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Java and converting displayed value into local time zone and daylight savings

I know this is an oft asked type of question, and I've been looking around the web for solutions, but to no avail. The problem is that we're fetching a date value from the database and want to display it in a PDF in local time. The raw formatted value is "2022/05/24 15:18:10" and using Costa Rica as an example client time zone (we're in LA), we'd want this "2022/05/24 16:18:10". However, we're getting this: "2022/05/24 17:18:10".
One of the odd things I'm seeing when I run the code below is that it seems that our server time zone is PST, according to Java, but is actually PDT.
creationDate from db=Tue May 24 15:18:10 PDT 2022
Desired creationDate output=2022/05/24 16:18:10
cal.getTimeZone.getDisplayName()=Pacific Standard Time
formatted creationDate=2022/05/24 17:18:10
So one question is: why are we seeing PST instead of PDT and the second question is how do I fix this?
Example code:
public static void main(
String[] args)
{
final String DATE_TIME_PATTERN = "yyyy/MM/dd HH:mm:ss";
final String LA_TIMEZONE_ID = "America/Los_Angeles";
DateFormat df = new SimpleDateFormat(DATE_TIME_PATTERN);
TimeZone serverTimeZone = TimeZone.getTimeZone(LA_TIMEZONE_ID);
Calendar cal = Calendar.getInstance(/* serverTimeZone */); // works same with or without param
TimeZone clientTimeZone = TimeZone.getTimeZone("CST"); // Costa Rica = Central Standard Time
Date creationDate;
df.setTimeZone(clientTimeZone);
// Values as fetched from database.
cal.set(Calendar.DAY_OF_MONTH, 24);
cal.set(Calendar.MONTH, Calendar.MAY);
cal.set(Calendar.YEAR, 2022);
cal.set(Calendar.HOUR_OF_DAY, 15);
cal.set(Calendar.MINUTE, 18);
cal.set(Calendar.SECOND, 10);
creationDate = cal.getTime();
System.out.println("creationDate from db=" + creationDate.toString());
System.out.println("Desired creationDate output=2022/05/24 16:18:10");
System.out.println("cal.getTimeZone.getDisplayName()=" + cal.getTimeZone().getDisplayName());
System.out.println("formatted creationDate=" + df.format(creationDate));
}

So, after a bit of hacking and googling, it would appear (at least to me), that "Central Standard Time" isn't what you want to use (nor should you use it generally).
From time-and-date/Central Standard Time (CST)
Caution: This is NOT the current local time in most locations in that time zone
North America: Only some locations are currently on CST because most places in this time zone are currently on summer time / daylight saving time and are observing CDT.
And then add in time-and-date/Time Zone in Costa Rica
Costa Rica observes Central Standard Time all year. There are no Daylight Saving Time clock changes.
That's not confusing at all 🙄. So, as I "understand" it, CST is normally -6 hours and CDT is -5 hours, but Costa Rica is always -6 hours.
So, based on the observations of your code, CST seems to be having the day light savings value applied to it, regardless of what you do.
So, what to do about it? Well, the simple answer is, don't use it, in fact, stop using the java.util.Date and related APIs altogether and instead, make use of the replacement java.time APIS and the America/Costa_Rica time zone directly, for example...
final String DATE_TIME_PATTERN = "yyyy/MM/dd HH:mm:ss";
final String LA_TIMEZONE_ID = "America/Los_Angeles";
final String dateStringValue = "2022/05/24 15:18:10";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
LocalDateTime ldt = LocalDateTime.parse(dateStringValue, formatter);
ZoneId zoneId = ZoneId.of(LA_TIMEZONE_ID);
ZonedDateTime zdt = ldt.atZone(zoneId);
System.out.println(" Local = " + ldt);
System.out.println(" zdt = " + zdt);
System.out.println("Costa_Rica = " + zdt.withZoneSameInstant(ZoneId.of("America/Costa_Rica")));
System.out.println("US/Central = " + zdt.withZoneSameInstant(ZoneId.of("US/Central")));
which prints...
Local = 2022-05-24T15:18:10
zdt = 2022-05-24T15:18:10-07:00[America/Los_Angeles]
Costa_Rica = 2022-05-24T16:18:10-06:00[America/Costa_Rica]
US/Central = 2022-05-24T17:18:10-05:00[US/Central]
This is probably also a good (and over due) reason to dump the old java.util.Date and related classes and update to the java.time APIs, see the date/time trail for more details
Handling Daylight Savings Time in Java might also be worth a read

