Zugriff auf mehrere Datenbanken aus einer Java-web-Anwendung mit JPA/EclipseLink/EJB

Ich gebaut habe, eine einfache SOAP java-Anwendung(server-Seite) und ich bin mit Glassfish4,JPA/EclipseLink,EJB. Ich habe den db-verbindungen(Ressourcen/pools) in Glassfish. Schlagen Sie bitte einige design-Muster/wissen zu nutzen, um mehrere Datenbanken von einer einzigen Anwendung. Ist die Erstellung mehrerer persistence-unit eine gute Idee für mehrere access?? Oder gibt es eine andere optimale Lösung ?
Ich habe eine generische Klasse für den Datenbank-Zugriff.

public class GenericDAO<T> {

/*
* private static final EntityManagerFactory emf =
* Persistence.createEntityManagerFactory("icanPU"); private EntityManager
* em;
*/
/*
* Persistence context is injected with following @PersistenceContext
* annotation. This uses all persistence configurations as specified in the
* persistence.xml.
* 
* Note this kind of injection can only be done for JTA data sources.
*/
@PersistenceContext(unitName = "SavingBalanceDemoServer_PU")
private EntityManager em;
private Class<T> entityClass;

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

public void joinTransaction() {
/* em = emf.createEntityManager(); */
em.joinTransaction();
}

public GenericDAO(Class<T> entityClass) {
this.entityClass = entityClass;
}

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

//Added by Sudeep for bulk Insert of List object.
public void saveList(List<T> objList) {
for (Iterator<T> iterator = objList.iterator(); iterator.hasNext();) {
T t = (T) iterator.next();
em.persist(t);
}
}

public void delete(Object id, Class<T> classe) {
T entityToBeRemoved = em.getReference(classe, id);

em.remove(entityToBeRemoved);
}

public T update(T entity) {
return em.merge(entity);
}

public int truncateUsingNative(String tableName) {
Query qry = em.createNativeQuery("TRUNCATE TABLE " + tableName);

return qry.executeUpdate();
}

//Added by Sudeep for bulk Update of List object.
public void updateList(List<T> entity) {
for (Iterator<T> iterator = entity.iterator(); iterator.hasNext();) {
T t = (T) iterator.next();
em.merge(t);
}
}

public T find(int entityID) {
//em.getEntityManagerFactory().getCache().evict(entityClass, entityID);
return em.find(entityClass, entityID);
}

public T find(long entityID) {
//em.getEntityManagerFactory().getCache().evict(entityClass, entityID);
return em.find(entityClass, entityID);
}

public T find(Object compositePkObject) {
//em.getEntityManagerFactory().getCache().evict(entityClass, entityID);
return em.find(entityClass, compositePkObject);
}

public T findReferenceOnly(int entityID) {
return em.getReference(entityClass, entityID);
}

//Using the unchecked because JPA does not have a
//em.getCriteriaBuilder().createQuery()<T> method
@SuppressWarnings({ "unchecked", "rawtypes" })
public List<T> findAll() {
CriteriaQuery cq = null;
if (isDbAccessible()) {
try {
cq = em.getCriteriaBuilder().createQuery();
cq.select(cq.from(entityClass));
return em.createQuery(cq).getResultList();
} catch (org.eclipse.persistence.exceptions.DatabaseException ex) {
System.out.println("The zzz error is :" + ex.toString());
/*JSFMessageUtil jsfMessageUtil = new JSFMessageUtil();
jsfMessageUtil
.sendErrorMessageToUser("Database Server is unavailable or not accessible! Please, contact your system admin!");*/
return null;
}
}
return null;
}

private boolean isDbAccessible() {
return em.isOpen();
}

@SuppressWarnings("unchecked")
public List<T> findAllWithGivenCondition(String namedQuery,
Map<String, Object> parameters) {
List<T> result = null;
Query query = em.createNamedQuery(namedQuery);

if (parameters != null && !parameters.isEmpty()) {
populateQueryParameters(query, parameters);
}

result = (List<T>) query.getResultList();

return result;
}

@SuppressWarnings("unchecked")
public List<T> findAllWithGivenConditionLazyLoading(String namedQuery,
Map<String, Object> parameters,int startingAt, int maxPerPage) {
List<T> result = null;
Query query = em.createNamedQuery(namedQuery);

if (parameters != null && !parameters.isEmpty()) {
populateQueryParameters(query, parameters);
}
query.setFirstResult(startingAt);
query.setMaxResults(maxPerPage);

result = (List<T>) query.getResultList();

return result;

