Develop Reference

Showing correct time from Milliseconds with desired TimeZone

I'm developing an application which takes data from Google TimeZone API.
Simply I have time in milliseconds of desired place on Earth.
For Example : 1504760156000 it's showing Date time In London which is
Thu Sep 07 2017 09:55:56
As I'm in TimeZone +05:00 from UTC if I manipulate 1504760156000 these milliseconds it will show me whole date time like below:
Thu Sep 07 2017 09:55:56 GMT+0500 (Pakistan Standard Time)
but I want to show:
Thu Sep 07 2017 09:55:56 GMT+0100 (British Summer Time)
The problem is: I have correct date and time for London but enable to show/change TimeZone without changing Time because Time is correct according to London.
UPDATED
After getting some comments. You are not getting me here in my example.
Suppose I am in Pakistan and Time here is 1:55 PM so I asked GOOGLE API via my application to tell me whats the time in London at moment. Google API tell me time in London is 1504760156000 (9:55 AM) in milliseconds if I convert these milliseconds to Date Object it will print out like below:
Date date =new Date(1504760156000)
Thu Sep 07 2017 09:55:56 GMT+0500 (Pakistan Standard Time)
It will manipulate it according to my Local TimeZone but I want results like below
Thu Sep 07 2017 09:55:56 GMT+0100 (British Summer Time)
Updated 2
I prepared timestamp in seconds in UTC as Google Time Zone API needed timestamp UTC in form of seconds
"https://maps.googleapis.com/maps/api/timezone/json?location="+Latitude +","+Longitude+"&timestamp="+currentTimeUTCinSeonds+"&key="API KEY"
Google API respond me with below JSON against London.
{
"dstOffset" : 3600,
"rawOffset" : 0,
"status" : "OK",
"timeZoneId" : "Europe/London",
"timeZoneName" : "British Summer Time"
}
According to Docs:
Calculating the Local Time
The local time of a given location is the sum of the timestamp
parameter, and the dstOffset and rawOffset fields from the result.
I Sum up result timestamp+rawoffset+dstoffset*1000='1504760156000' (at moment when I tried it)
Code from Project
Long ultimateTime=((Long.parseLong(timeObject1.getDstOffset())*1000)+(Long.parseLong(timeObject1.getRawOffset())*1000)+timestamp*1000);
timeObject1.setTimestamp(ultimateTime); //its Sime POJO object to save current time of queried Location
Date date=new Date(ultimateTime);
date1.setText("Date Time : "+date);
As I said I'm manipulating result in Local Time Zone so it gave me below result at that time:
Thu Sep 07 2017 09:55:56 GMT+0500 (Pakistan Standard Time)
But I knew API gave me correct time. The problem is Local offset from UTC . I just want to change GMT+0500 to GMT+0100

