Chapter 99. Persistence Unit/Context Injection

99.1. @PersistenceContext Injection
99.2. @PersistenceUnit Injection
99.3. Context and Dependency Injection (CDI)
99.4. Summary

@PersistenceContext

Injected with EntityManager

Transaction Scoped (default)

persistence context only sees a single Tx
container injects EntityManager with Tx active

@PersistenceContext(unitName="ejbjpa-hotel", type=PersistenceContextType.TRANSACTION)

private EntityManager em;

Extended Scope

persistence context may see multiple Tx
only relevant for Stateful EJBs

@PersistenceContext(unitName="ejbjpa-hotel", type=PersistenceContextType.EXTENDED)

private EntityManager em;

@PersistenceUnit

Injected with EntityManagerFactory

May be used to implement BEAN-managed transactions

99.1. @PersistenceContext Injection

@PersistenceContext.unitName is the name used within the persistence.xml
@PersistenceContext.name would be the ENC name normally defined in ejb-jar.xml

@Stateless

public class HotelMgmtEJB implements HotelMgmtRemote, HotelMgmtLocal {

    @PersistenceContext(unitName="ejbjpa-hotel")

    private EntityManager em;


    private HotelDAO dao;

    private HotelMgmt hotelMgmt; 

    

    @PostConstruct

    public void init() {

        dao = new JPAHotelDAO();

        ((JPAHotelDAO)dao).setEntityManager(em);

        

        hotelMgmt = new HotelMgmtImpl();

        ((HotelMgmtImpl)hotelMgmt).setHotelDao(dao);

    }

@PersistenceContext.synchronization
- SynchronizationType.SYNCHRONIZED (default) -- EntityManager automatically joined with jtaTransaction
- SynchronizationType.UNSYNCHRONIZED -- EntityManager manually joined with jtaTransaction. Useful for Stateful Session EJBs where interaction with EntityManager may span multiple client method calls.
@PersistenceContext.type
- PersistenceContextType.TRANSACTION (default) - EntityManager transactions automatically managed by container and will invoke each root method once per transaction
- PersistenceContextType.EXTENDED - EntityManager transactions may span multiple calls. Useful for Stateful Session EJBs to retain state during a complete session

99.2. @PersistenceUnit Injection

Persistence unit (EntityManagerFactory) being injected from a JTA-managed source
- i.e., the transaction must be managed at JTA level
BEAN-managed transactions means JTA transaction controlled thru injected UserTransaction
Method programmatically controlling scope of JTA transaction
em.joinTransaction() called on EntityManager created outside scope of JTA transaction

@Singleton

@Startup

@TransactionManagement(TransactionManagementType.BEAN)

public class HotelInitEJB implements HotelInitRemote {

    @PersistenceUnit(unitName="ejbjpa-hotel")

    private EntityManagerFactory emf;

    

    @Resource

    private UserTransaction tx;

    

    @Override

    public void businessMethod() {

        EntityManager em=emf.createEntityManager();

        HotelDAO dao = new JPAHotelDAO();

        ((JPAHotelDAO)dao).setEntityManager(em);

        tx.begin();        

        em.joinTransaction(); //tells the EM to join the JTA Tx

        ...

        tx.commit();

        em.close();

    }

}

99.3. Context and Dependency Injection (CDI)

Newer technique -- JavaEE's answer to Spring Configuration

Define qualifier annotation

package ejava.examples.jndidemo;


import java.lang.annotation.Retention;

import java.lang.annotation.Target;

import static java.lang.annotation.RetentionPolicy.*;

import static java.lang.annotation.ElementType.*;

import javax.inject.Qualifier;


@Qualifier

@Retention(RUNTIME)

@Target({METHOD, FIELD, PARAMETER, TYPE})

public @interface JndiDemo {

}

Define producer of Persistence Context

import javax.enterprise.inject.Produces;

import javax.persistence.EntityManager;

import javax.persistence.PersistenceContext;


public class SchedulerResources {

    @PersistenceContext(unitName="jndidemo")

    @Produces

    @JndiDemo

    public EntityManager em;

Define injection point

@Stateless

public class TrainSchedulerEJB 

    extends SchedulerBase implements TrainSchedulerRemote {


    @Inject @JndiDemo

    private EntityManager em;

Qualifier not always necessary

The Qualifier annotation is only necessary when the deployed application contains multiple producers of an EntityManager.