java处理 夏令时、冬令时问题

最近接到一个需求：

给一个在美国洛杉矶时区（America/Los_Angeles）的机器上生成的long的时间，要在中国时区的机器上，把这个时间转换成美国时间？

业务方提醒，需要特别主要夏令时、冬令时问题。

 

于是就研究了下夏令时、冬令时问题：

1，首先搜索到这篇问题，知道了java中已经自带处理了这个问题，Java中不是每天都是标准的24个小时，可能是23，也可能是25。23小时和25小时就是夏令时、冬令时引起的。

 

package com.mike.test;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;

public class WhatTime {

	/**
	 * Dates those have not EXACTLY 24 hours ?
	 **/
	public static void testDayTime(TimeZone timeZone) {

		SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

		System.out.println("Time Zone is " + timeZone.getDisplayName() + " " + timeZone.getID());

		Calendar start = Calendar.getInstance(timeZone);
		start.setTime(new Date(0));// UTC 1970-01-01

		System.out.println("start=" + fmt.format(start.getTime()));

		long now = Calendar.getInstance(timeZone).getTimeInMillis();
		long year = 1000l * 3600 * 24 * 365;
		long end = now + year * 5;//

		// System.out.println("now=" + now + "\tend" + end);

		System.out.println(new Date(end));
		// time

		boolean find = false;
		for (long i = start.getTimeInMillis(); i < end; i = start.getTimeInMillis()) {
			start.add(Calendar.DATE, 1); // add one day

			if ((start.getTimeInMillis() - i) % (24 * 3600 * 1000L) != 0) {
				find = true;
				System.out.println("from " + fmt.format(new Date(i)) + "to " + fmt.format(start.getTime()) + " has "
						+ (start.getTimeInMillis() - i) + "ms" + "[" + (start.getTimeInMillis() - i) / (3600 * 1000L)
						+ "hours]");
			}
		}
		if (!find) {
			System.out.println("Every day is ok.");
		}
	}

	public static void main(String argv[]) throws Exception {

		TimeZone timeZone = TimeZone.getDefault();
		WhatTime.testDayTime(timeZone);

		System.out.println("----------------------------------------------------------------");

		timeZone = TimeZone.getTimeZone("GMT");
		WhatTime.testDayTime(timeZone);

		System.out.println("----------------------------------------------------------------");

		timeZone = TimeZone.getTimeZone("America/Los_Angeles");
		WhatTime.testDayTime(timeZone);
	}

} 

输出:

