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Java DateFormat conversion automatically increases hour by 1

I am trying to take date in string and its input format string and converting the date in output format. However after conversion into Date, the java code increases the number of hours by one. I am not able to understand what causes the bug.
My Code:
try {
DateFormat outputFormat = new SimpleDateFormat("dd/MM/yyyy hh:mm:ss");
DateFormat inputFormat = new SimpleDateFormat(format);
Date date = inputFormat.parse(parameterValue);
parameterValue = outputFormat.format(date);
return parameterValue;
} catch (ParseException ex) {
// take action
}
format string: ddMMMyyyy / hh:mm z
Input Date: 07DEC2015 / 10:02 GMT
Output Date: 07/12/2015 11:02:00

outputFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
resolved it.

If you don't want to use timezone, in java 8 you can use LocalDate/LocalTime/LocalDateTime:
LocalDateTime localDateTimeInstance = LocalDateTime.parse(dateToBeConverted, DateTimeFormatter.ofPattern(formatOfDateToBeConverted));
return localDateTimeInstance.format("dd/MM/yyyy hh:mm:ss");
/*
Also check out ZoneDate, ZoneTime (for timezone)
Checkout - LocalDate, LocalTime
*/

How do I convert date/time from one timezone to another? [duplicate]

i have written this code to convert the current system date and time to some other timezone. I am not getting any error but i am not getting my output as expected. Like if i execute my program at a particular time.. My output is ::
The current time in India is :: Fri Feb 24 16:09:23 IST 2012
The date and time in :: Central Standard Time is :: Sat Feb 25 03:39:23 IST 2012
And the actual Time according to CST time zone is ::
Friday, 24 February 4:39:16 a.m(GMT - 6:00)
So there's some time gap. and i don't know why this is happening. Any help will be appreciated.. The code is ::
package MyPackage;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;
public class Temp2 {
public static void main(String[] args) {
try {
Calendar currentdate = Calendar.getInstance();
String strdate = null;
DateFormat formatter = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
strdate = formatter.format(currentdate.getTime());
TimeZone obj = TimeZone.getTimeZone("CST");
formatter.setTimeZone(obj);
//System.out.println(strdate);
//System.out.println(formatter.parse(strdate));
Date theResult = formatter.parse(strdate);
System.out.println("The current time in India is :: " +currentdate.getTime());
System.out.println("The date and time in :: "+ obj.getDisplayName() + "is ::" + theResult);
} catch (ParseException e) {
e.printStackTrace();
}
}
}

It's over the web. Could have googled. Anyways, here is a version for you (shamelessly picked and modified from here):
Calendar calendar = Calendar.getInstance();
TimeZone fromTimeZone = calendar.getTimeZone();
TimeZone toTimeZone = TimeZone.getTimeZone("CST");
calendar.setTimeZone(fromTimeZone);
calendar.add(Calendar.MILLISECOND, fromTimeZone.getRawOffset() * -1);
if (fromTimeZone.inDaylightTime(calendar.getTime())) {
calendar.add(Calendar.MILLISECOND, calendar.getTimeZone().getDSTSavings() * -1);
}
calendar.add(Calendar.MILLISECOND, toTimeZone.getRawOffset());
if (toTimeZone.inDaylightTime(calendar.getTime())) {
calendar.add(Calendar.MILLISECOND, toTimeZone.getDSTSavings());
}
System.out.println(calendar.getTime());

Your mistake is to call parse instead of format.
You call parse to parse a Date from a String, but in your case you've got a Date and need to format it using the correct Timezone.
Replace your code with
Calendar currentdate = Calendar.getInstance();
DateFormat formatter = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
TimeZone obj = TimeZone.getTimeZone("CST");
formatter.setTimeZone(obj);
System.out.println("Local:: " +currentdate.getTime());
System.out.println("CST:: "+ formatter.format(currentdate.getTime()));
and I hope you'll get the output you are expecting.

SimpleDateFormat#setTimezone() is the answer. One formatter with ETC timezone you use for parsing, another with UTC for producing output string:
DateFormat dfNy = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.ROOT);
dfNy.setTimeZone(TimeZone.getTimeZone("EST"));
DateFormat dfUtc = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.ROOT);
dfUtc.setTimeZone(TimeZone.getTimeZone("UTC"));
try {
return dfUtc.format(dfNy.parse(input));
} catch (ParseException e) {
return null; // invalid input
}

Handling dates in Java in my daily work is a non-trivial task. I suggest you to use Joda-Time that simplify our coding days and you don't have to "re-invent the wheel".

