Describe please a typical lifecycle of a Hibernate object (that maps to a db table) in a web app. Suppose, you create a new instance of an object and persist in the db. But during the app lifetime you'll be working on a detached object and finally you need to update it in the database, for example on exit. How does it look like with hibernate and spring?

p.s. Can transactions and sessions live between servlet transitions? So that we opened 1 session and use it in all servlets without a need to reopen it?