本文翻译自:Convert java.util.Date to java.time.LocalDate
What is the best way to convert a java.util.Date
object to the new JDK 8/JSR-310 java.time.LocalDate
? 将java.util.Date
对象转换为新的JDK 8 / JSR-310 java.time.LocalDate
的最佳方法是什么?
Date input = new Date();
LocalDate date = ???
参考:https://stackoom.com/question/1R82g/将java-util-Date转换为java-time-LocalDate
Short answer 简短答案
Date input = new Date();
LocalDate date = input.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();
Explanation 说明
Despite its name, java.util.Date
represents an instant on the time-line, not a "date". 尽管其名称, java.util.Date
表示时间轴上的一个瞬间,而不是“日期”。 The actual data stored within the object is a long
count of milliseconds since 1970-01-01T00:00Z (midnight at the start of 1970 GMT/UTC). 自1970-01-01T00:00Z(1970 GMT / UTC开始的午夜)以来,存储在对象中的实际数据是很long
的毫秒数。
The equivalent class to java.util.Date
in JSR-310 is Instant
, thus there is a convenient method toInstant()
to provide the conversion: JSR-310中与java.util.Date
等效的类是Instant
,因此有一个方便的方法toInstant()
提供转换:
Date input = new Date();
Instant instant = input.toInstant();
A java.util.Date
instance has no concept of time-zone. 一个java.util.Date
实例没有时区的概念。 This might seem strange if you call toString()
on a java.util.Date
, because the toString
is relative to a time-zone. 如果在java.util.Date
上调用toString()
,这似乎很奇怪,因为toString
是相对于时区的。 However that method actually uses Java's default time-zone on the fly to provide the string. 但是,该方法实际上在运行时使用了Java的默认时区来提供字符串。 The time-zone is not part of the actual state of java.util.Date
. 时区不是java.util.Date
实际状态的一部分。
An Instant
also does not contain any information about the time-zone. Instant
也不包含有关时区的任何信息。 Thus, to convert from an Instant
to a local date it is necessary to specify a time-zone. 因此,要将Instant
日期转换为本地日期,必须指定一个时区。 This might be the default zone - ZoneId.systemDefault()
- or it might be a time-zone that your application controls, such as a time-zone from user preferences. 这可能是默认区域ZoneId.systemDefault()
-或可能是您的应用程序控制的时区,例如用户首选项中的时区。 Use the atZone()
method to apply the time-zone: 使用atZone()
方法应用时区:
Date input = new Date();
Instant instant = input.toInstant();
ZonedDateTime zdt = instant.atZone(ZoneId.systemDefault());
A ZonedDateTime
contains state consisting of the local date and time, time-zone and the offset from GMT/UTC. ZonedDateTime
包含由本地日期和时间,时区和距GMT / UTC的偏移量组成的状态。 As such the date - LocalDate
- can be easily extracted using toLocalDate()
: 作为这样的时间- LocalDate
-可以使用容易地提取toLocalDate()
Date input = new Date();
Instant instant = input.toInstant();
ZonedDateTime zdt = instant.atZone(ZoneId.systemDefault());
LocalDate date = zdt.toLocalDate();
Java 9 answer Java 9答案
In Java SE 9, a new method has been added that slightly simplifies this task: 在Java SE 9中,添加了一个新方法 ,该方法稍微简化了此任务:
Date input = new Date();
LocalDate date = LocalDate.ofInstant(input.toInstant(), ZoneId.systemDefault());
This new alternative is more direct, creating less garbage, and thus should perform better. 这个新的替代方法更直接,产生更少的垃圾,因此应该表现得更好。
If you're using Java 8, @JodaStephen's answer is obviously the best. 如果您使用的是Java 8,@ JodaStephen的答案显然是最好的。 However, if you're working with the JSR-310 backport , you unfortunately have to do something like this: 但是,如果您使用的是JSR-310反向端口 ,那么很遗憾,您必须执行以下操作:
Date input = new Date();
Calendar cal = Calendar.getInstance();
cal.setTime(input);
LocalDate date = LocalDate.of(cal.get(Calendar.YEAR),
cal.get(Calendar.MONTH) + 1,
cal.get(Calendar.DAY_OF_MONTH));
Better way is: 更好的方法是:
Date date = ...;
Instant.ofEpochMilli(date.getTime()).atZone(ZoneId.systemDefault()).toLocalDate()
Advantages of this version: 此版本的优点:
works regardless the input is an instance of java.util.Date
or it's subclass java.sql.Date
(unlike @JodaStephen's way). 无论输入是java.util.Date
的实例还是其子类java.sql.Date
(与@JodaStephen的方式不同),它都可以工作。 This is common with JDBC originated data. 这对于JDBC原始数据很常见。 java.sql.Date.toInstant()
always throws an exception. java.sql.Date.toInstant()
总是抛出异常。
it's the same for JDK8 and JDK7 with JSR-310 backport 具有JSR-310反向端口的JDK8和JDK7相同
I personally use an utility class (but this is not backport-compatible): 我个人使用实用程序类(但这与backport不兼容):
/**
* Utilities for conversion between the old and new JDK date types
* (between {@code java.util.Date} and {@code java.time.*}).