You can use two SimpleDateFormat, one for parse the date string with EST timezone, one for print the date with UTC timezone
String format = "yyyy-MM-dd HH:mm:ss";
SimpleDateFormat estFormatter = new SimpleDateFormat(format);
estFormatter.setTimeZone(TimeZone.getTimeZone("EST"));
Date date = estFormatter.parse("2015-11-01 01:00:00");
SimpleDateFormat utcFormatter = new SimpleDateFormat(format);
utcFormatter.setTimeZone(TimeZone.getTimeZone("UTC"));
System.out.println(utcFormatter.format(date));

You can just use "CST6CDT"
because in some countries they follow CDT in summer and CST in winter
public static String getDateInCST() {
Calendar calendar = Calendar.getInstance();
DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
formatter.setTimeZone(TimeZone.getTimeZone( "CST6CDT"));
String strdate = formatter.format(calendar.getTime());
TimeZone.getAvailableIDs();
return strdate;
}

Problem is when you print date obj it call toString method and it will print in your machines default time zone. Try this code and see difference.
Calendar currentdate = Calendar.getInstance();
String strdate = null;
DateFormat formatter = new SimpleDateFormat("dd-MM-yyyy HH:mm:ssz");
strdate = formatter.format(currentdate.getTime());
System.out.println("strdate=>" + strdate);
TimeZone obj = TimeZone.getTimeZone("CST");
formatter.setTimeZone(obj);
strdate = formatter.format(currentdate.getTime());
Date theResult = formatter.parse(strdate);
System.out.println("The current time in India is :: " +currentdate.getTime());
System.out.println("The date and time in :: " + obj.getDisplayName() + "is ::" + theResult);
System.out.println("The date and time in :: " + obj.getDisplayName() + "is ::" + strdate);

First message, don’t handle your date and time as strings in your code. Just as you don’t handle numbers and Boolean values as strings (I hope). Use proper date-time objects.
java.time
Sometimes we get date and time as string input. It may be from a text file, from the user or from data exchange with another system, for example. In those cases parse into a proper date-time object first thing. Second message, use java.time, the modern Java date and time API, for your date and time work.
DateTimeFormatter formatter
= DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss");
String input = "2015-11-01 01:00:00";
ZonedDateTime nyTime = LocalDateTime.parse(input, formatter)
.atZone(ZoneId.of("America/New_York"));
System.out.println("Time in New York: " + nyTime);
Output from this snippet is:
Time in New York: 2015-11-01T01:00-04:00[America/New_York]
To convert to GMT:
OffsetDateTime gmtTime = nyTime.toOffsetDateTime()
.withOffsetSameInstant(ZoneOffset.UTC);
System.out.println("GMT Time: " + gmtTime);
GMT Time: 2015-11-01T05:00Z
If you need to give string output, format using a date-time formatter. Here’s an example of formatting for an American audience:
DateTimeFormatter userFormatter
= DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM)
.withLocale(Locale.US);
String formattedDateTime = gmtTime.format(userFormatter);
System.out.println("GMT Time formatted for user: " + formattedDateTime);
GMT Time formatted for user: Nov 1, 2015, 5:00:00 AM
You additionally asked:
Between the two results below, which one should you take?
I understand that you ask because both are valid answers. On November 1, 2015 summer time (DST) ended at 2 AM. That is, after 01:59:59 came 01:00:00 a second time. So when we have got 2015-11-01 01:00:00 as input, it is ambiguous. It could be in Eastern Daylight Time, equal to 05:00 GMT, or it could be in Eastern Standard Time, one hour later, hence equal to 06:00 GMT. There is no way that I can tell you which of them is correct in your case. You may control which result you get using withEarlierOffsetAtOverlap() or withLaterOffsetAtOverlap(). Above we got the DST interpretation. So to get the standard time interpretation:
nyTime = nyTime.withLaterOffsetAtOverlap();
System.out.println("Alternate time in New York: " + nyTime);
Alternate time in New York: 2015-11-01T01:00-05:00[America/New_York]
We notice that the hour of day is still 01:00, but the offset is now -05:00 instead of -04:00. This also gives us a different GMT time:
GMT Time: 2015-11-01T06:00Z
GMT Time formatted for user: Nov 1, 2015, 6:00:00 AM
Avoid SimpleDateFormat and friends
While the other answers are generally correct, the classes DateFormat, SimpleDateFormat, Date and Calendar used there are poorly designed and long outdated. The first two are particularly troublesome. I recommend you avoid all of them. I frankly find the modern API so much nicer to work with.
Link
Oracle tutorial: Date Time explaining how to use java.time.

