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Simple servlet question

Vinnie Jenks
Ranch Hand

Joined: Apr 26, 2004
Posts: 207
I've been learning java on and off for about a year now and while I've covered a lot of ground and built a few small applications successfully, I'm still confused about one simple thing - the scope of global variables in a servlet.

A servlet being multi-threaded, wouldn't global variables in a servlet be unsafe to rely on from request-to-request? For example, an object stored globally could change between two users and the data wouldn't be reliable, is that correct? What about a Hibernate session, as another example? Couldn't the session be closed in one thread invalidating another user's request to that session in another thread?

I was reading this article about optimizing servlets/jsp for performance:

...they talk about using init() to make references to a data source, which is then stored in a global variable.

I'm using hibernate and would love it if I could call objects once in init() and not have to make subsequent calls each time the page is requested.

So, with init(), is it only called once per thread (per user request)?

Thanks in advance for clearing it up!

Ernest Friedman-Hill
author and iconoclast

Joined: Jul 08, 2003
Posts: 24199

Classes have members, not "globals"! Yes, init() is only called once, when a servlet is created.

Moving this to the "Servlets" forum.

[Jess in Action][AskingGoodQuestions]
I agree. Here's the link:
subject: Simple servlet question
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