Question

I am building a simple web application for which I would like to use JPA. Although I expect to be deploying on Glassfish I was think that it may be beneficial to manage entity persistence within the application rather than through JTA datasource. I acknowledge that this may not be a very bright idea?

Some time ago I put the following together (possibly from a now lost web reference):

public class PersistenceManager {
    private static final PersistenceManager instance = new PersistenceManager();
    protected EntityManagerFactory emf;

    public static PersistenceManager getInstance() {
        return instance;
    }

    private PersistenceManager() {
    }

    public EntityManagerFactory getEntityManagerFactory() {
        if (emf == null) {
            createEntityManagerFactory();
        }
        return emf;
    }

    public void closeEntityManagerFactory() {
        if (emf != null) {
            emf.close();
            emf = null;
        }
    }

    protected void createEntityManagerFactory() {
        this.emf = Persistence.createEntityManagerFactory("Met");
    }
}

So, my questions; Is this a reasonable approach – are there any pitfalls here?

Answer 1

I’ve always deployed JPA without container managed persistence. I’ve even used it with Atomikos JTA transaction manager. The simplest way is to not use JNDI based lookup. I would recomment using Spring’s JPATransactionManager and to configure everything either with persistence.xml or spring-xml.

Persistence manager in Spring-xml:

<bean id="pum" class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager">
    <property name="defaultDataSource" ref="dataSource" />
    <property name="persistenceXmlLocations">
        <list>
            <value>classpath:META-INF/etf-persistence.xml</value>
        </list>
    </property>
</bean>

<bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="persistenceUnitManager" ref="pum" />
    <property name="persistenceUnitName" value="my-pu" />
    <property name="jpaProperties">
        <props>
            <prop key="hibernate.ejb.cfgfile">my-hibernate.cfg.xml</prop>

            <prop key="hibernate.session_factory_name">mySessionFactory</prop>
            <prop key="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</prop>
            <prop key="hibernate.archive.autodetection">none</prop>

            <prop key="hibernate.show_sql">false</prop>
            <prop key="hibernate.format_sql">false</prop>       
    </property>
</bean>

Don’t specify non-jta or jta-data-source tags in persistence.xml. The rest of the setup is standard-spring (EntityManagerFactory, DataSource etc.).