Please refer to below mentioned code.
DateFormat utcConverter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
utcConverter.setTimeZone(TimeZone.getTimeZone("GMT"));
String sampleDateTime = "2015-11-01 01:00:00";
DateFormat nyConverter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
nyConverter.setTimeZone(TimeZone.getTimeZone("EST"));
Calendar nyCal = Calendar.getInstance();
nyCal.setTime(nyConverter.parse(sampleDateTime));
System.out.println("NY TIME :" +nyConverter.format(nyCal.getTime()));
System.out.println("GMT TIME :" +utcConverter.format(nyCal.getTime()));

2020 Answer Here
If you want the new java.time.* feature but still want to mess with java.util.Date:
public static Date convertBetweenTwoTimeZone(Date date, String fromTimeZone, String toTimeZone) {
ZoneId fromTimeZoneId = ZoneId.of(fromTimeZone);
ZoneId toTimeZoneId = ZoneId.of(toTimeZone);
ZonedDateTime fromZonedDateTime =
ZonedDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault()).withZoneSameLocal(fromTimeZoneId);
ZonedDateTime toZonedDateTime = fromZonedDateTime
.withZoneSameInstant(toTimeZoneId)
.withZoneSameLocal(ZoneId.systemDefault())
;
return Date.from(toZonedDateTime.toInstant());
}
for java.sql.Timestamp
public static Timestamp convertBetweenTwoTimeZone(Timestamp timestamp, String fromTimeZone, String toTimeZone) {
ZoneId fromTimeZoneId = ZoneId.of(fromTimeZone);
ZoneId toTimeZoneId = ZoneId.of(toTimeZone);
LocalDateTime localDateTimeBeforeDST = timestamp.toLocalDateTime();
ZonedDateTime fromZonedDateTime = ZonedDateTime.of(localDateTimeBeforeDST, fromTimeZoneId);
ZonedDateTime toZonedDateTime = fromZonedDateTime.withZoneSameInstant(toTimeZoneId);
return Timestamp.valueOf(toZonedDateTime.toLocalDateTime());
}

For google calendar API
private String getFormatedDate(Date date)
{
DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss+05:30");
df.setTimeZone(TimeZone.getTimeZone("GMT+05:30"));
return df.format(date);
}

Java- milliseconds (SSS) not being parsed with SimpleDateFormat [duplicate]

This question already has answers here:
Java date is not preserving milliseconds in conversion with simple date format
(5 answers)
Closed 7 years ago.
Basically I'm attempting to parse date/time to Java, but having issues when trying to parse the milliseconds.
Example of data to be parsed: a[0] = 16/03/2015, a[1] = 10:00:18.120
I read in the two values and concatenate them.
Getting: dateTime = (java.lang.String) "16/03/2015 10:00:18.120"
As you can see the string has the milliseconds when i debug it. From here I parse it to SimpleDateFormat. It works- however the milliseconds are not displayed
DateFormat df = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss.SSS", Locale.ENGLISH);
String dateTime;
dateTime= a[0]+" "+a[1];
Date d = df.parse(dateTime);
Current output: d = (java.util.Date) Mon Mar 16 10:00:18 GMT 2015
Thanks for your help.

Your code is fine, but not your interpretation of the result. As correctly mentioned in one comment, the method toString() of class java.util.Date does not output the millisecond part. But the millisecond part is still part of the state of your result object. Proof:
SimpleDateFormat df = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss.SSS", Locale.ENGLISH);
String dateTime = "16/03/2015 10:00:18.120";
Date d = df.parse(dateTime);
System.out.println(d); // Mon Mar 16 10:00:18 CET 2015
System.out.println(d.getTime()); // 1426496418120
System.out.println("millisecond-part=" + (d.getTime() % 1000)); // millisecond-part=120
So all is fine. You can even format your result back to a string using the same (or another instance of SimpleDateFormat - maybe with different pattern, locale and timezone).
If java.util.Date was correctly implemented as value-type then the inventors of that class would have taken care of making the output of toString() representing the whole exact state of the object but it has not happened - another example why this class is broken.

