我尝试使用Sun Java PetStore Demo。
在CatalogFacade类有以下注释:@PersistenceUnit注释将不会创建一个EntityManageFactory emf = null
@PersistenceUnit(unitName="myPetStorePU")
private EntityManagerFactory emf;
在CatalogFacade太阳的所有方法有:
EntityManager em = emf.createEntityManager();
但我得到了EMF一个空指针异常试图createEntityManager时。但是...如果我添加上面这条线以下行这样
EntityManagerFactory emf = javax.persistence.Persistence.createEntityManagerFactory("myPetStorePU");
EntityManager em = emf.createEntityManager();
那么EMF被成功地创建和持久性单元myPetStorePU也成功地连接到数据库。所以它看起来像persistence.xml语法,并且它的位置是正确的。我想了解为什么注解不起作用,因为我认为有一个使用注释的原因,而不是在每个方法中添加createEntityManagerFactory行。
我的src/META-INF/persistence.xml文件看起来是这样的:
<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是在petstore.model包,并实现了ServletContextListener
<listener>
<listener-class>com.sun.javaee.blueprints.petstore.model.CatalogFacade</listener-class>
</listener>
in the index.jsp Sun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;
}
告诉我们你是如何获得CatalogFacade`的`一个实例发生这种情况。它是什么 - 一个pojo,一个ejb或? – Bozho 2010-12-07 21:23:42