Changing Persistence Unit dynamically - JPA

You can use Persistence.createEntityManagerFactory(Map) to pass properties to choose the database URL and other settings.

Keep the persistence unit file (Persistence.xml) as it's. You can override the properties in it as follows.

EntityManagerFactory managerFactory = null;
Map<String, String> persistenceMap = new HashMap<String, String>();

persistenceMap.put("javax.persistence.jdbc.url", "<url>");
persistenceMap.put("javax.persistence.jdbc.user", "<username>");
persistenceMap.put("javax.persistence.jdbc.password", "<password>");
persistenceMap.put("javax.persistence.jdbc.driver", "<driver>");

managerFactory = Persistence.createEntityManagerFactory("<current persistence unit>", persistenceMap);
manager = managerFactory.createEntityManager();