Dynamic Persistence Unit

public static EntityManager getEntityManager( String server ) {
        EntityManagerFactory emf;
        Map properties = new HashMap();
        properties.put("javax.persistence.jdbc.driver", DatabaseProperty.DRIVER);
        properties.put("javax.persistence.jdbc.url", "jdbc:postgresql://" + server + ":5432/prepaid_canteen");
        properties.put("javax.persistence.jdbc.user", DatabaseProperty.USERNAME);
        properties.put("javax.persistence.jdbc.password", DatabaseProperty.PASSWORD);

        connectionTimeout.start();

        try {
            emf = Persistence.createEntityManagerFactory("PrepaidCanteenPU", properties);
            EntityManager entity_manager = emf.createEntityManager();

            connectionTimeout.stop();
            return entity_manager;
        } catch( Exception e ) {
            JOptionPane.showMessageDialog(null, "Server connection error!\n" +
                                                "See log for more information.", "Connection refused", JOptionPane.ERROR_MESSAGE);
            createLog(e.toString(), ErrorLevel.ERROR);
            System.exit(1);
            return null;
        }
    }