问方式,不管是基于何种类型的Provider,我们都可以调用其Load()方法加载配置项。此外,IConfigurationBuilder本身有很多的扩展方法来注册数据源,比如AddJsonFile()扩展方法。我们来看一下,我们常见的写法,
1: var builder = new ConfigurationBuilder()
2:
3: .SetBasePath(env.ContentRootPath)
4:
5: .AddJsonFile("appsettings1.json", false, true)
6:
7: .AddJsonFile("appsettings2.json", false, true);
8:
9: Configuration = builder.Build();
IConfigurationSource
该接口表示应用程序配置的键值对。其派生类包括Microsoft.Extensions.Configuration.ChainedConfigurationSource、Microsoft.Extensions.Configuration.Memory.MemoryConfigurationSource。另外该派生类还会在文件类配置场景下依赖Microsoft.Extensions.Configuration.FileExtensions组件。
它是所有配置源的抽象表示,包括JSON、XML、INI、环境变量等等。通过上文我们也知道了,IConfigurationBuilder会注册多个IConfigurationSource实例。它只有一个方法,就是Build()方法,并返回IConfigurationProvider,由此可见,IConfigurationProvider的创建依赖于IConfigurationSource,这也是一一对应的关系。所有不同的源最终都会转化成统一的键值对表示。
以下为
1: /// <summary>
2: /// Represents a source of configuration key/values for an application.
3: /// </summary>
4: public interface IConfigurationSource
5: {
6: /// <summary>
7: /// Builds the <see cref="IConfigurationProvider"/> for this source.
8: /// </summary>
9: /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>
10: /// <returns>An <see cref="IConfigurationProvider"/></returns>
11: IConfigurationProvider Build(IConfigurationBuilder builder);
12: }
以下是MemoryConfigurationSource的源码
1: /// <summary>
2: /// Represents in-memory data as an <see cref="IConfigurationSource"/>.
3: /// </summary>
4: public class MemoryConfigurationSource : IConfigurationSource
5: {
6: /// <summary>
7: /// The initial key value configuration pairs.
8: /// </summary>
9: public IEnumerable<KeyValuePair<string, string>> InitialData { get; set; }
10:
11: /// <summary>
12: /// Builds the <see cref="MemoryConfigurationProvider"/> for this source.
13: /// </summary>
14: /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>
15: /// <returns>A <see cref="MemoryConfigurationProvider"/></returns>
16: public IConfigurationProvider Build(IConfigurationBuilder builder)
17: {
18: return new MemoryConfigurationProvider(this);
19: }
20: }
IConfigurationProvider
通过上文的介绍,我们可以知道IConfigurationProvider是统一的对外接口,对用户提供配置的查询、重新加载等功能。其派生类包括Microsoft.Extensions.Configuration.ConfigurationProvider、Microsoft.Extensions.Configuration.ChainedConfigurationProvider、Microsoft.Extensions.Configuration.Memory.MemoryConfigurationProvider。另外该派生类还会在文件类配置场景下依赖Microsoft.Extensions.Configuration.FileExtensions组件。
以下是Microsoft.Extensions.Configuration.ConfigurationProvider的源码:
1: /// <summary>
2: /// Base helper class for implementing an <see cref="IConfigurationProvider"/>
3: /// </summary>
4: public abstract class ConfigurationProvider : IConfigurationProvider
5: {
6: private ConfigurationReloadToken _reloadToken = new ConfigurationReloadToken();
7:
8: /// <summary>
9: /// Initializes a new <see cref="IConfigurationProvider"/>
10: /// </summary>
11: protected ConfigurationProvider()
12: {
13: Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
14: }
15:
16: /// <summary>
17: /// The configuration key value pairs for this provider.
18: /// </summary>
19: protected IDictionary<string, string> Data { get; set; }
20:
21: /// <summary>
22: /// Attempts to find a value with the given key, returns true if one is found, false otherwise.
