blocks|key|359042|text|实现TimeZone类以将时区设置为Calendar会处理夏令时。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|359043|java.util.TimeZone表示时区偏移量，并计算出夏令时。|359044|示例代码：|359045|TimeZone+est_timeZone+=+TimeZoneIDProvider.getTimeZoneID(TimeZoneID.US_EASTERN).getTimeZone();
Calendar+enteredCalendar+=+Calendar.getInstance();
enteredCalendar.setTimeZone(est_timeZone);|code-block|syntax|javascript|359046|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|O|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|P|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Implementing the TimeZone class to set the timezone to the Calendar takes care of the daylight savings.

java.util.TimeZone represents a time zone offset, and also figures out daylight savings.

sample code:

<pre><code>TimeZone est_timeZone = TimeZoneIDProvider.getTimeZoneID(TimeZoneID.US_EASTERN).getTimeZone();
Calendar enteredCalendar = Calendar.getInstance();
enteredCalendar.setTimeZone(est_timeZone);
</code></pre>

blocks|key|574767|text|根据此answer|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|574768|TimeZone+tz+=+TimeZone.getTimeZone("EST");
boolean+inDs+=+tz.inDaylightTime(new+Date());|code-block|syntax|javascript|574769|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/1060517/1515058^0|3|6|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

As per this <a href="https://stackoverflow.com/a/1060517/1515058">answer</a>:

<pre><code>TimeZone tz = TimeZone.getTimeZone("EST");
boolean inDs = tz.inDaylightTime(new Date());
</code></pre>

blocks|key|359143|text|在java中，DateFormatter默认使用DST，为了避免夏令时(DST)，您需要手动执行一项操作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|359144|首先，您必须获取DST偏移量，即应用了多少毫秒的DST，对于某些地方，DST也是45分钟，对于某些地方，它是30分钟|359145|但在大多数情况下，DST是1小时|359146|你必须使用时区对象，并检查它的日期是否在DST以下，然后您必须手动添加DST的偏移量。例如：|359147|+TimeZone+tz+=+TimeZone.getTimeZone("EST");
+boolean+isDST+=+tz.inDaylightTime(yourDateObj);
+if(isDST){
+int+sec=+tz.getDSTSavings()/1000;//+for+no.+of+seconds
+Calendar+cal=+Calendar.getInstance();
+cal.setTime(yourDateObj);
+cal.add(Calendar.Seconds,sec);
+System.out.println(cal.getTime());//+your+Date+with+DST+neglected
++}|code-block|syntax|javascript|359148|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Q|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|R|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|S|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

In java, DateFormatter by default uses DST,To avoid day Light saving (DST) you need to manually do a trick, 
first you have to get the DST offset i.e. for how many millisecond DST applied, for ex somewhere DST is also for 45 minutes and for some places it is for 30 min 
but in most cases DST is of 1 hour 
you have to use Timezone object and check with the date whether it is falling under DST or not and then you have to manually add offset of DST into it. for eg:

<pre><code> TimeZone tz = TimeZone.getTimeZone("EST");
 boolean isDST = tz.inDaylightTime(yourDateObj);
 if(isDST){
 int sec= tz.getDSTSavings()/1000;// for no. of seconds
 Calendar cal= Calendar.getInstance();
 cal.setTime(yourDateObj);
 cal.add(Calendar.Seconds,sec);
 System.out.println(cal.getTime());// your Date with DST neglected
 }
</code></pre>

