源码解析.Net中IConfiguration配置的实现

前言

关于IConfituration的使用,我觉得大部分人都已经比较熟悉了,如果不熟悉的可以看这里。因为本篇不准备讲IConfiguration都是怎么使用的,但是在源码部分的解读,网上资源相对少一点,所以本篇准备着重源码这一块的设计,尽量的让读者能够理解它的内部实现。

IConfiguration类之间的关系

这里我整理了一个UML(可能不是那么标准,一些依赖关系没有体现)。可能直接看会有点不懂,下面我会慢慢讲这些东西。

源码解析

我们知道.net中的配置加载是有优先级的,如果有相同的key的话,一般后面加载的会覆盖前面的值,它们的优先级顺序如下图:

  • 在Host.CreateDefaultBuilder(args)执行的代码中,将委托添加到一个IConfigurationBuilder的集合中,builder为HostBuilder,hostingContext为HostBuilderContext,config就是IConfigurationBuilder,我们先来看下加载的代码,如下:
builder.ConfigureAppConfiguration((hostingContext, config) =>
{
    IHostEnvironment env = hostingContext.HostingEnvironment;
    bool reloadOnChange = GetReloadConfigOnChangeValue(hostingContext);
    config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: reloadOnChange) //加载appsettings.json
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: reloadOnChange); //根据环境变量加载appsettings.json
    if (env.IsDevelopment() && env.ApplicationName is { Length: > 0 })
    {
        var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
        if (appAssembly is not null)
        {
            config.AddUserSecrets(appAssembly, optional: true, reloadOnChange: reloadOnChange); //开发环境加载UserSecrets
        }
    }
    config.AddEnvironmentVariables(); //加载环境变量
    if (args is { Length: > 0 })
    {
        config.AddCommandLine(args); //加载命令行参数
    }
})
  • 接下来我们拿其中一个例子,加载命令行参数,看看在AddCommandLine中都做了什么事情,是如何构建出IConfiguration对象的。
  1. 从UML图中可以看到,扩展对象都实现了IConfigurationSource,并且继承了抽象类ConfigurationProvider,源码如下:
//ConfigurationBuilder扩展类
public static class CommandLineConfigurationExtensions
{
    public static IConfigurationBuilder AddCommandLine(this IConfigurationBuilder configurationBuilder, string[] args)
    {
        return configurationBuilder.AddCommandLine(args, switchMappings: null);
    }
    public static IConfigurationBuilder AddCommandLine(
        this IConfigurationBuilder configurationBuilder,
        string[] args,
        IDictionary<string, string> switchMappings)
    {
        //SwitchMappings是Key映射,可以看微软文档
        configurationBuilder.Add(new CommandLineConfigurationSource { Args = args, SwitchMappings = switchMappings });
        return configurationBuilder;
    }
}
public class CommandLineConfigurationSource : IConfigurationSource
{
    public IDictionary<string, string> SwitchMappings { get; set; }
    public IEnumerable<string> Args { get; set; }
    public IConfigurationProvider Build(IConfigurationBuilder builder)
    {
        return new CommandLineConfigurationProvider(Args, SwitchMappings);
    }
}
//主要实现其Load方法,将kv加载到Data中,以便拿取。
public class CommandLineConfigurationProvider : ConfigurationProvider
{
    private readonly Dictionary<string, string> _switchMappings;
    public CommandLineConfigurationProvider(IEnumerable<string> args, IDictionary<string, string> switchMappings = null)
    {
        Args = args ?? throw new ArgumentNullException(nameof(args));
        //默认情况下mapping是null
        if (switchMappings != null)
        {
            //是个私有方法,源码就不贴了,可以自己下载来看看。
            _switchMappings = GetValidatedSwitchMappingsCopy(switchMappings);
        }
    }
    protected IEnumerable<string> Args { get; private set; }
    //load方法,主要是来设置kv,因为data是个字典类型,要把kv给设置和获取到。
    public override void Load()
    {
        var data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        string key, value;

