Hibernate JTA多用户会话事务映射

Question

I am referring to https://developer.jboss.org/wiki/SessionsAndTransactions and currently trying to understand demarcation with JTA. It states that within a particular transaction using getCurrentSession() always gives the same current session. Does it mean:

1. If another user is executing the same piece of code (which fetches a transaction by lookup, then uses getCurrentSession() and then closes the transaction) in another thread - that user will have his own transaction and his own current session ie the current sessions of 2 users are same for themselves but different from each other?
2. If 1 is true and based on the code shown in the link for JTA demarcation - how does the system (read Hibernate) understand which session to respond to which user when getCurrentSession() is used? After all we don't pass the transaction as argument to getCurrentSession().

Any pointers/help is much appreciated.

Thanks

Answer 1

According to javadoc SessionFactory.getCurrentSession()

The definition of what exactly "current" means controlled by the {@link org.hibernate.context.spi.CurrentSessionContext} impl configured for use.

JTA is configured this will default to the {@link org.hibernate.context.internal.JTASessionContext} impl.

Then you can see JTASessionContext javadoc and implementation.

If a session is not already associated with the current JTA transaction at the time {@link #currentSession()} is called, a new session will be opened and it will be associated with that JTA transaction.

public Session currentSession() throws HibernateException {
  ...
  final TransactionManager transactionManager = jtaPlatform.retrieveTransactionManager();
  ...
  txn = transactionManager.getTransaction();
  ...
  final Object txnIdentifier = jtaPlatform.getTransactionIdentifier( txn );
  ...
  Session currentSession = currentSessionMap.get( txnIdentifier );
  ...
}

TransactionManager javadoc

Internally, the transaction manager associates transactions with threads, and the methods here operate on the transaction associated with the calling thread.

So, it's similar (but more clearly) to Sessions and Transactions/Transaction demarcation with plain JDBC :

In other words, the session is bound to the thread behind the scenes, but scoped to a transaction, just like in a JTA environment.