IConfiguration服务是net core 默认依懒注入的一个对象 直接注入（推荐使用）

　　新建控制器 然后构造函数直接注入

 [Route("api/[controller]")]
    public class ValuesController : Controller
    {
        private IConfiguration _configuration { get; }

        public ValuesController(IConfiguration configuration)
        {
            _configuration = configuration;
        }
        // GET: api/values
        [HttpGet]
        public IEnumerable<string> Get()
        {
            return new string[] { _configuration["appSettings:SvcUrl"] };
        }
    }

创建一个ConfigurationBuilder 来加载配置文件

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

            string SvcUrl = configuration["appSettings:SvcUrl"];