Timestamps represent an "absolute" value of a time elapsed since epoch. Your currentTimeUTCinSeconds, for example, represent the number of seconds since unix epoch (which is 1970-01-01T00:00Z, or January 1st 1970 at midnight in UTC). Java API's usually work with the number of milliseconds since epoch.
But the concept is the same - those values are "absolute": they are the same for everyone in the world, no matter where they are. If 2 people in different parts of the world (in different timezones) get the current timestamp at the same time, they'll all get the same number.
What changes is that, in different timezones, this same number represents a different local date and time.
For example, the timestamp you're using, that corresponds to Sep 7th 2017 08:55:56 UTC, which value is 1504774556 (the number of seconds since epoch). This same number corresponds to 09:55 in London, 13:55 in Karachi, 17:55 in Tokyo and so on. Changing this number will change the local times for everyone - there's no need to manipulate it.
If you want to get a java.util.Date that represents this instant, just do:
int currentTimeUTCinSeconds = 1504774556;
// cast to long to not lose precision
Date date = new Date((long) currentTimeUTCinSeconds * 1000);
This date will keep the value 1504774556000 (the number of milliseconds since epoch). This value corresponds to 09:55 in London, 13:55 in Karachi and 17:55 in Tokyo.
But printing this date will convert it to your JVM default timezone (here is a good explanation about the behaviour of Date::toString() method). When you do "Date Time : "+date, it implicity calls toString() method, and the result is the date converted to your default timezone.
If you want the date in a specific format and in a specific timezone, you'll need a SimpleDateFormat. Just printing the date (with System.out.println or by logging it) won't work: you can't change the format of the date object itself, because a Date has no format.
I also use a java.util.Locale to specify that the month and day of week must be in English. If you don't specify a locale, it'll use the system default, and it's not guaranteed to always be English (and this can be changed, even at runtime, so it's better to always specify a locale):
// use the same format, use English for month and day of week
SimpleDateFormat sdf = new SimpleDateFormat("EEE MMM dd yyyy HH:mm:ss 'GMT'Z (zzzz)", Locale.ENGLISH);
// set the timezone I want
sdf.setTimeZone(TimeZone.getTimeZone("Europe/London"));
// format the date
System.out.println(sdf.format(date));
The output will be:
Thu Sep 07 2017 09:55:56 GMT+0100 (British Summer Time)
Note that I don't need to manipulate the timestamp value. I don't use the google API, but I think their explanation is too confusing and the code above achieve the same results with less complication.
In your specific case, you can do:
date1.setText("Date Time : "+sdf.format(date));
Java new Date/Time API
The old classes (Date, Calendar and SimpleDateFormat) have lots of problems and design issues, and they're being replaced by the new APIs.
In Android you can use the ThreeTen Backport, a great backport for Java 8's new date/time classes. To make it work, you'll also need the ThreeTenABP (more on how to use it here).
To get a date from a timestamp, I use a org.threeten.bp.Instant with a org.threeten.bp.ZoneId to convert it to a timezone, creating a org.threeten.bp.ZonedDateTime. Then I use a org.threeten.bp.format.DateTimeFormatter to format it:
int currentTimeUTCinSeconds = 1504774556;
// get the date in London from the timestamp
ZonedDateTime z = Instant.ofEpochSecond(currentTimeUTCinSeconds).atZone(ZoneId.of("Europe/London"));
// format it
DateTimeFormatter fmt = DateTimeFormatter.ofPattern("EEE MMM dd yyyy HH:mm:ss 'GMT'XX (zzzz)", Locale.ENGLISH);
System.out.println(fmt.format(z));
The output is the same:
Thu Sep 07 2017 09:55:56 GMT+0100 (British Summer Time)
In your case, just do:
date1.setText("Date Time : "+fmt.format(z));

Data integrity violated in function "set" of class GregorianCalendar

I'am using GregorianCalendar class to manipulate with date and time.
I need to get only a current date without time.
My code:
Calendar today = new GregorianCalendar();
today.set(GregorianCalendar.HOUR,0);
today.set(GregorianCalendar.MINUTE,0);
today.set(GregorianCalendar.SECOND,0);
today.set(GregorianCalendar.MILLISECOND,0);
Date todayDate = new Date();
todayDate.setTime(today.getTime().getTime());
I expect todayDate will be like this "Wed Dec 07 00:00:00 EET 2016"
But actually todayDate is "Wed Dec 07 12:00:00 EET 2016".
Which is the correct way to do it?
Ia understend difference between fields HOUR and HOUR_OF_DAY when I get value, but why when I set value of HOUR to "0" the HOUR_OF_DAY is not seting to "0" automatically. Zero is always zero...
Question is about Data integrity...

It is a mistake to thought zero is always zero... It is not true for hours after midday. Zero hours after midday in short form (am/pm) is 12 hours in 24 form.
Thanks to #selvin

How to calculate the difference of hours between two current times based on location

I know this may be a simple/duplicate question but somehow I can't manage to calculate it
Hello, I am fetching today's twitter feeds with their tweeting times and have to calculate the difference of hours between them based on location to show. This is a sample date Sun Jul 21 21:14:40 +0000 2013 and I need to calculate the difference of hours with current time.

So, the first thing to do is to parse that string into a date:
Date postDate = new java.text.SimpleDateFormat("E MMM d HH:mm:ss Z yyyy")
.parse("Sun Jul 21 21:14:40 +0000 2013");
Now, you can get the difference between the post date and the current date in milliseconds:
long diffMSec = new Date().getTime() - postDate.getTime();
Finally, you can convert the milliseconds to hours, or any other time unit:
int diffHours = diffMSec / (1000*60*60);
Note that dates only have time zones when represented as strings - internally they're stored as milliseconds since midnight, Jan. 1, 1980, UTC. So parsing the string to a date (using a time zone), and calculating the diff between two dates takes care of the timezone difference for you.

