Let we have jboss running on the server and deployed application (based on Hibernate) working with some database server.

Suppose system administrator has rebooted database server (but not jboss, or another appserver).

Is there way to "transparent" restore cottection to database after reboot, without redeploy and server restart? Does hibernate support this feature, or how can I obviously reset Hibernate's database connection state?

I would think that this is a function of your database driver and not Hibernate.

If your driver doesn't support validation of connections, you could of course wrap your driver and validate a connection before handing it off if you wanted a custom solution. (You may also have to do this in you DB Connection pool).