# Java
시간을 기반으로 한 유니크한 문자열 만드는 방법
https://stackoverflow.com/questions/9191288/creating-a-unique-timestamp-in-java
private static final AtomicLong LAST_TIME_MS = new AtomicLong();
private static long uniqueCurrentTimeMS() {
long now = System.currentTimeMillis();
while (true) {
long lastTime = LAST_TIME_MS.get();
if (lastTime >= now)
now = lastTime + 1;
if (LAST_TIME_MS.compareAndSet(lastTime, now))
return now;
}
}
소요시간 구하기
https://www.baeldung.com/java-measure-elapsed-time
long start = System.currentTimeMillis();
// ... code
long finish = System.currentTimeMillis();
long timeElapsed = finish - start;
# MySql
시간 차이 구하는 SQL
https://stackoverflow.com/questions/10907750/calculate-difference-between-two-datetimes-in-mysql
SELECT TIMESTAMPDIFF(SECOND, '2020-06-02 14:11:20', '2020-06-01 16:10:25')