In Spring I Use @Transactional in save methos, throw RollbackException

I use @Transaction on method like this

@Transactional
public void savePerson(Person person){
...
}

then throw exception

org.springframework.transaction.TransactionSystemException: Could not commit JPA transaction; nested exception is javax.persistence.RollbackException: 

I use

@Transactional(readonly=true)

for other method that only fetch data like

public Person findPerson(Long personId){...}

What is wrong?