Java.Hibernate.Beginner.Session lifecycle

✅ Hibernate Session Lifecycle

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🔹 1) Open

• You open a new Session from a SessionFactory:

Session session = sessionFactory.openSession();

A new first-level cache is created, and the session is ready to interact with the database.

🔹 2) Begin Transaction (optional but recommended)

• Start a database transaction associated with the session:

Transaction tx = session.beginTransaction();

🔹 3) Perform Operations

• Perform CRUD operations inside the session:

User user = new User();
user.setUsername("john");
session.save(user); // entity becomes persistent in the session cache

User fetched = session.get(User.class, user.getId()); // served from cache or DB
fetched.setEmail("john@example.com"); // change is tracked automatically

🔹 4) Flush (automatic or manual)

• Hibernate flushes pending changes in the session cache to the database, generating SQL statements.
• This happens automatically:
  • Before committing the transaction.
  • Or manually if you call session.flush().

🔹 5) Commit or Rollback Transaction

• Commit writes the changes permanently:

tx.commit();

Or rollback discards the changes if an error occurs:

tx.rollback();

🔹 6) Close Session

• Releases JDBC connections and destroys the first-level cache:

session.close();

🔹 Lifecycle summary diagram:

openSession() → beginTransaction() → [CRUD] → flush → commit/rollback → closeSession()

✅ Important points:

• Session is lightweight but not thread-safe → use one session per unit of work (e.g., per request).
• While the session is open, Hibernate tracks changes to persistent entities and caches them in first-level cache.
• Closing the session releases resources and evicts the first-level cache.

🔹 Example full lifecycle:

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();

User user = session.get(User.class, 1L); // fetch or load entity
user.setUsername("newName");            // modification tracked

tx.commit();                            // flush + commit
session.close();                        // releases resources

✅ Key takeaway:
The session lifecycle spans opening → transaction → CRUD → flush → commit/rollback → close, and understanding it is critical to writing efficient, bug-free Hibernate code.