Spring JPA and Sharing Entity Manager across multiple WARS and @Persistence Context thread safety

Question

I read about about Persistence Context but not able to get a clear picture about my doubts which are as follows.
1. I have a DAO class which as a @PersistenceContext(unitName="") private EntityManager entityManager and from my Service method i am starting the transaction(Spring Managed) using @Transactional(propagation = Propagation.REQUIRED). I understand here is every time this Service method is called, a Transaction will start and when it reaches to DAO class it will use the same Transaction but for every EntityManager operation it look for Active PersistenceContext and create it as required. Is this approach correct and thread safe? So, if a new thread starts the same service method then a new Transaction and a persistence Context will be created and flushed away when the method ends?
2. I have multiple WARS which need to interact with database so I am sharing the EntityManagerFactory using Spring Shared contexts. I am having all the Hibernate related configurations at a common place and in every WAR i am specifying where transactionManager will be shared. Is it right?
Please clarify my doubts and your comments are valued. Thanks in advance.