When using Spring transaction proxy
org.springframework.transaction.interceptor.TransactionProxyFactoryBean with an Hibernate transaction manager
org.springframework.orm.hibernate.HibernateTransactionManager you should know that Hibernate session will be opened at the start of the transaction and closed at the end. Any modification to persistent objects will be flushed to database, so be careful when in service managers (aka business delegates or facades) you touch Hibernate persisted objects. What I’ve done is return clones of them in my DAOs so they can be used as Transfer Objects, changing its state will not change database state.
Be sure that in the TransactionProxyFactoryBean bean definition you add transactionAttributes for every method in the facade or the session will be closed every time a DAO call spring HibernateTemplate.execute method. I forgot this for get* methods and got errors difficult to debug.