Thrown exception AS-WEB-CORE-00089 while forwarding to a different servlet path

I tried to redirect from doPost to doGet from ControllerServlet urlPattern = "/ remove_person" so I can re-update the findAll request inside my doGet method of ControllerServlet class and then forward remove_person.jsp from doGet method, but AS-WEB-CORE-00089 is thrown

WARNING:   StandardWrapperValve[ControllerServlet]: Servlet.service() for servlet ControllerServlet threw exception
javax.servlet.ServletException: AS-WEB-CORE-00089
    at org.apache.catalina.core.ApplicationDispatcher.doInvoke(ApplicationDispatcher.java:863)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:739)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:575)
    at org.apache.catalina.core.ApplicationDispatcher.doDispatch(ApplicationDispatcher.java:546)
    at org.apache.catalina.core.ApplicationDispatcher.dispatch(ApplicationDispatcher.java:428)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:378)
    at server.ControllerServlet.doPost(ControllerServlet.java:130)

      

        
        
        
      

    

where the line ControllerServlet.java:130 is in the doPost () method:

request.getRequestDispatcher(url).forward(request, response);

      

        
        
        
      

    

Here is the code for the servlet class:

@WebServlet(
    name = "ControllerServlet", 
    loadOnStartup = 1,
    urlPatterns = {
        "/index", 
        "/search_person", 
        "/add_person",
        "/remove_person"})
public class ControllerServlet extends HttpServlet {

    @PersistenceUnit
    private EntityManagerFactory emf;
    @Resource
    private UserTransaction utx;
    private EntityManager em;

    @Override
    public void init() throws ServletException {
        assert emf != null;
        em = emf.createEntityManager();
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String servletPath = request.getServletPath();

        if (servletPath.equals("/index")) {
        }
        else if (servletPath.equals("/search_person")) {
            List persons = em.createNamedQuery("Person.findAll").getResultList();
            request.setAttribute("findByNameAndYearBirth", persons);
        }
        else if (servletPath.equals("/add_person")) {
        }
        else if (servletPath.equals("/remove_person")) {
            List persons = em.createNamedQuery("Person.findAll").getResultList();
            request.setAttribute("findAll", persons);
        }
        String url = servletPath + ".jsp";
        request.getRequestDispatcher(url).forward(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String servletPath = request.getServletPath();

        if (servletPath.equals("/index")) {
        }
        else if (servletPath.equals("/search_person")) {
            String name = request.getParameter("name");
            String yearBirth = request.getParameter("yearBirth");

            Query query = em.createNamedQuery("Person.findAll");
            if (!name.isEmpty() && !yearBirth.isEmpty()) {
                query = em.createNamedQuery("Person.findByNameAndYearBirth");
                query.setParameter("name", name);
                query.setParameter("yearBirth", Short.parseShort(yearBirth));
            }
            else if (!name.isEmpty()) {
                query = em.createNamedQuery("Person.findByModel");
                query.setParameter("name", name);
            }
            else if (!yearBirth.isEmpty()) {
                try  {
                    Short sYearBirth = Short.parseShort(yearBirth);
                    query = em.createNamedQuery("Person.findByYearBirth");
                    query.setParameter("yearBirth", sYearBirth);
                } catch (NumberFormatException nfe) {}
            }
            List persons = query.getResultList();
            request.setAttribute("findByNameAndYearBirth", persons);
        }
        else if (servletPath.equals("/add_person")) {
            String name = request.getParameter("name");
            String hobby = request.getParameter("hobby");
            String yearBirth = request.getParameter("yearBirth");

            int personsLen = em.createNamedQuery("Person.findAll").getResultList().size();
            Person newPerson = new Person(
                ++personsLen, name, hobby, Short.parseShort(yearBirth)
            );
            try {
                utx.begin();
                em = emf.createEntityManager();
                em.persist(newPerson);
                utx.commit();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        else if (servletPath.equals("/remove_person")) {
            String id = request.getParameter("id");

            Person person = null;  
            try {
                utx.begin();
                person = em.find(Person.class, Integer.parseInt(id));
                em.remove(person);
                utx.commit();
            } catch (Exception e) {
                e.printStackTrace();
            }
            servletPath = "/remove_person";
        }
        String url = servletPath;
        request.getRequestDispatcher(url).forward(request, response);
    }

}

      

        
        
        
      

    

The problem is my line inside the doPost method

String url = path; 

      

        
        
        
      

    

does not contain the .jsp part.

But if I add the ".jsp" part to the string url, how would I update the findAll request data inside remove_person.jsp, unless I go to the doGet servlet to collect new data first after adding or removing objects?

remove_person.jsp

<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%> 
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    </head>
    <body>
        <h1>Remove Person</h1>
        <form action="remove_person" method="post">
            <table border="3">
                <tr>
                    <th>ID</th>
                    <th>Name</th>
                </tr>
                <c:forEach var="person" begin="0" items="${findAll}"> 
                    <tr>
                        <td>${person.id}</td> 
                        <td>${person.name}</td> 
                    </tr> 
                </c:forEach>
            </table>
            <strong>Remove person: </strong>
            <select name="id">
            <c:forEach var="person" items="${findAll}">
                <option value="${person.id}">${person.id}. ${person.name} </option>
            </c:forEach>
            </select>
            <input type="submit" id="remove_person" value="Remove" />
        </form>
        <br>
        <a href="index">Home page</a>
    </body>
</html>

      

        
        
        
      

    

Actually, is it possible to forward from doPost the doGet method of the same servlet? The reason I was trying to do this is because inside doGet I am already using this code:

List persons = em.createNamedQuery("Person.findAll").getResultList();
request.setAttribute("findAll", persons);

      

        
        
        
      

    

So why should I duplicate this code inside the doPost method, when I can forward the doGet method from doPost and call this code?

UPDATE:

Bad approach:

String url = servletPath;
request.getRequestDispatcher(url).forward(request, response);

      

        
        
        
      

    

The right approach:

String url = request.getContextPath() + servletPath;
response.sendRedirect(url);