*
*
* All methods are null-safe.
*/
public class DateConvertUtils {
/**
* Calls {@link #asLocalDate(Date, ZoneId)} with the system default time zone.
*/
public static LocalDate asLocalDate(java.util.Date date) {
return asLocalDate(date, ZoneId.systemDefault());
}
/**
* Creates {@link LocalDate} from {@code java.util.Date} or it's subclasses. Null-safe.
*/
public static LocalDate asLocalDate(java.util.Date date, ZoneId zone) {
if (date == null)
return null;
if (date instanceof java.sql.Date)
return ((java.sql.Date) date).toLocalDate();
else
return Instant.ofEpochMilli(date.getTime()).atZone(zone).toLocalDate();
}
/**
* Calls {@link #asLocalDateTime(Date, ZoneId)} with the system default time zone.
*/
public static LocalDateTime asLocalDateTime(java.util.Date date) {
return asLocalDateTime(date, ZoneId.systemDefault());
}
/**
* Creates {@link LocalDateTime} from {@code java.util.Date} or it's subclasses. Null-safe.
*/
public static LocalDateTime asLocalDateTime(java.util.Date date, ZoneId zone) {
if (date == null)
return null;
if (date instanceof java.sql.Timestamp)
return ((java.sql.Timestamp) date).toLocalDateTime();
else
return Instant.ofEpochMilli(date.getTime()).atZone(zone).toLocalDateTime();
}
/**
* Calls {@link #asUtilDate(Object, ZoneId)} with the system default time zone.
*/
public static java.util.Date asUtilDate(Object date) {
return asUtilDate(date, ZoneId.systemDefault());
}
/**
* Creates a {@link java.util.Date} from various date objects. Is null-safe. Currently supports:
* - {@link java.util.Date}
*
- {@link java.sql.Date}
*
- {@link java.sql.Timestamp}
*
- {@link java.time.LocalDate}
*
- {@link java.time.LocalDateTime}
*
- {@link java.time.ZonedDateTime}
*
- {@link java.time.Instant}
*
*
* @param zone Time zone, used only if the input object is LocalDate or LocalDateTime.
*
* @return {@link java.util.Date} (exactly this class, not a subclass, such as java.sql.Date)
*/
public static java.util.Date asUtilDate(Object date, ZoneId zone) {
if (date == null)
return null;
if (date instanceof java.sql.Date || date instanceof java.sql.Timestamp)
return new java.util.Date(((java.util.Date) date).getTime());
if (date instanceof java.util.Date)
return (java.util.Date) date;
if (date instanceof LocalDate)
return java.util.Date.from(((LocalDate) date).atStartOfDay(zone).toInstant());
if (date instanceof LocalDateTime)
return java.util.Date.from(((LocalDateTime) date).atZone(zone).toInstant());
if (date instanceof ZonedDateTime)
return java.util.Date.from(((ZonedDateTime) date).toInstant());
if (date instanceof Instant)
return java.util.Date.from((Instant) date);
throw new UnsupportedOperationException("Don't know hot to convert " + date.getClass().getName() + " to java.util.Date");
}
/**
* Creates an {@link Instant} from {@code java.util.Date} or it's subclasses. Null-safe.
*/
public static Instant asInstant(Date date) {
if (date == null)
return null;
else
return Instant.ofEpochMilli(date.getTime());
}
/**
* Calls {@link #asZonedDateTime(Date, ZoneId)} with the system default time zone.
*/
public static ZonedDateTime asZonedDateTime(Date date) {
return asZonedDateTime(date, ZoneId.systemDefault());
}
/**
* Creates {@link ZonedDateTime} from {@code java.util.Date} or it's subclasses. Null-safe.
*/
public static ZonedDateTime asZonedDateTime(Date date, ZoneId zone) {
if (date == null)
return null;
else
return asInstant(date).atZone(zone);
}
}
The asLocalDate()
method here is null-safe, uses toLocalDate()
, if input is java.sql.Date
(it may be overriden by the JDBC driver to avoid timezone problems or unnecessary calculations), otherwise uses the abovementioned method. 如果输入为java.sql.Date
(如果为避免时区问题或不必要的计算而被JDBC驱动程序覆盖toLocalDate()
,则此处的asLocalDate()
方法为null安全,使用toLocalDate()
),否则使用上述方法。
LocalDate ld = new java.sql.Date( new java.util.Date().getTime() ).toLocalDate();
LocalDate localDate = LocalDate.parse( new SimpleDateFormat("yyyy-MM-dd").format(date) );