백기선 님의 <더 자바, Java 8>를 보고 공부한 내용을 기록합니다.
<dependency>
<groupId>joda-time</groupId>
<artifactId>joda-time</artifactId>
<version>2.12.2</version>
</dependency>
public class BeforeJava8Test {
@Test
void DateApiTest() {
Date date = new Date();
System.out.println("date = " + date); //Thu Mar 16 14:16:15 KST 2023
long time = date.getTime();
System.out.println("time = " + time); //1678943775380
date.setTime(time - 1); //1678944050334
System.out.println("changed time = " + date.getTime()); //1678944050333
}
@Test
void CalendarApiTest() {
Calendar calendar = new GregorianCalendar(-1000, 2, 15); //month는 0부터 시작하므로 숫자를 바로 쓸 수 없음
assertThat(calendar.getWeekYear()).isEqualTo(-1000);
Calendar calendar2 = new GregorianCalendar(2002, Calendar.FEBRUARY, 15);
System.out.println(calendar2);
}
@Test
void jodaTimeApiTest() {
DateTime dateTime = new DateTime();
assertThat(dateTime.getYear()).isEqualTo(2023);
assertThat(dateTime.getMonthOfYear()).isEqualTo(3);
assertThat(dateTime.getDayOfMonth()).isEqualTo(16);
}
}
2. Java8 부터 Date-Time API 의 등장
public class AfterJava8Test {
@Test
void instant로_기계용_시간_표현하기() {
System.out.println("Instant.now() = " + Instant.now());
System.out.println("Instant.now().atZone(ZoneId.of(\"UTC\")) = " + Instant.now().atZone(ZoneId.of("UTC")));
//Instant.now() = 2023-03-16T05:52:42.740808Z
//Instant.now().atZone(ZoneId.of("UTC")) = 2023-03-16T05:52:42.753796Z[UTC]
}
@Test
void zonedDateTIme으로_타임존_표현하기() {
ZonedDateTime zonedDateTime = ZonedDateTime.now();
System.out.println("zonedDateTime = " + zonedDateTime); //2023-03-16T14:52:15.378961+09:00[Asia/Seoul]
ZonedDateTime zonedDateTime2 = ZonedDateTime.now(ZoneId.systemDefault());
System.out.println("zonedDateTime2 = " + zonedDateTime2); //2023-03-16T14:52:15.383428+09:00[Asia/Seoul]
}
@Test
void localDateTime으로_인류용_시간_표현하기() {
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println("localDateTime = " + localDateTime); //localDateTime = 2023-03-16T14:53:32.503884
LocalDateTime localDateTime1 = LocalDateTime.of(2002, 2, 15, 11, 23, 30);
System.out.println("localDateTime1 = " + localDateTime1); //localDateTime1 = 2002-02-15T11:23:30
ZonedDateTime zonedDateTime = ZonedDateTime.of(localDateTime1, ZoneId.of("Asia/Seoul"));
System.out.println("zonedDateTime = " + zonedDateTime); //zonedDateTime = 2002-02-15T11:23:30+09:00[Asia/Seoul]
}
@Test
void period로_기간표현하기() {
System.out.println("LocalDate.now() = " + LocalDate.now());
Period period = Period.between(LocalDate.of(1994, 8, 11), LocalDate.now());
System.out.println("period = " + period); //P-28Y-7M-5D
System.out.println("period.getYears() = " + period.getYears()); //28
System.out.println("period.getMonths() = " + period.getMonths()); //7
Period period2 = Period.between(LocalDate.now(), LocalDate.of(2023, 8, 11));
System.out.println("period2.getYears() = " + period2.getYears()); //0
System.out.println("period2.getMonths() = " + period2.getMonths()); //4
System.out.println("period2.getDays() = " + period2.getDays()); //26
System.out.println("period2.get(ChronoUnit.DAYS) = " + period2.get(ChronoUnit.DAYS)); //26
}
@Test
void duration으로_기간표현하기() {
Instant now = Instant.now();
Instant plus = now.plus(10, ChronoUnit.SECONDS);
Duration duration = Duration.between(now, plus);
assertThat(duration.getSeconds()).isEqualTo(10);
}
@Test
void parsing하는법() {
DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
System.out.println("LocalDate.now().format(dateTimeFormatter) = " + LocalDate.now().format(dateTimeFormatter));
//LocalDate.now().format(dateTimeFormatter) = 2023-03-16
LocalDate parsed = LocalDate.parse("1998-08-30", dateTimeFormatter);
System.out.println("parsed = " + parsed); //parsed = 1998-08-30 (localDate)
}
@Test
void legacyAPI지원() {
ZoneId pst = TimeZone.getTimeZone("PST").toZoneId();
System.out.println("pst = " + pst); //America/Los_Angeles
TimeZone legacyZoneAPI = TimeZone.getTimeZone(ZoneId.of("Asia/Seoul"));
System.out.println("legacyZoneAPI = " + legacyZoneAPI);
//legacyZoneAPI = sun.util.calendar.ZoneInfo[id="Asia/Seoul",offset=32400000,dstSavings=0,useDaylight=false,transitions=30,lastRule=null]
Instant newInstant = new Date().toInstant();
System.out.println("newInstant = " + newInstant); //newInstant = 2023-03-16T07:09:46.767Z
Date legacyInstant = Date.from(newInstant);
System.out.println("legacyInstant = " + legacyInstant); //legacyInstant = Thu Mar 16 16:09:46 KST 2023
}
}
