public class ConexionDB {
  private Connection cnn;

  private static ConexionDB instance;

  private ConexionDB() {

      try {
          Class.forName("com.mysql.jdbc.Driver");
          cnn = DriverManager.getConnection("jdbc:mysql://localhost:3306/control?useSSL=false",

e.printStackTrace();
      }
  }

  public static ConexionDB estado() {
      if (instance == null) {
          instance = new ConexionDB();
      }
      return instance;
  }

  public Connection getCnn() {
      return cnn;
  }

  public void cerraConexion() {
      instance = null;
  }

}

String error;
            String email = request.getParameter("email");
            String password = request.getParameter("password");
            HttpSession session = request.getSession();
            EmpleadosDAO empleadoDAO = new EmpleadosDAO();
        EmpleadosDTO userName = empleadoDAO.login(new EmpleadosDTO(email, password));


if (userName == null) {
        error = "Invalid Email or password";
        session.setAttribute("error", error);
        response.sendRedirect("index.jsp");
} else {
        session.setAttribute("user", userName);
        response.sendRedirect("welcome.jsp");
}

private final String SQL_LOGIN = "SELECT email from empleados where email=? and password=?";
private ConexionDB con = ConexionDB.estado();

public EmpleadosDTO login(EmpleadosDTO c) {

  java.sql.PreparedStatement ps;
  ResultSet res;
  EmpleadosDTO l = null;

  try {

      ps = con.getCnn().prepareStatement(SQL_LOGIN);

      ps.setString(1, c.getEmail());
      ps.setString(2, c.getPassword());

      res = ps.executeQuery();
      while (res.next()) {
          l = new EmpleadosDTO(res.getString(1), res.getString(2));
      }
      return l;
  } catch (SQLException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
  } finally {
      con.cerraConexion();
  }
      return l;
}