How to get value from appsettings.json in Program class in asp.net core console application

Question

Could you please tell me how to get the value from an appsettings.json in the "Program.cs". If I start at the "Startup.cs" like this:

Model

class AppConfiguration
    {
        public string UrlProperty { get; set; }
    }

Startup.cs

services.AddSingleton(Configuration.GetSection("Url").Get<AppConfiguration>());

Then go to the "Program.cs" and code it like so:

Program.cs

public static string Url { get; set; }
public static AppConfiguration configurtion { get; set; }

public Program(AppConfiguration configuration)
{
    Url = configuration.ToString();
}

static void Main(string[] args)
{
    CreateWebHostBuilder(args).Run();
}

public static IWebHost CreateWebHostBuilder(string[] args) =>
     WebHost.CreateDefaultBuilder(args)
     .UseStartup<Startup>()
     .UseKestrel((hostingContext, options) =>
     {
         var ipAddress = IPAddress.Parse(Url); // ERROR HERE
             options.Listen(ipAddress, 9001);
     }).Build();

I would have an error since the main gets executed first then the CreateWebHostBuilder so the Url will not get filled in first. But if I use this code:

static void Main(string[] args)
        {
            var serviceProvider = new ServiceCollection()
                   .AddSingleton(Configuration.GetSection("Url").Get<AppConfiguration>());
            CreateWebHostBuilder(args).Run();
        }

The Configuration.GetSection("Url") is not recognized. How do I get the value from an appsettings.json in the Program.Main?

Update

as per "Tan" I made the necessary edits to my Program.cs. I think I am near solving it. It's just that the "Url" is still null when it loads. Please see my edit:

static void Main(string[] args)
        {
            var builder = CreateWebHostBuilder(args);
            builder.ConfigureLogging((context, builder) =>
            {
                Url = context.Configuration["ApplicationUrl"];
            }).Build().Run();
        }

       
        public static IHostBuilder CreateWebHostBuilder(string[] args) =>
           Host.CreateDefaultBuilder(args)
           .ConfigureWebHostDefaults(webBuilder =>
           {
               webBuilder.UseStartup<Startup>()
               .UseKestrel((hostingContext, options) =>
               {
                   var ipAddress = IPAddress.Parse(Url);
                   options.Listen(ipAddress, 9001);
                   options.Limits.MaxRequestBodySize = null;
               });
           });

Please see the screenshot:

This is the appsettings.json

{
  "AllowedHosts": "*",
  "AcceptedOrigin": [ "http://localhost:4200" ],
  "ApplicationUrl":  "192.168.1.4"
}

Update 2

This is the appsettings.json

{
  "AllowedHosts": "*",
  "AcceptedOrigin": [ "http://localhost:4200" ],
  "ApplicationUrl":  "192.168.1.4"
}

static void Main(string[] args) {

        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
   Host.CreateDefaultBuilder(args)
   .ConfigureWebHostDefaults(webBuilder =>
   {
       webBuilder.UseStartup<Startup>()
       .UseKestrel((context, options) =>
       {
           options.Limits.MaxRequestBodySize = null;

            // "192.168.1.4"
            string url = context.Configuration["Url"];
           var ipAddress = System.Net.IPAddress.Parse(url);
       });
   });

This is what I get in the Startup.cs:

In the Program.cs:

Answer 1

In the file appsettings.json, you can define Url property like this:

{
  "Url": "https://example.com"
}

In the file Program.cs, inside Main method, you can access that property via ConfigureLogging extension method:

public class Program
{
    public static void Main(string[] args)
    {
        var builder = CreateHostBuilder(args);

        builder.ConfigureLogging((context, builder) => {
            // "https://example.com"
            string url = context.Configuration["Url"];

            // do stuff...
        }).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>()
            .UseKestrel(options =>
            {
                options.Limits.MaxRequestBodySize = null;
            });
        });
}

---

Update:

If you want to get the property value via UseKestrel extension method, you can assign it directly, no need to store in the field.

Because you will lose that value when the extension method finish (Url will become null outside the extension method)

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>()
            .UseKestrel((context, options) =>
            {
                options.Limits.MaxRequestBodySize = null;

                // "192.168.1.4"
                string url = context.Configuration["Url"];
                var ipAddress = System.Net.IPAddress.Parse(url);
            });
        });
}

Screenshot: