我有few classes very like the following LinkFacade。如何制作一个“通用”外观来消除或至少减少在不同“外观”类中复制的方法？
示例“facade”：
package net.bounceme.dur.jpa.facades;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import net.bounceme.dur.jpa.controllers.LinkJpaController;
import net.bounceme.dur.jpa.entities.Link;
import net.bounceme.dur.jpa.exceptions.NonexistentEntityException;
public class LinkFacade {
private final static Logger log = Logger.getLogger(LinkFacade.class.getName());
private final EntityManagerFactory emf = Persistence.createEntityManagerFactory("SeleniumIteratorPU");
private final LinkJpaController controller = new LinkJpaController(emf);
public LinkFacade() {
}
public void create(Link link) {
controller.create(link);
}
public void edit(Link link) {
try {
controller.edit(link);
} catch (NonexistentEntityException ex) {
Logger.getLogger(LinkFacade.class.getName()).log(Level.SEVERE, null, ex);
} catch (Exception ex) {
Logger.getLogger(LinkFacade.class.getName()).log(Level.SEVERE, null, ex);
}
}
public void destroy(int id) {
try {
controller.destroy(id);
} catch (NonexistentEntityException ex) {
Logger.getLogger(LinkFacade.class.getName()).log(Level.SEVERE, null, ex);
}
}
public List<Link> findEntities() {
return controller.findLinkEntities();
}
public void findEntity(int id) {
controller.findLink(id);
}
public int getCount() {
return controller.getLinkCount();
}
}
这些类中的方法非常重复。如果正确使用这些方法，我如何在泛型类中抽象，例如：
package net.bounceme.dur.jpa.facades;
import java.util.List;
import java.util.logging.Logger;
import javax.persistence.EntityManager;
public abstract class AbstractFacade<T> {
private final static Logger log = Logger.getLogger(AbstractFacade.class.getName());
private final Class<T> entityClass;
public AbstractFacade(Class<T> entityClass) {
this.entityClass = entityClass;
}
protected abstract EntityManager getEntityManager();
public void create(T entity) {
}
public void edit(T entity) {
}
public void remove(T entity) {
}
public T find(Object id) {
}
public List<T> findAll() {
}
public List<T> findRange(int[] range) {
}
public int count() {
}
}
与此“外观”相关的相应JpaController：
package net.bounceme.dur.jpa.controllers;
import net.bounceme.dur.jpa.entities.Feed;
import net.bounceme.dur.jpa.entities.Link;
import net.bounceme.dur.jpa.exceptions.NonexistentEntityException;
import java.io.Serializable;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Query;
import javax.persistence.EntityNotFoundException;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Root;
public class LinkJpaController implements Serializable {
public LinkJpaController(EntityManagerFactory emf) {
this.emf = emf;
}
private EntityManagerFactory emf = null;
public EntityManager getEntityManager() {
return emf.createEntityManager();
}
public void create(Link link) {
EntityManager em = null;
try {
em = getEntityManager();
em.getTransaction().begin();
Feed feedId = link.getFeedId();
if (feedId != null) {
feedId = em.getReference(feedId.getClass(), feedId.getId());
link.setFeedId(feedId);
}
em.persist(link);
if (feedId != null) {
feedId.getLinkCollection().add(link);
feedId = em.merge(feedId);
}
em.getTransaction().commit();
} finally {
if (em != null) {
em.close();
}
}
}
public void edit(Link link) throws NonexistentEntityException, Exception {
EntityManager em = null;
try {
em = getEntityManager();
em.getTransaction().begin();
Link persistentLink = em.find(Link.class, link.getId());
Feed feedIdOld = persistentLink.getFeedId();
Feed feedIdNew = link.getFeedId();
if (feedIdNew != null) {
feedIdNew = em.getReference(feedIdNew.getClass(), feedIdNew.getId());
link.setFeedId(feedIdNew);
}
link = em.merge(link);
if (feedIdOld != null && !feedIdOld.equals(feedIdNew)) {
feedIdOld.getLinkCollection().remove(link);
feedIdOld = em.merge(feedIdOld);
}
if (feedIdNew != null && !feedIdNew.equals(feedIdOld)) {
feedIdNew.getLinkCollection().add(link);
feedIdNew = em.merge(feedIdNew);
}
em.getTransaction().commit();
} catch (Exception ex) {
String msg = ex.getLocalizedMessage();
if (msg == null || msg.length() == 0) {
Integer id = link.getId();
if (findLink(id) == null) {
throw new NonexistentEntityException("The link with id " + id + " no longer exists.");
}
}
throw ex;
} finally {
if (em != null) {
em.close();
}
}
}
public void destroy(Integer id) throws NonexistentEntityException {
EntityManager em = null;
try {
em = getEntityManager();
em.getTransaction().begin();
Link link;
try {
link = em.getReference(Link.class, id);
link.getId();
} catch (EntityNotFoundException enfe) {
throw new NonexistentEntityException("The link with id " + id + " no longer exists.", enfe);
}
Feed feedId = link.getFeedId();
if (feedId != null) {
feedId.getLinkCollection().remove(link);
feedId = em.merge(feedId);
}
em.remove(link);
em.getTransaction().commit();
} finally {
if (em != null) {
em.close();
}
}
}
public List<Link> findLinkEntities() {
return findLinkEntities(true, -1, -1);
}
public List<Link> findLinkEntities(int maxResults, int firstResult) {
return findLinkEntities(false, maxResults, firstResult);
}
private List<Link> findLinkEntities(boolean all, int maxResults, int firstResult) {
EntityManager em = getEntityManager();
try {
CriteriaQuery cq = em.getCriteriaBuilder().createQuery();
cq.select(cq.from(Link.class));
Query q = em.createQuery(cq);
if (!all) {
q.setMaxResults(maxResults);
q.setFirstResult(firstResult);
}
return q.getResultList();
} finally {
em.close();
}
}
public Link findLink(Integer id) {
EntityManager em = getEntityManager();
try {
return em.find(Link.class, id);
} finally {
em.close();
}
}
public int getLinkCount() {
EntityManager em = getEntityManager();
try {
CriteriaQuery cq = em.getCriteriaBuilder().createQuery();
Root<Link> rt = cq.from(Link.class);
cq.select(em.getCriteriaBuilder().count(rt));
Query q = em.createQuery(cq);
return ((Long) q.getSingleResult()).intValue();
} finally {
em.close();
}
}
}
具体外观应该是什么样的？
另见：
答案 0 :(得分：1)
你是正确的，假设这些部分是重复的，因此是可以避免的。当您使用向导创建JSF Pages form Entity Classes时，Netbeans会向您展示实现它的方法。结果如下：
AbstractFacade.java：
public abstract class AbstractFacade<T> {
private final Class<T> entityClass;
public AbstractFacade(Class<T> entityClass) {
this.entityClass = entityClass;
}
protected abstract EntityManager getEntityManager();
public void create(T entity) {
getEntityManager().persist(entity);
}
public T edit(T entity) {
return getEntityManager().merge(entity);
}
public void remove(T entity) {
getEntityManager().remove(getEntityManager().merge(entity));
}
// some more find helper methods ...
}
ConcreteEntityFacade.java：
public class ConcreteEntityFacade extends AbstractFacade<ConcreteEntity> {
@PersistenceContext
private EntityManager em;
@Override
protected EntityManager getEntityManager() {
return em;
}
public ConcreteEntityFacade() {
super(ConcreteEntity.class);
}
}
我希望有所帮助。