[java] How to manually force a commit in a @Transactional method?

I'm using Spring / Spring-data-JPA and find myself needing to manually force a commit in a unit test. My use case is that I am doing a multi-threaded test in which I have to use data that is persisted before the threads are spawned.

Unfortunately, given that the test is running in a @Transactional transaction, even a flush does not make it accessible to the spawned threads.

   @Transactional   
   public void testAddAttachment() throws Exception{
        final Contract c1 = contractDOD.getNewTransientContract(15);
        contractRepository.save(c1);

        // Need to commit the saveContract here, but don't know how!                
        em.getTransaction().commit();

        List<Thread> threads = new ArrayList<>();
        for( int i = 0; i < 5; i++){
            final int threadNumber = i; 
            Thread t =  new Thread( new Runnable() {
                @Override
                @Transactional
                public void run() {
                    try {
                        // do stuff here with c1

                        // sleep to ensure that the thread is not finished before another thread catches up
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            });
            threads.add(t);
            t.start();
        }

        // have to wait for all threads to complete
        for( Thread t : threads )
            t.join();

        // Need to validate test results.  Need to be within a transaction here
        Contract c2 = contractRepository.findOne(c1.getId());
    }

I've tried using the entity manager to, but get an error message when I do:

org.springframework.dao.InvalidDataAccessApiUsageException: Not allowed to create transaction on shared EntityManager - use Spring transactions or EJB CMT instead; nested exception is java.lang.IllegalStateException: Not allowed to create transaction on shared EntityManager - use Spring transactions or EJB CMT instead
    at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:293)
    at org.springframework.orm.jpa.aspectj.JpaExceptionTranslatorAspect.ajc$afterThrowing$org_springframework_orm_jpa_aspectj_JpaExceptionTranslatorAspect$1$18a1ac9(JpaExceptionTranslatorAspect.aj:33)

Is there any way to commit the transaction and continue it? I have been unable to find any method that allows me to call a commit().

Why don't you use spring's TransactionTemplate to programmatically control transactions? You could also restructure your code so that each "transaction block" has it's own @Transactional method, but given that it's a test I would opt for programmatic control of your transactions.

Also note that the @Transactional annotation on your runnable won't work (unless you are using aspectj) as the runnables aren't managed by spring!

@RunWith(SpringJUnit4ClassRunner.class)
//other spring-test annotations; as your database context is dirty due to the committed transaction you might want to consider using @DirtiesContext
public class TransactionTemplateTest {

@Autowired
PlatformTransactionManager platformTransactionManager;

TransactionTemplate transactionTemplate;

@Before
public void setUp() throws Exception {
    transactionTemplate = new TransactionTemplate(platformTransactionManager);
}

@Test //note that there is no @Transactional configured for the method
public void test() throws InterruptedException {

    final Contract c1 = transactionTemplate.execute(new TransactionCallback<Contract>() {
        @Override
        public Contract doInTransaction(TransactionStatus status) {
            Contract c = contractDOD.getNewTransientContract(15);
            contractRepository.save(c);
            return c;
        }
    });

    ExecutorService executorService = Executors.newFixedThreadPool(5);

    for (int i = 0; i < 5; ++i) {
        executorService.execute(new Runnable() {
            @Override  //note that there is no @Transactional configured for the method
            public void run() {
                transactionTemplate.execute(new TransactionCallback<Object>() {
                    @Override
                    public Object doInTransaction(TransactionStatus status) {
                        // do whatever you want to do with c1
                        return null;
                    }
                });
            }
        });
    }

    executorService.shutdown();
    executorService.awaitTermination(10, TimeUnit.SECONDS);

    transactionTemplate.execute(new TransactionCallback<Object>() {
        @Override
        public Object doInTransaction(TransactionStatus status) {
            // validate test results in transaction
            return null;
        }
    });
}

}

I know that due to this ugly anonymous inner class usage of TransactionTemplate doesn't look nice, but when for some reason we want to have a test method transactional IMHO it is the most flexible option.

In some cases (it depends on the application type) the best way to use transactions in Spring tests is a turned-off @Transactional on the test methods. Why? Because @Transactional may leads to many false-positive tests. You may look at this sample article to find out details. In such cases TransactionTemplate can be perfect for controlling transaction boundries when we want that control.