Java中时间数据转换关系

2018.01.26

假设已经有如下变量:

long l;
Date date;
LocalDateTime localDateTime;
Timestamp timestamp;
Calendar c;
String str;
Instant instant;

ZoneId zoneId = ZoneId.of("UTC+8").normalized();
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

快捷查询窗口：

Source:	Target:
=	=

下表中等号表示可以直接赋值；空白表示没有可用的转换方法；其他为代码示例

long->long
```
=
```
long->Date
```
new Date(long)
```

long->LocalDateTime

LocalDateTime.ofEpochSecond(timestamp / 1000,
	(int) (timestamp % 1000),
	ZoneOffset.of(zoneId.getId()));

long->Timestamp
```
new Timestamp(time)
```

long->Calendar

Calendar c = Calendar.getInstance();
c.setTimeInMillis(time);

long->String
```
format.format(new Date(time));
```
long->Instant
```
Instant.ofEpochMilli(l)
```
Date->long
```
date.getTime();
```
Date->Date
```
=
```

Date->LocalDateTime

LocalDateTime.ofInstant(date.toInstant(), zoneId);

Date->Timestamp
```
Timestamp.from(date.toInstant());
```

Date->Calendar

Calendar c = Calendar.getInstance();
c.setTime(date);

Date->String
```
format.format(date);
```
Date->Instant
```
date.toInstant()
```

LocalDateTime->long

ZonedDateTime zdt = localDateTime.atZone(zoneId);
l = zdt.toEpochSecond() * 1000 + zdt.getNano();

LocalDateTime->Date

Date.from(localDateTime.atZone(zoneId).toInstant());

LocalDateTime->LocalDateTime
```
=
```

LocalDateTime->Timestamp

Timestamp.from(localDateTime.atZone(zoneId).toInstant());

LocalDateTime->Calendar

Calendar c = Calendar.getInstance();
c.setTime(Date.from(localDateTime.atZone(zoneId).toInstant()));

LocalDateTime->String
```
localDateTime.format(dateTimeFormatter)
```

LocalDateTime->Instant

localDateTime.toInstant(ZoneOffset.of(zoneId.getId()));

Timestamp->long
```
timestamp.getTime()
```
Timestamp->Date
```
=
```

Timestamp->LocalDateTime

LocalDateTime.ofInstant(timestamp.toInstant(), zoneId);

Timestamp->Timestamp
```
=
```

Timestamp->Calendar

Calendar c = Calendar.getInstance();
c.setTime(timestamp);

Timestamp->String
```
format.format(timestamp);
```
Timestamp->Instant
```
timestamp.toInstant()
```
Calendar->long
```
c.getTimeInMillis()
```
Calendar->Date
```
c.getTime()
```

Calendar->LocalDateTime

LocalDateTime.ofInstant(c.toInstant(), zoneId);

Calendar->Timestamp
```
Timestamp.from(c.toInstant())
```
Calendar->Calendar
```
=
```
Calendar->String
```
simpleDateFormat.format(c.getTime());
```
Calendar->Instant
```
c.toInstant()
```
String->long
```
simpleDateFormat.parse(str).getTime();
```
String->Date
```
simpleDateFormat.parse(str);
```

String->LocalDateTime

LocalDateTime.parse("2018-01-26T17:34:41.000")

String->Timestamp

Timestamp.valueOf("2018-01-26 17:34:41.000");

String->Calendar
String->String
```
=
```
String->Instant
Instant->long
```
instant.toEpochMilli()
```
Instant->Date
```
Date.from(instant)
```

Instant->LocalDateTime

LocalDateTime.ofInstant(instant, zoneId);

Instant->Timestamp
```
Timestamp.from(instant)
```

Instant->Calendar

Calendar c = Calendar.getInstance();
c.setTimeInMillis(instant.toEpochMilli());

Instant->String
```
 
```
Instant->Instant
```
=
```

△

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Java中时间数据转换关系