It is a common misconception that time (a measurable 4th dimension) is different over the world. Timestamp as a moment in time is unique. Date however is influenced how we "see" time but actually it is "time of day".
An example: two people look at the clock at the same moment. The timestamp is the same, right? But one of them is in London and sees 12:00 noon (GMT, timezone offset is 0), and the other is in Belgrade and sees 14:00 (CET, Central Europe, daylight saving now, offset is +2).
Their perception is different but the moment is the same.
You can find more details in this answer.
OK, it's not a duplicate of this question but it is pointless since you are confusing the terms "Timestamp = moment in time (objective)" and "Date[Time] = time of day (subjective)".
Let's look at your original question code broken down like this:
// Get the "original" value from database.
Timestamp momentFromDB = rs.getTimestamp("anytimestampcolumn");
// Turn it into a Joda DateTime with time zone.
DateTime dt = new DateTime(momentFromDB, DateTimeZone.forID("anytimezone"));
// And then turn it back into a timestamp but "with time zone".
Timestamp ts = new Timestamp(dt.getMillis());
I haven't run this code but I am certain it will print true and the same number of milliseconds each time:
System.out.println("momentFromDB == dt : " + (momentFromDB.getTime() == dt.getTimeInMillis());
System.out.println("momentFromDB == ts : " + (momentFromDB.getTime() == ts.getTime()));
System.out.println("dt == ts : " + (dt.getTimeInMillis() == ts.getTime()));
System.out.println("momentFromDB [ms] : " + momentFromDB.getTime());
System.out.println("ts [ms] : " + ts.getTime());
System.out.println("dt [ms] : " + dt.getTimeInMillis());
But as you said yourself printing them out as strings will result in "different" time because DateTime applies the time zone. That's why "time" is stored and transferred as Timestamp objects (which basically wraps a long) and displayed or entered as Date[Time].
In your own answer you are artificially adding an offset and creating a "wrong" time.
If you use that timestamp to create another DateTime and print it out it will be offset twice.
// Turn it back into a Joda DateTime with time zone.
DateTime dt = new DateTime(ts, DateTimeZone.forID("anytimezone"));
P.S. If you have the time go through the very complex Joda Time source code to see how it holds the time (millis) and how it prints it.
import static org.junit.Assert.*;
import static org.hamcrest.CoreMatchers.*;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;
import org.junit.Before;
import org.junit.Test;
public class WorldTimeTest {
private static final int MILLIS_IN_HOUR = 1000 * 60 * 60;
private static final String ISO_FORMAT_NO_TZ = "yyyy-MM-dd'T'HH:mm:ss.SSS";
private static final String ISO_FORMAT_WITH_TZ = "yyyy-MM-dd'T'HH:mm:ss.SSSXXX";
private TimeZone londonTimeZone;
private TimeZone newYorkTimeZone;
private TimeZone sydneyTimeZone;
private long nowInMillis;
private Date now;
public static SimpleDateFormat createDateFormat(String pattern, TimeZone timeZone) throws Exception {
SimpleDateFormat result = new SimpleDateFormat(pattern);
// Must explicitly set the time zone with "setCalendar()".
result.setCalendar(Calendar.getInstance(timeZone));
return result;
}
public static SimpleDateFormat createDateFormat(String pattern) throws Exception {
return createDateFormat(pattern, TimeZone.getDefault());
}
public static SimpleDateFormat createDateFormat() throws Exception {
return createDateFormat(ISO_FORMAT_WITH_TZ, TimeZone.getDefault());
}
public void printSystemInfo() throws Exception {
final String[] propertyNames = {
"java.runtime.name", "java.runtime.version", "java.vm.name", "java.vm.version",
"os.name", "os.version", "os.arch",
"user.language", "user.country", "user.script", "user.variant",
"user.language.format", "user.country.format", "user.script.format",
"user.timezone" };
System.out.println();
System.out.println("System Information:");
for (String name : propertyNames) {
if (name == null || name.length() == 0) {
continue;
}
String value = System.getProperty(name);
if (value != null && value.length() > 0) {
System.out.println(" " + name + " = " + value);
}
}
final TimeZone defaultTZ = TimeZone.getDefault();
final int defaultOffset = defaultTZ.getOffset(nowInMillis) / MILLIS_IN_HOUR;
final int userOffset = TimeZone.getTimeZone(System
.getProperty("user.timezone")).getOffset(nowInMillis) / MILLIS_IN_HOUR;
final Locale defaultLocale = Locale.getDefault();
System.out.println(" default.timezone-offset (hours) = " + userOffset);
System.out.println(" default.timezone = " + defaultTZ.getDisplayName());
System.out.println(" default.timezone.id = " + defaultTZ.getID());
System.out.println(" default.timezone-offset (hours) = " + defaultOffset);
System.out.println(" default.locale = "
+ defaultLocale.getLanguage() + "_" + defaultLocale.getCountry()
+ " (" + defaultLocale.getDisplayLanguage()
+ "," + defaultLocale.getDisplayCountry() + ")");
System.out.println(" now = " + nowInMillis + " [ms] or "
+ createDateFormat().format(now));
System.out.println();
}
@Before
public void setUp() throws Exception {
// Remember this moment.
