java - Spring @Async: null hibernate session on LAZY collection

Question

I'm using an @Async annotation on a service layer method.

Everything works fine when I EAGERLY load @OneToMany collection fields, but when I try to access LAZY loaded element I found that Hibernate SessionImplementor object session is null. That obviously give me an exception:

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role:
....    

Here is my collection field:

@OneToMany(mappedBy="abc", fetch=FetchType.LAZY, cascade=CascadeType.REMOVE)
@OrderBy(value="xsd asc")
@JsonIgnore
private Set<Item> items = new HashSet<Item>();

How can I bind hibernate session in order to LAZELY load my object inside @Async context?

EDIT

Here is my trancactionManager / entityManager configuration

<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="emf"/>
</bean>

<tx:annotation-driven transaction-manager="transactionManager" />

<bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="jpaVendorAdapter" ref="hibernateJpaVendorAdapter">

    </property>
    <property name="packagesToScan" value="it.domain"/>

    <property name="persistenceUnitName" value="persistenceUnit"/>
    <property name="jpaProperties">
        <props>
            <prop key="hibernate.dialect">${hibernate.dialect}</prop>
            <prop key="hibernate.ejb.naming_strategy">org.hibernate.cfg.ImprovedNamingStrategy</prop>
            <!--${hibernate.format_sql} -->
            <prop key="hibernate.format_sql">true</prop>
            <prop key="hibernate.hbm2ddl.auto">${hibernate.hbm2ddl.auto}</prop>
            <!-- ${hibernate.show_sql} -->
            <prop key="hibernate.show_sql">false</prop> 

            <prop key="hibernate.connection.charSet">UTF-8</prop>

            <prop key="hibernate.max_fetch_depth">3</prop>
            <prop key="hibernate.jdbc.fetch_size">50</prop>
            <prop key="hibernate.jdbc.batch_size">20</prop>

            <prop key="org.hibernate.envers.audit_table_suffix">_H</prop>
            <prop key="org.hibernate.envers.revision_field_name">AUDIT_REVISION</prop>
            <prop key="org.hibernate.envers.revision_type_field_name">ACTION_TYPE</prop>
            <prop key="org.hibernate.envers.audit_strategy">org.hibernate.envers.strategy.ValidityAuditStrategy</prop>
            <prop key="org.hibernate.envers.audit_strategy_validity_end_rev_field_name">AUDIT_REVISION_END</prop>
            <prop key="org.hibernate.envers.audit_strategy_validity_store_revend_timestamp">True</prop>
            <prop key="org.hibernate.envers.audit_strategy_validity_revend_timestamp_field_name">AUDIT_REVISION_END_TS</prop>               
        </props>
    </property>
</bean>

<jpa:repositories base-package="it.repository"
                  entity-manager-factory-ref="emf"
                  transaction-manager-ref="transactionManager"/>

<jpa:auditing auditor-aware-ref="auditorAwareBean" />
<bean id="auditorAwareBean" class="it.auditor.AuditorAwareBean"/>

Answer 1

I had the same problem, spent few days trying to find a solution, finally got a solution. I would like to share the details I found for those who might have the same issue.

1st - Your @Async-annotated method should be declared in a separate bean rather than the @Controller- or @RestController-annotated bean.

2nd - You certainly need to declare the method @Transactional which is called from within @Async declared method. However, the very first method called from @Async method has to be defined @Transactional. I had the @Transactional method in second or third level in the method execution stack therefore the problem was not solved and I spent two days trying to figure out what was going on.

So the best thing to do is

@Controller
ControllerBean {

    @Autowired
    AsyncService asyncService;

    public controllerMethod() {
        asyncService.asyncMethod();
    }
}

@Service
AsyncService {
    @Autowired
    TransactionalService transactionalService;

    @Async
    public asyncMethod() {
        transactionalService.transactionalMethod();
    }
}

@Service
TransactionalService {
    @Autowired
    SomeOtherService someOtherService;

    @Autowired
    EntityRepository entityRepository;

    @Transactional
    public transactionalMethod() {
        Entity entity = entityRepository.findOne(12345);

        someOtherService.doWork(entity);
    }
}

@Service
SomeOtherService {

    @Autowired
    EntityRepository entityRepository;

    @Transactional
    public doWork(Entity entity) {
        // fetch lazy properties, save, etc. without any session problems...
        entity.getLazyProperties(); 

        entityRepository.save(entity);
    }
}