我在一些场景中使用 EJB 继承,有时在超类中使用注释,例如这个通用 entityDAO:
public class JpaDAO<T>{
protected Class<T> entityClass;
@PersistenceContext(unitName="CarrierPortalPU")
protected EntityManager em;
protected CriteriaBuilder cb;
@PostConstruct
private void init() {
cb = em.getCriteriaBuilder();
}
public JpaDAO(Class<T> type) {
entityClass = type;
}
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public void create(T entity) {
em.persist(entity);
}
@TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
public T find(Object id) {
return em.find(entityClass, id);
}
@TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
public List<T> findAll(){
CriteriaQuery<T> cq = cb.createQuery(entityClass);
Root<T> entity = cq.from(entityClass);
cq.select(entity);
return em.createQuery(cq).getResultList();
}
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public void remove(T entity) {
em.remove(em.merge(entity));
}
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public T edit(T entity) {
return em.merge(entity);
}
}
使用这样实现的示例子类:
@Stateless
@TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
public class DepartmentDAO extends JpaDAO<Department> {
public DepartmentDAO() {
super(Department.class);
}
public Department findByName(String name){
CriteriaQuery<Department> cq = cb.createQuery(Department.class);
Root<Department> department = cq.from(Department.class);
cq.where(cb.equal(department.get(Department_.name), name));
cq.select(department);
try{
return em.createQuery(cq).getSingleResult();
}catch(Exception e){
return null;
}
}
}
我最近读到 java 注释不是继承的(来源)。这应该会导致我的 JpaDAO 在访问它的 entitymanager 或它的标准构建器时抛出一个空指针异常(因为 @PersistanceContext 和 @PostConstruct 都将被忽略),但事实并非如此。有人可以澄清这是如何工作的吗?我有点担心超类中我的@TransactionAttributes 会发生什么,当子类将NOT_SUPPORTED 作为类默认值时,我是否可以相信从子类调用时需要实际使用事务?