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

Using

private static final Object LOCK = new Object();

you are using the same lock for all sessions and it was the core reason for deadlock I did face. So every session in your implementation has the same race condition, which is bad.

It needs change.

Other suggested answer:

Object mutex = session.getAttribute(SESSION_MUTEX_ATTRIBUTE);
if (mutex == null) {
  mutex = session;
}
return mutex;

seems much better.