Accessing multiple database from a Java web application using JPA/EclipseLink/EJB

Question

I have built a simple SOAP java application(server side) and I am using Glassfish4,JPA/EclipseLink,EJB. I have set the db connections(resources/poo

Answer 1

My solution would be to add a second persistence unit for the second database, then refactor your GenericDAO so that the EntityManager is not an attribute of the class, but passed into each method. I would then create facade objects for each of your databases which get the GenericDAO and the relevent EntityManager injected into them. If you really wanted you could have a common interface to keep the api the same. It might look like this:

persistence.xml

    
        org.eclipse.persistence.jpa.PersistenceProvider
        jdbc/simfin
        org.demo.model.MemRegMcgEntity
        org.demo.model.SavAccHolderMcgEntity
        org.demo.model.SavAccMcgEntity
        org.demo.model.SavTransactionEntity
    

    
        org.eclipse.persistence.jpa.PersistenceProvider
        jdbc/other-jta-datasource
        org.demo.model.OtherEntityOne
        org.demo.model.OtherEntityTwo
        org.demo.model.OtherEntityThree
        org.demo.model.OtherEntityFour
    

Generic DAO:

public class GenericDAO {

public void  save(EntityManager em, T entity) {
    em.persist(entity);
}

Entity Interface:

public Interface IEntity {
    ....
}

Entity Class:

public class SomeEntity implements IEntity {
    ....
}

DAO Facade Database One:

public class GenericFacadeOne {

@PersistenceContext(unitName = "SavingBalanceDemoServer_PU")
private EntityManager em; 
@Autowired
private GenericDao dao;

@Transactional(propogation=Propogation.REQUIRED)
public void saveSomeEntity(SomeEntity entity) {
    getDao().save(getEm(), entity);
}

public void setEm(EntityManager em) {
    this.em = em;
}   

public EntityManager getEntityManager() {
    return this.em;
}

public void setDao(GenericDao dao) {
    this.em = em;
}   

public GenericDao getDao() {
    return this.dao;
}
}

DAO Facade Database Two:

public class GenericFacadeTwo {

@PersistenceContext(unitName = "MySecondPersistenceUnit_PU")
private EntityManager em; 
@Autowired
private GenericDao dao;

@Transactional(propogation=Propogation.REQUIRED)
public void saveSomeEntity(SomeEntity entity) {
    getDao().save(getEm(), entity);
}

public void setEm(EntityManager em) {
    this.em = em;
}   

public EntityManager getEntityManager() {
    return this.em;
}

public void setDao(GenericDao dao) {
    this.em = em;
}   

public GenericDao getDao() {
    return this.dao;
}
}

Hopefully that makes sense, let me know if you need any clarification!