Java 以YYYYMMDD格式快速获取日数的方法？

我知道我可以用SimpleDateFormat获得yyyyMMdd格式的日字符串，但这会带来一些成本，当我在我的机器上测试时，1000万次操作需要2秒钟

当然，我可以缓存这个值，并在00:00Am安排一个计时器，更新这个日期缓存，但我希望我可以以一种足够简单的方式获得这个值，如果可以的话，这不会带来显式的成本

我将以100万tps的价格称之为这次行动

---

有没有一种简单快捷的方法可以做到这一点。

我已经在本地进行了检查：

1M-~2.5秒：

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);

    for (Date date : dates)
        res.add(new SimpleDateFormat("YYYYMMdd", Locale.US).format(date));

    return res;
}

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);
    DateFormat df = new SimpleDateFormat("YYYYMMdd", Locale.US);

    for (Date date : dates)
        res.add(df.format(date));

    return res;
}

public static List<String> convert3(Date[] dates) throws ExecutionException, InterruptedException {
    int size = 1000;
    ThreadLocal<SimpleDateFormat> df = ThreadLocal.withInitial(() -> new SimpleDateFormat("YYYYMMdd", Locale.US));
    ExecutorService pool = Executors.newFixedThreadPool(10);

    List<Future<List<String>>> futures = new ArrayList<>(dates.length);

    for (int i = 0; i < dates.length; i += size) {
        int ii = i;
        futures.add(pool.submit(() -> {
            List<String> res = new ArrayList<>(size);
            SimpleDateFormat sdf = df.get();

            for (int j = 0; j < size && ii + j < dates.length; j++)
                res.add(sdf.format(dates[ii + j]));

            return res;
        }));
    }

    List<String> res = new ArrayList<>(dates.length);

    for (Future<List<String>> future : futures)
        res.addAll(future.get());

    pool.shutdown();

    return res;
}

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);
    long msOneDay = TimeUnit.DAYS.toMillis(1);

    for (Date date : dates)
        res.add(String.valueOf(date.getTime() / msOneDay));

    return res;
}

10M-~49秒：

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);

    for (Date date : dates)
        res.add(new SimpleDateFormat("YYYYMMdd", Locale.US).format(date));

    return res;
}

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);
    DateFormat df = new SimpleDateFormat("YYYYMMdd", Locale.US);

    for (Date date : dates)
        res.add(df.format(date));

    return res;
}

public static List<String> convert3(Date[] dates) throws ExecutionException, InterruptedException {
    int size = 1000;
    ThreadLocal<SimpleDateFormat> df = ThreadLocal.withInitial(() -> new SimpleDateFormat("YYYYMMdd", Locale.US));
    ExecutorService pool = Executors.newFixedThreadPool(10);

    List<Future<List<String>>> futures = new ArrayList<>(dates.length);

    for (int i = 0; i < dates.length; i += size) {
        int ii = i;
        futures.add(pool.submit(() -> {
            List<String> res = new ArrayList<>(size);
            SimpleDateFormat sdf = df.get();

            for (int j = 0; j < size && ii + j < dates.length; j++)
                res.add(sdf.format(dates[ii + j]));

            return res;
        }));
    }

    List<String> res = new ArrayList<>(dates.length);

    for (Future<List<String>> future : futures)
        res.addAll(future.get());

    pool.shutdown();

    return res;
}

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);
    long msOneDay = TimeUnit.DAYS.toMillis(1);

    for (Date date : dates)
        res.add(String.valueOf(date.getTime() / msOneDay));

    return res;
}

1M-~1秒：

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);

    for (Date date : dates)
        res.add(new SimpleDateFormat("YYYYMMdd", Locale.US).format(date));

    return res;
}

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);
    DateFormat df = new SimpleDateFormat("YYYYMMdd", Locale.US);

    for (Date date : dates)
        res.add(df.format(date));

    return res;
}

public static List<String> convert3(Date[] dates) throws ExecutionException, InterruptedException {
    int size = 1000;
    ThreadLocal<SimpleDateFormat> df = ThreadLocal.withInitial(() -> new SimpleDateFormat("YYYYMMdd", Locale.US));
    ExecutorService pool = Executors.newFixedThreadPool(10);

    List<Future<List<String>>> futures = new ArrayList<>(dates.length);

    for (int i = 0; i < dates.length; i += size) {
        int ii = i;
        futures.add(pool.submit(() -> {
            List<String> res = new ArrayList<>(size);
            SimpleDateFormat sdf = df.get();

            for (int j = 0; j < size && ii + j < dates.length; j++)
                res.add(sdf.format(dates[ii + j]));

            return res;
        }));
    }

    List<String> res = new ArrayList<>(dates.length);

    for (Future<List<String>> future : futures)
        res.addAll(future.get());

    pool.shutdown();

    return res;
}

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);
    long msOneDay = TimeUnit.DAYS.toMillis(1);

    for (Date date : dates)
        res.add(String.valueOf(date.getTime() / msOneDay));

    return res;
}

10M-~10.6秒：

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);

    for (Date date : dates)
        res.add(new SimpleDateFormat("YYYYMMdd", Locale.US).format(date));

    return res;
}

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);
    DateFormat df = new SimpleDateFormat("YYYYMMdd", Locale.US);

    for (Date date : dates)
        res.add(df.format(date));

    return res;
}

public static List<String> convert3(Date[] dates) throws ExecutionException, InterruptedException {
    int size = 1000;
    ThreadLocal<SimpleDateFormat> df = ThreadLocal.withInitial(() -> new SimpleDateFormat("YYYYMMdd", Locale.US));
    ExecutorService pool = Executors.newFixedThreadPool(10);

    List<Future<List<String>>> futures = new ArrayList<>(dates.length);

    for (int i = 0; i < dates.length; i += size) {
        int ii = i;
        futures.add(pool.submit(() -> {
            List<String> res = new ArrayList<>(size);
            SimpleDateFormat sdf = df.get();

            for (int j = 0; j < size && ii + j < dates.length; j++)
                res.add(sdf.format(dates[ii + j]));

            return res;
        }));
    }

    List<String> res = new ArrayList<>(dates.length);

    for (Future<List<String>> future : futures)
        res.addAll(future.get());

    pool.shutdown();

    return res;
}

public static List<String> convert(Date[] dates) {
    List<String> res = new ArrayList<>(dates.length);
    long msOneDay = TimeUnit.DAYS.toMillis(1);

    for (Date date : dates)
        res.add(String.valueOf(date.getTime() / msOneDay));

    return res;
}

公共静态列表转换（日期[]日期）{
List res=新数组列表（dates.length）；
long msOneDay=时间单位.DAYS.toMillis（1）；
用于（日期：日期）
res.add（String.valueOf（date.getTime（）/msOneDay））；
返回res；
}

为什么需要此日期字符串？是否为每个格式操作创建新的SimpleDataFormat？考虑合并实例或使用线程安全的等价物，或者，SimpleDateFormat在TimBiegeleisen中很昂贵，我需要用高TPS在内存中积累一些数字，然后用ST{{DATANO}将它们保存在ReDIS中。