A Session is also known as an interface that is used to get a physical connectivity with a database. It is instantiated every time we need to interact with the database for the CRUD (Create, Read, Update, Delete) operations. Persistent objects always travel from the application to the database and vice versa only through the Session.
Now, let's find out more about Session and how to open a new Session using a SessionFactory.
Before we create a Session object, we need to get an object such as a SessionFactory as a prerequisite:
- Use the following code to open a new session:
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Now, we will open a new Session with the database:
Session session = sessionFactory.openSession();
Other methods are also available to open a Session, as shown in the following code:
Session openSession(org.hibernate.Interceptor interceptor); Session openSession(java.sql.Connection connection, org.hibernate.Interceptor interceptor);
This will open a brand new Session for us. It opens the database connection when it is created and holds it until the session is closed. A Session created using these methods is not associated with any thread, so it's our responsibility to flush or close it once we are done with the database operation.
A Session is a bridge between the Java application and hibernate. The Session interface wraps the JDBC connection. A Session always tries to be in sync with the persistent store where all transactions are made.
A Session is always a part of first-level cache; it caches all the objects that are transmitted through that particular session. All cached objects will be destroyed once this session is closed.
We can use the same session instead of creating a brand-new session; hibernate provides the facility to reuse an already created session.
Let's look at how to do it:
- Enter the following code to get the current session from
sessionFactory:SessionFactory sessionFactory = HibernateUtil.getSessionFactory(); Session session = sessionFactory.getCurrentSession();
It may seem easy to get the current session, but the twist here is that you have to provide more configuration to the Configuration object if you plan to reuse the Session, as shown in the following code:
<property name="hibernate.current_session_context_class"> Thread </property>
In the preceding code, we set a thread value for the hibernate.current_session_context_class key, meaning that the context of the current Session is limited to the life of the current thread only.
For example, in a non-multithreaded environment, a Session is created when the main thread is started. It will close automatically once the SessionFactory is closed.