Java8-无限流补全日期，折线图补零

原始数据

自2020-11-27 过去一周的数据，日期不连续

补全日期数据，没有的日期，数据默认补0

/**
 * 折线图数据
 *
 * @param preDate 开始日期，不传默认近一周
 * @return
 */
public List<DailyDataChartVo> getChartData(LocalDate preDate) {
    if (Objects.isNull(preDate)) {
        preDate = LocalDate.now().minusWeeks(1);
    }
    LocalDate endDate = LocalDate.now();
    List<DailyDataChartVo> list = this.dailyDataMapper.selectChartData(preDate, endDate);
    return this.completeData(preDate, endDate, list);
}

/**
 * 补全数据
 *
 * @param preDate 开始日期
 * @param endDate 截止日期
 * @param oldList 未补全的列表
 * @return 补全后的列表
 */
private List<DailyDataChartVo> completeData(LocalDate preDate, LocalDate endDate, List<DailyDataChartVo> oldList) {
    List<DailyDataChartVo> newList = new ArrayList<>();
    if (CollectionUtils.isEmpty(oldList)) {
        return newList;
    }
    //间隔的日期列表
    List<LocalDate> dates = this.getRangeDays(preDate, endDate);
    Map<LocalDate, DailyDataChartVo> map = oldList.stream()
            .collect(Collectors.toMap(DailyDataChartVo::getDate, Function.identity()));
    dates.forEach(c -> {
        if (map.containsKey(c)) {
            newList.add(map.get(c));
        } else {
            //没有这一天的数据，默认补0
            newList.add(new DailyDataChartVo(c, BigDecimal.ZERO));
        }
    });
    return newList;
}

/**
 * 获取间隔的日期列表
 *
 * @param preDate 开始日期
 * @param endDate 截止日期
 * @return
 */
private List<LocalDate> getRangeDays(LocalDate preDate, LocalDate endDate) {
    List<LocalDate> dates = new ArrayList<>();
    //间隔的天数
    long betweenDays = ChronoUnit.DAYS.between(preDate, endDate);
    if (betweenDays < 1) {
        //开始日期<=截止日期
        return dates;
    }
    //创建一个从开始日期、每次加一天的无限流，限制到截止日期为止
    Stream.iterate(preDate, c -> c.plusDays(1))
            .limit(betweenDays + 1)
            .forEach(dates::add);
    return dates;
}

补全后的数据

点击查看代码

[
    {
        "date": "2020-11-20",
        "revenue": 22.88
    },
    {
        "date": "2020-11-21",
        "revenue": 93.06
    },
    {
        "date": "2020-11-22",
        "revenue": 0
    },
    {
        "date": "2020-11-23",
        "revenue": 7.99
    },
    {
        "date": "2020-11-24",
        "revenue": 0
    },
    {
        "date": "2020-11-25",
        "revenue": 50.98
    },
    {
        "date": "2020-11-26",
        "revenue": 0
    },
    {
        "date": "2020-11-27",
        "revenue": 0
    }
]

核心方法

Stream.iterate()：接收一个初始元素seed，生成从seed到f的迭代流

/**
 * @param seed 初始元素
 * @param f UnaryOperator，函数式接口，接收T类型参数，调用apply后返回T本身，应用于上一个元素以产生新元素
 */
public static<T> Stream<T> iterate(final T seed, final UnaryOperator<T> f) {}

//创建一个从开始日期、每次加一天的无限流，限制到截止日期为止
Stream.iterate(preDate, c -> c.plusDays(1))
        .limit(betweenDays + 1)
        .forEach(dates::add);