Using DateFormat.format(Date date) function might meet your requirement
Date date = new Date();
DateFormat df = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss.SSS",Locale.ENGLISH);
String dateTime;
dateTime=df.format(date);
String[] a=dateTime.split(" ");
System.out.println(a[0]+" "+a[1]);

DateFormat df = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss.SSS",Locale.ENGLISH);
String dateTime;
dateTime= "03/16/2015"+" "+"10:00:18.120";
Date d = df.parse(dateTime);
System.out.println(df.format(d));

Try this:
String[] a = new String[]{"16/03/2015", "10:00:18.120"};
DateFormat df = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss.SSS", Locale.ENGLISH);
String dateTime = a[0] + " " + a[1];
try {
Date d = df.parse(dateTime);
System.out.println(d.getTime());//Returns milliseconds
} catch (ParseException ex) {
Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
}
The result: 1426492818120

How can i get data in format "YYYY-MM-DD 00:00:00.0" using class Date?

How can i get data in format "YYYY-MM-DD 00:00:00.0" using class Date (it's extremly important to use exactly this class)?
I tried to do everything i can think of:
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
df.format(date)
and
String pattern = "yyyy-MM-dd HH:mm:ss.S";
SimpleDateFormat format = new SimpleDateFormat(pattern);
try {
Date date = format.parse("2011-01-18 00:00:00.0");
} catch (ParseException e) {
e.printStackTrace();
}
byt when i print date using logger i get this format "Tue Sep 30 00:00:00 MSK 1913".

Try this
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.S");
Date date = format.parse("2011-01-18 00:00:00.0");
System.out.println(format.format(date));

Are you sure you want the hours, minutes, secs to be zeroes?
Or do you mean the pattern yyyy-MM-dd HH:mm:ss ?
The date class is always independent of the formatting. It only needs to be translated when you print it, like this:
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String out = df.format(date)
System.out.println(out);
Or do you want to strip the time out of the date object? or something.

You are confused by Date.toString() and SimpleDateFormat.format()
An object of Date (java.util.Date) has no format information. If you call date.toString(), (which is called by your logger), you got default representation of this object, you have seen what it is.
However, SimpleDateFormat.format() will give you a string as return value, this value will format the Date object with a pattern defined by SimpleDateFormat.
In your code, you first parsed the string, with certain pattern, to get the date object. If it was successful, you got the Date object, here, for this date object, you don't have any format information, even if you have defined a pattern to parse the input string. If you want to print/output (to string again) the date object, you have to use the SimpleDateFormat.format() method.

I hope the below one will solve your problem when you need to do for dynamic dates.
Date today = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd 00:00:00");
String formattedDate = sdf.format(today);
System.out.println(formattedDate);
//Above line output (formatted String object) is 2017-12-29 00:00:00
System.out.println(format.format(formattedDate));
//Above line output(parsed Date object) is Fri Dec 29 00:00:00 IST 2017
For Date object you can't get the output as yyyy-MM-dd 00:00:00, but you will get this format in String object type.

Date and time conversion to some other Timezone in java

i have written this code to convert the current system date and time to some other timezone. I am not getting any error but i am not getting my output as expected. Like if i execute my program at a particular time.. My output is ::
The current time in India is :: Fri Feb 24 16:09:23 IST 2012
The date and time in :: Central Standard Time is :: Sat Feb 25 03:39:23 IST 2012
And the actual Time according to CST time zone is ::
Friday, 24 February 4:39:16 a.m(GMT - 6:00)
So there's some time gap. and i don't know why this is happening. Any help will be appreciated.. The code is ::
package MyPackage;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;
public class Temp2 {
public static void main(String[] args) {
try {
Calendar currentdate = Calendar.getInstance();
String strdate = null;
DateFormat formatter = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
strdate = formatter.format(currentdate.getTime());
TimeZone obj = TimeZone.getTimeZone("CST");
formatter.setTimeZone(obj);
//System.out.println(strdate);
//System.out.println(formatter.parse(strdate));
Date theResult = formatter.parse(strdate);
System.out.println("The current time in India is :: " +currentdate.getTime());
System.out.println("The date and time in :: "+ obj.getDisplayName() + "is ::" + theResult);
} catch (ParseException e) {
e.printStackTrace();
}
}
}

