Hibernate session

Session

Session is used to obtain a physical connection to the database. S ession objects are lightweight and are designed to be instantiated each time you need to interact with the database. Persistent objects are saved and retrieved through the Session object.

Session objects should not remain open for long periods of time because they are generally not thread-safe and should be created and destroyed as needed. S ession's primary function is to provide creation, read, and delete operations for mapping instances of entity classes. These instances may exist in one of three states at a given point in time:

• Instant State: A new persistent instance, considered transient by Hibernate, is not associated with Session, has no records associated with it in the database, and has no identifier values.
• Persistence: An instantaneous instance can be transformed into a persistent state instance by association to a Session. Persistent state instances do not have records associated with them in the database, have identifier values, and are associated with a Session.
• De-piped state: Once Hibernate Session is closed, the persistent state instance becomes the de-piped instance.

If the persistent state category of a Session instance is serialized, the Session instance is serialized. A typical transaction should use the following syntax:

Session session = factory.openSession();
Transaction tx = null;
try {
   tx = session.beginTransaction();
   // do some work
   ...
   tx.commit();
}
catch (Exception e) {
   if (tx!=null) tx.rollback();
   e.printStackTrace(); 
}finally {
   session.close();
}

If Session throws an exception, the transaction must be rolled back and the session must be discarded.

Session interface method

The Session interface provides a number of methods, but in the following instructions I'll list only a few important methods that we'll apply in this tutorial. You can view the Hibernate file and query the full method catalog related to Session and SessionFactory.