java - Using request.getSession() as a locking object?

Question

I have some java code that gets and sets a session attribute:

Object obj = session.getAttribute(TEST_ATTR);
if (obj==null) {
  obj = new MyObject();
  session.setAttribute(obj);
}

In order to make this code thread-safe, I'd like to wrap it in a synchronized block. But what do I use as the locking object? Does it make sense to use the session?

synchronized (session) {
  Object obj = session.getAttribute(TEST_ATTR);
  if (obj==null) {
    obj = new MyObject();
    session.setAttribute(obj);
  }
}

Answer 1

It is generally frowned upon to use a lock that you have no control over. A lock should be scoped as tightly as possible and since the session is more or less a global object, it does not fit the bill. Try to use a separate lock from the java.util.concurrent.locks package and scope it to your class.