Why are life-cycle listeners in Hibernate Serializable?

Question

The Hibernate interfaces that you implement to provide event listeners, for example: org.hibernate.event.PostInsertEventListener; all extend Serializable.

However, it doesn't seem to explain anywhere why your listeners need to be serializable. We've been injecting DAOs with database connections into them for a while, and it hasn't failed yet, however I'm worried that there might be a case where Hibernate will pass the listener over a serialized link, and so lose the database connection.

So the question is: Why do hibernate event listeners have to be serializable?

Answer 1

Although I'm not sure I understand your question correctly I don't know what the problem with a serializable event listener could be.

A event listener has to be implemented as if it was a singleton and they aren't supposed to hold any state in instance variables.

So serializing shouldn't be a problem.

A DAO can't be serialized (for obvious reasons).

If you really have an event listener with a reference to a DAO, mark the DAO instance variable as transient. When you use the DAO check for null and if null get the appropratie DAO from the DAOFactory.