private static EntityManager getEntityManager(String persistenceUnit) {
   if (persistenceUnit != null) {
     return Stripersist.getEntityManager(persistenceUnit);
   } else {
     return getEntityManager();
   }
 }
 private static EntityManager getEntityManager() {
   if (defaultPersistenceUnit == null) {
     return Stripersist.getEntityManager();
   }
   return Stripersist.getEntityManager(defaultPersistenceUnit);
 }