.NET Core WebApi中返回 json 數據首字母大小寫問題

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc().AddJsonOptions(opt =>
    {
       opt.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver();//json字符串大小寫原樣輸出
    });
}