失眠网 > 将java.util.Date转换为java.time.LocalDate

将java.util.Date转换为java.time.LocalDate

时间：2022-08-17 23:11:10

本文翻译自：Convert java.util.Date to java.time.LocalDate

What is the best way to convert ajava.util.Dateobject to the new JDK 8/JSR-310java.time.LocalDate?将java.util.Date对象转换为新的JDK 8 / JSR-310java.time.LocalDate的最佳方法是什么？

Date input = new Date();LocalDate date = ???

#1楼

参考：/question/1R82g/将java-util-Date转换为java-time-LocalDate

#2楼

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.Daterepresents 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 alongcount 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 tojava.util.Datein JSR-310 isInstant, thus there is a convenient methodtoInstant()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();

Ajava.util.Dateinstance 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 calltoString()on ajava.util.Date, because thetoStringis 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 ofjava.util.Date.时区不是java.util.Date实际状态的一部分。

AnInstantalso 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 anInstantto 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 theatZone()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());

AZonedDateTimecontains 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 usingtoLocalDate():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 answerJava 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。

#3楼

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));

#4楼

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 ofjava.util.Dateor it's subclassjava.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.*}).* * <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();elsereturn 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();elsereturn 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;elsereturn 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;elsereturn asInstant(date).atZone(zone);}}

TheasLocalDate()method here is null-safe, usestoLocalDate(), if input isjava.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。