Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Three.Services;

namespace Three
{
    public class Startup
    {
        private readonly IConfiguration _configuration;

        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        public Startup(IConfiguration configuration)
        {
            this._configuration = configuration;
            //var three = _configuration["Three:BoldDepartmentEmployeeCountThreshold"];
        }
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
            services.AddSingleton<IClock, ChinaClock>();
            services.AddSingleton<IDepartmentService, DepartmentService>();
            services.AddSingleton<IEmployeeService, EmployeeService>();
            services.Configure<ThreeOptions>(_configuration.GetSection("Three"));
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseStaticFiles();
            //app.UseHttpsRedirection();
            //app.UseAuthentication();
            app.UseRouting();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Department}/{action=Index}/{id?}");
            });
        }
    }
}