Net Core 3.0 and AspNet 3.0

AspNet 3.0 Startup and Configuration:

1, Host, IHost generic host,

     The official document:  https://docs.microsoft.com/zh-cn/aspnet/core/fundamentals/host/generic-host?view=aspnetcore-3.0

2, IHostBuilder builder:

      Primary knowledge: the interface method parameter, many have adopted Lamada function, => is a sign, the target parameter function is probably to be configured, and returned as the entire application system settings.

      Method ConfigureHostConfiguration () configure the host:

          configHost => {

                    configHost.SetBasePath(Directory.GetCurrentDirectory());
                    configHost.AddJsonFile("hostsettings.json", optional: true);
                    configHost.AddEnvironmentVariables(prefix: "PREFIX_");
                    configHost.AddCommandLine(args);
                }

      Method ConfigureAppConfiguration () configuration application: