TimeZone以及時區有關的操作Date/Calendar/SimpleDateFormat

阿新 • • 發佈：2019-02-10

TimeZone

1. System.getProperty("user.timezone") System.setProperty("user.timezone","GMT+8")

2. TimeZone.getDefault().getID() TimeZone.setDefault(TimeZone.getTimeZone("Asia/Shanghai"))

                Date date = new Date();		
		System.out.println("date.toString():"+date.toString());
		System.out.println("date.getTime()"+date.getTime());
		Calendar cal = Calendar.getInstance();
		System.out.println("Calendar.getInstance().getTime():"+cal.getTime());
		System.out.println("Calendar.getInstance().getTimeInMillis():"+cal.getTimeInMillis());
		System.out.println("Calendar.getInstance().getTimeZone():"+cal.getTimeZone());
		System.out.println("system user.timezone:" + System.getProperty("user.timezone"));
		System.out.println("system user.country:" + System.getProperty("user.country"));
		System.out.println("預設時區：" + TimeZone.getDefault().getID());
		System.out.println("--------------------------------------");
		
		System.out.println("After setTimeZone0:");
		TimeZone.setDefault(TimeZone.getTimeZone("GMT+2"));
		date = new Date();
		System.out.println("date.toString():"+date);
		System.out.println("date.getTime()"+date.getTime());
		cal = Calendar.getInstance();
		System.out.println("Calendar.getInstance().getTime():"+cal.getTime());
		System.out.println("Calendar.getInstance().getTimeInMillis():"+cal.getTimeInMillis());
		System.out.println("Calendar.getInstance().getTimeZone():"+cal.getTimeZone());
		System.out.println("system user.timezone:" + System.getProperty("user.timezone"));
		System.out.println("system user.country:" + System.getProperty("user.country"));
		System.out.println("預設時區：" + TimeZone.getDefault().getID());
		System.out.println("--------------------------------------");
		
		TimeZone.setDefault(TimeZone.getTimeZone("Asia/Shanghai"));
		System.setProperty("user.timezone", "GMT+2");
		date = new Date();
		System.out.println("date.toString():"+date);
		System.out.println("date.getTime()"+date.getTime());
		cal = Calendar.getInstance();
		System.out.println("Calendar.getInstance().getTime():"+cal.getTime());
		System.out.println("Calendar.getInstance().getTimeInMillis():"+cal.getTimeInMillis());
		System.out.println("Calendar.getInstance().getTimeZone():"+cal.getTimeZone());
		System.out.println("system user.timezone:" + System.getProperty("user.timezone"));
		System.out.println("system user.country:" + System.getProperty("user.country"));
		System.out.println("預設時區：" + TimeZone.getDefault().getID());
		System.out.println("--------------------------------------");

結果：

date.toString():Wed Nov 23 14:41:32 CST 2016
date.getTime()1479883292507
Calendar.getInstance().getTime():Wed Nov 23 14:41:32 CST 2016
Calendar.getInstance().getTimeInMillis():1479883292535
Calendar.getInstance().getTimeZone():sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=19,lastRule=null]
system user.timezone:Asia/Shanghai
system user.country:CN
預設時區：Asia/Shanghai
--------------------------------------
After setTimeZone0:
date.toString():Wed Nov 23 08:41:32 GMT+02:00 2016
date.getTime()1479883292538
Calendar.getInstance().getTime():Wed Nov 23 08:41:32 GMT+02:00 2016
Calendar.getInstance().getTimeInMillis():1479883292538
Calendar.getInstance().getTimeZone():sun.util.calendar.ZoneInfo[id="GMT+02:00",offset=7200000,dstSavings=0,useDaylight=false,transitions=0,lastRule=null]
system user.timezone:Asia/Shanghai
system user.country:CN
預設時區：GMT+02:00
--------------------------------------
date.toString():Wed Nov 23 14:41:32 CST 2016
date.getTime()1479883292539
Calendar.getInstance().getTime():Wed Nov 23 14:41:32 CST 2016
Calendar.getInstance().getTimeInMillis():1479883292539
Calendar.getInstance().getTimeZone():sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=19,lastRule=null]
system user.timezone:GMT+2
system user.country:CN
預設時區：Asia/Shanghai
--------------------------------------

由此可見:

1）Date.toString()依賴於TimeZone中defaultTimezone；Calendar同樣；TimeZone同樣；

2）System.property 中 “user.timezone”與TimeZone中defaultTimezone的關係：

TimeZone取預設值，先取該物件已經設定好的預設值，如果沒有則取system.property中的"user.timezone",再沒有的話才根據“java.home”和“user.country”來獲取。。。。（從TimeZone.getDefault()原始碼可知)；

System.property中user.timezone會在TimeZone執行由“java.home”和“user.country”獲取timezone的方法後獲得初值；

link:http://2005713.blog.51cto.com/1995713/698032

3）System.property中 “user.timezone"與 "user.country"無關；

4）Date.getTime() 和 Calendar.getTimeInMillis()相差無幾，此毫秒數都是相對於1970.1.1 00:00:00 GMT.

