我有一个小的教育项目。 JPA-Servlet-JSP。现在我想使用 PersistanceUnit 注释:
public class UsersListServlet extends HttpServlet {
@PersistenceUnit
private EntityManagerFactory emf;
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
EntityManager em = null;
try {
em = emf.createEntityManager();
//query for all the persons in database
List persons = em.createQuery("select u from Users u").getResultList();
request.setAttribute("usersList",persons);
//Forward to the jsp page for rendering
request.getRequestDispatcher("UsersList.jsp").forward(request, response);
} catch (Exception ex) {
throw new ServletException(ex);
} finally {
//close the em to release any resources held up by the persistebce provider
if(em != null) {
em.close();
}
}
response.setContentType("text/html;charset=UTF-8");
}
但我在尝试 emf.createEntityManager();
时看到了 NPE
我的 persistance.xml:
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
<persistence-unit name="AdressBookPU">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<jta-data-source>jdbc/__adressbook</jta-data-source>
<class>com.prokopenko.adressbook.entity.Users</class>
<class>com.prokopenko.adressbook.entity.MobilePhone</class>
</persistence-unit>
</persistence>
它是一个 Maven 项目和位于 src/main/resources/META-INF 的 persistance.xml(就像在 j2ee7 教程中一样)。 更新 尝试过:
@PersistenceContext(unitName = "AdressBookPU")
private EntityManager em;
和
@PersistenceUnit(unitName="AdressBookPU")
private EntityManagerFactory emf;
最佳答案
您使用的是哪个容器?并且您是否在此容器中定义了您的 jta-data-source(jdbc/__adressbook)?
关于java - PersistanceUnit 注解不注入(inject),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23496116/