EntityManagerFactory未被注入 - JPA

Question

我是JPA的begginer，當我在servlet中使用@PersistenceUnit時遇到問題。 EntityManagerFactory沒有被注入，我不知道爲什麼。

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(); 
    } 

} 

我已經配置persistence.xml文件（META-INF目錄中）這樣的：

<?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> 

爲什麼不EntityManagerFactory的注入？

我正在使用Jboss 4.2.3，並且我還使用oracle-ds.xml文件配置了一個數據源。

UPDATE：

如果我試圖以編程方式獲得的EntityManagerFactory，效果很好：

EntityManagerFactory emf = Persistence.createEntityManagerFactory("MiddlewareExpedElectrModel"); 

但我想通過注射獲得EntityManagerFactory實例。 謝謝！

Answer 1

你可以嘗試

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

據我所知，在EntityManager接口方法不是線程安全的，並且可能不多個併發請求之間共享。因此，不要將EntityManager注入到servlet實例變量中。

這不是線程安全的，並且避免

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

您仍然可以在servlet類類型級別注入的EntityManager，並請求處理過程中需要時查找。

@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) { 
    ... 
    }