Java 从日期中提取日期
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extract day from Date
提问by Daniel
I receive a timestamp from a SOAPservice in milliseconds. So I do this:
我从SOAP服务收到一个以毫秒为单位的时间戳。所以我这样做：
Date date = new Date( mar.getEventDate() );
How can I extract the day of the month from date, since methods such as Date::getDay()are deprecated?
由于Date::getDay()不推荐使用诸如此类的方法，我如何从日期中提取月份中的哪一天？
I am using a small hack, but I do not think this is the proper way to obtain day-of-month.
我正在使用一个小技巧，但我认为这不是获取月份的正确方法。
SimpleDateFormat sdf = new SimpleDateFormat( "dd" );
int day = Integer.parseInt( sdf.format( date ) );
回答by cletus
回答by Ortomala Lokni
Given the Date constructorused in the question
鉴于问题中使用的日期构造函数
Date date = new Date(mar.getEventDate());
The method mar.getEventDate()returns a longthat represent the specified number of milliseconds since the standard base time known as "the epoch", namely January 1, 1970, 00:00:00 GMT.
该方法mar.getEventDate()返回一个long表示自称为“纪元”的标准基准时间（即格林威治标准时间 1970 年 1 月 1 日 00:00:00）以来的指定毫秒数。
Java 8 and later
Java 8 及更高版本
In Java 8, you can extract the day of the month from this value, assuming UTC, with
在 Java 8 中，假设 UTC，您可以从此值中提取月份中的第几天，
LocalDateTime.ofEpochSecond(mar.getEventDate(),0,ZoneOffset.UTC).getDayOfMonth();
Note also that the answer given by cletus assume that mar.getEventDate()returns a Dateobject which is not the case in the question.
另请注意，cletus 给出的答案假定mar.getEventDate()返回的Date对象与问题中的情况不同。
回答by Basil Bourque
Update:The Joda-Timeproject is now in maintenance mode, with the team advising migration to the java.timeclasses. See Tutorial by Oracle.
更新：该乔达时间的项目现在处于维护模式，与团队的建议迁移java.time类。请参阅Oracle 教程。
See the correct Answerby Ortomala Lokni, using the modern java.timeclasses. I am leaving this outmoded Answer intact as history.
请参阅Ortomala Lokni 使用现代java.time类编写的正确答案。我将这个过时的答案作为历史原封不动地保留下来。
The Answerby Lokni is correct.
Lokni的回答是正确的。
Here is the same idea but using Joda-Time2.8.
这是相同的想法，但使用Joda-Time2.8。
long millisSinceEpoch = mar.getEventDate() ;
DateTimeZone zone = DateTimeZone.forID( "America/Montreal" ) ; // Or DateTimeZone.UTC
LocalDate localDate = new LocalDate( millisSinceEpoch , zone ) ;
int dayOfMonth = localDate.getDayOfMonth() ;
