Java 为什么即使事务已提交,EntityManager也会关闭?
我正在用JPA和Hibernate做一些简单的测试,我碰巧在我不希望的时候关闭了EntityManager 这是我的主要测试:Java 为什么即使事务已提交,EntityManager也会关闭?,java,hibernate,jpa,Java,Hibernate,Jpa,我正在用JPA和Hibernate做一些简单的测试,我碰巧在我不希望的时候关闭了EntityManager 这是我的主要测试: public class TestMain { public static void main(String[] args) { DBResourcesManager.initPeristence(); List<Event> allEvents = EventDao.findAllEventsA();
public class TestMain {
public static void main(String[] args) {
DBResourcesManager.initPeristence();
List<Event> allEvents = EventDao.findAllEventsA();
Event e1 = new Event("Event", new Date());
EventDao.store(e1);
DBResourcesManager.shutdown();
}
}
实体和对应的DAO:
public class Event {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String title;
@Temporal(TemporalType.DATE)
private Date date;
/*...*/
}
public class EventDao {
public static void store(Event e) {
EntityManager em = DBResourcesManager.getEntityManager();
EntityTransaction t = em.getTransaction();
t.begin();
em.persist(e);
t.commit();
em.close();
}
public static List<Event> findAllEventsA() {
EntityManager em = DBResourcesManager.getEntityManager();
EntityTransaction t = em.getTransaction();
t.begin();
List<Event> events = em.createQuery("from Event", Event.class)
.getResultList();
t.commit();
return events;
}
}
未执行关闭方法。
为什么实体管理器关闭
为了完整起见,下面是persistence.xml:
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="pu">
<class>com.lh.hibernateexample.Event</class>
<properties>
<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver" />
<property name="hibernate.connection.url"
value="jdbc:mysql://localhost:3306/myfirsthibernatedb" />
<property name="hibernate.connection.username" value="XXXXXXXX" />
<property name="hibernate.connection.password" value="XXXXXXXX" />
<property name="hibernate.hbm2ddl.auto" value="update" />
<property name="hibernate.archive.autodetection" value="class" />
</properties>
</persistence-unit>
</persistence>
com.lh.hibernateeexample.Event
在store方法中关闭实体管理器,然后在shutdown方法中再次尝试关闭它
在DAO中使用静态方法很奇怪 不应该有这么近的距离,谢谢。它来自于以前的版本。为什么静态方法在这里很奇怪?您只需要使用一个实体管理器,无需为每个方法调用不断创建。在编写单元测试时,静态方法更难模仿。实际上,我在DBResourcesManager类中只创建了一次实体管理器,然后就得到了它。DBResourcesManager的风格不是很好,但仍然。。。顺便说一句,我的DAO没有状态,所以使用静态方法似乎是合理的。您通常会注入实体管理器,您的代码将很难测试。我通常会注入整个DAO,这将成为一个单例。
Exception in thread "main" java.lang.IllegalStateException: EntityManager is closed
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="pu">
<class>com.lh.hibernateexample.Event</class>
<properties>
<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver" />
<property name="hibernate.connection.url"
value="jdbc:mysql://localhost:3306/myfirsthibernatedb" />
<property name="hibernate.connection.username" value="XXXXXXXX" />
<property name="hibernate.connection.password" value="XXXXXXXX" />
<property name="hibernate.hbm2ddl.auto" value="update" />
<property name="hibernate.archive.autodetection" value="class" />
</properties>
</persistence-unit>
</persistence>