数据按半小时统计显示

List<Chart> charts = new ArrayList<>();
        SimpleDateFormat format = newSimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        charts.add(new Chart(format.parse("2020-01-01 01:10:00"), 2d));
        charts.add(new Chart(format.parse("2020-01-01 01:20:00"), 3d));
        charts.add(new Chart(format.parse("2020-01-01 01:40:00"), 4d));
        charts.add(new Chart(format.parse("2020-02-01 01:50:00"), 3d));
        charts.add(new Chart(format.parse("2020-01-01 02:20:00"), 26d));
        Map<Long, Chart> collect = charts.stream().collect(Collectors.toMap(chart ->
        {
            return chart.date.getTime() / (30 * 60 * 1000);
        }, Function.identity(), (k1, k2)
                -> {
            return k1.date.getTime() > k2.date.getTime() ? k1 : k2;
        }));
        Map<String, Double> map = new HashMap<>();
        format = new
                SimpleDateFormat("yyyy-MM-dd");
        SimpleDateFormat finalFormat = format;
        collect.forEach((k, v) -> { //此处把v.date转换为半小时的标准格式
            String format1 = finalFormat.format(v.date);
            String hours = v.date.getHours() + "";
            int minutes = v.date.getMinutes();
            if
            (minutes >= 0 && minutes < 30) {
                hours = format1 + " " + hours + ":00";
            } else {
                hours = format1 + " " + hours + ":30";
            }
            map.put(hours, v.value);
        });
        Map<String, Double> stringDoubleMap = sortByKey(map);
        static class Chart {
            public Date date;
            public Double value;
            public Chart(Date date, Double value) {
                this.date = date;
                this.value = value;
            }
        }