Java：我如何扫描地图？

Question

This is my controller:

public class AccessLogController extends ControllerServlet {

private static final long serialVersionUID = 1L;

public void buildAccessLogPaginationView() {

    HttpServletRequest req = getThreadLocalRequest();
    AccessLogRepository accessLogRepo = FactoryDAO.getFactory().getAccessLogRepository(getHibernateSession());

    String resultForPageSelect = "10";

    if(StringUtils.trimAndNullIfEmpty(req.getParameter("resultForPageSelect")) != null)
        resultForPageSelect = req.getParameter("resultForPageSelect");


    AccessLogPaginationView accessLogPaginationView = new AccessLogPaginationView();
    Integer page = new Integer(1);
    if (req.getParameter("page") != null)
        page = new Integer(req.getParameter("page"));
    accessLogPaginationView.setPage(page);
    StringBuffer urlPagination = new StringBuffer();
    urlPagination.append("/accessLog/accessLogController?serviceName=buildAccessLogPaginationView");
    UserIntermediary userIntermediary = getUserInformation();
    if (userIntermediary != null) {

        try {

            List<Date> loginTimes = accessLogRepo.getLoginTime();

            if(loginTimes.size() > 0){
                Map<Integer, Date> datesMap = new TreeMap<Integer, Date>();
                Calendar date = Calendar.getInstance();
                         date.setTime(loginTimes.get(0));
                         date.set(Calendar.HOUR_OF_DAY, 0);
                         date.set(Calendar.MINUTE, 0);
                         date.set(Calendar.SECOND, 0);
                datesMap.put(0, date.getTime());

                int key = 1;
                for (int i = 1; i < loginTimes.size(); i++) {
                    Calendar nextDate = Calendar.getInstance();
                             nextDate.setTime(loginTimes.get(i));
                             nextDate.set(Calendar.HOUR_OF_DAY, 0);
                             nextDate.set(Calendar.MINUTE, 0);
                             nextDate.set(Calendar.SECOND, 0);
                    if (nextDate.getTime().compareTo(datesMap.get(key - 1)) != 0) {
                        datesMap.put(key, nextDate.getTime());
                        key++;
                    }
                }

                for (int j = 0; j < datesMap.size(); j++) {
                    Date minTime = datesMap.get(j);

                    Calendar maxTime = Calendar.getInstance();
                             maxTime.setTime(minTime);
                             maxTime.set(Calendar.HOUR_OF_DAY, 23);
                             maxTime.set(Calendar.MINUTE, 59);
                             maxTime.set(Calendar.SECOND, 59);


                    @SuppressWarnings("unchecked")

                    List<AccessLog> accessesLog = accessLogRepo.getByPeriod(minTime, maxTime.getTime(),((page.intValue() - 1) * Integer.parseInt(resultForPageSelect)), Integer.parseInt(resultForPageSelect));
                    List<Long> accessesTimes = new ArrayList<Long>();
                    for (AccessLog accessLog : accessesLog) {
                        if(accessLog.getLogoutTime() != null){
                            long accessTime = accessLog.getLogoutTime().getTime() - accessLog.getLoginTime().getTime();
                            accessesTimes.add(accessTime / 1000 % 60);
                        }
                    }

                    Long maxAccessTime = new Long(0);
                    for (Long time : accessesTimes) {
                        if (time > maxAccessTime) {
                            maxAccessTime = time;
                        }

                    }
                    DailyAccessLogView dailyAccessLogView = accessLogPaginationView.new DailyAccessLogView(); 
                    dailyAccessLogView.setDate(minTime);
                    dailyAccessLogView.setAccessesNumber(new Long(accessesLog.size()));
                    dailyAccessLogView.setMaxAccessTime( accessesLog.size() > 0 ? (maxAccessTime + 1) : 0 );

                    if(!dailyAccessLogView.getAccessesNumber().equals(new Long(0))){
                        if(accessLogPaginationView.getDailyAccessesLogView().size() < Integer.parseInt(resultForPageSelect)){
                            accessLogPaginationView.getDailyAccessesLogView().add(dailyAccessLogView);
                    }
                }
                }
                Integer count = datesMap.size();
                PaginationView paginationView = PaginationView.paginate(count, Integer.parseInt(resultForPageSelect), urlPagination);
                accessLogPaginationView.setPaginationView(paginationView);
                req.setAttribute(RequestAttributeKeys.VIEW_KEY, accessLogPaginationView);
            }



            dispatchForward("accessLogPagination.tiles");

        } catch (Throwable t) {
            throw new RuntimeException(t);
        }
    } else {
        // user not logged
        dispatchForward("/jsp/login/login.jsp");
    }
}

My question is: how can i scan my dateMap Map using the variable resultForPageSelect .

Ex: if the results of the first page are 20, the Map has to visualize the first 20 elements of the map. If i change the number of the page (aka, i go to next page),on the second page i have to visualize the elements from 20 to 40. Someone can help me please? Thank you.

Answer 1

What you can use is NavigableMap#subMap(K fromKey, K toKey) (that is already available from your TreeMap as it is already a NavigableMap ) as your key is the index of the results starting from 0 .

NavigableMap<Integer, Date> datesMap = new TreeMap<>();
...
// Get only the 20 first entries
Map<Integer, Date> subMap = datesMap.subMap(0, 20);
...
// Get only the next 20 entries
Map<Integer, Date> nextSubMap = datesMap.subMap(20, 40);

subMap(K fromKey, K toKey) : Returns a view of the portion of this map whose keys range from fromKey , inclusive, to toKey , exclusive