我想使用Sun Java PetStore演示。
在CatalogFacade类中有以下注释:
@PersistenceUnit(unitName="myPetStorePU")
private EntityManagerFactory emf;
在CatalogFacade中,Sun拥有以下所有方法:
EntityManager em = emf.createEntityManager();
当我尝试创建EntityManager时,emf出现空指针异常。但是...如果我在那行代码之前添加以下代码:
EntityManagerFactory emf = javax.persistence.Persistence.createEntityManagerFactory("myPetStorePU");
EntityManager em = emf.createEntityManager();
然后emf成功创建,持久化单元myPetStorePU也成功连接到数据库。因此,看起来persistence.xml语法及其位置是正确的。我想知道为什么注释不起作用,因为我认为只使用注释而不是在每个方法中添加createEntityManagerFactory行是有原因的。
我的src/META-INF/persistence.xml文件如下:
<persistence-unit name="myPetStorePU">
<description>Petstore Persistence Unit</description>
<provider>oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider</provider>
<class>com.sun.javaee.blueprints.petstore.model.Tag</class>
<class>com.sun.javaee.blueprints.petstore.model.SellerContactInfo</class>
<class>com.sun.javaee.blueprints.petstore.model.Product</class>
<class>com.sun.javaee.blueprints.petstore.model.Item</class>
<class>com.sun.javaee.blueprints.petstore.model.Category</class>
<class>com.sun.javaee.blueprints.petstore.model.Address</class>
<class>com.sun.javaee.blueprints.petstore.model.ZipLocation</class>
<properties>
<property name="toplink.jdbc.driver" value="oracle.jdbc.driver.OracleDriver"/>
<property name="toplink.jdbc.url" value="jdbc:oracle:thin:@#############"/>
<property name="toplink.jdbc.user" value="####"/>
<property name="toplink.jdbc.password" value="#####"/>
<property name="toplink.logging.level" value="INFO"/>
</properties>
</persistence-unit>
编辑: CatalogFacade位于petstore.model包中,并实现了ServletContextListener接口。
<listener>
<listener-class>com.sun.javaee.blueprints.petstore.model.CatalogFacade</listener-class>
</listener>
在index.jsp中,Sun公司有以下内容:
<%
CatalogFacade cf = (CatalogFacade)config.getServletContext().getAttribute("CatalogFacade");
List<Tag> tags=cf.getTagsInChunk(0, 12);
%>
public List<Tag> getTagsInChunk(int start, int chunkSize) {
//The next line is required since the @PersistenceUnit annotation at the top of this class does not work
EntityManagerFactory emf = javax.persistence.Persistence.createEntityManagerFactory("myPetStorePU");
EntityManager em = emf.createEntityManager();
System.out.println("Entity manager " + emf);
Query query = em.createQuery("SELECT t FROM Tag t ORDER BY t.refCount DESC, t.tag");
List<Tag> tags = query.setFirstResult(start).setMaxResults(chunkSize).getResultList();
em.close();
return tags;
}
CatalogFacade
的实例。它是一个POJO、EJB还是其他类型的对象? - Bozho