It's over the web. Could have googled. Anyways, here is a version for you (shamelessly picked and modified from here):
Calendar calendar = Calendar.getInstance();
TimeZone fromTimeZone = calendar.getTimeZone();
TimeZone toTimeZone = TimeZone.getTimeZone("CST");
calendar.setTimeZone(fromTimeZone);
calendar.add(Calendar.MILLISECOND, fromTimeZone.getRawOffset() * -1);
if (fromTimeZone.inDaylightTime(calendar.getTime())) {
calendar.add(Calendar.MILLISECOND, calendar.getTimeZone().getDSTSavings() * -1);
}
calendar.add(Calendar.MILLISECOND, toTimeZone.getRawOffset());
if (toTimeZone.inDaylightTime(calendar.getTime())) {
calendar.add(Calendar.MILLISECOND, toTimeZone.getDSTSavings());
}
System.out.println(calendar.getTime());

Your mistake is to call parse instead of format.
You call parse to parse a Date from a String, but in your case you've got a Date and need to format it using the correct Timezone.
Replace your code with
Calendar currentdate = Calendar.getInstance();
DateFormat formatter = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
TimeZone obj = TimeZone.getTimeZone("CST");
formatter.setTimeZone(obj);
System.out.println("Local:: " +currentdate.getTime());
System.out.println("CST:: "+ formatter.format(currentdate.getTime()));
and I hope you'll get the output you are expecting.

SimpleDateFormat#setTimezone() is the answer. One formatter with ETC timezone you use for parsing, another with UTC for producing output string:
DateFormat dfNy = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.ROOT);
dfNy.setTimeZone(TimeZone.getTimeZone("EST"));
DateFormat dfUtc = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.ROOT);
dfUtc.setTimeZone(TimeZone.getTimeZone("UTC"));
try {
return dfUtc.format(dfNy.parse(input));
} catch (ParseException e) {
return null; // invalid input
}

Handling dates in Java in my daily work is a non-trivial task. I suggest you to use Joda-Time that simplify our coding days and you don't have to "re-invent the wheel".

You can use two SimpleDateFormat, one for parse the date string with EST timezone, one for print the date with UTC timezone
String format = "yyyy-MM-dd HH:mm:ss";
SimpleDateFormat estFormatter = new SimpleDateFormat(format);
estFormatter.setTimeZone(TimeZone.getTimeZone("EST"));
Date date = estFormatter.parse("2015-11-01 01:00:00");
SimpleDateFormat utcFormatter = new SimpleDateFormat(format);
utcFormatter.setTimeZone(TimeZone.getTimeZone("UTC"));
System.out.println(utcFormatter.format(date));

You can just use "CST6CDT"
because in some countries they follow CDT in summer and CST in winter
public static String getDateInCST() {
Calendar calendar = Calendar.getInstance();
DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
formatter.setTimeZone(TimeZone.getTimeZone( "CST6CDT"));
String strdate = formatter.format(calendar.getTime());
TimeZone.getAvailableIDs();
return strdate;
}

Problem is when you print date obj it call toString method and it will print in your machines default time zone. Try this code and see difference.
Calendar currentdate = Calendar.getInstance();
String strdate = null;
DateFormat formatter = new SimpleDateFormat("dd-MM-yyyy HH:mm:ssz");
strdate = formatter.format(currentdate.getTime());
System.out.println("strdate=>" + strdate);
TimeZone obj = TimeZone.getTimeZone("CST");
formatter.setTimeZone(obj);
strdate = formatter.format(currentdate.getTime());
Date theResult = formatter.parse(strdate);
System.out.println("The current time in India is :: " +currentdate.getTime());
System.out.println("The date and time in :: " + obj.getDisplayName() + "is ::" + theResult);
System.out.println("The date and time in :: " + obj.getDisplayName() + "is ::" + strdate);

