javaspringatomicintegersequence-generators

How to write a Java sequence generator for UniqueId, which will Auto-Reset to '1' (base seq. number) at midnight everyday

We have a Spring boot service where we receive files everyday, because of some issue (on producer) we are receiving multiple files with same name & date appended. The new file overwriting the old, to handle it we want to append a sequence (starting from 1) at every file name. But sequence should be auto-reset to '1' at midnight everyday.

Can anybody suggest a API or a way to reset the sequence.

To generate auto sequence, we are using AtomicSequenceGenerator , but we are unable to implement a simple auto-reset logic.

public class AtomicSequenceGenerator implements SequenceGenerator {

    private AtomicLong value = new AtomicLong(1);

    @Override
    public long getNext() {
        return value.getAndIncrement();
    }
}
Solution

  • To not receive twice a 1:

    public class AtomicSequenceGenerator implements SequenceGenerator {

    private AtomicLong value = new AtomicLong(1);
    private volatile LocalDate lastDate = LocalDate.now();

    @Override
    public long getNext() {
        LocalDate today = LocalDate.now();
        if (!today.equals(lastDate)) {
            synchronized(this) {
                if (!today.equals(lastDate)) {
                    lastDate = today;
                    value.set(1);
                }
            }
        }
        return value.getAndIncrement();
    }
}

    That is a bit ugly, so try a single counter:

    public class AtomicSequenceGenerator implements SequenceGenerator {

    private static long countWithDate(long count, LocalDate date) {
        return (((long)date.getDayOfYear()) << (63L-9)) | count;
    }

    private static long countPart(long datedCount) {
        return datedCount & ((1L << (63L-9)) - 1);
    }

    private static boolean dateChanged(long datedCount, LocalDate date) {
         return (int)(datedCount >>> (63L-9)) != date.getDayOfYear();
    }

    private AtomicLong value = new AtomicLong(countWithDate(1, LocalDate.now()));

    @Override
    public long getNext() {
        long datedCount = value.getAndIncrement();
        LocalDate today = LocalDate.now();
        if (dateChanged(dateCount, today)) {
            long next = countWithDate(1L, today);
            if (value.compareAndSet(datedCount+1, next)) {
                datedCount = next;
            } else {
                datedCount = getNext();
            }
        }
        return datedCount;
    }
}

    This uses an AtomicLong with the day-of-year packed into the counter.