Tentei todas as instruções dos outros Fóruns mas nada funcionou. Segue o erro:
Exception in thread "main" java.lang.ExceptionInInitializerError
at br.com.caelum.livraria.dao.PopulaBanco.main(PopulaBanco.java:17)
Caused by: javax.persistence.PersistenceException: [PersistenceUnit: livraria] Unable to build EntityManagerFactory
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:915)
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:890)
at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:57)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:63)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:47)
at br.com.caelum.livraria.dao.JPAUtil.<clinit>(JPAUtil.java:10)
... 1 more