CORS header 'Access-Control-Allow-Origin' missing and Java Servlet

 As it is answered here, HttpServlet.doOptions() method has to be overridden the following way:

import java.io.IOException;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@SuppressWarnings("serial")
@WebServlet(
    name = "MyServlet",
    urlPatterns = {"/myservlet"}
)
public class MyServlet extends HttpServlet {
	
    @Override
    protected void doOptions
        (
            HttpServletRequest req, 
            HttpServletResponse resp
        )
        throws IOException {

        resp.setHeader("Access-Control-Allow-Origin",  "*");
        resp.setHeader("Access-Control-Allow-Methods", "POST, OPTIONS");
        resp.setHeader("Access-Control-Allow-Headers", "*");
    }
	
    @Override
    protected void doPost
        (
            HttpServletRequest req, 
            HttpServletResponse resp
        )
        throws IOException {
		
        resp.setHeader("Access-Control-Allow-Origin", "*");
        resp.setContentType("text/plain");
        resp.setCharacterEncoding("UTF-8");
        resp.getOutputStream().println("OK");		
    }

    @Override
    protected void doGet
        (
            HttpServletRequest req, 
            HttpServletResponse resp
        ) 
        throws IOException {
        doPost(req, resp);
    }
}