now = new Date();
nowInMillis = now.getTime(); // == System.currentTimeMillis();
// Print out some system information.
printSystemInfo();
// "Europe/London" time zone is DST aware, we'll use fixed offset.
londonTimeZone = TimeZone.getTimeZone("GMT");
// The same applies to "America/New York" time zone ...
newYorkTimeZone = TimeZone.getTimeZone("GMT-5");
// ... and for the "Australia/Sydney" time zone.
sydneyTimeZone = TimeZone.getTimeZone("GMT+10");
}
@Test
public void testDateFormatting() throws Exception {
int londonOffset = londonTimeZone.getOffset(nowInMillis) / MILLIS_IN_HOUR; // in hours
Calendar londonCalendar = Calendar.getInstance(londonTimeZone);
londonCalendar.setTime(now);
int newYorkOffset = newYorkTimeZone.getOffset(nowInMillis) / MILLIS_IN_HOUR;
Calendar newYorkCalendar = Calendar.getInstance(newYorkTimeZone);
newYorkCalendar.setTime(now);
int sydneyOffset = sydneyTimeZone.getOffset(nowInMillis) / MILLIS_IN_HOUR;
Calendar sydneyCalendar = Calendar.getInstance(sydneyTimeZone);
sydneyCalendar.setTime(now);
// Check each time zone offset.
assertThat(londonOffset, equalTo(0));
assertThat(newYorkOffset, equalTo(-5));
assertThat(sydneyOffset, equalTo(10));
// Check that calendars are not equals (due to time zone difference).
assertThat(londonCalendar, not(equalTo(newYorkCalendar)));
assertThat(londonCalendar, not(equalTo(sydneyCalendar)));
// Check if they all point to the same moment in time, in milliseconds.
assertThat(londonCalendar.getTimeInMillis(), equalTo(nowInMillis));
assertThat(newYorkCalendar.getTimeInMillis(), equalTo(nowInMillis));
assertThat(sydneyCalendar.getTimeInMillis(), equalTo(nowInMillis));
// Check if they all point to the same moment in time, as Date.
assertThat(londonCalendar.getTime(), equalTo(now));
assertThat(newYorkCalendar.getTime(), equalTo(now));
assertThat(sydneyCalendar.getTime(), equalTo(now));
// Check if hours are all different (skip local time because
// this test could be executed in those exact time zones).
assertThat(newYorkCalendar.get(Calendar.HOUR_OF_DAY),
not(equalTo(londonCalendar.get(Calendar.HOUR_OF_DAY))));
assertThat(sydneyCalendar.get(Calendar.HOUR_OF_DAY),
not(equalTo(londonCalendar.get(Calendar.HOUR_OF_DAY))));
// Display London time in multiple forms.
SimpleDateFormat dfLondonNoTZ = createDateFormat(ISO_FORMAT_NO_TZ, londonTimeZone);
SimpleDateFormat dfLondonWithTZ = createDateFormat(ISO_FORMAT_WITH_TZ, londonTimeZone);
System.out.println("London (" + londonTimeZone.getDisplayName(false, TimeZone.SHORT)
+ ", " + londonOffset + "):");
System.out.println(" time (ISO format w/o TZ) = "
+ dfLondonNoTZ.format(londonCalendar.getTime()));
System.out.println(" time (ISO format w/ TZ) = "
+ dfLondonWithTZ.format(londonCalendar.getTime()));
System.out.println(" time (default format) = "
+ londonCalendar.getTime() + " / " + londonCalendar.toString());
// Using system default time zone.