How to specify time after daylight saveing time shift in Java

Using the following code:
class Test {
public static void main(String [] args) {
LocalDate date = LocalDate.of(2018, 11, 4);
LocalTime time = LocalTime.of(1, 59);
ZonedDateTime dt = ZonedDateTime.of(date, time, ZoneId.of("America/New_York"));
System.out.println(dt.getHour() + ":" + dt.getMinute() + ":" + dt.getSecond());
dt = dt.plusMinutes(1);
System.out.println(dt.getHour() + ":" + dt.getMinute() + ":" + dt.getSecond());
dt = dt.plusMinutes(59);
System.out.println(dt.getHour() + ":" + dt.getMinute() + ":" + dt.getSecond());
dt = dt.plusMinutes(1);
System.out.println(dt.getHour() + ":" + dt.getMinute() + ":" + dt.getSecond());
}
}
I get
1:59:0
1:0:0
1:59:0
2:0:0
Is there a way to get to the 1:00:00 from after daylight saving time without going through the 1:00:00 from before daylight saving time?

Use ofStrict to specify which offset you want the resulting zoned date time to be on. America/New_York changes from -04:00 to -05:00 at around the time in question, so you want ZoneOffset.ofHours(-5).
ZonedDateTime dt = ZonedDateTime.ofStrict(
LocalDateTime.of(date, time),
ZoneOffset.ofHours(-5),
ZoneId.of("America/New_York")
);
In case you cannot hardcode the offset in, you can get the offset after using:
var dateTime = LocalDateTime.of(date, time)
var zone = ZoneId.of("America/New_York");
var offsetAfter = zone.getRules()
.getTransition(dateTime)
.getOffsetAfter();
ZonedDateTime dt = ZonedDateTime.ofStrict(
dateTime,
offsetAfter,
zone
);
Or, as Ole V.V. pointed out, you can also use the much shorter:
ZonedDateTime dt = ZonedDateTime.of(
date, time, ZoneId.of("America/New_York")
).withLaterOffsetAtOverlap();

The problem with time zones that honor Daylight Saving Time is that such times are ambiguous. The "America/New_York" zone has two times that are both labeled 2008-11-04T01:00:00. Technically, one of them is 01:00 EDT and the other is 01:00 EST, but not a lot of software will let you make the distinction that way, not least since such three-letter time zone designations are not necessarily globally unique.
The solution is to specify the time either in or relative to Universal time, which doesn't have daylight saving: the first 01:00 Eastern time is 05:00Z, and the second is 06:00Z. So you can either give the time as one of those and the zone as "UTC" (and then convert the result to "America/New_York"), or specify the offset from UTC using ofStrict.

Convert String to Date and time in java

My program reading data from a database and I want to convert some fields to date format (date and time separately). I can do this from sql query but is it possible to do from java code.
date format in table = MMDDHHMISS (month day hour minute sec)
and these are sql queries now I'm using-
TO_CHAR(TO_DATE(DATETIMECOLUMN, 'MMDDHH24MISS'),'DD/MM/YYYY') AS MY_DATE
TO_CHAR(TO_DATE(DATETIMECOLUMN, 'MMDDHH24MISS'),'HH24:MI:SS') AS MY_TIME
Thanks in advance!

