ObservationHandler.java

            Map<String, List<Observation>> result = new TreeMap<String, List<Observation>>();
            ExecutorService e = Executors.newCachedThreadPool();
            
            for(Map.Entry<String, Map<LocalDate, Integer>> item : observations.entrySet()) {
                Future<List<Observation>> f = e.submit(new GetObservationPart(start, end, item));
                
                if(f.isDone()) {
                    Future<Map<String, List<Observation>>> f2 = e.submit(new MergeObservationParts(result, item.getKey(), f.get()));
                    if(f2.isDone()) {
                        result = f2.get();
                    }
                }
            }