sping data jpa 如何注入的entitymanager

public class JpaRepositoryFactoryBean<T extends JpaRepository<S, ID>, S, ID extends Serializable> extends
		TransactionalRepositoryFactoryBeanSupport<T, S, ID> {

	private EntityManager entityManager;

	/**
	 * The {@link EntityManager} to be used.
	 * 
	 * @param entityManager the entityManager to set
	 */
	@PersistenceContext
	public void setEntityManager(EntityManager entityManager) {

		this.entityManager = entityManager;
	}

可以看到entityManager是通过PersistenceContext注解获取的。

2.如果要是希望在spring环境中使用@PersistenceContext和@PersistenceUnit，则在application.xml中配置

<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor"/>

特别注意的是 ：如果你在application.xml中配置过context:annotation-config" 或者 "context:component-scan tag，则会默认register一个默认的PersistenceAnnotationBeanPostProcessor。所以如果你要是希望自定义PersistenceAnnotationBeanPostProcessor。则Remove or turn off the default annotation configuration，具体怎么操作，正在研究，不好意思

可以通过这个类指定多个"persistenceUnits"

 <bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor">
   <property name="persistenceUnits">
     <map/gt;
       <entry key="unit1" value="persistence/unit1"/>
       <entry key="unit2" value="persistence/unit2"/>
     </map/gt;
   </property>
 </bean>

 也可以指定多个persistenceContexts

 <bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor">
   <property name="persistenceContexts">
     <map/gt;
       <entry key="unit1" value="persistence/context1"/>
       <entry key="unit2" value="persistence/context2"/>
     </map/gt;
   </property>
 </bean>