Java日期（日历）计算给定日期时间的本地时间中一天的开始 [英] Java Date (Calendar) calculating the start of a day in local time given a date time

问题描述

全部，

在办公室里度过艰难的一天...我想在当地时间（即午夜00）开始一天的训练

在以下几天，我想计算当天午夜的一天的开始时间：

 时间开始日（本地）开始日（GMT）
 2011-03-27 00:00:00 GMT  - > 2011-03-27 00:00:00 GMT  - > 2011-03-27 00:00:00 GMT 
 2011-03-27 01:00:00 GMT  - > 2011-03-27 00:00:00 GMT  - > 2011-03-27 00:00:00 GMT 
 2011-03-27 02:00:00 GMT  - > 2011-03-27 00:00:00 GMT  - > 2011-03-27 00:00:00 GMT 
 2011-04-01 00:00:00 BST  - > 2011-04-01 00:00:00 BST  - > 2011-03-31 23:00:00 GMT 
 2011-10-30 00:00:00 BST  - > 2011-10-30 00:00:00 BST  - > 2011-10-29 23:00:00 GMT 
 2011-10-30 01:00:00 BST  - > 2011-10-30 00:00:00 BST  - > 2011-10-29 23:00:00 GMT 
 2011-10-30 01:00:00 GMT  - > 2011-10-30 00:00:00 BST  - > 2011-10-29 23:00:00 GMT 
 2011-11-01 00:00:00 GMT  - > 2011-11-01 00:00:00 GMT  - > 2011-11-01 00:00:00 GMT 
  

目前，我将String Time解析为使用SimpleDateFormat的GregorianCalendar。这给我的GMT / UTC时间来计算。

所以我有一些代码将字符串解析为GregorianCalendar：

  public GregorianCalendar getCalendar（String dateTime）{
 SimpleDateFormat sdf = new SimpleDateFormat（yyyy-MM-dd HH：mm：ss）; 
 GregorianCalendar cal = new GregorianCalendar（）; 
 cal.setTime（sdf.parse（dateTime，new ParsePosition（0）））; 
 
 return cal; 
} 
  

现在我需要将它设置为午夜：

  public void setToStartOfDayLocally（GregorianCalendar cal）{
 ???? 
} 
  

我不太确定我在日历上需要做什么。不幸的是，我们不会在不久的将来搬到JODA的日期。

感谢您，

p>

Andez

解决方案

我认为此代码可能会解决您的问题。我使用它从当地时区的时间转换到另一个。

  public static Date convertLocalDateToDateTimezone（Date localDate，String timezone）{ 
 TimeZone localTimeZone = TimeZone.getDefault（）; 
 TimeZone timezone = TimeZone.getTimeZone（timezone）; 
 long gmtMillis = localDate.getTime（）; 
 long result = gmtMillis + timezone.getOffset（gmtMillis） -  localTimeZone.getOffset（gmtMillis）; 
 return new Date（results）; 
} 
  

希望这有帮助。

All,

Having a hard day in the office with this one... I am trying to workout the start of a day in Local Time, i.e. Midnight 00:00:00, given any calendar date.

Given the following days, I want to calculate the start of the day at local time midnight:

       Time                     Start Day (Local)            Start Day (GMT)
2011-03-27 00:00:00 GMT -->     2011-03-27 00:00:00 GMT -->  2011-03-27 00:00:00 GMT
2011-03-27 01:00:00 GMT -->     2011-03-27 00:00:00 GMT -->  2011-03-27 00:00:00 GMT
2011-03-27 02:00:00 GMT -->     2011-03-27 00:00:00 GMT -->  2011-03-27 00:00:00 GMT
2011-04-01 00:00:00 BST -->     2011-04-01 00:00:00 BST -->  2011-03-31 23:00:00 GMT
2011-10-30 00:00:00 BST -->     2011-10-30 00:00:00 BST -->  2011-10-29 23:00:00 GMT
2011-10-30 01:00:00 BST -->     2011-10-30 00:00:00 BST -->  2011-10-29 23:00:00 GMT
2011-10-30 01:00:00 GMT -->     2011-10-30 00:00:00 BST -->  2011-10-29 23:00:00 GMT
2011-11-01 00:00:00 GMT -->     2011-11-01 00:00:00 GMT -->  2011-11-01 00:00:00 GMT

At present, I am parsing the String Time into a GregorianCalendar using a SimpleDateFormat. This gives me the GMT/UTC time to calculate from.

So I have some code which parses the string into a GregorianCalendar:

public GregorianCalendar getCalendar(String dateTime) {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); 
    GregorianCalendar cal = new GregorianCalendar();
    cal.setTime(sdf.parse(dateTime, new ParsePosition(0)));

    return cal;
}

Now I need to set it to midnight locally:

public void setToStartOfDayLocally(GregorianCalendar cal) {
    ????
}

I am not too sure what I need to do at the minute with the Calendar. Unfortunately we are not moving to JODA date in the near future. I am also not accounting for different time zones with my example.

Any thoughts?

Thanks,

Andez

解决方案

I think this code might solve your issue. I am using it to convert from time in local timezone to another.

public static Date convertLocalDateToDateTimezone( Date localDate, String timezone ) {
   TimeZone localTimeZone = TimeZone.getDefault();
   TimeZone timezone = TimeZone.getTimeZone( timezone );
   long gmtMillis = localDate.getTime();
   long result = gmtMillis + timezone.getOffset( gmtMillis ) - localTimeZone.getOffset(     gmtMillis );
   return new Date( result );
}

Hope this helps.

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