Time Zone is 中国标准时间 Asia/Shanghai
start=1970-01-01 08:00:00
Mon Sep 02 20:46:37 CST 2019
from 1986-05-03 08:00:00to 1986-05-04 08:00:00 has 82800000ms[23hours]
from 1986-09-13 08:00:00to 1986-09-14 08:00:00 has 90000000ms[25hours]
from 1987-04-11 08:00:00to 1987-04-12 08:00:00 has 82800000ms[23hours]
from 1987-09-12 08:00:00to 1987-09-13 08:00:00 has 90000000ms[25hours]
from 1988-04-09 08:00:00to 1988-04-10 08:00:00 has 82800000ms[23hours]
from 1988-09-10 08:00:00to 1988-09-11 08:00:00 has 90000000ms[25hours]
from 1989-04-15 08:00:00to 1989-04-16 08:00:00 has 82800000ms[23hours]
from 1989-09-16 08:00:00to 1989-09-17 08:00:00 has 90000000ms[25hours]
from 1990-04-14 08:00:00to 1990-04-15 08:00:00 has 82800000ms[23hours]
from 1990-09-15 08:00:00to 1990-09-16 08:00:00 has 90000000ms[25hours]
from 1991-04-13 08:00:00to 1991-04-14 08:00:00 has 82800000ms[23hours]
from 1991-09-14 08:00:00to 1991-09-15 08:00:00 has 90000000ms[25hours]
----------------------------------------------------------------
Time Zone is 格林威治时间 GMT
start=1970-01-01 08:00:00
Mon Sep 02 20:46:37 CST 2019
Every day is ok.
----------------------------------------------------------------
Time Zone is 太平洋标准时间 America/Los_Angeles
start=1970-01-01 08:00:00
Mon Sep 02 20:46:37 CST 2019
from 1970-04-26 08:00:00to 1970-04-27 07:00:00 has 82800000ms[23hours]
from 1970-10-25 07:00:00to 1970-10-26 08:00:00 has 90000000ms[25hours]
from 1971-04-25 08:00:00to 1971-04-26 07:00:00 has 82800000ms[23hours]
from 1971-10-31 07:00:00to 1971-11-01 08:00:00 has 90000000ms[25hours]
from 1972-04-30 08:00:00to 1972-05-01 07:00:00 has 82800000ms[23hours]
from 1972-10-29 07:00:00to 1972-10-30 08:00:00 has 90000000ms[25hours]
from 1973-04-29 08:00:00to 1973-04-30 07:00:00 has 82800000ms[23hours]
from 1973-10-28 07:00:00to 1973-10-29 08:00:00 has 90000000ms[25hours]
from 1974-01-06 08:00:00to 1974-01-07 07:00:00 has 82800000ms[23hours]
from 1974-10-27 07:00:00to 1974-10-28 08:00:00 has 90000000ms[25hours]
from 1975-02-23 08:00:00to 1975-02-24 07:00:00 has 82800000ms[23hours]
from 1975-10-26 07:00:00to 1975-10-27 08:00:00 has 90000000ms[25hours]
from 1976-04-25 08:00:00to 1976-04-26 07:00:00 has 82800000ms[23hours]
from 1976-10-31 07:00:00to 1976-11-01 08:00:00 has 90000000ms[25hours]
from 1977-04-24 08:00:00to 1977-04-25 07:00:00 has 82800000ms[23hours]
from 1977-10-30 07:00:00to 1977-10-31 08:00:00 has 90000000ms[25hours]
from 1978-04-30 08:00:00to 1978-05-01 07:00:00 has 82800000ms[23hours]
from 1978-10-29 07:00:00to 1978-10-30 08:00:00 has 90000000ms[25hours]
from 1979-04-29 08:00:00to 1979-04-30 07:00:00 has 82800000ms[23hours]
from 1979-10-28 07:00:00to 1979-10-29 08:00:00 has 90000000ms[25hours]
from 1980-04-27 08:00:00to 1980-04-28 07:00:00 has 82800000ms[23hours]
from 1980-10-26 07:00:00to 1980-10-27 08:00:00 has 90000000ms[25hours]
from 1981-04-26 08:00:00to 1981-04-27 07:00:00 has 82800000ms[23hours]
from 1981-10-25 07:00:00to 1981-10-26 08:00:00 has 90000000ms[25hours]
from 1982-04-25 08:00:00to 1982-04-26 07:00:00 has 82800000ms[23hours]
from 1982-10-31 07:00:00to 1982-11-01 08:00:00 has 90000000ms[25hours]
from 1983-04-24 08:00:00to 1983-04-25 07:00:00 has 82800000ms[23hours]
from 1983-10-30 07:00:00to 1983-10-31 08:00:00 has 90000000ms[25hours]
from 1984-04-29 08:00:00to 1984-04-30 07:00:00 has 82800000ms[23hours]
from 1984-10-28 07:00:00to 1984-10-29 08:00:00 has 90000000ms[25hours]
from 1985-04-28 08:00:00to 1985-04-29 07:00:00 has 82800000ms[23hours]
from 1985-10-27 07:00:00to 1985-10-28 08:00:00 has 90000000ms[25hours]
from 1986-04-27 08:00:00to 1986-04-28 07:00:00 has 82800000ms[23hours]
from 1986-10-26 07:00:00to 1986-10-27 08:00:00 has 90000000ms[25hours]
from 1987-04-05 08:00:00to 1987-04-06 07:00:00 has 82800000ms[23hours]
from 1987-10-25 07:00:00to 1987-10-26 08:00:00 has 90000000ms[25hours]
from 1988-04-03 08:00:00to 1988-04-04 07:00:00 has 82800000ms[23hours]
from 1988-10-30 07:00:00to 1988-10-31 08:00:00 has 90000000ms[25hours]
from 1989-04-02 08:00:00to 1989-04-03 07:00:00 has 82800000ms[23hours]
from 1989-10-29 07:00:00to 1989-10-30 08:00:00 has 90000000ms[25hours]
from 1990-04-01 08:00:00to 1990-04-02 07:00:00 has 82800000ms[23hours]
