小编jay*_*jay的帖子

我在创建EntityManager时看到的常用习惯是这样的:

public class BaseDao {
    private static final String PERSISTENCE_UNIT_NAME = "Employee";

    EntityManagerFactory factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);

    public EntityManager getEntityManager() {
      return factory.createEntityManager();
    } 
}

然后就像这样使用:

Employee emp = new Employee();
emp.setName("Joe M");
getEntityManager().persist(emp);

问题是为什么不这样做:

public class BaseDao{
    private static final String PERSISTENCE_UNIT_NAME = "Employee";
    EntityManagerFactory factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
    private EntityManager entityManager = null;


public void setEntityManger() {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
    this.entityManager = factory.createEntityManager();

    }

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

换句话说,是否需要始终通过factory.createEntityManager()获取实体管理器？或者它可以创建为实例(甚至静态)变量并像这样检索？

为了澄清,我在谈论一个不使用EJB或Spring容器的环境.

谢谢.