Spring Data JPA streaming query methods cause an exception about transactions

Question

If I use a Spring Data repository methods that returns a Stream, I always get the following exception:

org.springframework.dao.InvalidDataAccessApiUsageException: You're trying to execute a streaming query method without a surrounding transaction that keeps the connection open so that the Stream can actually be consumed. Make sure the code consuming the stream uses @Transactional or any other way of declaring a (read-only) transaction.
    org.springframework.data.jpa.repository.query.JpaQueryExecution$StreamExecution.doExecute(JpaQueryExecution.java:338)
    org.springframework.data.jpa.repository.query.JpaQueryExecution.execute(JpaQueryExecution.java:85)
    org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:116)
    org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:106)
    org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:483)
    org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:461)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:61)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99)
    org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:282)
    org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:136)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:133)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    org.springframework.data.repository.core.support.SurroundingTransactionDetectorMethodInterceptor.invoke(SurroundingTransactionDetectorMethodInterceptor.java:57)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213)
    com.sun.proxy.$Proxy201.findByPodcast(Unknown Source)
    <my controller class>$$Lambda$118/2013513791.apply(Unknown Source)

The code in question really ought to be executing in a transaction, however. I have:

• Used the OpenSessionManagerInViewFilter
• Enabled declarative transaction management (@EnableTransactionManagement in my root context configuration) and annotated by the controller class and the request method with @Transactional

I've also tried wrapping the code in a TransactionTemplate and collecting the results in a List to avoid the transaction going out of scope, but that still hasn't worked. Controller methods:

@RequestMapping ( "/pod/{id}" )
@Transactional
public Stream<RSSPodcastItem> podItems (@PathVariable("id") UUID id)
{
    return pods.get (id).map (items::findByPodcast).orElseThrow (() -> new RuntimeException ("failed"));
}
@RequestMapping ( "/podlist/{id}" )
@Transactional
public List<RSSPodcastItem> podItemsList (@PathVariable("id") UUID id)
{
    return tt.execute (ts -> 
        pods.get (id).map (items::findByPodcast).orElseThrow (() -> new RuntimeException ("failed"))
        .collect (Collectors.toList()));
}

the context root configuration class:

@Configuration
@ComponentScan ( ... my package names ...)
@EnableTransactionManagement
@EnableJpaRepositories( ... package with repositories ...)
public class SharedConfig
{
    @Bean
    public DataSource dataSource ()
    {
         // .... snipped
    }

    @Bean
    EntityManagerFactory entityManagerFactory ()
    {
        LocalContainerEntityManagerFactoryBean entityManagerFactoryBean = new LocalContainerEntityManagerFactoryBean ();
        entityManagerFactoryBean.setDataSource (dataSource());
        entityManagerFactoryBean.setJpaVendorAdapter (new HibernateJpaVendorAdapter ());
        entityManagerFactoryBean.setPackagesToScan ( ... package with entities ...);
        entityManagerFactoryBean.setJpaPropertyMap (hibernateProperties());
        entityManagerFactoryBean.afterPropertiesSet ();
        return entityManagerFactoryBean.getObject ();
    }

    @Bean
    JpaTransactionManager transactionManager ()
    {
        JpaTransactionManager transactionManager = new JpaTransactionManager ();
        transactionManager.setEntityManagerFactory (entityManagerFactory());

        return transactionManager;
    }

    @Bean
    TransactionTemplate transactionTemplate (JpaTransactionManager tm)
    {
        return new TransactionTemplate (tm);
    }

    @Bean
    Map<String, ?> hibernateProperties ()
    {
        Map<String, Object> m = new HashMap<> ();
        m.put ("hibernate.dialect", MySQL5Dialect.class);
        m.put ("hibernate.dialect.storage_engine", "innodb");
        boolean devSystem = isDevSystem ();
        m.put ("hibernate.hbm2ddl.auto", devSystem ? "update" : "create-only");  // will need to handle updates by hand on live system, but creation is OK.
        m.put ("hibernate.show_sql", "" + devSystem);
        m.put ("hibernate.cache.use_second_level_cache", "" + !devSystem);
        return m;
    }

Any suggestions what's going wrong here?

Answer 1

In accordance with this post:

Repository clients can ... use the result of the method call in a try-with-resources block.

And Spring Data reference:

A Stream potentially wraps underlying data store specific resources and must therefore be closed after usage. You can either manually close the Stream using the close() method or by using a Java 7 try-with-resources block.

So I think you should wrap your stream to try-with-resource block and, as exception suggest, set read-only transaction, something like this:

@RequestMapping("/pod/{id}")
@Transactional(readOnly = true)
public Stream<RSSPodcastItem> podItems (@PathVariable("id") UUID id) {
    try (Stream<RSSPodcastItem> items = repository.findByPodcast(...)) {
        return items...;
    }
}

Additional info: Spring Data - Java 8 examples