Here’s a suggestion:
DateTimeFormatter databaseStringFormatter = DateTimeFormatter.ofPattern("MMddHHmmss");
String sampleDatabaseString = "1129225145";
MonthDay myDate = MonthDay.parse(sampleDatabaseString, databaseStringFormatter);
LocalTime myTime = LocalTime.parse(sampleDatabaseString, databaseStringFormatter);
System.out.println("Date: " + myDate + ". Time: " + myTime + '.');
The above prints
Date: --11-29. Time: 22:51:45.
MonthDay is a date without a year, useful for birthdays and other anniversary dates.
Unless there are specific reasons to avoid it, I think you should rather change the datatype of your database column to datetime or similar and then retrieve LocalDateTime objects from your result set as shown in this answer. This would free you from any conversion from string to date and time in either the database query or in Java.

Joda Api handle Time Zone for isBeforeNow isAfterNow comparision

I want to check if a given DateTime is before or after current
DateTime. I was converting input time and current time to a common
time zone (say UTC) and comparing DateTime. But I stumbled upon Joda
Api, hence I was curious to know if Joda is capable of doing this
without a time zone conversion. Example:
clientDateTime.isBeforeNow()

Yes, Joda DateTime comparisons with current time do not require a time zone conversion.
When comparing with current time, such as DateTime.isBeforeNow and DateTime.isAfterNow, Joda simply compares the underlying absolute milliseconds since Jan 1, 1970. The same instant in time has exactly the same absolute milliseconds value, regardless of the timezone.
For example, the instant 1355625068295 corresponds to:
DateTime dt = new DateTime(1355625068295L);
DateTime utc = dt.withZone(DateTimeZone.UTC);
DateTime ny = dt.withZone(DateTimeZone.forID("America/New_York"));
DateTime tk = dt.withZone(DateTimeZone.forID("Asia/Tokyo"));
System.out.println(utc.getMillis() + " is " + utc);
System.out.println(ny.getMillis() + " is " + ny);
System.out.println(tk.getMillis() + " is " + tk);
Output:
1355625068295 is 2012-12-16T02:31:08.295Z
1355625068295 is 2012-12-15T21:31:08.295-05:00
1355625068295 is 2012-12-16T11:31:08.295+09:00
And when comparing with "now":
System.out.println("now: " + new DateTime().getMillis());
System.out.println(ny.isBeforeNow());
System.out.println(ny.plusHours(1).isAfterNow());
System.out.println(tk.isBeforeNow());
System.out.println(tk.plusHours(1).isAfterNow());
Output:
now: 1355625752323
true
true
true
true

problems with Java daylight savings time

I have a Java app that needs to be cognizant of the time zone. When I take a Unix epoch time and try to convert it into a timestamp to use for an Oracle SQL call, it is getting the correct timezone, but the timezone "useDaylightTime" value is not correct, i.e., it is currently returning "true", when we are NOT in DST (I am in Florida in TZ "America/New_York").
This is running on Red Hat Linux Enterprise 6, and as far as I can tell, it is correctly set up for the timezone, e.g. 'date' returns:
Wed Nov 28 12:30:12 EST 2012
I can also see, using the 'zdump' utility, that the current value for 'isdst' is 0.
My Java version is 1.6.0_31.
I have Googled this and seen the numerous issues this has caused, but many of them simply say to set the TZ manually, but my issue is not the TZ, but the fact that the default TZ has the "isDaylight" set to 'true'. I believe this is causing my query to return data that is one hour off (I can see that it is).
Here is a simple code piece I have run to try and reproduce this in the simplest way possible:
public class TZdefault {
public static void main(String[] args) throws IOException {
long startTime = System.currentTimeMillis()/1000;
Calendar start = Calendar.getInstance();
start.setTimeInMillis(startTime);
start.setTimeZone(TimeZone.getDefault());
System.out.println("Start UTC: " + start + "ms: " + start.getTimeInMillis());
System.out.println("use daylight: " + start.getTimeZone().useDaylightTime());
} // end main
} // end class
One final thing. If in my code I set the TZ to "EST", it of course does return a TZ with 'isDaylight' set to False. But that is not a good solution.
I wanted to add some more detail that I had been hoping to hide.
I have records in an Oracle 11g database that use TIMESTAMP with TIMEZONE fields. I am simply doing JDBC queries where two of the parameters are using BETWEEN a start timestamp and end timestamp.
When I query this table, I am using a prepared statement that is using a Calendar entry, the sole purpose of which was to try and manipulate the timezone. The bottom line is that I am doing a pstmt.setTimestamp() call using the 'getTimeInMillis' method for the start and end time after the "default" timezone was applied. The log output shows that in fact it is putting in the correct milliseconds, but the returned SQL results are clearly off by one hour exactly!
I am still trying to verify that there is not an issue on the data insertion side as well.
But I have a lot of debug information, and it looks like I am asking for the correct time in my JDBC query.

