Obtaining EntityManager in Spring + Hibernate configuration

Question

I have a Spring MVC 4.0 application, and I am learning JPA. I use Hibernate as the JPA implementation.

I can configure Hibernate as described in this tutorial. It works fine, but I have to use Hibernate's Session object:

@Autowired
SessionFactory sessionFactory;

...

Session session = sessionFactory.openSession();

Now, I want to use JPA's EntityManager instead. I have followed this tutorial on the same web site (the configuration is very similar). And I tried to obtain an EntityManager object this way:

@PersistenceContext
EntityManager entityManager;

I got a runtime message:

java.lang.IllegalStateException: No transactional EntityManager available

Then, I followed the suggestion in this answer, and tried to use the following code:

@PersistenceContext
EntityManager entityManager;

...

entityManager=entityManager.getEntityManagerFactory().createEntityManager();

It works a few times (about 9 repetitive method invocations), and then the application freezes.

What is the right way to get EntityManager in Spring + Hibernate configuration?

I do not need any Spring transaction functionality for now. I just want to get an access to EntityManager and play with JPA.

Spring/Hibernate configuration file (hibernate.xml)

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd">

    <bean id="dataSource" class="org.apache.tomcat.dbcp.dbcp.BasicDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/test_db" />
        <property name="username" value="test" />
        <property name="password" value="test" />
    </bean>

    <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="packagesToScan" value="net.myproject" />
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" />
        </property>
        <property name="jpaProperties">
            <props>
                <prop key="hibernate.hbm2ddl.auto">update</prop>
                <prop key="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</prop>
                <prop key="hibernate.show_sql">true</prop>
            </props>
        </property>
    </bean>

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

    <bean id="persistenceExceptionTranslationPostProcessor" class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor" />

    <tx:annotation-driven />

</beans>

The class where I attempt to use EntityManager

@Repository
public class ProductsService {

    @PersistenceContext
    EntityManager entityManager;

    @Transactional
    public GridResponse<Product> getProducts(GridRequest dRequest) {

        // The following line causes the exception: "java.lang.IllegalStateException: No transactional EntityManager available"
        Session session = entityManager.unwrap(Session.class);

        //...
    }

...

Answer 1

For the @PersistenceContext EntityManager entityManager; approach, add tx:annotation-driven to your .xml configuration and mark your methods where you use entityManager as @Transactional.