Hibernate Transaction

[Fight Ice]

java code:

Transaction ts=session.beginTransaction();
Criteria criteria=session.createCriteria(Item.class);
criteria.add(Restrictions.idEq(product.getItem().getId()));
criteria.setLockMode(LockMode.PESSIMISTIC_WRITE);
Item item=(Item)criteria.list().get(0);
...
ts.commit();
...
Transaction tc=session.beginTransaction();
...
tc.commit();

Then I got the Exception:
Transaction not successfully started.