asp.net core json 大小写问题

返回json 串，首字母小写了，解决办法

public void ConfigureServices(IServiceCollection services)

        {

            // Add framework services.

            //返回json  大小写

            services.AddMvc()

                    .AddJsonOptions( op => op.SerializerSettings.ContractResolver =

                                           new Newtonsoft.Json.Serialization.DefaultContractResolver() );