Form info to Servlet and JSP - java

I've been stuck for a few days and I can not move forward.

• I collect data from a form in SERVLET .
• I create a ArrayList where I will save the objects that will be created with the fields received through the form
• I pass the flow (the list in my case) to the JSP, I go through it and I get the value. So far so good.
• I re-enter the different values in the form and when I add it and go through the list again I see that the object previously entered in the list is no longer there.

Student Class:

package model;

import java.util.ArrayList;
import java.util.List;

public class Alumno {
    private String name;
    private String dni;
    private String exam;
    private double nota;

    public Alumno(String name, String dni, String exam, Double nota) {

        this.name = name;
        this.dni = dni;
        this.exam = exam;
        this.nota = nota;
    }

    @Override
    public String toString() {
        return "Alumno [name=" + name + ", dni=" + dni + ", exam=" + exam + ", nota=" + nota + "]";
    }

    // GETTERS AND SETERS
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getDni() {
        return dni;
    }
    public void setDni(String dni) {
        this.dni = dni;
    }
    public String getExam() {
        return exam;
    }
    public void setExam(String exam) {
        this.exam = exam;
    }
    public double getNota() {
        return nota;
    }
    public void setNota(double nota) {
        this.nota = nota;
    }
}

Driver:

package control;

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

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

import model.Alumno;

/**
 * Servlet implementation class Controlador
 */
@WebServlet("/Controlador")
public class Controlador extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public Controlador() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.getWriter().append("Served at: ").append(request.getContextPath());

        // Recojo lops parámetros del formulrio

        String nombre = request.getParameter("nombre");
        String dni = request.getParameter("dni");
        String exam = request.getParameter("examen");
        Double nota = Double.parseDouble(request.getParameter("nota"));

        // Creo un ARRAYLIST de Alumnos
        List<Alumno> listaAlumnos = new ArrayList<Alumno>();

        // Añado varios objetos Alumno a la lista
        listaAlumnos.add(new Alumno("Luis","56567878g", "MATE", 7.2));
        listaAlumnos.add(new Alumno("Manu","56546878g", "Lengua", 5.4));
        listaAlumnos.add(new Alumno("Jorge","56569878g", "Inglés", 6.2));
        listaAlumnos.add(new Alumno("Col","5656709g", "Informática", 0.2));


        // Añado los objeto Alumno a la lista   OJOOOOOOOO
        listaAlumnos.add(new Alumno(nombre, dni, exam, nota));  // Aquí creo un objeto alumno con los datos introducidos en el formulario

        // Dejo la lista en el request
        request.setAttribute("listaAlumnos", listaAlumnos);

        // Le paso el flujo a la jsp
         request.getRequestDispatcher("/Presentacion.jsp").forward(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }
}

JSP:

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@page import="java.util.*"%>
<%@page import="model.Alumno"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Datos de los alumnos registrados</title>
</head>

<body>
    <h1>Datos de los alumnos</h1>
    <%
        // El problema es que en la lista 
        // solo me esta guardando un valor y luego vuelve a empezar de 0 
        // Creo una lista y le agrego la que tenía en el REQUEST
        ArrayList<Alumno> listaAlumnos = (ArrayList<Alumno>) request.getAttribute("listaAlumnos");
    %>   
    <% 
    for(int i = 0; i < listaAlumnos.size(); i++) {
    %>
<ul>
    <li><% out.println(listaAlumnos.get(i)); %></li>
    <%} %>
</ul>

    <a href="index.html">Añadir mas alumnos</a>
</body>
</html>