Chapter 97. Persistence Unit/Context Injection

97.1. @PersistenceContext Injection
97.2. @PersistenceUnit Injection
97.3. Context and Dependency Injection (CDI)
97.4. Summary

@PersistenceContext

Injected with EntityManager

Transaction Scoped

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

Extended Scope

persistence context may see multiple Tx
only relevant for Stateful EJBs

@PersistenceUnit

Injected with EntityManagerFactory

May be used to implement BEAN-managed transactions

97.1. @PersistenceContext Injection

Figure 97.1. @PersistenceContext Injection

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

97.2. @PersistenceUnit Injection

Figure 97.2. @PersistenceUnit Injection

@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();

    }

}

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

97.3. 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(name="jndidemo") //using ENC-name

    @Produces

    @JndiDemo

    public EntityManager em;

Define injection point



@Stateless

public class TrainSchedulerEJB 

    extends SchedulerBase implements TrainSchedulerRemote {


    @Inject @JndiDemo

    private EntityManager em;