[訊真科技技術園地] New Java Time (Java8 SE)

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New Java Time (Java8 SE)
http://ingramchen.io/blog/2014/02/brand-new-java-time.html


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java.time.* API

首先來看 java.time 提供的新 API，它引進相當多的 class。好在常用的就只有幾個:LocalDateTime、Instant、ZoneOffset、Clock。轉換的第一步驟是將過去使用 Date 物件的地方，都換成 LocalDate*，下面是一個常見的帳戶 entity：

public class Person {

  String name;
  LocalDate birthday;
  LocalDateTime createTime;
  LocalDateTime lastLoginTime;
  //你幾歲
  int age(LocalDate refDate) {
    return Period.between(birthday, refDate).getYears();
  }
  //生日到了沒？
  boolean isBirthday(MonthDay refDay) {
    return MonthDay.from(birthday).equals(refDay);
  }
  //距上次登入已經過了幾天
  long lastLoginDaySince(LocalDateTime refTime) {
    return Duration.between(lastLoginTime, refTime).toDays();
  }
}

//測試
@Test
public void variousDate() {
  LocalDate birthday = LocalDate.of(1985, 3, 16);
  LocalDateTime createTime = LocalDateTime.of(2014, 2, 3, 5, 0);
  LocalDateTime lastLoginTime = LocalDateTime.of(2014, 2, 7, 19, 11);
  Person person = new Person("Ingram", 
      birthday, createTime, lastLoginTime);

  LocalDate today = LocalDate.of(2014, 2, 28);
  assertEquals(28, person.age(today));
  assertTrue(person.isBirthday(MonthDay.of(3, 16)));
  LocalDateTime now = LocalDateTime.of(today, LocalTime.of(14, 51));
  assertEquals(20, person.lastLoginDaySince(now));
}

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