private void refreshLiveEtaDataCache() {
        Map<Date, List<JourneyLiveEta>> oldDateJourneyLiveEtaMap = cacheInMemoryHolder.getCachedJourneyLiveEtas();
        Map<Date, List<JourneyLiveEta>> dateJourneyLiveEtaMap = null;

        // declare as null - will be set later.
        List<LiveEta> liveEtas = null;

        // Get all dates from the database.
        List<Date> dates = journeyLiveEtaManager.findAllDates();
        if (dates.size() > 0) {

            // Define what dates are needed.
            Date startDate = dates.get(Math.max(0, dates.size() - numberOfLastJourneyDatesToReload));
            Date endDate = dates.get(dates.size() - 1);

            LOG.info("Loading liveEtas...");
            liveEtas = loadLiveEtasBasedOnDateConditions(startDate, endDate);
            LOG.info("Loading liveEtas... finished. liveEtas.size={}", liveEtas.size());

            // filter present.
            if (dataAlreadyCached(oldDateJourneyLiveEtaMap)) {
                dateJourneyLiveEtaMap = oldDateJourneyLiveEtaMap.entrySet()
                        .stream()
                        .filter(cacheDateKeyIsBefore(startDate))
                        .collect(Collectors.toMap(e -> e.getKey(), e -> e.getValue()));

                // update old map data with reloaded journeys
                dateJourneyLiveEtaMap.putAll(JourneyLiveEtaUtils.groupLiveEtaByJourneyAndDate(liveEtas));
            } else {
                // initial caching
                dateJourneyLiveEtaMap = JourneyLiveEtaUtils.groupLiveEtaByJourneyAndDate(liveEtas);
            }
        } else {
            dateJourneyLiveEtaMap = new HashMap<>();
        }

        // map liveEta's to their bus stops.
        Map<String, List<LiveEta>> tmpCacheLiveEtasByBusStops = mapLiveEtasToBusStopIds(dateJourneyLiveEtaMap);
        LOG.info("cacheLiveEtasByBusStops.size={}", tmpCacheLiveEtasByBusStops.size());

        // cache/re-cache
        cacheInMemoryHolder.setCachedLiveEtasByBusStops(tmpCacheLiveEtasByBusStops);
        cacheInMemoryHolder.setCachedJourneyLiveEtas(dateJourneyLiveEtaMap);
    }

    /**
     * Load liveEtas checking what the start / end dates. If the start date =
     * end date then it will findByDate enabled index lookup on date.
     *
     * @param startDate
     * @param endDate
     * @return
     */
    private List<LiveEta> loadLiveEtasBasedOnDateConditions(final Date startDate, final Date endDate) {
        List<LiveEta> liveEtas;
        if (startDate.equals(endDate)) {
            // load by single date to enable index lookup.
            liveEtas = liveEtaManager.findByDate(startDate);
        } else {
            liveEtas = liveEtaManager.findByDateRange(startDate, endDate);
        }
        return liveEtas;
    }

    /**
     * @param dateJourneyLiveEtaMap
     * @return
     */
    private Map<String, List<LiveEta>>
            mapLiveEtasToBusStopIds(final Map<Date, List<JourneyLiveEta>> dateJourneyLiveEtaMap) {
        return dateJourneyLiveEtaMap.values()
                .stream()
                .flatMap(ds -> ds.stream())
                .flatMap(jle -> jle.getStopLiveEta()
                        .stream())
                .collect(Collectors.groupingBy(le -> le.getBusStopId()));
    }

    /**
     * Predicate to check if dateKeyIsBefore startKey. To filter from cache.
     *
     * @param startDate
     * @return
     */
    private Predicate<? super Entry<Date, List<JourneyLiveEta>>> cacheDateKeyIsBefore(final Date startDate) {
        return e -> e.getKey()
                .before(startDate);
    }

    /**
     * @param oldDateJourneyLiveEtaMap
     * @return
     */
    private boolean dataAlreadyCached(final Map<Date, List<JourneyLiveEta>> oldDateJourneyLiveEtaMap) {
        return oldDateJourneyLiveEtaMap != null && oldDateJourneyLiveEtaMap.size() > 0;
    }