First message, don’t handle your date and time as strings in your code. Just as you don’t handle numbers and Boolean values as strings (I hope). Use proper date-time objects.
java.time
Sometimes we get date and time as string input. It may be from a text file, from the user or from data exchange with another system, for example. In those cases parse into a proper date-time object first thing. Second message, use java.time, the modern Java date and time API, for your date and time work.
DateTimeFormatter formatter
= DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss");
String input = "2015-11-01 01:00:00";
ZonedDateTime nyTime = LocalDateTime.parse(input, formatter)
.atZone(ZoneId.of("America/New_York"));
System.out.println("Time in New York: " + nyTime);
Output from this snippet is:
Time in New York: 2015-11-01T01:00-04:00[America/New_York]
To convert to GMT:
OffsetDateTime gmtTime = nyTime.toOffsetDateTime()
.withOffsetSameInstant(ZoneOffset.UTC);
System.out.println("GMT Time: " + gmtTime);
GMT Time: 2015-11-01T05:00Z
If you need to give string output, format using a date-time formatter. Here’s an example of formatting for an American audience:
DateTimeFormatter userFormatter
= DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM)
.withLocale(Locale.US);
String formattedDateTime = gmtTime.format(userFormatter);
System.out.println("GMT Time formatted for user: " + formattedDateTime);
GMT Time formatted for user: Nov 1, 2015, 5:00:00 AM
You additionally asked:
Between the two results below, which one should you take?
I understand that you ask because both are valid answers. On November 1, 2015 summer time (DST) ended at 2 AM. That is, after 01:59:59 came 01:00:00 a second time. So when we have got 2015-11-01 01:00:00 as input, it is ambiguous. It could be in Eastern Daylight Time, equal to 05:00 GMT, or it could be in Eastern Standard Time, one hour later, hence equal to 06:00 GMT. There is no way that I can tell you which of them is correct in your case. You may control which result you get using withEarlierOffsetAtOverlap() or withLaterOffsetAtOverlap(). Above we got the DST interpretation. So to get the standard time interpretation:
nyTime = nyTime.withLaterOffsetAtOverlap();
System.out.println("Alternate time in New York: " + nyTime);
Alternate time in New York: 2015-11-01T01:00-05:00[America/New_York]
We notice that the hour of day is still 01:00, but the offset is now -05:00 instead of -04:00. This also gives us a different GMT time:
GMT Time: 2015-11-01T06:00Z
GMT Time formatted for user: Nov 1, 2015, 6:00:00 AM
Avoid SimpleDateFormat and friends
While the other answers are generally correct, the classes DateFormat, SimpleDateFormat, Date and Calendar used there are poorly designed and long outdated. The first two are particularly troublesome. I recommend you avoid all of them. I frankly find the modern API so much nicer to work with.
Link
Oracle tutorial: Date Time explaining how to use java.time.

Please refer to below mentioned code.
DateFormat utcConverter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
utcConverter.setTimeZone(TimeZone.getTimeZone("GMT"));
String sampleDateTime = "2015-11-01 01:00:00";
DateFormat nyConverter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
nyConverter.setTimeZone(TimeZone.getTimeZone("EST"));
Calendar nyCal = Calendar.getInstance();
nyCal.setTime(nyConverter.parse(sampleDateTime));
System.out.println("NY TIME :" +nyConverter.format(nyCal.getTime()));
System.out.println("GMT TIME :" +utcConverter.format(nyCal.getTime()));

2020 Answer Here
If you want the new java.time.* feature but still want to mess with java.util.Date:
public static Date convertBetweenTwoTimeZone(Date date, String fromTimeZone, String toTimeZone) {
ZoneId fromTimeZoneId = ZoneId.of(fromTimeZone);
ZoneId toTimeZoneId = ZoneId.of(toTimeZone);
ZonedDateTime fromZonedDateTime =
ZonedDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault()).withZoneSameLocal(fromTimeZoneId);
ZonedDateTime toZonedDateTime = fromZonedDateTime
.withZoneSameInstant(toTimeZoneId)
.withZoneSameLocal(ZoneId.systemDefault())
;
return Date.from(toZonedDateTime.toInstant());
}
for java.sql.Timestamp
public static Timestamp convertBetweenTwoTimeZone(Timestamp timestamp, String fromTimeZone, String toTimeZone) {
ZoneId fromTimeZoneId = ZoneId.of(fromTimeZone);
ZoneId toTimeZoneId = ZoneId.of(toTimeZone);
LocalDateTime localDateTimeBeforeDST = timestamp.toLocalDateTime();
ZonedDateTime fromZonedDateTime = ZonedDateTime.of(localDateTimeBeforeDST, fromTimeZoneId);
ZonedDateTime toZonedDateTime = fromZonedDateTime.withZoneSameInstant(toTimeZoneId);
return Timestamp.valueOf(toZonedDateTime.toLocalDateTime());
}

For google calendar API
private String getFormatedDate(Date date)
{
DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss+05:30");
df.setTimeZone(TimeZone.getTimeZone("GMT+05:30"));
return df.format(date);
}