OpenEntityManagerInViewFilter and Worker Thread

[dtrott]

Hi,

I am using:

• Spring 2.5.5
• Hibernate 3.3.0.ga

I have a web app where I am using OpenEntityManagerInViewFilter which works fine for http requests.

However I have a need for a background thread to do some processing.
Processing in the worker thread is trigger by events in the http request threads (ie not scheduled).
I start a single thread when the application starts (Thread.start)

However in this thread I am unable to access any data as I get:

org.hibernate.LazyInitializationException: could not initialize proxy - no Session

Is it possible to create a session in the worker thread and bind it so that the normal JPA annotations, will work correctly?

TIA

[Andrei Tsibets]

Try:

        EntityManagerFactory entityManagerFactory = getEntityManagerFactory();
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        TransactionSynchronizationManager.bindResource(entityManagerFactory, new EntityManagerHolder(entityManager));

        try {

            // your functionality
            
        } finally {
            EntityManagerHolder emHolder = (EntityManagerHolder)
            TransactionSynchronizationManager.unbindResource(entityManagerFactory);
            EntityManagerFactoryUtils.closeEntityManager(emHolder.getEntityManager());
        }

[dtrott]

That worked,
Thank you.

[dejanp]

EntityManager instances are not threadsafe (because jdbc Connection instances are not threadsafe). It may appear that it works, but I wouldn't bet on it.

[Andrei Tsibets]

The idea is to open EntityManager in one thread and not share it with other threads, the same as in OpenEntityManagerInViewFilter.

        new Thread(new Runnable() {
            public void run() {
                EntityManagerFactory entityManagerFactory = getEntityManagerFactory();
                EntityManager entityManager = entityManagerFactory.createEntityManager();
                TransactionSynchronizationManager.bindResource(entityManagerFactory, new EntityManagerHolder(entityManager));

                try {

                    // your functionality

                } finally {
                    EntityManagerHolder emHolder = (EntityManagerHolder)
                    TransactionSynchronizationManager.unbindResource(entityManagerFactory);
                    EntityManagerFactoryUtils.closeEntityManager(emHolder.getEntityManager());
                }
            }
        }).start();

[dejanp]

Sorry, I missed the create part. Why not simply creating a new transaction in the thread then?

[Andrei Tsibets]

Yes, alternative solutions is to use transaction management.

[dtrott]

Sorry, I missed the create part. Why not simply creating a new transaction in the thread then?

I tried to do this, but it is necessary to bind the transaction to spring otherwise you get an error when you enter an @Transactional method (nested transaction).

Anyway with this solution you are free to start and finish transactions using the JPA notation.

[dejanp]

Yes, but you can use TransactionTemplate for that instead of doing it manually.