IHttpClientFactory in .NET Framework 4.7.2 without Dependency Injection

I am planning to use Microsoft.Extensions.Http package in my ASP.NET Framework 4.7.2 Webforms project. Since there is no built-in DI Container in .NET Framework, I am not using the DI packages. Based on this answer, I am not sure about the last line -

Microsoft.Extensions.Http provides the HttpClientFactory only, not the new optimized HttpClient. This is only available in .NET Core 2.1

Can I implement IHttpClientFactory without DI and using singleton method in my Framework project and get rid of the 2 problems of using HttpClient directly - Socket Exhaustion and DNS resolution? Is there something else that needs to be done based on the above comment

Unfortunately, the use of the HttpClientFactory is tightly integrated with the DI framework. Fortunately, creating a new IHttpClientFactory without making use of the full DI infrastructure can be done in a few lines:

IHttpClientFactory factory = new ServiceCollection()
    .AddHttpClient()
    .BuildServiceProvider()
    .GetRequiredService<IHttpClientFactory>();

With the code above you create new new service provider (which is the MS.DI Container) that just contains the registrations for the HTTP client package, which includes a registration for IHttpClientFactory, and the IHttpClientFactory is directly pulled from the container. The factory is stored in a variable, while the container itself is no longer used.

A full working Console application would like like this:

// This requires the 'Microsoft.Extensions.Http` package to be installed
using Microsoft.Extensions.DependencyInjection;
using System;
using System.Net.Http;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Web;

internal class Program
{
    static async Task Main(string[] args)
    {
        IHttpClientFactory factory = new ServiceCollection()
            .AddHttpClient()
            .BuildServiceProvider()
            .GetRequiredService<IHttpClientFactory>();

        HttpClient client = factory.CreateClient();

        string html = await client.GetStringAsync(
            "https://blogs.cuttingedge.it/steven/posts/2011/" +
            "meanwhile-on-the-command-side-of-my-architecture/");

        string plainText = HttpUtility.HtmlDecode(
            Regex.Replace(
                Regex.Replace(html, "<[^>]*>", string.Empty),
                @"^\s*$\n", string.Empty, RegexOptions.Multiline));

        Console.WriteLine(plainText);

        Console.ReadLine();
    }
}

Best is to cache the IHttpClientFactory for the lifetime of your application and not recreate it on the fly.