blocks|key|574954|text|其他答案是正确的，特别是the+one+by+Jon+Skeet，但已经过时了。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|574955|java.time|574956|这些旧的date-time类已经被Java8和更高版本中内置的java.time框架所取代。|574957|如果您只是想要当前时间，请使用Instant类。|style|CODE|574958|Instant+now+=+Instant.now();|code-block|syntax|javascript|574959|正如correct+Answer+by+Jon+Skeet中所述，EST不是时区。这种3-4个字母的代码既不是标准化的，也不是唯一的，这进一步造成了对夏令时(DST)的混淆。使用“大陆/地区”格式的正确时区名称。|574960|也许你指的是北美东海岸的东部标准时间？还是埃及标准时间？还是欧洲标准时间？|574961|ZoneId+zoneId+=+ZoneId.of(+"America/New_York"+);
ZoneId+zoneId+=+ZoneId.of(+"Africa/Cairo"+);
ZoneId+zoneId+=+ZoneId.of(+"Europe/Lisbon"+);|574962|使用任何这样的ZoneId对象来获取调整到特定时区的当前时刻，以生成ZonedDateTime对象。|574963|ZonedDateTime+zdt+=+ZonedDateTime.now(+zoneId+)+;|574964|通过在第一个时区中生成另一个ZonedDateTime对象，将该ZonedDateTime调整为不同的时区。java.time框架使用immutable+objects，而不是更改(突变)现有对象。|574965|ZonedDateTime+zdtGuam+=+zdt.withZoneSameInstant(+ZoneId.of(+"Pacific/Guam"+)+)+;|574966|​|574967|📷|atomic|574968|574969|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/10546083/642706|1|http://docs.oracle.com/javase/8/docs/api/java/time/package-summary.html|2|3|http://docs.oracle.com/javase/8/docs/api/java/time/ZonedDateTime.html|4|https://en.wikipedia.org/wiki/Immutable_object|5|IMAGE|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/0081be3be8d1490c4a98f0447dce9369.png|imageAlt^0|C|K|0|0|0|V|9|1|0|F|7|0|0|X|3|2|R|2|0|0|0|7|6|Y|D|Y|D|3|0|0|1V|H|4|0|0|0|0|1|5|0|0^^$0|@$1|2|3|4|5|6|7|1V|8|@]|9|@$A|1W|B|1X|1|1Y]]|C|$]]|$1|D|3|E|5|6|7|1Z|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|20|8|@]|9|@$A|21|B|22|1|23]]|C|$]]|$1|H|3|I|5|6|7|24|8|@$A|25|B|26|J|K]]|9|@]|C|$]]|$1|L|3|M|5|N|7|27|8|@]|9|@]|C|$O|P]]|$1|Q|3|R|5|6|7|28|8|@$A|29|B|2A|J|K]]|9|@$A|2B|B|2C|1|2D]]|C|$]]|$1|S|3|T|5|6|7|2E|8|@]|9|@]|C|$]]|$1|U|3|V|5|N|7|2F|8|@]|9|@]|C|$O|P]]|$1|W|3|X|5|6|7|2G|8|@$A|2H|B|2I|J|K]|$A|2J|B|2K|J|K]]|9|@$A|2L|B|2M|1|2N]]|C|$]]|$1|Y|3|Z|5|N|7|2O|8|@]|9|@]|C|$O|P]]|$1|10|3|11|5|6|7|2P|8|@]|9|@$A|2Q|B|2R|1|2S]]|C|$]]|$1|12|3|13|5|N|7|2T|8|@]|9|@]|C|$O|P]]|$1|14|3|15|5|6|7|2U|8|@]|9|@]|C|$]]|$1|16|3|17|5|18|7|2V|8|@]|9|@$A|2W|B|2X|1|2Y]]|C|$]]|$1|19|3|15|5|6|7|2Z|8|@]|9|@]|C|$]]|$1|1A|3|-4|5|6|7|30|8|@]|9|@]|C|$]]]|1B|$1C|$5|1D|1E|1F|C|$1G|1H]]|1I|$5|1D|1E|1F|C|$1G|1J]]|1K|$5|1D|1E|1F|C|$1G|1H]]|1L|$5|1D|1E|1F|C|$1G|1M]]|1N|$5|1D|1E|1F|C|$1G|1O]]|1P|$5|1Q|1E|1R|C|$1S|1T|1U|-4]]]]

Other answers are correct, especially <a href="https://stackoverflow.com/a/10546083/642706">the one by Jon Skeet</a>, but outdated. 

<h1>java.time</h1>

These old date-time classes have been supplanted by the <a href="http://docs.oracle.com/javase/8/docs/api/java/time/package-summary.html" rel="noreferrer">java.time</a> framework built into Java 8 and later.

If you simply want the current time in UTC, use the <code>Instant</code> class.

<pre><code>Instant now = Instant.now();
</code></pre>

<code>EST</code> is not a time zone, as explained in the <a href="https://stackoverflow.com/a/10546083/642706">correct Answer by Jon Skeet</a>. Such 3-4 letter codes are neither standardized nor unique, and further the confusion over Daylight Saving Time (DST). Use a proper time zone name in the "continent/region" format.

Perhaps you meant Eastern Standard Time in east coast of north America? Or Egypt Standard Time? Or European Standard Time?

<pre><code>ZoneId zoneId = ZoneId.of( "America/New_York" );
ZoneId zoneId = ZoneId.of( "Africa/Cairo" );
ZoneId zoneId = ZoneId.of( "Europe/Lisbon" );
</code></pre>

Use any such <code>ZoneId</code> object to get the current moment adjusted to a particular time zone to produce a <a href="http://docs.oracle.com/javase/8/docs/api/java/time/ZonedDateTime.html" rel="noreferrer"><code>ZonedDateTime</code></a> object.

<pre><code>ZonedDateTime zdt = ZonedDateTime.now( zoneId ) ;
</code></pre>

Adjust that ZonedDateTime into a different time zone by producing another ZonedDateTime object from the first. The java.time framework uses <a href="https://en.wikipedia.org/wiki/Immutable_object" rel="noreferrer">immutable objects</a> rather than changing (mutating) existing objects.

