Why can i get an EntityManagerFactory object from a LocalContainerEntityManagerFactoryBean bean definition?

Question

I have the following bean definition in a file called beans.xml :

<bean id="entityManager"
    class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="packagesToScan" value="mypackagename" />
    <property name="persistenceProviderClass"
        value="org.hibernate.jpa.HibernatePersistenceProvider" />
    <property name="jpaPropertyMap">
        <map>
            <entry key="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect" />
            <entry key="hibernate.hbm2ddl.auto" value="update" />
        </map>
    </property>
</bean>

And i can obtain this bean as an EntityManagerFactory object with the following code:

ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
EntityManagerFactory emf = context.getBean(EntityManagerFactory.class);

How is this possible?

As i see LocalContainerEntityManagerFactoryBean does not implement EntityManagerFactory .

How does this work exactly?

Answer 1

The chain is as follows: LocalContainerEntityManagerFactoryBean extends AbstractEntityManagerFactoryBean which implements FactoryBean<EntityManagerFactory> and thus you're getting your EntityManagerFactory .

In fact you're requesting EntityManagerFactory from the ApplicationContext which already has EntityManagerFactory that created by appropriate FactoryBean .

Refer to FactoryBean documentation for more details.