because i'll have to delploy JForum again
That's what I'm asking - why do you think you need to do that? You don't need to, and should not.
When new version of JForum will be avalible i'll download it, and i'll deploy it on my server. And i'll want to use my old DB, how Will I import it?
In that case you would run the upgrade procedure, not the installation procedure, so there's no need to export or import the DB. If a DB migration is necessary, then that version's wiki page (e.g. https://sourceforge.net/p/jforum2/wiki2/NewFeatures241/
) would mention it, and there would be a DB script in the "upgrade" directory (see the source at https://sourceforge.net/p/jforum2/code/HEAD/tree/trunk/