23: /// </summary>
24: /// <param name="key">The key to lookup.</param>
25: /// <param name="value">The value found at key if one is found.</param>
26: /// <returns>True if key has a value, false otherwise.</returns>
27: public virtual bool TryGet(string key, out string value)
28: => Data.TryGetValue(key, out value);
29:
30: /// <summary>
31: /// Sets a value for a given key.
32: /// </summary>
33: /// <param name="key">The configuration key to set.</param>
34: /// <param name="value">The value to set.</param>
35: public virtual void Set(string key, string value)
36: => Data[key] = value;
37:
38: /// <summary>
39: /// Loads (or reloads) the data for this provider.
40: /// </summary>
41: public virtual void Load()
42: { }
43:
44: /// <summary>
45: /// Returns the list of keys that this provider has.
46: /// </summary>
47: /// <param name="earlierKeys">The earlier keys that other providers contain.</param>
48: /// <param name="parentPath">The path for the parent IConfiguration.</param>
49: /// <returns>The list of keys for this provider.</returns>
50: public virtual IEnumerable<string> GetChildKeys(
51: IEnumerable<string> earlierKeys,
52: string parentPath)
53: {
54: var prefix = parentPath == null ? string.Empty : parentPath + ConfigurationPath.KeyDelimiter;
55:
56: return Data
57: .Where(kv => kv.Key.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
58: .Select(kv => Segment(kv.Key, prefix.Length))
59: .Concat(earlierKeys)
60: .OrderBy(k => k, ConfigurationKeyComparer.Instance);
61: }
62:
63: private static string Segment(string key, int prefixLength)
64: {
65: var indexOf = key.IndexOf(ConfigurationPath.KeyDelimiter, prefixLength, StringComparison.OrdinalIgnoreCase);
66: return indexOf < 0 ? key.Substring(prefixLength) : key.Substring(prefixLength, indexOf - prefixLength);
67: }
68:
69: /// <summary>
70: /// Returns a <see cref="IChangeToken"/> that can be used to listen when this provider is reloaded.
71: /// </summary>
72: /// <returns></returns>
73: public IChangeToken GetReloadToken()
74: {
75: return _reloadToken;
76: }
77:
78: /// <summary>
79: /// Triggers the reload change token and creates a new one.
80: /// </summary>
81: protected void OnReload()
82: {
83: var previousToken = Interlocked.Exchange(ref _reloadToken, new ConfigurationReloadToken());
84: previousToken.OnReload();
85: }
86:
87: /// <summary>
88: /// Generates a string representing this provider name and relevant details.
89: /// </summary>
90: /// <returns> The configuration name. </returns>
91: public override string ToString() => $"{GetType().Name}";
92: }
通过源码,我们可以知道ConfigurationProvider以字典类型缓存了多个Provider对象,有需要的时候,从内存中获取即可,配置的加载通过Load()方法实现,在ConfigurationRoot里我们介绍了其Reload,并且说明其方法是在循环调用ConfigurationProvider的Load方法,但是此处只提供了一个虚方法,其目的是要交给其他具体的Provider,比如环境变量、JSON、XML等,这些具体的Provider可以从相应的配置源中获取配置信息。所有的子节点KEY通过GetChildKeys方法实现,其重新加载方式通过ConfigurationReloadToken实例完成。
另外需要说明一下,在ConfigurationProvider构造函数里,对字典进行了初始化,并同时设置了字典Key不受大小写限制,这是一个需要注意的细节。
Configuration组件结构
通过查看.NET配置功能的源码,所有依赖均基于Microsoft.Extensions.Configuration.Abstractions,在其上有一层实现,即Microsoft.Extensions.Configuration,其内部也多数是抽象实现,并提供了多个虚方法交给其派生组件,比如环境变量、命令行参数、各种文件型配置等,当然各种文件型配置还要依赖Microsoft.Extensions.Configuration.FileExtensions组件。
以下是.NET Core 3.0预览版里的Configuration各个组件的结构图:
原文地址:https://www.cnblogs.com/lonelyxmas/p/10891626.html