        using (IEnumerator<string> enumerator = Args.GetEnumerator())
        {
            while (enumerator.MoveNext())
            {
                string currentArg = enumerator.Current;
                int keyStartIndex = 0;

                if (currentArg.StartsWith("--"))
                {
                    keyStartIndex = 2;
                }
                else if (currentArg.StartsWith("-"))
                {
                    keyStartIndex = 1;
                }
                else if (currentArg.StartsWith("/"))
                {
                    currentArg = $"--{currentArg.Substring(1)}";
                    keyStartIndex = 2;
                }
                int separator = currentArg.IndexOf('=');
                if (separator < 0)
                {
                    if (keyStartIndex == 0)
                    {
                        continue;
                    }
                    if (_switchMappings != null && _switchMappings.TryGetValue(currentArg, out string mappedKey))
                    {
                        key = mappedKey;
                    }
                    else if (keyStartIndex == 1)
                    {
                        continue;
                    }
                    else
                    {
                        key = currentArg.Substring(keyStartIndex);
                    }

                    string previousKey = enumerator.Current;
                    if (!enumerator.MoveNext())
                    {
                        continue;
                    }
                    value = enumerator.Current;
                }
                else
                {
                    string keySegment = currentArg.Substring(0, separator);
                    if (_switchMappings != null && _switchMappings.TryGetValue(keySegment, out string mappedKeySegment))
                    {
                        key = mappedKeySegment;
                    }
                    else if (keyStartIndex == 1)
                    {
                        throw new FormatException(SR.Format(SR.Error_ShortSwitchNotDefined, currentArg));
                    }
                    else
                    {
                        key = currentArg.Substring(keyStartIndex, separator - keyStartIndex);
                    }

                    value = currentArg.Substring(separator + 1);
                }

                data[key] = value;
            }
        }
        Data = data;
    }
}

2.在构建主机信息HostBuilder,下面只贴出主要代码,可以看到最后执行了ConfigurationBuilder的Build方法,构建IConfiguration,源码如下:

public class HostBuilder : IHostBuilder
{
    private List<Action<IConfigurationBuilder>> _configureHostConfigActions = new List<Action<IConfigurationBuilder>>();
    public IHostBuilder ConfigureAppConfiguration(Action<HostBuilderContext, IConfigurationBuilder> configureDelegate)
    {
        _configureAppConfigActions.Add(configureDelegate ?? throw new ArgumentNullException(nameof(configureDelegate)));
        return this;
    }
    //即我们在main函数中看到的Build方法
    public IHost Build()
    {
        //只能执行一次这个方法
        if (_hostBuilt)
        {
            throw new InvalidOperationException(SR.BuildCalled);
        }
        _hostBuilt = true;
        using var diagnosticListener = new DiagnosticListener("Microsoft.Extensions.Hosting");
        const string hostBuildingEventName = "HostBuilding";
        const string hostBuiltEventName = "HostBuilt";

        if (diagnosticListener.IsEnabled() && diagnosticListener.IsEnabled(hostBuildingEventName))
        {
            Write(diagnosticListener, hostBuildingEventName, this);
        }
        //执行Host配置(应用程序执行路径,增加_dotnet环境变量,获取命令行参数,加载预配置)
        BuildHostConfiguration();
        //设置主机环境变量
        CreateHostingEnvironment();
        //设置上下文
        CreateHostBuilderContext();
        //构建程序配置(加载appsetting.json)
        BuildAppConfiguration();
        //构造容器,加载服务
        CreateServiceProvider();
        var host = _appServices.GetRequiredService<IHost>();
        if (diagnosticListener.IsEnabled() && diagnosticListener.IsEnabled(hostBuiltEventName))
        {
            Write(diagnosticListener, hostBuiltEventName, host);
        }

        return host;
    }
    private void BuildAppConfiguration()
    {
        //对于已经加载过的配置不再重新加载
        IConfigurationBuilder configBuilder = new ConfigurationBuilder()
            .SetBasePath(_hostingEnvironment.ContentRootPath)
            .AddConfiguration(_hostConfiguration, shouldDisposeConfiguration: true);

