自定义Configuration配置源

实现自定义配置源至少需要添加如下成员：

• 实现IConfigurationSource接口的配置源；
• 实现IConfigurationProvider接口或虚基类ConfigurationProvider的配置提供程序；
• 添加配置源的IConfigurationBuilder扩展方法；

如自定义一个TXT文本文件配置源：

添加配置源

配置源负责创建配置提供程序，以及监听文件修改。监听文件修改可以使用FileSystemWatcher，通过监听Changed事件监听配置文件的修改。使用ConfigurationReloadToken作为IChangeToken，当监听到文件修改时调用取消令牌的取消操作，进而通知订阅者文件已更改。

public class TxtConfigurationSource : IConfigurationSource, IDisposable
{
    private FileSystemWatcher? _fileWatcher;
    private ConfigurationReloadToken _reloadToken;

    public TxtConfigurationSource(string path, bool reloadOnChange = true)
    {
        FilePath = path;
        ReloadOnChange = reloadOnChange;
        _fileWatcher = new FileSystemWatcher(Directory.GetCurrentDirectory());
        _fileWatcher.Filter = "*.txt";
        _fileWatcher.EnableRaisingEvents = true;
        _fileWatcher.Changed += _fileWatcher_Changed;

        _reloadToken = new ConfigurationReloadToken();
    }

    private void _fileWatcher_Changed(object sender, FileSystemEventArgs e)
    {
        if (e.FullPath != FilePath)
            return;
        
        if (_reloadToken.HasChanged)
            return;

        // 触发事件
        ConfigurationReloadToken previousToken = Interlocked.Exchange(ref _reloadToken, 
            new ConfigurationReloadToken());
        previousToken.OnReload();
    }

    public bool ReloadOnChange { get; set; }

    public string FilePath { get; set; }

    public IConfigurationProvider Build(IConfigurationBuilder builder)
    {
        return new TxtConfigurationProvider(this);
    }

    public IChangeToken GetChangeToken() => _reloadToken;

    public void Dispose() => Dispose(true);

    protected virtual void Dispose(bool disposing)
    {
        _fileWatcher?.Dispose();
    }
}

添加配置提供程序

配置提供程序负责加载配置文件，并订阅配置源中的配置修改事件。通过ChangeToken.OnChange()方法进行事件订阅，当监听到文件改变时，重新加载文件：

public class TxtConfigurationProvider : ConfigurationProvider, IDisposable
{
    private readonly IDisposable _changeTokenRegistration;

    public TxtConfigurationProvider(TxtConfigurationSource source)
        :base()
    {
        Source = source ?? throw new ArgumentNullException(nameof(source));

        if (Source.ReloadOnChange)
        {
            _changeTokenRegistration = ChangeToken.OnChange(
                () => Source.GetChangeToken(),
                () =>
                {
                    Thread.Sleep(300);
                    Load();
                });
        }
    }

    public TxtConfigurationSource Source { get; }

    public override void Load()
    {
        if (!File.Exists(Source.FilePath))
            return;
        else
        {
            Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
            var lines = File.ReadAllLines(Source.FilePath);
            foreach (var line in lines)
            {
                var array = line.Replace("：", ":").Split(':');
                if (array.Length < 2)
                    continue;

                Data.Add(line.Substring(0, line.LastIndexOf(':')), array.Last());
            }
        }

        OnReload();
    }

    public void Dispose() => Dispose(true);

    protected virtual void Dispose(bool disposing)
    {
        _changeTokenRegistration?.Dispose();
    }
}

添加配置源扩展方法

添加IConfigurationBuilder扩展方法，方便将自定义配置源添加到IConfigurationBuilder中：

public static IConfigurationBuilder AddTxtFile(this IConfigurationBuilder builder, 
    string path, bool reloadOnChange)
{
    if (builder == null)
        throw new ArgumentNullException(nameof(builder));
    if (string.IsNullOrEmpty(path))
        throw new ArgumentException($"文件不能为空：{nameof(path)}");

    return builder.Add(new TxtConfigurationSource(path, reloadOnChange));
}

使用

首先通过扩展方法添加配置源，调用IConfigurationBuilder.Build()方法后即可通过IConfiguration获取配置项。通过ChangeToken.OnChange()方法订阅配置修改事件。

using ConfigurationTest;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Primitives;

IConfigurationBuilder configurationBuilder = new ConfigurationBuilder()
    .AddTxtFile(Path.Combine(Directory.GetCurrentDirectory(), "config.txt"), reloadOnChange: true);

// 通过IConfiguration直接读取指定配置
IConfiguration configuration = configurationBuilder.Build();
Console.WriteLine($"FileProvider:Source:{configuration.GetSection("FileProvider:Source").Value}");
Console.WriteLine($"Provider:{configuration["FileProvider:Provider"]}");
Console.WriteLine();

// 通过绑定选项获取配置
FileProviderOptions fileProviderOptions = new FileProviderOptions();
configuration.GetSection("FileProvider").Bind(fileProviderOptions);
Console.WriteLine($"FileProvider.Source = {fileProviderOptions.Source}");
Console.WriteLine($"FileProvider.Provider = {fileProviderOptions.Provider}");
Console.WriteLine();

// 监听配置修改
var disable = ChangeToken.OnChange(() => configuration.GetReloadToken(),
                                   () =>
                                   {
                                       foreach (var section in configuration.GetChildren())
                                       {
                                           PrintAllConfig(section);
                                       }
                                       
                                       Console.WriteLine();
                                       Console.WriteLine("按“q”退出");
                                   });

Console.WriteLine("按“q”退出");
while (Console.ReadLine() != "q")
{
}

disable.Dispose();

void PrintAllConfig(IConfigurationSection config)
{
    var sections = config.GetChildren();
    if(sections == null || sections.Count() == 0)
        Console.WriteLine($"{config.Key} : {config.Value}");
    else
    {
        foreach (var section in sections)
        {
            PrintAllConfig(section);
        }
    }
}

class FileProviderOptions
{
    public string Source { get; set; }
    public string Provider { get; set; }
}

// config.txt
FileProvider:Source:TxtSource
FileProvider:Provider:TxtProvider