* Get the EntityManagerFactory that this filter should use.
* @return the EntityManagerFactory to use
* @see #lookupEntityManagerFactory(OpenEntityManager)
*/
protected EntityManagerFactory getEntityManagerFactory(OpenEntityManager openEntityManager) {
final CacheKey key = this.createEntityManagerFactoryKey(openEntityManager);
EntityManagerFactory emf = this.entityManagerFactories.get(key);
if (emf == null) {
emf = this.lookupEntityManagerFactory(openEntityManager);
this.entityManagerFactories.put(key, emf);
}