public ListOfCheckins readFromDB(double CoreMinY, double CoreMaxY) {
        //checkins = new HashMap<String, Integer>();
        ListOfCheckins checkins = new ListOfCheckins();

        Connection con = null;
        java.sql.PreparedStatement pst = null;
        ResultSet rs = null;

        String url = "jdbc:mysql://83.212.117.76:3306/ds_systems_2016?autoReconnect=true&useSSL=false";
        String user = "omada8";
        String password = "omada8db";

        try {
            con = DriverManager.getConnection(url, user, password);
            pst = con.prepareStatement("select POI, POI_name, POI_category, POI_category_id, latitude, longitude, time, photos"
                    +" from checkins where (latitude between " + CoreMinY + " and " + CoreMaxY
                    + ") " + "and (longitude between " + minX + " and " + maxX + ") " + "and time between \'" + minDatetime +"\' and \'"+ maxDatetime +"\';");
            rs = pst.executeQuery();

            String POI, POI_name, POI_category, POI_category_id, time, photos;
            double latitude, longitude;

            while (rs.next()) {
                POI = rs.getString(1);
                POI_name = rs.getString(2);
                POI_category = rs.getString(3);
                POI_category_id = rs.getString(4);
                latitude = rs.getDouble(5);
                longitude = rs.getDouble(6);
                time = rs.getString(7);
                photos = rs.getString(8);
                checkins.addCheckin(POI, POI_name, POI_category, POI_category_id, longitude, latitude, time, photos);
            }
        } catch (SQLException ex) {
            Logger lgr = Logger.getLogger(Mapper.class.getName());
            lgr.log(Level.SEVERE, ex.getMessage(), ex);

        } finally {
            try {
                if (rs != null) {
                    rs.close();
                }
                if (pst != null) {
                    pst.close();
                }
                if (con != null) {
                    con.close();
                }

            } catch (SQLException ex) {
                Logger lgr = Logger.getLogger(Mapper.class.getName());
                lgr.log(Level.WARNING, ex.getMessage(), ex);
            }
        }
        return checkins;
    }