Locking/Transaction handling for servlets

[sgodden]

How do I obtain a lock when I am in a servlet, and have that lock retained over several invocations of a web page?

I can't store the user transaction in the session, because it is not serializable.

So my lock will be released, and I'll be unable to prevent conflicting updates.

[juhalindfors]

you'd most likely want to use optimistic locking in this case

[sgodden]

OK, but a user could get fairly hacked off if we let him into an order with loads of complex stuff on the screen, he then takes 5 minutes to enter stuff, and then we find that conflicting updates have occurred.

I really need pessimistic locking (which I know introduces other issues), but that depends on a transaction(?). If I need to do my own thing, fair enough, but if there's a way of achieving it within the spec, I'd obviously prefer to do that.

[sgodden]

Actually, when you think it through, pessimistic locking isn't the answer.

If someone just wanders off half-way through the transaction (for lunch or whatever), or their plug gets pulled from the wall, then pessimistic locking is going to cause all sorts of problems.

It's more a question of designing the application so that two users will not naturally be updating the same entity at the same time, and then using optimistic locking.

[juhalindfors]

I agree ;-)