Transazioni primaverili e AOP

Question

Sono ancora in una fase di apprendimento con le transazioni primaverili e AOP, e ho alcuni malintesi:
1. Se non utilizzo, avere un consumo AOP e specifico per ogni servizio qualcosa come:

@Transactional (rollbackFor = java.lang.exception.class, readonly = true)

E poi guardo il registro primaverile che tutto sembra funzionare come previsto. Quello che intendo con questo è che viene creata una transazione e, in caso di eccezione, ottengo un rollback. Ma se usi qualcosa di simile:

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

      <tx:annotation-driven transaction-manager="txManagerVA" />
<aop:config>
  <aop:pointcut id="transactionalServiceMethodsVA" expression="execution(* xxx.services.vs.*.*(..))"/>
  <aop:advisor advice-ref="txManagerVAAdvice" pointcut-ref="transactionalServiceMethodsVA"/>
</aop:config>

 <tx:advice id="txManagerVAAdvice" transaction-manager="txManagerVA">
    <tx:attributes>
     <tx:method name="get*" rollback-for="java.lang.Exception" read-only="true"/>    
     <tx:method name="*" rollback-for="java.lang.Exception" />   
    </tx:attributes>
 </tx:advice>

Quindi, quando guardo il registro Spring, usando questo scenario, sembra che ci siano 2 transazioni, all'interno di un'altra, perché dopo il rollback ottengo qualcosa di simile:

(IntermedServiceImpl.java:45) - WE HAVE AN EXCEPTION !!!! nullCrocodilu
(TransactionAspectSupport.java:406) - Completing transaction for [xxx.IntermedServiceImpl.getIntermed] after exception: java.lang.Exception: Crocodilu
(RuleBasedTransactionAttribute.java:130) - Applying rules to determine whether transaction should rollback on java.lang.Exception: Crocodilu
(RuleBasedTransactionAttribute.java:147) - Winning rollback rule is: RollbackRuleAttribute with pattern [java.lang.Exception]
(AbstractPlatformTransactionManager.java:935) - Triggering beforeCompletion synchronization
(TransactionSynchronizationManager.java:243) - Removed value [org.springframework.orm.jpa.ExtendedEntityManagerCreator$ExtendedEntityManagerSynchronization@63fd1f47] for key [org.hibernate.ejb.EntityManagerImpl@4eb35bed] from thread [thread-pool-1-8080(6)]
(AbstractPlatformTransactionManager.java:843) - Initiating transaction rollback
//SO FAR SO GOOD
(JpaTransactionManager.java:533) - Rolling back JPA transaction on EntityManager [org.hibernate.ejb.EntityManagerImpl@b3fbd77]
(AbstractPlatformTransactionManager.java:964) - Triggering afterCompletion synchronization
(TransactionSynchronizationManager.java:331) - Clearing transaction synchronization
(TransactionSynchronizationManager.java:243) - Removed value [org.springframework.orm.jpa.EntityManagerHolder@45a27493] for key [org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean@7ed30037] from thread [thread-pool-1-8080(6)]
(JpaTransactionManager.java:593) - Closing JPA EntityManager [org.hibernate.ejb.EntityManagerImpl@b3fbd77] after transaction
(EntityManagerFactoryUtils.java:343) - Closing JPA EntityManager
--> (AbstractPlatformTransactionManager.java:1012) - Resuming suspended transaction after completion of inner transaction <--
(TransactionSynchronizationManager.java:272) - Initializing transaction synchronization
(TransactionAspectSupport.java:406) - Completing transaction for [xxx.IntermedServiceImpl.getIntermed] after exception: java.lang.Exception: Crocodilu
(RuleBasedTransactionAttribute.java:130) - Applying rules to determine whether transaction should rollback on java.lang.Exception: Crocodilu
(RuleBasedTransactionAttribute.java:147) - Winning rollback rule is: null
(RuleBasedTransactionAttribute.java:152) - No relevant rollback rule found: applying default rules
(AbstractPlatformTransactionManager.java:922) - Triggering beforeCommit synchronization
(AbstractPlatformTransactionManager.java:935) - Triggering beforeCompletion synchronization
(AbstractPlatformTransactionManager.java:752) - Initiating transaction commit
(JpaTransactionManager.java:507) - Committing JPA transaction on EntityManager [org.hibernate.ejb.EntityManagerImpl@405c9cef]
(AbstractPlatformTransactionManager.java:948) - Triggering afterCommit synchronization
(AbstractPlatformTransactionManager.java:964) - Triggering afterCompletion synchronization
(TransactionSynchronizationManager.java:331) - Clearing transaction synchronization
(TransactionSynchronizationManager.java:243) - Removed value [org.springframework.orm.jpa.EntityManagerHolder@1f0cf366] for key [org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean@6012b597] from thread [thread-pool-1-8080(6)]
(JpaTransactionManager.java:593) - Closing JPA EntityManager [org.hibernate.ejb.EntityManagerImpl@405c9cef] after transaction
(EntityManagerFactoryUtils.java:343) - Closing JPA EntityManager

Come puoi vedere lì ho segnato la linea che non capisco.

E il secondo numero: nello stesso file di registro ho notato una riga come:

(JpaTransactionManager.java:407) - Not exposing JPA transaction [org.hibernate.ejb.EntityManagerImpl@b3fbd77] as JDBC transaction because JpaDialect [org.springframework.orm.jpa.DefaultJpaDialect@77acf1c0] does not support JDBC Connection retrieval

E ho cercato su Google un po 'e dopo aver aggiunto questo:

<property name="jpaVendorAdapter">
        <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
            <property name="databasePlatform" value="org.hibernate.dialect.MySQL5InnoDBDialect" />
        </bean>
   </property> 

EntityManager Bean, ora sembra che JPA esponi la transazione alla transazione JDBC. Il problema è che non so quali siano i vantaggi/svantaggi di questa configurazione.