Is synchronization within an HttpSession feasible?

Question

UPDATE: Solution right after question.

Question:

Usually, synchronization is serializing parallel requests within a JVM, e.

Answer 1

Another solution suggested in "Murach's Java Servlets and JSP (3rd Edition)" book:

Cart cart;
final Object lock = request.getSession().getId().intern();
synchronized (lock) {
    cart = (Cart) session.getAttribute("cart");
}