Java Question

Spring managed transactions without @Transactional annotation

I'm using Spring annotations to manage my transactions like so:

@Transactional(readOnly = true)
public class AlertServiceImpl implements AlertService {

private AlertDAO alertDAO;

public List<Alert> getAlerts(){
List<Alert> alerts = alertDAO.getAlerts();
return alerts;
}

}


I'm wondering what happens if I forget the annotation:

// Oops! Forgot to use transactional annotation
public class AlertServiceImpl implements AlertService {

private AlertDAO alertDAO;

public List<Alert> getAlerts(){
List<Alert> alerts = alertDAO.getAlerts();
return alerts;
}

}


When the alertDAO implementation is following:

import org.springframework.orm.hibernate3.support.HibernateDaoSupport;

// no annotation here either
public class HibernateAlertDAO extends HibernateDaoSupport implements AlertDAO {

public List<Alert> getAlerts(){
// some implementation details that define queryString

Query query = getSession().createQuery(queryString);
List<Alert> alerts = query.list();

return alerts;
}

}


It seems like Hibernate allows me to fetch data from database even without the annotation.

What are the consequences of this kind of carelessness and what are the worst case scenarios that could happen?

Answer Source

According to the documentation (Spring docs) it's just metadata to give an indication that the method or interface can be configured by something that is 'transactionally aware' (i.e. <tx:annotation-driven/>).

With just tx:annotation-driven and no @Transactional attribute I believe you get the "default" transactionality applied:

  • Propagation setting is REQUIRED.
  • Isolation level is DEFAULT.
  • Transaction is read/write.
  • Transaction timeout defaults to the default timeout of the underlying transaction system, or none if timeouts are not supported.
  • any RuntimeException triggers rollback, and any checked Exception does not.

Assuming you're using the <tx:annotation-driven /> to drive it via a transaction manager then missing out the @Transactional attribute means you can't apply such properties as readOnly, isolation, propagation, rollbackFor, noRollbackFor etc.

I believe that MVC is slightly different - the Hibernate session is tied directly to the MVC request - i.e. when the request is received the transaction starts.

Back to your example, the code for getSession() in HibernateDAOSupport is as follows:

protected final Session getSession()
    throws DataAccessResourceFailureException, IllegalStateException 
{
    return getSession(this.hibernateTemplate.isAllowCreate());
}

Which in turn calls to:

/**
 * Obtain a Hibernate Session, either from the current transaction or
 * a new one. The latter is only allowed if "allowCreate" is true.
 *.......
 */
protected final Session getSession()
    throws DataAccessResourceFailureException, IllegalStateException {
    return getSession(this.hibernateTemplate.isAllowCreate());
}

which ultimately calls to :

/** 
 * ....
 * @param allowCreate whether a non-transactional Session should be created
 * when no transactional Session can be found for the current thread
 * ....
 */
private static Session doGetSession(
    SessionFactory sessionFactory, Interceptor entityInterceptor,
SQLExceptionTranslator jdbcExceptionTranslator, boolean allowCreate)

Fundamentally, a Transaction:Session is tied 1:1 AFAIK, and the only way to run without a transaction is by using say JBoss which has a 'baked in' persistence layer which provides the transactionality for you (under the covers). Even if you call getQuery() after getSession() you still effectively have a transaction occurring as it's a JDBC/Hibernate connection.

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