Java8時間處理

Java時間處理

Java8新增的時間處理API

常用時間處理方法的問題

1. java.util.Date和java.util.Calendar不是線程安全的類
2. SimpleDateFormat也是非線程安全的類
3. Calendar獲取月份時需要計算，因爲月份從0開始

日期/時間類

• LocalDate與LocalTime

  LocalDate類表示一個具體的日期，但不包含具體時間，也不包含時區信息，LocalTime表示一個具體的時間

  LocalDate localDate = LocalDate.of(2017, 1, 4);     // 初始化一個日期：2017-01-04
  LocalTime localTime = LocalTime.of(17, 23, 52);     // 初始化一個時間：17:23:52

• LocalDateTime

  上述兩個類的結合體

  LocalDateTime ldt1 = LocalDateTime.of(2017, Month.JANUARY, 4, 17, 23, 52);

• Instant

  Instant表示一個時間戳，精確到納秒

  Instant instant = Instant.ofEpochSecond(120, 100000);
  //參數：seconds表示從1970-01-01 00:00:00開始到現在的秒數，nanos表示納秒部分（nanos的值不會超過999,999,999）

• Duration

  Duration表示一個時間段，精確到納秒

  LocalDateTime from = LocalDateTime.of(2017, Month.JANUARY, 5, 10, 7, 0);    // 2017-01-05 10:07:00
  LocalDateTime to = LocalDateTime.of(2017, Month.FEBRUARY, 5, 10, 7, 0);     // 2017-02-05 10:07:00
  Duration duration = Duration.between(from, to);     // 表示從 2017-01-05 10:07:00 到 2017-02-05 10:07:00 這段時間

日期格式化

• DateTimeFormatter類處理日期格式化
• java.time.ZoneId類處理時區

LocalTime to sql.time

LocalTime now = LocalTime.now();
Time time = Time.valueOf(now);

sql.time to LocalTime

//Get SQL time instance
Time sqlTime = new Time(new Date().getTime());
//Get LocalTime from SQL time
LocalTime localtime = sqlTime.toLocalTime();

Date類型與LocalTime轉換

// 01. java.util.Date --> java.time.LocalDateTime
public void UDateToLocalDateTime() {
    java.util.Date date = new java.util.Date();
    Instant instant = date.toInstant();
    ZoneId zone = ZoneId.systemDefault();
    LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
}

// 02. java.util.Date --> java.time.LocalDate
public void UDateToLocalDate() {
    java.util.Date date = new java.util.Date();
    Instant instant = date.toInstant();
    ZoneId zone = ZoneId.systemDefault();
    LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
    LocalDate localDate = localDateTime.toLocalDate();
}

// 03. java.util.Date --> java.time.LocalTime
public void UDateToLocalTime() {
    java.util.Date date = new java.util.Date();
    Instant instant = date.toInstant();
    ZoneId zone = ZoneId.systemDefault();
    LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
    LocalTime localTime = localDateTime.toLocalTime();
}

// 04. java.time.LocalDateTime --> java.util.Date
public void LocalDateTimeToUdate() {
    LocalDateTime localDateTime = LocalDateTime.now();
    ZoneId zone = ZoneId.systemDefault();
    Instant instant = localDateTime.atZone(zone).toInstant();
    java.util.Date date = Date.from(instant);
}

// 05. java.time.LocalDate --> java.util.Date
public void LocalDateToUdate() {
    LocalDate localDate = LocalDate.now();
    ZoneId zone = ZoneId.systemDefault();
    Instant instant = localDate.atStartOfDay().atZone(zone).toInstant();
    java.util.Date date = Date.from(instant);
}

// 06. java.time.LocalTime --> java.util.Date
public void LocalTimeToUdate() {
    LocalTime localTime = LocalTime.now();
    LocalDate localDate = LocalDate.now();
    LocalDateTime localDateTime = LocalDateTime.of(localDate, localTime);
    ZoneId zone = ZoneId.systemDefault();
    Instant instant = localDateTime.atZone(zone).toInstant();
    java.util.Date date = Date.from(instant);
}

獲取時區偏移量

String zoneStr = "Asia/Shanghai";
LocalDateTime dt = LocalDateTime.now();
ZoneId zoneId = ZoneId.of(zoneStr);
ZoneDateTime zdt = dt.atZone(zoneId);
ZoneOffset offset = zdt.getOffset();
System.out.println(offset);
//output: +08：00

將給定時間轉化爲UTC時間

ZoneId australia = ZoneId.of("Australia/Sydney"); 
String str = "2018-08-31 17:00"; 
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm"); 
LocalDateTime localtDateAndTime = LocalDateTime.parse(str, formatter); 
ZonedDateTime dateAndTimeInSydney = ZonedDateTime.of(localtDateAndTime, australia); 

System.out.println("Current date and time in a particular timezone : " + dateAndTimeInSydney); 

ZonedDateTime utcDate = dateAndTimeInSydney.withZoneSameInstant(ZoneOffset.UTC); 

System.out.println("Current date and time in UTC : " + utcDate); 

• 另一種方式，設置與相應的時區格式化

String input = "2018-08-31 17:00"; 
ZoneId zone = ZoneId.of("Australia/Sydney"); 

DateTimeFormatter fmt = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm").withZone(zone); 
ZonedDateTime utc = ZonedDateTime.parse(input, fmt).withZoneSameInstant(UTC); 

參考鏈接

參考鏈接