java 如何将 LocalDateTime 转换为 GregorianCalendar？
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How to convert LocalDateTime to GregorianCalendar?
提问by membersound
Why is it possible to pass a LocalDateTimeobject into the ZonedDateTime.from()method, if it's not possible to parse a simple DateTime, as follows?
如果无法解析一个简单的，为什么可以将LocalDateTime对象传递给ZonedDateTime.from()方法，DateTime如下所示？
@Test
public void test() throws Exception {
GregorianCalendar.from(ZonedDateTime.from(LocalDateTime.parse("2016-08-31T23:00:59")));
}
Result:
结果：
java.time.DateTimeException: Unable to obtain ZonedDateTime from TemporalAccessor: 2016-08-31T23:00:59 of type java.time.LocalDateTime
at java.time.ZonedDateTime.from(ZonedDateTime.java:565)
回答by Unknown
Why is it possible to pass a LocalDateTime object into the ZonedDateTime.from() method if it's not possible to parse a simple datetime?
如果无法解析简单的日期时间，为什么可以将 LocalDateTime 对象传递给 ZonedDateTime.from() 方法？
Both LocalDateTimeand ZonedDateTimeimplement the interface called Temporal, which extends TemporalAccessor.
双方LocalDateTime并ZonedDateTime实现所谓的接口Temporal，它扩展TemporalAccessor。
LocalDateTimeis datetime withouta time-zone in the ISO-8601 calendar system, such as 2007-12-03T10:15:30
LocalDateTime是ISO-8601 日历系统中没有时区的日期时间，例如 2007-12-03T10:15:30
ZonedDateTimeis datetime witha time-zone in the ISO-8601 calendar system, such as 2007-12-03T10:15:30+01:00 Europe/Paris.
ZonedDateTime是带有ISO-8601 日历系统中时区的日期时间，例如 2007-12-03T10:15:30+01:00 Europe/Paris。
Now, if you see the implementation of from(TemporalAccessor temporal)method that is expecting the TemporalAccessor… Both LocalDateTimeand ZonedDateTimeimplements the method of super interface TemporalAccessor(Temporal extends TemporalAccessor), which is normal (i.e. has a polymorphic behavior) to allow us to pass both the local as well as zoned datetime.
现在，如果你看到的实现from(TemporalAccessor temporal)方法是期待TemporalAccessor......都LocalDateTime和ZonedDateTime农具超接口的方法TemporalAccessor（Temporal extends TemporalAccessor），这是正常的（即具有多态），使我们能够同时通过本地和分区日期时间。
Code:
代码：
public static ZonedDateTime from(final TemporalAccessor temporal) {
if (temporal instanceof ZonedDateTime) {
return (ZonedDateTime) temporal;
}
try {
final ZoneId zone = ZoneId.from(temporal);
if (temporal.isSupported(INSTANT_SECONDS)) {
long epochSecond = temporal.getLong(INSTANT_SECONDS);
int nanoOfSecond = temporal.get(NANO_OF_SECOND);
return create(epochSecond, nanoOfSecond, zone);
} else {
LocalDate date = LocalDate.from(temporal);
LocalTime time = LocalTime.from(temporal);
return of(date, time, zone);
}
} catch (final DateTimeException ex) {
throw new DateTimeException("Unable to obtain ZonedDateTime from TemporalAccessor: " +
temporal + " of type " + temporal.getClass().getName(), ex);
}
}
Now, we come to your problem.
现在，我们来解决您的问题。
You are passing LocalDateTime.parse("2016-08-31T23:00:59")to the from(TemporalAccessor temporal)method. So, the temporal is not an instance of ZonedDateTime, it comes ZoneId zone = ZoneId.from(temporal);.
您正在传递LocalDateTime.parse("2016-08-31T23:00:59")给该from(TemporalAccessor temporal)方法。因此，时间不是 的实例ZonedDateTime，而是ZoneId zone = ZoneId.from(temporal);。
So, your are getting the error since the LocalDateTimedoes not contain the
timezone.
因此，您收到错误，因为LocalDateTime不包含时区。
How to solve the issue?
如何解决问题？
Use the Zone ID with the ZonedDateTime:
将区域 ID 与ZonedDateTime：
LocalDateTime ldt = LocalDateTime.parse("2016-08-31T23:00:59");
ZoneId zoneId = ZoneId.of("Europe/Paris");
ZonedDateTime zdt = ldt.atZone(zoneId);
GregorianCalendar gc = GregorianCalendar.from(zdt);
with JUnit test
使用 JUnit 测试
@Test
public void test() throws Exception {
ZoneId zoneId = ZoneId.of("Europe/Paris");
GregorianCalendar.from(LocalDateTime.parse("2016-08-31T23:00:59").atZone(zoneId));
}
回答by Ramachandran.A.G
You will have to provide the ZoneIdas well. I will have to look up on the behavior as to why this is. I will edit and post as soon as I see it.
您还必须提供ZoneId。我将不得不调查这种行为的原因。我一看到就会编辑和发帖。
LocalDateTime ldt = LocalDateTime.parse("2016-08-31T23:00:59");
GregorianCalendar gc = GregorianCalendar.from(ZonedDateTime.of(ldt, ZoneId.systemDefault()));
System.out.println(gc);
This results:
结果如下：
java.util.GregorianCalendar[time=1472664659000,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Calcutta",offset=19800000,dstSavings=0,useDaylight=false,transitions=6,lastRule=null],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA=1,YEAR=2016,MONTH=7,WEEK_OF_YEAR=35,WEEK_OF_MONTH=5,DAY_OF_MONTH=31,DAY_OF_YEAR=244,DAY_OF_WEEK=4,DAY_OF_WEEK_IN_MONTH=5,AM_PM=1,HOUR=11,HOUR_OF_DAY=23,MINUTE=0,SECOND=59,MILLISECOND=0,ZONE_OFFSET=19800000,DST_OFFSET=0]
Edits:Just came across this interesting thread...
编辑：刚刚遇到这个有趣的线程......
The Java 8 java.time.* package is a very strict package. It doesn't allow flexibility between types and inputs - if you want a ZonedDateTime object, you must construct it from an input that has a time zone, a date & a time.
Java 8 java.time.* 包是一个非常严格的包。它不允许类型和输入之间的灵活性 - 如果您想要 ZonedDateTime 对象，则必须从具有时区、日期和时间的输入构建它。