        //注意这里是AppConfig
        foreach (Action<HostBuilderContext, IConfigurationBuilder> buildAction in _configureAppConfigActions)
        {
            buildAction(_hostBuilderContext, configBuilder);
        }
        _appConfiguration = configBuilder.Build();
        //将新的配置赋值给config
        _hostBuilderContext.Configuration = _appConfiguration;
    }
}
  1. ConfigurationBuilder的Build方法中加载对用Provider类里面的Load方法,加载配置信息。在获取对应Key值时,由加载的顺序,按照从后到前的顺序,依次查询key对应的value值,源码如下:
public class ConfigurationBuilder : IConfigurationBuilder
{
    //所有的配置源集合
    public IList<IConfigurationSource> Sources { get; } = new List<IConfigurationSource>();
    public IDictionary<string, object> Properties { get; } = new Dictionary<string, object>();
    public IConfigurationBuilder Add(IConfigurationSource source)
    {
        if (source == null)
        {
            throw new ArgumentNullException(nameof(source));
        }

        Sources.Add(source);
        return this;
    }

    public IConfigurationRoot Build()
    {
        var providers = new List<IConfigurationProvider>();
        foreach (IConfigurationSource source in Sources)
        {
            //通过配置源构建provider对象。
            IConfigurationProvider provider = source.Build(this);
            providers.Add(provider);
        }
        //构建配置根对象
        return new ConfigurationRoot(providers);
    }
}

 public class ConfigurationRoot : IConfigurationRoot, IDisposable
 {
    private readonly IList<IConfigurationProvider> _providers;
    private readonly IList<IDisposable> _changeTokenRegistrations;
    private ConfigurationReloadToken _changeToken = new ConfigurationReloadToken();

    public ConfigurationRoot(IList<IConfigurationProvider> providers)
    {
        if (providers == null)
        {
            throw new ArgumentNullException(nameof(providers));
        }

        _providers = providers;
        _changeTokenRegistrations = new List<IDisposable>(providers.Count);
        foreach (IConfigurationProvider p in providers)
        {
            p.Load();
            _changeTokenRegistrations.Add(ChangeToken.OnChange(() => p.GetReloadToken(), () => RaiseChanged()));
        }
    }
    public IEnumerable<IConfigurationProvider> Providers => _providers;
    //通过索引拿数据,比如其他获取value的方法,其都是扩展类中实现的,读者可以自己看下。
    public string this[string key]
    {
        get
        {
            //从后往前查Porvider里面对应的KV,每个Provider里面都有一个Data(字典)对象,只获取第一个的。
            for (int i = _providers.Count - 1; i >= 0; i--)
            {
                IConfigurationProvider provider = _providers[i];

                if (provider.TryGet(key, out string value))
                {
                    return value;
                }
            }
            return null;
        }
        set
        {
            if (_providers.Count == 0)
            {
                throw new InvalidOperationException(SR.Error_NoSources);
            }
            //修改时,所有的key对应的value值都修改
            foreach (IConfigurationProvider provider in _providers)
            {
                provider.Set(key, value);
            }
        }
    }
}

总结

  1. 可以看到微软为了保留扩展性,增加了抽象类和抽象接口,让用户能够自定义的扩展实现自己的配置。

  2. 配置的加载顺序尤为重要,后加载的会覆盖前面的key。

  3. 文件监听,由于篇幅原因,不写那么多了,原理是通过ChangeToken和FileProvider实现的。

    这里只是把核心代码给提出来,并不是全部代码,所以读者如果想看其他的,需要自己翻下源码。其实在读源码的过程中,一方面是为了探究实现原理,更大的收获是能够学习到人家巧妙的设计,能够用到自己的代码中。其实笔者的水平的也不是很高,如果有差错的地方,望读者能够提出来,以便我及时改正。

posted @ 2021-08-16 11:47  SnailZz  阅读(480)  评论(0编辑  收藏  举报