the timezone useDaylightTime value is not correct, i.e., it is currently returning "true", when we are NOT in DST
I think you're confusing useDaylightTime with inDaylightTime. The former tells you whether there is a transition between daylight time and standard time in the future, not which side of that transition you're on. For example, it returns false for Chinese time zones because China does not adjust for daylight savings time, but it returns true for most US time zones because most US states (except Arizona) do observe daylight savings time.
inDaylightTime
public abstract boolean inDaylightTime(Date date)
Queries if the given date is in Daylight Saving Time in this time zone.
vs
useDaylightTime
public abstract boolean useDaylightTime()
Queries if this TimeZone uses Daylight Saving Time.
If an underlying TimeZone implementation subclass supports historical and future Daylight Saving Time schedule changes, this method refers to the last known Daylight Saving Time rule that can be a future prediction and may not be the same as the current rule. Consider calling observesDaylightTime() if the current rule should also be taken into account.

If you want to disable daylight saving calculation, then you must set your timezone to EST. Else otherwise time will be calculated based on default time zone set for AMERICA/NEW_YORK
TimeZone zoneEST = TimeZone.getTimeZone("EST");
System.out.println(zoneEST.getDSTSavings()); //0 hour
System.out.println(zoneEST.getRawOffset()); //5 hour
TimeZone.setDefault(zoneEST);
System.out.println("");
TimeZone zoneNY = TimeZone.getTimeZone("America/New_York");
System.out.println(zoneNY.getDSTSavings()); // 1 hour
System.out.println(zoneNY.getRawOffset()); // 5 hour

I have found a way to ensure the daylight saving is ignored
TimeZone tz = TimeZone.getTimeZone("GMT");
TimeZone.setDefault(tz);
GregorianCalendar calendar;
calendar = new GregorianCalendar();
Set the timezone before you create your GregorianCalendar object

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;
public class TimeZoneTest {
public static void main(String[] argv) throws ParseException {
SimpleDateFormat formatter = new SimpleDateFormat("dd-M-yyyy hh:mm:ss a");
String dateInString = "22-01-2015 10:15:55 AM";
Date date = formatter.parse(dateInString);
TimeZone tz = TimeZone.getDefault();
// From TimeZone Asia/Singapore
System.out.println("TimeZone : " + tz.getID() + " - " + tz.getDisplayName());
System.out.println("TimeZone : " + tz);
System.out.println("Date : " + formatter.format(date));
// To TimeZone America/New_York
SimpleDateFormat sdfAmerica = new SimpleDateFormat("dd-M-yyyy hh:mm:ss a");
TimeZone tzInAmerica = TimeZone.getTimeZone("America/New_York");
sdfAmerica.setTimeZone(tzInAmerica);
String sDateInAmerica = sdfAmerica.format(date); // Convert to String first
Date dateInAmerica = formatter.parse(sDateInAmerica);
System.out.println("\nTimeZone : " + tzInAmerica.getID() +
" - " + tzInAmerica.getDisplayName());
System.out.println("TimeZone : " + tzInAmerica);
System.out.println("Date (String) : " + sDateInAmerica);
System.out.println("Date (Object) : " + formatter.format(dateInAmerica));
}
}