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 = ???
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 = ???
当前回答
LocalDate localDate = LocalDate.parse( new SimpleDateFormat("yyyy-MM-dd").format(date) );
其他回答
更好的方法是:
Date date = ...;
Instant.ofEpochMilli(date.getTime()).atZone(ZoneId.systemDefault()).toLocalDate()
本版本优点:
不管输入是java.util.Date的实例还是java.sql.Date的子类(不像@JodaStephen的方式)。这对于起源于jdbc的数据很常见。java.sql.Date.toInstant()总是抛出异常。 JDK8和JDK7带JSR-310后端口也是一样的
我个人使用一个实用程序类(但它不兼容后端口):
/**
* Utilities for conversion between the old and new JDK date types
* (between {@code java.util.Date} and {@code java.time.*}).
*
* <p>
* 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:<ul>
* <li>{@link java.util.Date}
* <li>{@link java.sql.Date}
* <li>{@link java.sql.Timestamp}
* <li>{@link java.time.LocalDate}
* <li>{@link java.time.LocalDateTime}
* <li>{@link java.time.ZonedDateTime}
* <li>{@link java.time.Instant}
* </ul>
*
* @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);
}
}
这里的asLocalDate()方法是空安全的,如果输入是java.sql.Date(它可能被JDBC驱动程序覆盖以避免时区问题或不必要的计算),则使用tollocaldate(),否则使用上述方法。
如果你正在使用Java 8, @JodaStephen的答案显然是最好的。然而,如果你使用的是JSR-310后端口,你不得不做这样的事情:
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));
为了简化将LocalDate/time转换为Date的过程,反之亦然,我创建了两个图表:
将LocalDate转换为Date,反之亦然:
将LocalDateTime转换为Date,反之亦然:
Date input = new Date();
LocalDateTime conv=LocalDateTime.ofInstant(input.toInstant(), ZoneId.systemDefault());
LocalDate convDate=conv.toLocalDate();
Date实例也包含时间和日期,而LocalDate不包含。因此,您可以首先将它转换为LocalDateTime使用它的方法的finstant(),然后如果你想要它没有时间,然后将实例转换为LocalDate。
我在JBoss EAP 6上的@JodaStephen的实现有问题。因此,我按照http://docs.oracle.com/javase/tutorial/datetime/iso/legacy.html中的Oracle Java教程重写了转换。
Date input = new Date();
GregorianCalendar gregorianCalendar = (GregorianCalendar) Calendar.getInstance();
gregorianCalendar.setTime(input);
ZonedDateTime zonedDateTime = gregorianCalendar.toZonedDateTime();
zonedDateTime.toLocalDate();