ServicePointManager.DefaultConnectionLimit = 200;

    public void ConfigureServices(IServiceCollection services)
    {
      services.AddHttpClient("HttpClientFactoryDemo");
    }

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;
using System.Web;
using Microsoft.AspNetCore.Mvc;
 
namespace HttpClientFactoryDemo.Controllers
{
  [Route("api/[controller]")]
  [ApiController]
  public class ValuesController : ControllerBase
  {
    private readonly IHttpClientFactory _httpClientFactory;
 
    public ValuesController(IHttpClientFactory httpClientFactory)
    {
      _httpClientFactory = httpClientFactory;
    }
 
    public static string UrlEncode(string temp, Encoding encoding)
    {
      StringBuilder stringBuilder = new StringBuilder();
      for (int i = 0; i < temp.Length; i++)
      {
        string t = temp[i].ToString();
        string k = HttpUtility.UrlEncode(t, encoding);
        if (t == k)
        {
          stringBuilder.Append(t);
        }
        else
        {
          stringBuilder.Append(k.ToUpper());
        }
      }
      return stringBuilder.ToString();
    }
 
    [HttpGet]
    public async Task<ActionResult> Get()
    {
      Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
      string xmlContent = "<"1.0\" encoding=\"GBK\" standalone=\"yes\"";
      xmlContent = UrlEncode(xmlContent, Encoding.GetEncoding("GBK"));
 
      Dictionary<string, string> nvs = new Dictionary<string, string> { { "req", xmlContent } };
      Encoding encoding = Encoding.GetEncoding("GBK");
      StringBuilder buffer = new StringBuilder();
      int i = 0;
      IDictionary<string, string> sortedParams = new SortedDictionary<string, string>(nvs);
      foreach (KeyValuePair<string, string> kvp in nvs)
      {
        buffer.AppendFormat(i > 0 "&{0}={1}" : "{0}={1}", kvp.Key,
          UrlEncode(kvp.Value, Encoding.GetEncoding("GBK")));
        i++;
      }
      byte[] postBody = encoding.GetBytes(buffer.ToString());
 
      var client = _httpClientFactory.CreateClient("HttpClientFactoryDemo");
      var request = new HttpRequestMessage
      {
        RequestUri = new Uri("https://spay.fuiou.com/commonQuery"),
        Method = HttpMethod.Post,
        Content = new ByteArrayContent(postBody),
      };
 
      request.Content.Headers.ContentType =
        new MediaTypeHeaderValue("application/x-www-form-urlencoded");
 
      return Ok(await client.SendAsync(request));
 
    }
  }
}