joda-time can't read Parse dateTime string

I'm having an issue with joda-time formatting a date time string that Parse (parse.com) has stored in an sqlite table.
Sqlite creation string: "createdDate date time"
Storing parse date into table: "insert... parseObject.getCreatedAt()"
If i then use a SQLite browser to inspect the table, I see the date stored like this:
Sat Jun 15 15:44:52 PDT 2013
So going along with that, I wrote the following to convert it back into a DateTime object to give to parse as part of a query to get items that are newer than the last inserted in my table:
DateTimeFormatter format = DatetimeFormat.forPattern("yyyy'-'MM'-'dd'T'HH':'mm':'ss.SSS'Z'");
DateTime dt = formatter.parseDateTime(datahelper.getLastInsertDate(..));
The formatter is this way, because in Parse's databrowser, I can see dateTimes being stored like this:
2013-06-24T08:11:45.280Z
I get an ANR though, so I tried using the following formatter:
DateTimeFormatter format = DatetimeFormat.forPattern("EEE' 'MMM' 'dd' 'HH':'mm':'ss 'z'' 'YYYY");
DateTime dt = formatter.parseDateTime(datahelper.getLastInsertDate(..));
and I still get an ANR. The trace in eclipse shows the following:
Caused by: java.lang.IllegalArgumentException: invalid format: "Tue Jun 25 00:13:29 PDT 2013"
at org.joda.time.format.DateTimeFormatter.parseDateTime"
The second ANR trace shows:
Invalid format: "Tue Jun 25 00:13:29 PDT 2013" is malformed at "PDT
2013"
I've tried getting around that, as joda time does not parse "z" to PDT/PST, so I've put 'PDT' in my formatter to hopefully get it to work, but nothing seems to work.
Any ideas?
Edit 1: Using the accepted answer, I have a timezone formatting issue)
DateFormat originalFormat = new SimpleDateFormat("EEE MMM DDD HH:mm:ss z yyyy");
Date originaldate = originalFormat.parse(datahelper.getLastInsertdate);
Log.i("converted date: ", String.valueOf(originalDate);
Log.i("a real date: ", "String.valueOf(new Date(new Date().getTime)));
I get two outputs:
Fri Jan 25 15:14:11 PST 2013
Tue Jun 25 17:11:44 PDT 2013
why does the converted date show PST, and a standard Date shows PDT?

It seems to be a known problem Joda cannot parse Timezone names sadly. In the documentation before all the pattern syntaxes you will see this line:
The pattern syntax is mostly compatible with java.text.SimpleDateFormat - time zone names cannot be parsed and a few more symbols are supported. All ASCII letters are reserved as pattern letters, which are defined as follows:
You can see that in the documentation link here
Now the solution to your answer can be found in this answer by #BalusC located here
Hope this helps.

I think that with SQLite, because the date type is somewhat broken, the best thing to do is to store the long that you get from Date.getTime() or related Joda methods.
When you get the long from the database, re-construct your date object (e.g. new Date(long)), and then format that.
Above all, remember that (IMHO) the only sensible way to store a date is in reference to UTC, which is what you get with Date.getTime() and new Date(long) : milliseconds since Jan 1, 1970 UTC.
Once you retrieve your date, format it with whatever timezone is appropriate.

SimpleDateFormat bug with Large Dates

update: I thought the Android version was to blame, but it turns out it is the user-timezone
This code produces incorrect output when my tablets time is in Central European time (+2 in summer time):
SimpleDateFormat dateTimeFormatter = new SimpleDateFormat(
"yyyy-MM-dd HH:mm:ss Z", Locale.GERMAN);
Date testDate = dateTimeFormatter
.parse("2999-01-01 00:00:00 +0100");
Log.v(TAG, "test 1 " + testDate);
testDate = dateTimeFormatter.parse("2099-01-01 00:00:00 +0100");
Log.v(TAG, "test 2 " + testDate);
"test 1 Mon Dec 31 23:19:32 CET 2998"
"test 2 Thu Jan 01 00:00:00 CET 2099"
There is a time difference. Why the 40 minutes and some seconds difference on the larger date?
The bug is not present when I put my tablet in (most) other timezones. Something to do with timezones that have dailight saving hours?

Guess I cannot overcome this bug, I've built my own date parser.
Update: my own parser has the same problem
My current solution is just not using these large dates. If date > 100 years in future, I set it to 100 years in the future.