System.out.println(" time (default TZ) = "
+ createDateFormat(ISO_FORMAT_NO_TZ).format(londonCalendar.getTime())
+ " / " + createDateFormat().format(londonCalendar.getTime()));
// Display New York time in multiple forms.
SimpleDateFormat dfNewYorkNoTZ = createDateFormat(ISO_FORMAT_NO_TZ, newYorkTimeZone);
SimpleDateFormat dfNewYorkWithTZ = createDateFormat(ISO_FORMAT_WITH_TZ, newYorkTimeZone);
System.out.println("New York (" + newYorkTimeZone.getDisplayName(false, TimeZone.SHORT)
+ ", " + newYorkOffset + "):");
System.out.println(" time (ISO format w/o TZ) = "
+ dfNewYorkNoTZ.format(newYorkCalendar.getTime()));
System.out.println(" time (ISO format w/ TZ) = "
+ dfNewYorkWithTZ.format(newYorkCalendar.getTime()));
System.out.println(" time (default format) = "
+ newYorkCalendar.getTime() + " / " + newYorkCalendar.toString());
// Using system default time zone.
System.out.println(" time (default TZ) = "
+ createDateFormat(ISO_FORMAT_NO_TZ).format(newYorkCalendar.getTime())
+ " / " + createDateFormat().format(newYorkCalendar.getTime()));
// Display Sydney time in multiple forms.
SimpleDateFormat dfSydneyNoTZ = createDateFormat(ISO_FORMAT_NO_TZ, sydneyTimeZone);
SimpleDateFormat dfSydneyWithTZ = createDateFormat(ISO_FORMAT_WITH_TZ, sydneyTimeZone);
System.out.println("Sydney (" + sydneyTimeZone.getDisplayName(false, TimeZone.SHORT)
+ ", " + sydneyOffset + "):");
System.out.println(" time (ISO format w/o TZ) = "
+ dfSydneyNoTZ.format(sydneyCalendar.getTime()));
System.out.println(" time (ISO format w/ TZ) = "
+ dfSydneyWithTZ.format(sydneyCalendar.getTime()));
System.out.println(" time (default format) = "
+ sydneyCalendar.getTime() + " / " + sydneyCalendar.toString());
// Using system default time zone.
System.out.println(" time (default TZ) = "
+ createDateFormat(ISO_FORMAT_NO_TZ).format(sydneyCalendar.getTime())
+ " / " + createDateFormat().format(sydneyCalendar.getTime()));
}
@Test
public void testDateParsing() throws Exception {
// Create date parsers that look for time zone information in a date-time string.
final SimpleDateFormat londonFormatTZ = createDateFormat(ISO_FORMAT_WITH_TZ, londonTimeZone);
final SimpleDateFormat newYorkFormatTZ = createDateFormat(ISO_FORMAT_WITH_TZ, newYorkTimeZone);
final SimpleDateFormat sydneyFormatTZ = createDateFormat(ISO_FORMAT_WITH_TZ, sydneyTimeZone);
// Create date parsers that ignore time zone information in a date-time string.
final SimpleDateFormat londonFormatLocal = createDateFormat(ISO_FORMAT_NO_TZ, londonTimeZone);
final SimpleDateFormat newYorkFormatLocal = createDateFormat(ISO_FORMAT_NO_TZ, newYorkTimeZone);
final SimpleDateFormat sydneyFormatLocal = createDateFormat(ISO_FORMAT_NO_TZ, sydneyTimeZone);
// We are looking for the moment this millenium started, the famous Y2K,
// when at midnight everyone welcomed the New Year 2000, i.e. 2000-01-01 00:00:00.
// Which of these is the right one?
// a) "2000-01-01T00:00:00.000-00:00"
// b) "2000-01-01T00:00:00.000-05:00"
// c) "2000-01-01T00:00:00.000+10:00"
// None of them? All of them?
// For those who guessed it - yes, it is a trick question because we didn't specify
// the "where" part, or what kind of time (local/global) we are looking for.
// The first (a) is the local Y2K moment in London, which is at the same time global.
// The second (b) is the local Y2K moment in New York, but London is already celebrating for 5 hours.
// The third (c) is the local Y2K moment in Sydney, and they started celebrating 15 hours before New York did.
// The point here is that each answer is correct because everyone thinks of that moment in terms of "celebration at midnight".
// The key word here is "midnight"! That moment is actually a "time of day" moment illustrating our perception of time based on the movement of our Sun.