from 1990-10-28 07:00:00to 1990-10-29 08:00:00 has 90000000ms[25hours]
from 1991-04-07 08:00:00to 1991-04-08 07:00:00 has 82800000ms[23hours]
from 1991-10-27 07:00:00to 1991-10-28 08:00:00 has 90000000ms[25hours]
from 1992-04-05 08:00:00to 1992-04-06 07:00:00 has 82800000ms[23hours]
from 1992-10-25 07:00:00to 1992-10-26 08:00:00 has 90000000ms[25hours]
from 1993-04-04 08:00:00to 1993-04-05 07:00:00 has 82800000ms[23hours]
from 1993-10-31 07:00:00to 1993-11-01 08:00:00 has 90000000ms[25hours]
from 1994-04-03 08:00:00to 1994-04-04 07:00:00 has 82800000ms[23hours]
from 1994-10-30 07:00:00to 1994-10-31 08:00:00 has 90000000ms[25hours]
from 1995-04-02 08:00:00to 1995-04-03 07:00:00 has 82800000ms[23hours]
from 1995-10-29 07:00:00to 1995-10-30 08:00:00 has 90000000ms[25hours]
from 1996-04-07 08:00:00to 1996-04-08 07:00:00 has 82800000ms[23hours]
from 1996-10-27 07:00:00to 1996-10-28 08:00:00 has 90000000ms[25hours]
from 1997-04-06 08:00:00to 1997-04-07 07:00:00 has 82800000ms[23hours]
from 1997-10-26 07:00:00to 1997-10-27 08:00:00 has 90000000ms[25hours]
from 1998-04-05 08:00:00to 1998-04-06 07:00:00 has 82800000ms[23hours]
from 1998-10-25 07:00:00to 1998-10-26 08:00:00 has 90000000ms[25hours]
from 1999-04-04 08:00:00to 1999-04-05 07:00:00 has 82800000ms[23hours]
from 1999-10-31 07:00:00to 1999-11-01 08:00:00 has 90000000ms[25hours]
from 2000-04-02 08:00:00to 2000-04-03 07:00:00 has 82800000ms[23hours]
from 2000-10-29 07:00:00to 2000-10-30 08:00:00 has 90000000ms[25hours]
from 2001-04-01 08:00:00to 2001-04-02 07:00:00 has 82800000ms[23hours]
from 2001-10-28 07:00:00to 2001-10-29 08:00:00 has 90000000ms[25hours]
from 2002-04-07 08:00:00to 2002-04-08 07:00:00 has 82800000ms[23hours]
from 2002-10-27 07:00:00to 2002-10-28 08:00:00 has 90000000ms[25hours]
from 2003-04-06 08:00:00to 2003-04-07 07:00:00 has 82800000ms[23hours]
from 2003-10-26 07:00:00to 2003-10-27 08:00:00 has 90000000ms[25hours]
from 2004-04-04 08:00:00to 2004-04-05 07:00:00 has 82800000ms[23hours]
from 2004-10-31 07:00:00to 2004-11-01 08:00:00 has 90000000ms[25hours]
from 2005-04-03 08:00:00to 2005-04-04 07:00:00 has 82800000ms[23hours]
from 2005-10-30 07:00:00to 2005-10-31 08:00:00 has 90000000ms[25hours]
from 2006-04-02 08:00:00to 2006-04-03 07:00:00 has 82800000ms[23hours]
from 2006-10-29 07:00:00to 2006-10-30 08:00:00 has 90000000ms[25hours]
from 2007-03-11 08:00:00to 2007-03-12 07:00:00 has 82800000ms[23hours]
from 2007-11-04 07:00:00to 2007-11-05 08:00:00 has 90000000ms[25hours]
from 2008-03-09 08:00:00to 2008-03-10 07:00:00 has 82800000ms[23hours]
from 2008-11-02 07:00:00to 2008-11-03 08:00:00 has 90000000ms[25hours]
from 2009-03-08 08:00:00to 2009-03-09 07:00:00 has 82800000ms[23hours]
from 2009-11-01 07:00:00to 2009-11-02 08:00:00 has 90000000ms[25hours]
from 2010-03-14 08:00:00to 2010-03-15 07:00:00 has 82800000ms[23hours]
from 2010-11-07 07:00:00to 2010-11-08 08:00:00 has 90000000ms[25hours]
from 2011-03-13 08:00:00to 2011-03-14 07:00:00 has 82800000ms[23hours]
from 2011-11-06 07:00:00to 2011-11-07 08:00:00 has 90000000ms[25hours]
from 2012-03-11 08:00:00to 2012-03-12 07:00:00 has 82800000ms[23hours]
from 2012-11-04 07:00:00to 2012-11-05 08:00:00 has 90000000ms[25hours]
from 2013-03-10 08:00:00to 2013-03-11 07:00:00 has 82800000ms[23hours]
from 2013-11-03 07:00:00to 2013-11-04 08:00:00 has 90000000ms[25hours]
from 2014-03-09 08:00:00to 2014-03-10 07:00:00 has 82800000ms[23hours]
from 2014-11-02 07:00:00to 2014-11-03 08:00:00 has 90000000ms[25hours]
from 2015-03-08 08:00:00to 2015-03-09 07:00:00 has 82800000ms[23hours]
from 2015-11-01 07:00:00to 2015-11-02 08:00:00 has 90000000ms[25hours]
from 2016-03-13 08:00:00to 2016-03-14 07:00:00 has 82800000ms[23hours]
from 2016-11-06 07:00:00to 2016-11-07 08:00:00 has 90000000ms[25hours]
from 2017-03-12 08:00:00to 2017-03-13 07:00:00 has 82800000ms[23hours]
from 2017-11-05 07:00:00to 2017-11-06 08:00:00 has 90000000ms[25hours]
from 2018-03-11 08:00:00to 2018-03-12 07:00:00 has 82800000ms[23hours]
from 2018-11-04 07:00:00to 2018-11-05 08:00:00 has 90000000ms[25hours]
from 2019-03-10 08:00:00to 2019-03-11 07:00:00 has 82800000ms[23hours]

