我试图理解事务是如何与Spring一起工作的。我有一个扩展CrudRepository的repository接口：

@Transactional
public interface MessageRepository extends CrudRepository<Message, Long> {
}

还有一个PersistenceConfig，我用它来创建我的BulletyManagerFactory和TransactionManager：

@Configuration
@EnableTransactionManagement
public class PersistenceConfig {
    final static Logger logger = LoggerFactory.getLogger(PersistenceConfig.class);

    public static EntityManagerFactory emf = null;

    @Bean
    public PlatformTransactionManager transactionManager() {
        return new JpaTransactionManager(entityManagerFactory());
    }

    @Bean
    public EntityManagerFactory entityManagerFactory() {
        if (emf == null) {
            synchronized (EntityManagerFactory.class) {
                if (emf == null) {
                    final StandardServiceRegistry sr = new StandardServiceRegistryBuilder()
                            .configure() // Configures setting from hibernate.cfg.xml
                            .build();
                    try {
                        emf = new MetadataSources(sr).buildMetadata().buildSessionFactory();
                    }
                    catch (Exception e) {
                        StandardServiceRegistryBuilder.destroy(sr);
                        throw e;
                    }
                }
            }
        }
        return emf;
    }
}

问题是，我使用一个logger来调试JpaTransactionManager，无论我是否使用注解@Transactional/@EnableTransactionManager，我都可以看到使用了事务：

3576 [main] DEBUG org.springframework.orm.jpa.JpaTransactionManager  - Creating new transaction with name [org.springframework.data.jpa.repository.support.SimpleJpaRepository.save]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT
3576 [main] DEBUG org.springframework.orm.jpa.JpaTransactionManager  - Opened new EntityManager [SessionImpl(2090037997<open>)] for JPA transaction
[...]
3576 [main] DEBUG org.springframework.orm.jpa.JpaTransactionManager  - Initiating transaction commit
3576 [main] DEBUG org.springframework.orm.jpa.JpaTransactionManager  - Committing JPA transaction on EntityManager [SessionImpl(2090037997<open>)]
[...]
3576 [main] DEBUG org.springframework.orm.jpa.JpaTransactionManager  - Closing JPA EntityManager [SessionImpl(2090037997<open>)] after transaction

所以，用这些有什么用？