通过XML注入EntityManager而不是使用注解

Question

我试图通过XML方式注入实体管理器（entity manager），这个过程与 @PersistenceContext 注解的用法几乎一致。我需要这样做是因为我需要将不同的实体管理器注入到同一个 DAO 中。这些数据库相互镜像，所以我宁愿只有一个基类并创建该基类的多个实例，而不是创建多个类来使用 @PersistenceContext 注解。

以下是我的示例。目前我正在使用下面的方法并已经能够正常工作。

public class ItemDaoImpl {
 protected EntityManager entityManager;

 public List<Item> getItems() {
     Query query = entityManager.createQuery("select i from Item i");
  List<Item> s = (List<Item>)query.getResultList();
  return s; 
 }
 public void setEntityManger(EntityManager entityManager) {
  this.entityManager = entityManager;
 }
}

@Repository(value = "itemDaoStore2")
public class ItemDaoImplStore2 extends ItemDaoImpl {

 @PersistenceContext(unitName = "persistence_unit_2")
 public void setEntityManger(EntityManager entityManager) {
  this.entityManager = entityManager;
 }
}

@Repository(value = "itemDaoStore1")
public class ItemDaoImplStore1 extends ItemDaoImpl {

 @PersistenceContext(unitName = "persistence_unit_1")
 public void setEntityManger(EntityManager entityManager) {
  this.entityManager = entityManager;
 }
}

下面定义了 TransactionManagers 和 EntityManagers...

<!-- Registers Spring's standard post-processors for annotation-based configuration like @Repository -->
<context:annotation-config />

<!-- For @Transactional annotations -->
<tx:annotation-driven transaction-manager="transactionManager1"  />
<tx:annotation-driven transaction-manager="transactionManager2"  />

<!-- This makes Spring perform @PersistenceContext/@PersitenceUnit injection: -->
<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor"/>

<!-- Drives transactions using local JPA APIs -->
<bean id="transactionManager1" class="org.springframework.orm.jpa.JpaTransactionManager">
 <property name="entityManagerFactory" ref="entityManagerFactory1" />
</bean>

<bean id="transactionManager2" class="org.springframework.orm.jpa.JpaTransactionManager">
 <property name="entityManagerFactory" ref="entityManagerFactory2" />
</bean>

<bean id="entityManagerFactory1" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
 <property name="persistenceUnitName" value="persistence_unit_1"/>
...
</bean>

<bean id="entityManagerFactory2" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
 <property name="persistenceUnitName" value="persistence_unit_2"/>
...
</bean>

我想要做的是不创建ItemDaoImplStore2或ItemDaoImplStore1类，而是通过xml将它们作为ItemDaoImpl的实例。然而，我不知道如何正确注入entitymanager。我想模拟将其注释为'Repository'注释，并且我也想能够通过持久性单位名称指定要注入的entityManager。我希望使用XML实现类似于下面的内容。

 <!-- Somehow annotate this instance as a @Repository annotation -->
 <bean id="itemDaoStore1" class="ItemDaoImpl">
  <!-- Does not work since it is a LocalContainerEntityManagerFactoryBean-->
  <!-- Also I would perfer to do it the same way PersistenceContext works
   and only provide the persistence unit name.  I would like to be
   able to specify persistence_unit_1-->
  <property name="entityManager"  ref="entityManagerFactory1"/> 
 </bean>

  <!-- Somehow annotate this instance as a @Repository annotation -->
 <bean id="itemDaoStore2" class="ItemDaoImpl">
  <!-- Does not work since it is a LocalContainerEntityManagerFactoryBean-->
  <!-- Also I would perfer to do it the same way PersistenceContext works
   and only provide the persistence unit name.  I would like to be
   able to specify persistence_unit_2-->
  <property name="entityManager"  ref="entityManagerFactory2"/> 
 </bean>

- user355543

Answer 1

使用SharedEntityManagerBean - 它会为EntityManagerFactory创建一个共享的EntityManager，方式与@PersistenceContext相同：

<bean id="itemDaoStore1" class="ItemDaoImpl"> 
    <property name="entityManager">
        <bean class = "org.springframework.orm.jpa.support.SharedEntityManagerBean">
            <property name = "entityManagerFactory" ref="entityManagerFactory1"/>  
        </bean>
    </property>
</bean>

- axtavt

Answer 2

您可以在XML配置中使用SharedEntityManagerBean提供持久化单元名称，如下所示：

<bean id="testDao" class="com.test.persistence.dao.BaseDAO">
    <property name="entityManager">
        <bean class="org.springframework.orm.jpa.support.SharedEntityManagerBean">
            <property name="persistenceUnitName" value="persistence-test-unit" />
        </bean>
    </property>
</bean>

当然，您可以将SharedEntityManagerBean作为一个单独的bean

这里，我正在使用@PersistenceContext(unitName="...")方式将entityManager注入到BaseDAO中，就像您所做的那样。

- manikanta