  

可以发现中国时区在1992年后就废除了夏令时、冬令时，GMT时区是不存在 夏令时、冬令时 ，美国洛杉矶一直在用 夏令时、冬令时。

 

2，好奇一天怎么会变23，25小时，继续试验。

package com.mike.test;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

public class GetAmericaLosTime {
	private static SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

	/**
	 * @param args
	 * @throws ParseException
	 */
	public static void main(String[] args) throws ParseException {
		//
		// // 相差15小时
		// String dateString = "2014-08-31 07:00:00";
		//
		// Date summer = fmt.parse(dateString);
		// printDate(summer.getTime());
		//
		// // 相差16小时
		// dateString = "2014-12-02 07:00:00";
		// Date winter = fmt.parse(dateString);
		// printDate(winter.getTime());

		// 特殊时间点1
		long abc = 1414918799000l;
		printDate(abc);
		abc = 1414918800000l;
		printDate(abc);

		// 特殊时间点2
		// long bcd = 1394359199000l;
		// printDate(bcd);
		// bcd = 1394359200000l;
		// printDate(bcd);

		// printSameTime();
		// 例如： long值： 1414918799000l 对应的中国时间：2014-11-2 16:59:59
		// 用 return new Date(time).toLocaleString()， 返回 美国时间 2014-11-2 1:59:59
		// 用 return new Date(time).toString(); 返回美国实际 ，Sun Nov 02 01:59:59 PDT
		// 2014
	}

	private static void printDate(long now) {
		// 中国时间
		// TimeZone.setDefault(TimeZone.getTimeZone("Asia/Shanghai"));
		// System.out.println(new Date(now).toString());
		// System.out.println(new Date(now).toLocaleString());
		// 美国时间
		TimeZone.setDefault(TimeZone.getTimeZone("America/Los_Angeles"));
		System.out.println(new Date(now));
		System.out.println(new Date(now).toLocaleString());
		System.out.println("============================================================");
	}

	private static String conventTime(long time) {
		// 中国时间
		// TimeZone.setDefault(TimeZone.getTimeZone("Asia/Shanghai"));
		// 美国时间
		TimeZone.setDefault(TimeZone.getTimeZone("America/Los_Angeles"));
		return new Date(time).toLocaleString();
	}

	private static void printSameTime() throws ParseException {
		TimeZone.setDefault(TimeZone.getTimeZone("Asia/Shanghai"));
		// 展示不同long，显示相同date
		String dateString = "2014-03-10 00:00:00";
		Date special = fmt.parse(dateString);
		long specialTime = special.getTime();
		System.out.println(specialTime);
		TimeZone.setDefault(TimeZone.getTimeZone("America/Los_Angeles"));
		long oneHour = 3600 * 1000l;
		for (int i = -26; i < 26; i++) {
			System.out.println("date long:" + (specialTime + oneHour * i) + " \tdate"
					+ new Date(specialTime + oneHour * i));
		}
	}

	private static void printTestDate() {
		long start = System.currentTimeMillis();
		System.out.println("start " + new Date(start));
		System.out.println("start+one hour " + new Date(start + 3600 * 1000));
		System.out.println("start+one day " + new Date(start + 3600 * 1000 * 24));
		System.out.println("start+one year " + new Date(start + 3600l * 1000 * 24 * 365));
		System.out.println("start+ten year " + new Date(start + 3600l * 1000 * 24 * 365 * 10));

		System.out.println("now " + new Date(0));
	}
}

 

输出：

Sun Nov 02 01:59:59 PDT 2014
2014-11-2 1:59:59
============================================================
Sun Nov 02 01:00:00 PST 2014
2014-11-2 1:00:00
============================================================

 发现long值为1414918799000l，美国时间是2014-11-2 1:59:59；增加一秒1414918800000l，美国时间是2014-11-2 1:00:00，嘿嘿，是不是很神奇！！

不过仔细观察下你会发现，1414918799000l是夏令时PDT的 Sun Nov 02 01:59:59 PDT 2014；而1414918800000l是冬令时PST的 Sun Nov 02 01:00:00 PST 2014。

 

至此问题问题就明白了！！！

 

3，回到需求

想到Date和时区有关系，那只要转换前设置下时区就解决问题了。

	private static String conventTime(long time) {
		// 中国时间
		// TimeZone.setDefault(TimeZone.getTimeZone("Asia/Shanghai"));
		// 美国时间
		TimeZone.setDefault(TimeZone.getTimeZone("America/Los_Angeles"));
		return new Date(time).toLocaleString();
	}

 

 

 

 

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