Servlets 未注入EntityManagerFactory-JPA

我是JPA的乞丐，在servlet中使用@PersistenceUnit时遇到了问题。EntityManagerFactory没有被注射，我不知道为什么

public class MyServlet extends HttpServlet
{   

  @PersistenceUnit
  private EntityManagerFactory emf = null; 

  public MyServlet ()
  {
    super();        
  }

  @Override
  public void init(ServletConfig config) throws ServletException
  {
    super.init(config);
  }


  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    Writer w = response.getWriter();
    w.append("HELLO HELLO");
    w.close();
  }

}

我将persistence.xml文件（在META-INF目录中）配置为：

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" 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_1_0.xsd">
<persistence-unit name="MiddlewareExpedElectrModel" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>     
    <non-jta-data-source>java:/OracleDS</non-jta-data-source>
    <class>com.ieci.mugeju.middleware.model.entities.FechaUltimaSolicitudProcesada</class>
    <properties>         
     <property name="hibernate.transaction.manager_lookup_class" value="org.hibernate.transaction.JBossTransactionManagerLookup"/>
     <property name="hibernate.show_sql" value="true"/>
     <property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect"/>         
  </properties>     
</persistence-unit>

但我希望通过注入获得EntityManagerFactory实例。 谢谢

你能试试吗

public class MyServlet extends HttpServlet {
//this is thread-safe
@PersistenceUnit(unitName="MiddlewareExpedElectrModel")
private EntityManagerFactory emf;

据我所知，EntityManager接口中的方法不是线程安全的，可能无法在多个并发请求之间共享。因此，不要将EntityManager注入servlet实例变量

这不是线程安全的，请避免它

@PersistenceContext(unitName="MiddlewareExpedElectrModel")
private EntityManager em;

您仍然可以在servlet类类型级别注入EntityManager，并在请求处理过程中需要时查找它

@PersistenceContext(unitName="MiddlewareExpedElectrModel", name="persistence/em")
public class MyServlet extends HttpServlet {
protected void doGet(
HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
try {
  InitialContext ic = new InitialContext();
  EntityManager em =
   (EntityManager) ic.lookup("java:comp/env/persistence/em");
  } catch (NamingException ex) {
    ...
  }

---

我在glassfish服务器上的应用程序中也遇到了同样的问题。 在我从web.xml中删除servlet声明并使用注释声明servlet之前，entitymanager工厂始终为空

@WebServlet("/GetRevisioniServlet")  // <-- this annotation solved all my problems
public class GetRevisioniServlet extends HttpServlet {

@PersistenceUnit(unitName = "clerpPU")
private EntityManagerFactory entityManagerFactory;

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

        EntityManager em = null;
        em = entityManagerFactory.createEntityManager(); 
        .....
    }
 }

---

@WebServlet（“/GetRevisioniServlet”）//谢谢您的回复！正如你告诉我的那样，我尝试过使用“unitName”属性，但它不再起作用。emf实例始终为空，未被注入。我不知道我做错了什么。你试过没有
null
<代码>私有实体管理器工厂emf@PersistenceContext（unitName=“middlewareexpedelectromodel”，name=“persistence/em”）

公共类MyServlet扩展了HttpServlet{？不，我没有试过。但是我想我读到过@PersistenceContext不能在HttpServlet中使用。PersistenceContext不应该在servlet中使用，因为它不是线程安全的，而且servlet不是线程安全的，您可能会遇到问题（相比之下，您可以在EJB中注入PersistenceContext，因为EJB实例调用是序列化的）。

@WebServlet("/GetRevisioniServlet")  // <-- this annotation solved all my problems
public class GetRevisioniServlet extends HttpServlet {

@PersistenceUnit(unitName = "clerpPU")
private EntityManagerFactory entityManagerFactory;

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

        EntityManager em = null;
        em = entityManagerFactory.createEntityManager(); 
        .....
    }
 }