}

@SuppressWarnings("unchecked")
public List<T> findAllWithGivenConditionJpql(String jpql,
Map<String, Object> parameters) {
List<T> result = null;
Query query = em.createQuery(jpql);

if (parameters != null && !parameters.isEmpty()) {
populateQueryParameters(query, parameters);
}

result = (List<T>) query.getResultList();

return result;
}

@SuppressWarnings("unchecked")
public T findOneWithGivenConditionJpql(String jpql,
Map<String, Object> parameters) {
Query query = em.createQuery(jpql);

if (parameters != null && !parameters.isEmpty()) {
populateQueryParameters(query, parameters);
}
return (T) query.getSingleResult();
}

//Using the unchecked because JPA does not have a
//query.getSingleResult()<T> method
@SuppressWarnings("unchecked")
protected T findOneResult(String namedQuery, Map<String, Object> parameters) {
T result = null;

try {
if (!em.isOpen()) {
/*JSFMessageUtil jsfMessageUtil = new JSFMessageUtil();
jsfMessageUtil
.sendErrorMessageToUser("Database Server is unavailable or not accessible! Please, contact your system admin!");*/
} else {
Query query = em.createNamedQuery(namedQuery);

//Method that will populate parameters if they are passed not
//null and empty
if (parameters != null && !parameters.isEmpty()) {
populateQueryParameters(query, parameters);
}

result = (T) query.getSingleResult();
}

} catch (NoResultException e) {
//JSFMessageUtil jsfMessageUtil = new JSFMessageUtil();
//jsfMessageUtil.sendErrorMessageToUser("No Information Found...!");

//e.printStackTrace();
return null;
} catch (org.eclipse.persistence.exceptions.DatabaseException e) {
/*JSFMessageUtil jsfMessageUtil = new JSFMessageUtil();
jsfMessageUtil
.sendErrorMessageToUser("Database Server is unavailable or not accessible!");*/
e.printStackTrace();
}

return result;
}

private void populateQueryParameters(Query query,
Map<String, Object> parameters) {
for (Entry<String, Object> entry : parameters.entrySet()) {
query.setParameter(entry.getKey(), entry.getValue());
}
}

/**
* @param startingAt
* @param maxPerPage
* @param t
* @return list of persisted entities which belong to this class t
*/
@SuppressWarnings("unchecked")
public List<T> getAllLazyEntities(int startingAt, int maxPerPage, Class<T> t) {
//regular query that will search for players in the db
Query query = getEntityManager().createQuery(
"select p from " + t.getName() + " p");
query.setFirstResult(startingAt);
query.setMaxResults(maxPerPage);

return query.getResultList();
}

/**
* @param clazz
* @return count of existing entity rows from backend
*/
public int countTotalRows(Class<T> clazz) {
Query query = getEntityManager().createQuery(
"select COUNT(p) from " + clazz.getName() + " p");

Number result = (Number) query.getSingleResult();

return result.intValue();
}

/**
* @return count of existing entity rows from backend acccording to given
*         condition
*/
public int countTotalRowsWithCond(Class<T> clazz, String Cond) {
Query query = getEntityManager()
.createQuery(
"select COUNT(p) from " + clazz.getName() + " p "
        + Cond + "  ");

Number result = (Number) query.getSingleResult();

return result.intValue();
}
}

Dynamisch ändern unitName im @PersistenceContext(unitName = "SavingBalanceDemoServer_PU") eine gute Idee ? Bitte schlagen Sie mich.

Meine persistence.xml ist :

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1"
xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
<persistence-unit name="SavingBalanceDemoServer_PU"
transaction-type="JTA">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<jta-data-source>jdbc/simfin</jta-data-source>
<class>org.demo.model.MemRegMcgEntity</class>
<class>org.demo.model.SavAccHolderMcgEntity</class>
<class>org.demo.model.SavAccMcgEntity</class>
<class>org.demo.model.SavTransactionEntity</class>
</persistence-unit>
</persistence>

Bitte vorschlagen, einige Optimierungen/Veränderungen in dieser Datei.

Und ich habe mit EJB um die Verwendung der Generischen Klasse.
eg:

@Stateless
public class MemberEJB extends GenericDAO<MemRegMcgEntity> {
/**
* @see GenericDAO#GenericDAO(Class<T>)
*/
public MemberEJB() {
super(MemRegMcgEntity.class);
//TODO Auto-generated constructor stub
}

public List<MemRegMcgEntity> getListOfMemberByName(String name){
Map<String, Object> parameters = new HashMap<String, Object>();
parameters.put("memName", name+'%');

return super.findAllWithGivenCondition("Mem.getMemberByName", parameters);
}

}

Die client-app bietet den Datenbank-Namen zu verwenden, und jede Datenbank hat dieselbe Struktur. Ich brauche einfach nur den Zugriff auf mehrere Datenbank entsprechend client ' s Anforderung.