request.getParameter() is null in DoPost (HttpServlet)

Question

I'm trying to send a JSON object using httpClient, but in the DoPost, the "HttpServletRequest request" is null, it has no parameters.

also, I tried using Postman chrome app to make a post request to the same class, and it also has the empty "HttpServletRequest request".

here it is how make the request:

public void CamposPost(){
    try{
    HttpClient   httpClient    = HttpClientBuilder.create().build();
    HttpPost     post          = new HttpPost(this.url);
    StringEntity postingString = new StringEntity(this.JSONObject.toString());
    post.setHeader("Content-type", "application/json");
    post.setEntity(postingString);

    HttpResponse  response = httpClient.execute(post);
    HttpEntity entity = response.getEntity();
    String responseString = EntityUtils.toString(entity, "UTF-8");
    this.respond=responseString;
    }
    catch(Exception ex){
        ex.printStackTrace();
    }
}

and the following code is the DoPost code

package com.itc.polux.request;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class post extends HttpServlet{
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

      List<String> parameterNames = new ArrayList<String>(request.getParameterMap().keySet());
      //request.getParameterNames();
      response.setContentType("text/html");
      PrintWriter out = response.getWriter();
      out.println(request.getParameter("json"));
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{

      List<String> parameterNames = new ArrayList<String>(request.getParameterMap().keySet());
      //request.getParameterNames();
      PrintWriter out = response.getWriter();
      response.setContentType("text/html");
      out.println(request.getParameter("json"));
}
}