// These are global Y2K moments, i.e. the same moment all over the world, UTC/GMT midnight.
final String MIDNIGHT_GLOBAL = "2000-01-01T00:00:00.000-00:00";
final Date milleniumInLondon = londonFormatTZ.parse(MIDNIGHT_GLOBAL);
final Date milleniumInNewYork = newYorkFormatTZ.parse(MIDNIGHT_GLOBAL);
final Date milleniumInSydney = sydneyFormatTZ.parse(MIDNIGHT_GLOBAL);
// Check if they all point to the same moment in time.
// And that parser ignores its own configured time zone and uses the information from the date-time string.
assertThat(milleniumInNewYork, equalTo(milleniumInLondon));
assertThat(milleniumInSydney, equalTo(milleniumInLondon));
// These are all local Y2K moments, a.k.a. midnight at each location on Earth, with time zone information.
final String MIDNIGHT_LONDON = "2000-01-01T00:00:00.000-00:00";
final String MIDNIGHT_NEW_YORK = "2000-01-01T00:00:00.000-05:00";
final String MIDNIGHT_SYDNEY = "2000-01-01T00:00:00.000+10:00";
final Date midnightInLondonTZ = londonFormatLocal.parse(MIDNIGHT_LONDON);
final Date midnightInNewYorkTZ = newYorkFormatLocal.parse(MIDNIGHT_NEW_YORK);
final Date midnightInSydneyTZ = sydneyFormatLocal.parse(MIDNIGHT_SYDNEY);
// Check if they all point to the same moment in time.
assertThat(midnightInNewYorkTZ, not(equalTo(midnightInLondonTZ)));
assertThat(midnightInSydneyTZ, not(equalTo(midnightInLondonTZ)));
// Check if the time zone offset is correct.
assertThat(midnightInLondonTZ.getTime() - midnightInNewYorkTZ.getTime(),
equalTo((long) newYorkTimeZone.getOffset(milleniumInLondon.getTime())));
assertThat(midnightInLondonTZ.getTime() - midnightInSydneyTZ.getTime(),
equalTo((long) sydneyTimeZone.getOffset(milleniumInLondon.getTime())));
// These are also local Y2K moments, just withouth the time zone information.
final String MIDNIGHT_ANYWHERE = "2000-01-01T00:00:00.000";
final Date midnightInLondon = londonFormatLocal.parse(MIDNIGHT_ANYWHERE);
final Date midnightInNewYork = newYorkFormatLocal.parse(MIDNIGHT_ANYWHERE);
final Date midnightInSydney = sydneyFormatLocal.parse(MIDNIGHT_ANYWHERE);
// Check if these are the same as the local moments with time zone information.
assertThat(midnightInLondon, equalTo(midnightInLondonTZ));
assertThat(midnightInNewYork, equalTo(midnightInNewYorkTZ));
assertThat(midnightInSydney, equalTo(midnightInSydneyTZ));
// Check if they all point to the same moment in time.
assertThat(midnightInNewYork, not(equalTo(midnightInLondon)));
assertThat(midnightInSydney, not(equalTo(midnightInLondon)));
// Check if the time zone offset is correct.
assertThat(midnightInLondon.getTime() - midnightInNewYork.getTime(),
equalTo((long) newYorkTimeZone.getOffset(milleniumInLondon.getTime())));
assertThat(midnightInLondon.getTime() - midnightInSydney.getTime(),
equalTo((long) sydneyTimeZone.getOffset(milleniumInLondon.getTime())));
// Final check - if Y2K moment is in London ..
final String Y2K_LONDON = "2000-01-01T00:00:00.000Z";
// .. New York local time would be still 5 hours in 1999 ..
final String Y2K_NEW_YORK = "1999-12-31T19:00:00.000-05:00";
// .. and Sydney local time would be 10 hours in 2000.
final String Y2K_SYDNEY = "2000-01-01T10:00:00.000+10:00";
final String londonTime = londonFormatTZ.format(milleniumInLondon);
final String newYorkTime = newYorkFormatTZ.format(milleniumInLondon);
final String sydneyTime = sydneyFormatTZ.format(milleniumInLondon);
// WHat do you think, will the test pass?
assertThat(londonTime, equalTo(Y2K_LONDON));
assertThat(newYorkTime, equalTo(Y2K_NEW_YORK));
assertThat(sydneyTime, equalTo(Y2K_SYDNEY));
}
}