<pre><code>ZonedDateTime zdtGuam = zdt.withZoneSameInstant( ZoneId.of( "Pacific/Guam" ) ) ;
</code></pre>

<a href="https://i.stack.imgur.com/V7t6V.png" rel="noreferrer"><img src="https://i.stack.imgur.com/V7t6V.png" alt="Table of date-time types in Java, both modern and legacy."></a>

blocks|key|359320|text|您可以输入"EST5EDT“作为时区，而不是输入"EST”。正如您所提到的，只使用"EDT“是行不通的。这将解决夏令时问题。代码行如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|359321|Calendar+cal+=+Calendar.getInstance(TimeZone.getTimeZone("EST5EDT"));|code-block|syntax|javascript|359322|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Instead of entering "EST" for the timezone you can enter "EST5EDT" as such. As you noted, just "EDT" does not work. This will account for the daylight savings time issue. The code line looks like this:

<pre><code>Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("EST5EDT"));
</code></pre>

blocks|key|359326|text|public+static+float+calculateTimeZone(String+deviceTimeZone)+{
++++float+ONE_HOUR_MILLIS+=+60+*+60+*+1000;

++++//+Current+timezone+and+date
++++TimeZone+timeZone+=+TimeZone.getTimeZone(deviceTimeZone);
++++Date+nowDate+=+new+Date();
++++float+offsetFromUtc+=+timeZone.getOffset(nowDate.getTime())+/+ONE_HOUR_MILLIS;

++++//+Daylight+Saving+time
++++if+(timeZone.useDaylightTime())+{
++++++++//+DST+is+used
++++++++//+I'm+saving+this+is+preferences+for+later+use

++++++++//+save+the+offset+value+to+use+it+later
++++++++float+dstOffset+=+timeZone.getDSTSavings()+/+ONE_HOUR_MILLIS;
++++++++//+DstOffsetValue+=+dstOffset
++++++++//+I'm+saving+this+is+preferences+for+later+use
++++++++//+save+that+now+we+are+in+DST+mode
++++++++if+(timeZone.inDaylightTime(nowDate))+{
++++++++++++Log.e(Utility.class.getName(),+"in+Daylight+Time");
++++++++++++return+-(ONE_HOUR_MILLIS+*+dstOffset);
++++++++}+else+{
++++++++++++Log.e(Utility.class.getName(),+"not+in+Daylight+Time");
++++++++++++return+0;
++++++++}
++++}+else
++++++++return+0;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|359327|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>public static float calculateTimeZone(String deviceTimeZone) {
 float ONE_HOUR_MILLIS = 60 * 60 * 1000;

 // Current timezone and date
 TimeZone timeZone = TimeZone.getTimeZone(deviceTimeZone);
 Date nowDate = new Date();
 float offsetFromUtc = timeZone.getOffset(nowDate.getTime()) / ONE_HOUR_MILLIS;

 // Daylight Saving time
 if (timeZone.useDaylightTime()) {
 // DST is used
 // I'm saving this is preferences for later use

 // save the offset value to use it later
 float dstOffset = timeZone.getDSTSavings() / ONE_HOUR_MILLIS;
 // DstOffsetValue = dstOffset
 // I'm saving this is preferences for later use
 // save that now we are in DST mode
 if (timeZone.inDaylightTime(nowDate)) {
 Log.e(Utility.class.getName(), "in Daylight Time");
 return -(ONE_HOUR_MILLIS * dstOffset);
 } else {
 Log.e(Utility.class.getName(), "not in Daylight Time");
 return 0;
 }
 } else
 return 0;
}
</code></pre>

blocks|key|575036|text|private+static+Long+DateTimeNowTicks(){
++++long+TICKS_AT_EPOCH+=+621355968000000000L;
++++TimeZone+timeZone+=+Calendar.getInstance().getTimeZone();
++++int+offs+=+timeZone.getRawOffset();
++++if+(timeZone.inDaylightTime(new+Date()))
++++++++offs+%2B=+60+*+60+*+1000;
++++return+(System.currentTimeMillis()+%2B+offs)+*+10000+%2B+TICKS_AT_EPOCH;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|575037|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>private static Long DateTimeNowTicks(){
 long TICKS_AT_EPOCH = 621355968000000000L;
 TimeZone timeZone = Calendar.getInstance().getTimeZone();
 int offs = timeZone.getRawOffset();
 if (timeZone.inDaylightTime(new Date()))
 offs += 60 * 60 * 1000;
 return (System.currentTimeMillis() + offs) * 10000 + TICKS_AT_EPOCH;
}
</code></pre>

I have to print the EST time in my Java application. I had set the time zone to EST using:

<pre><code>Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("EST"));
</code></pre>

But when the daylight savings is being followed in this timezone, my code does not print the correct time (it prints 1 hour less).

How to make the code work to read the correct time always, irrespective of whether the daylight savings are being observed or not?

PS: I tried setting the timezone to EDT, but it doesn't solve the problem.

How to tackle daylight savings using TimeZone in Java

我必须在我的Java应用程序中打印EST时间。我使用以下命令将时区设置为EST：Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("EST"));但是，当遵循这个时区的夏令时时，我的代码不能打印正确的时间(它少打印了一个小时)。如何使代码始终读取正确的时间...

问如何在Java中使用TimeZone解决夏令时问题
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