documentation: https://docs.asp.net/en/latest/fundamentals/configuration.html
github: https://github.com/aspnet/Configuration/

项目结构

• 配置的接口定义与基础实现
• Microsoft.Extensions.Configuration  配置文件的基础实现
• Microsoft.Extensions.Configuration.Abstractions  配置文件的基础实现的接口定义
• Microsoft.Extensions.Configuration.Binder  特殊配置文件实现
• 配置的扩展
• Microsoft.Extensions.Configuration.CommandLine  命令行扩展
• Microsoft.Extensions.Configuration.EnvironmentVariables  环境变量扩展
• Microsoft.Extensions.Configuration.FileExtensions  文本类型扩展
• Microsoft.Extensions.Configuration.FileProviderExtensions 用来检测配置文本是否变动
• Microsoft.Extensions.Configuration.Ini  Ini文件类型扩展
• Microsoft.Extensions.Configuration.Json Json文件类型扩展
• Microsoft.Extensions.Configuration.Xml   Xml文件类型扩展

ASP.NET Core 1.0 中抛弃了原先的web.config文件机制，引用了现有的appsettings.json文件机制，配置的文件的类型可以是JSON,XML,INI等，如在Startup类中:

    /// <summary>
    /// 配置信息
     /// </summary>
    public IConfigurationRoot Configuration { get; set; }

    /// <summary>
    /// 程序入口点
    /// </summary>
    /// <param name="env"></param>
    public Startup(IHostingEnvironment env)
    {
        var builder = new ConfigurationBuilder()
                     .AddJsonFile("appsettings.json")
                     .AddEnvironmentVariables();
        Configuration = builder.Build();
    }

新的配置机制基于Microsoft.Extensions.Configuration命名空间，IConfiguration类中定义配置信息的实例接口

    /// <summary>
    /// Represents a set of key/value application configuration properties.
    /// </summary>
    public interface IConfiguration
    {
        /// <summary>
        /// Gets or sets a configuration value.
        /// </summary>
        /// <param name="key">The configuration key.</param>
        /// <returns>The configuration value.</returns>
        string this[string key] { get; set; }

        /// <summary>
        /// Gets a configuration sub-section with the specified key.
        /// </summary>
        /// <param name="key">The key of the configuration section.</param>
        /// <returns>The <see cref="IConfigurationSection"/>.</returns>
        /// <remarks>
        ///     This method will never return <c>null</c>. If no matching sub-section is found with the specified key,
        ///     an empty <see cref="IConfigurationSection"/> will be returned.
        /// </remarks>
        IConfigurationSection GetSection(string key);

        /// <summary>
        /// Gets the immediate descendant configuration sub-sections.
        /// </summary>
        /// <returns>The configuration sub-sections.</returns>
        IEnumerable<IConfigurationSection> GetChildren();

        IChangeToken GetReloadToken();
    }