Multiple Threads calling static helper method

Question

I have a web application running on Tomcat.

There are several calculations that need to be done on multiple places in the web application. Can I make those calculations

Answer 1

I'll sum up here what has been said in the comments to the Matt Ball's answer, since it got pretty long at the end and the message gets lost: and the message was

in a shared environment like a web/application server you should try very hard to find a solution without synchronizing. Using static helpers synchronized on static object might work well enough for stand alone application with a single user in front of the screen, in a multiuser/multiapplication scenario doing this would most probably end in a very poor performance - it would effectively mean serializing access to your application, all users would have to wait on the same lock. You might not notice the problem for a long time: if the calculation are fast enough and load is evenly distributed.

But then all of a sudden all your users might try to go through the calculation at 9am and you app will stop to work! I mean not really stop, but they all would block on the lock and make a huge queue.

Now regardless the necessity of a shared state, since you originally named calculations as subject of synchronization: do their results need to be shared? Or are those calculations specific to a user/session? In the latter case a ThreadLocal as per Peter Lawrey would be enough. Otherwise I'd say for overall performance it would be better to duplicate the calculations for everybody needing them in order not to synchronize (depends on the cost).

Session management should also be better left to the container: it has been optimized to handle them efficiently, if necessary including clustering etc. I doubt one could make better solution without investing lot of work and making lots of bugs on the way there. But as Matt Ball has stated it should be better asked separately.