SimpleDateFormat

public class CalendarTest0 {
   public static void main(String[] args) {
	String dateStr = null;
	SimpleDateFormat format = null;
	Date date = null;
	   
	System.out.println("system user.timezone:" + System.getProperty("user.timezone"));
    System.out.println("system user.country:" + System.getProperty("user.country"));
	System.out.println("預設時區：" + TimeZone.getDefault().getID());
	format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z");
	date = new Date();
	dateStr = format.format(date);
	System.out.println(dateStr);
	System.out.println("Set system.user.timezone=GMT+2:");
	System.setProperty("user.timezone", "GMT+2");   
	Calendar cal = Calendar.getInstance();
	format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z");
	dateStr = format.format(cal.getTime());
	System.out.println(dateStr);
	System.out.println("system user.timezone:" + System.getProperty("user.timezone"));
	System.out.println("system user.country:" + System.getProperty("user.country"));
	System.out.println("預設時區：" + TimeZone.getDefault().getID());
	System.out.println("------------------------------");
	
	
	System.out.println("Set system.user.timezone to GMT+2:");
	format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z");	
	date = new Date();
    dateStr = format.format(date);
    System.out.println(dateStr);
	System.out.println("system user.timezone:" + System.getProperty("user.timezone"));
	System.out.println("system user.country:" + System.getProperty("user.country"));
	System.out.println("預設時區：" + TimeZone.getDefault().getID());
    System.out.println("------------------------------");
    
    System.out.println("Set format.settimezone to GMT+4:");
    format  = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z");
    date = new Date();
    format.setTimeZone(TimeZone.getTimeZone("GMT+4"));
    dateStr = format.format(date);
    System.out.println(dateStr);
	System.out.println("system user.timezone:" + System.getProperty("user.timezone"));
	System.out.println("system user.country:" + System.getProperty("user.country"));
	System.out.println("預設時區：" + TimeZone.getDefault().getID());
    System.out.println("------------------------------");

    System.out.println("Set format.settimezone to GMT+6 and TimeZone.setTimeZone to GMT+8 :");
    format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z");
    date = new Date();
    format.setTimeZone(TimeZone.getTimeZone("GMT+6"));
    TimeZone.setDefault(TimeZone.getTimeZone("GMT+8"));    
    dateStr = format.format(date);
    System.out.println(dateStr);
	System.out.println("system user.timezone:" + System.getProperty("user.timezone"));
	System.out.println("system user.country:" + System.getProperty("user.country"));
	System.out.println("預設時區：" + TimeZone.getDefault().getID());
    System.out.println("------------------------------");
}
}

Console:

system user.timezone:
system user.country:CN
預設時區：Asia/Shanghai
2016-11-24 18:34:43 +0800
Set system.user.timezone=GMT+2:
2016-11-24 18:34:43 +0800
system user.timezone:GMT+2
system user.country:CN
預設時區：Asia/Shanghai
------------------------------
Set system.user.timezone to GMT+2:
2016-11-24 18:34:43 +0800
system user.timezone:GMT+2
system user.country:CN
預設時區：Asia/Shanghai
------------------------------
Set format.settimezone to GMT+4:
2016-11-24 14:34:43 +0400
system user.timezone:GMT+2
system user.country:CN
預設時區：Asia/Shanghai
------------------------------
Set format.settimezone to GMT+6 and TimeZone.setTimeZone to GMT+8 :
2016-11-24 16:34:43 +0600
system user.timezone:GMT+2
system user.country:CN
預設時區：GMT+08:00
------------------------------

結論：

a.SimpleDateFormat使用的預設時區是TimeZone.getDefault()的時區而非System.getProperty("user.timezone")的時區；
b.SimpleDateFormat.setTimeZone()並不會改變TimeZone的值；
c.當既SimpleDateFormat.setTimeZone()又TimeZone.setDefault()時，SimpleDateFormat取SimpleDateFormat.setTimeZone()設定的值；

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