ASP.NETCore配置文件的获取和设置

{
  "ConnectionStrings": {
    "DefaultConnection": "Data Source=.;Initial Catalog=AcceSSManagement;Integrated Security=True"
  },
  "Logging": {
    "LogLevel": {
      "Default": "InfORMation"
    }
  },
  "AllowedHosts": "*",
  "MyOptions": {
    "Option1": "ww",
    "Option2": 3
  }
}

public Startup()
        {
            var builder = new ConfigurationBuilder();
            builder.SetBasePath(Directory.GetCurrentDirectory());
            builder.AddJsonFile("appsettings.json");
            var config = builder.Build();

            var _config = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("appsettings.json")
                .Build();
        }

        public Startup(IConfiguration configuration,IHostingEnvironment env)
        {

            var builder = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile(“appsettings.json",optional:true,reloadOnChange:true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json",optional:true);

            //配置环境变量
            builder.AddEnvironmentVariables();
            Configuration = builder.Build();
        }

        public IConfiguration Configuration { get; }

namespace mvcTest
{
    public class AppSettinGoptions
    {
        public DefaultConnec ConnectionStrings { get; set; }
        public string AllowedHosts { get; set; }
    }

    public class DefaultConnec
    {
        public string DefaultConnection { get; set; }
    }
}

public Startup(IConfiguration configuration,IHostingEnvironment env)
        {
            //Configuration = configuration;
            var builder = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("appsettings.json",optional:true,reloadOnChange:true)
                //.AddJsonFile($"appsettings.{env.EnvironmentName}.json",optional:true);

            //配置环境变量
            builder.AddEnvironmentVariables();
            Configuration = builder.Build();
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddOptions();//提供依赖注入
            services.Configure<AppSettingOptions>(Configuration); //绑定配置选项     
   services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        }

    public class HomeController : Controller
    {
        private readonly IOptions<AppSettingOptions> _options;
        public HomeController(IOptions<AppSettingOptions> options,)
        {
            _options = options;
        }
        public static Logger nlog = LogManager.GetCurrentClassLogger();
        public IActionResult Index()
        {
            var AllowedHosts = _options.Value.AllowedHosts;
            var DefaultConnection = _options.Value.ConnectionStrings.DefaultConnection;
        }
     }

    //通过代码编写
    services.Configure<AppSettingOptions>(options=>
    {
        options.AllowedHosts = "test";
    });
    //只配置部分
    services.Configure<AppSettingOptions>(Configuration.GetSection("ConnectionStrings"));