发生这种异常的case:

如果foo在调用bar的时候，bar抛出RuntimeException，Spring在bar return时将Transactional标记为Rollback only， 而foo捕获了bar的RuntimeException，所以Spring将会commit foo的事务，但是foo和bar使用的是同一事务，因此在commit foo事务时，将会抛出UnexpectedRollbackException。注意：如果foo和bar在同一class中，不会出现这种情况，因为：

Since this mechanism is based on proxies, only 'external' method calls coming in through the proxy will be intercepted. This means that 'self-invocation', i.e. a method within the target object calling some other method of the target object, won't lead to an actual transaction at runtime even if the invoked method is marked with @Transactional!

可以通过配置log4j来debug Spring事务获取情况：
To delve more into it I would turn up your log4j logging to debug and also look at what ExerciseModuleController is doing at line 91, e.g.: add a logger for org.springframework.transaction