asp.net core 类库获取appsettings.json的值

项目中添加appsettings.json，属性改成总是复制
{
  "name": "asp.net",
  "private": true,
  "dependencies": {
  },
  "AllowedHosts": "*",
  "AppSettings": {
    "BlacklistDB": "Server=your database server;Database=your database name;Integrated Security=SSPI;"
  }
}

NuGet 添加Packages
Microsoft.Extensions.Configuration
Microsoft.Extensions.Configuration.Json
Microsoft.Extensions.DependencyInjection
Microsoft.Extensions.Hosting
Microsoft.Extensions.Options
Microsoft.Extensions.Options.ConfigurationExtensions

定义AppSettings.cs类

    public class AppSettings
    {
        public string BlacklistDB { get; set; }
    }

定义ConfigurationHelper.cs类

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Configuration.Json;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;
using System.IO;

    public class ConfigurationHelper
    {
        public IConfiguration _config { get; set; }

        public ConfigurationHelper()
        {
            _config = new ConfigurationBuilder()
            .Add(new JsonConfigurationSource { Path = "appsettings.json", ReloadOnChange = true })//ReloadOnChange = true 当appsettings.json被修改时重新加载
            .Build();
        }

        public T GetAppSettings<T>(string key) where T : class, new()
        {
            var appconfig = new ServiceCollection()
                .AddOptions()
                .Configure<T>(_config.GetSection(key))
                .BuildServiceProvider()
                .GetService<IOptions<T>>()
                .Value;
            return appconfig;
        }

        public T Get<T>(string key)
        {
            IConfiguration config = new ConfigurationBuilder().SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("appsettings.json", true, true).Build();

            return config.GetSection(key).Get<T>();
        }

        //public T GetAppsettings<T>(string key) where T : class, new()
        //{
        //    string keyDir = System.IO.Directory.GetCurrentDirectory();

        //    IConfiguration config = new ConfigurationBuilder()
        //        .SetBasePath(keyDir)
        //        .Add(new JsonConfigurationSource { Path = "appsettings.json", ReloadOnChange = true })//ReloadOnChange = true 当appsettings.json被修改时重新加载
        //        .Build();
        //    var appconfig = new ServiceCollection()
        //        .AddOptions()
        //        .Configure<T>(config.GetSection(key))
        //        .BuildServiceProvider()
        //        .GetService<IOptions<T>>()
        //        .Value;
        //    return appconfig;
        //}

        /// <summary>
        /// 通过强类型绑定读取配置
        /// </summary>
        /// <typeparam name="Entity">要绑定的类型</typeparam>
        /// <param name="keyPath">配置文件路径</param>
        /// <returns>绑定的类</returns>
        public Entity GetSectionObject<Entity>(string keyPath = null) where Entity : new()
        {
            var entity = new Entity();
            if (string.IsNullOrEmpty(keyPath))
            {
                //将appsettings.json全部配置绑定到模型
                _config.Bind(entity);
            }
            else
            {
                //将指定路径下的配置项绑定到模型
                var section = _config.GetSection(keyPath);
                section.Bind(entity);
            }
            return entity;
        }
    }

添加项目类引用
调用
            var_connection = new ConfigurationHelper().GetAppSettings<AppSettings>("AppSettings").BlacklistDB;
            var temp = new ConfigurationHelper().Get<string>("AppSettings:BlacklistDB");