I have a Client-Server based java application.The client is running in US/Pacific timezone and the server in UTC( I am saving the time in the database in UTC)
So for example, if I save the date as 09:00 Hrs Pacific time, it gets saved in the DB as 14:00 Hrs UTC.
When I read this time back from DB, daylight saving gets applied and it now gets converted to 08:00 hrs pacific time instead of 09:00 hrs.
So when converting from Pacific time to UTC, no daylight saving is considered, but when converting back from UTC to Pacific, it is applied which is not consistent.
In the DB, the column type is TIME and in java I am reading it into a date object.
How do I handle this ?
Normally the DB server decides on the time, applies daylight savings or not, and the time zone, which UTC is a standard.
Suggestion:
Maybe you want to set the time by the client side as a string field with another field for the time zone PST, EST, or whatever.
Make a field just for the time zone, and calculate the time for display to the client side.
I think the best thing you can do is make sure as much of your time handling as possible is done free from time zones at all. For example, millis since the Unix Epoch. Then you only apply time zone data just before it is displayed to the user.
So, in this case, do not apply any local time assumptions when you report to the server and when you retrieve from the server. In this way, it is impossible to have mismatching time zone or DST treatment of the data.
With all this aside, I suggest you use getLong manually and construct the Date object yourself.
Related
I have many users and they are located in different timezones. When a user changes some data (for instance edits) with her or his timezone, others must see it with their timezone. For this what can I do? Firstly , I need to save date with UTC timezone and when user wants to get it, It does request to api and gets returned date. After that user can convert this date with its timezone. Other users also do so. I think it works such
In short:
if you have to deal with daylight saving time (DST), you have to stick to java.time.ZonedDateTime
If you don't care about DST - use java.time.OffsetDateTime
In any case for all communications use ISO8601 standard
If unix timestamp is the same across the world how is am I able to get local time.
Or is it based on the different timezones the timestamp is different. i.e. I am in US the current seconds from UTC 1970 is 5,000 but if I am in Asia and check timestamp it will be 4,000 seconds ?
UTC is the same for every country in the world, whether you check in the US or in Asia the value will be the same.
Local time is calculated by using a time-zone offset (usually provided through the IANA time zone database). This is added to UTC time to determine the "Local Time" since 1970.
Both oldschool java.util.Date and modern java.time.SystemClock are using System#currentTimeMillis() to get system time, so let's assume you have same Unix time value on both machines.
Unix time to local time conversion could be a Bachelor's degree thesis: you have to consider leap years, leap seconds, daylight savings time, some changes to country's timezones made by government. You can read more about all that in OpenJDK's tzdata sources.
So, you need both system time and tzdata to be the same on your machines.
I think epoch converter can answer your question:
http://www.epochconverter.com/
You will see that Unix time is the same across the world, and it will print date accordingly to your localization
I have a date stored in a database as a UTC date ('2015-04-24 00:00:00'). When I get this date (using Hibernate) on a server running in the Eastern US Timezone, is shown as the correct date, '2015-04-24 00:00:00'. However, when I get this data on a server running on AWS in the us-west-1 region, which I assume is Pacific Time, the date shows as '2015-04-23 20:00:00'. Does anyone know why this would happen? I assume it has something to do with the date converting to local time, rather than UTC, but how can I prevent this from happening? Thanks!
Short answer: Just convert your Date to utc
Somewhat longer answer: As long as we don't consider relativistic effects a date (or more appropriately named a point in time) doesn't have a time zone. But if you display it as a String there are many variants of displaying it. One kind of variation is the choice of a timezone.
If you don't take special care to use a specific time zone, many programs will choose the timezone that the machine is 'living' in, which is configured on the os level and set to the time zone that is apropriate for the location the computer is most of the time.
TimeZone.setDefault timezone doesn't seem to support daylight savings time. If I leave the default (without using the function setDefault) the application comes up displaying dates in EST/EDT. But if ever I want to change the time zone (I use a combo box of TimeZone.getAvailableIDs()), I can only select EST (and daylight savings is ignored).
Looking in the documentation there's all sorts of ways to determine daylight savings of a timezone, but it doesn't look like it can be set. Any ideas how I can force a timezone to use daylight savings?
You can use daylight savings by referring to times when daylight savings is active.
The only way to tell it you want daylight savings even when it is not daylight savings is to create your own TimeZone, but that doesn't sound like a good idea. Or you can use a timezone which has the time offset you want.
Hi i have a typical requirement in my web application, i have to fill a dropdown box with all system timezones and set the selected time zone where from the client is browsing.
Only timezoneoffset is not enough to handle this suituation, since there are two reasons
1.the latest OS having more than one time zone with the same offset
2.If Day light save is enabled or disable(can be detected from Javascript) the offset will vary.
is ther any ways of handling this in Java script?
Short answer:
Use this open source JavaScript project: jsTimezoneDetect. It is based on the code that MK linked here, which is great, but not enough since different regions within the same timezone start their daylight savings at different times. Hemisphere also plays a factor.
Long answer:
One example is the -07:00 UTC timezone which basically has three sub timezones.
US Mountain Standard Time (no daylight saving... this is Arizona)
US Mountain Time (with daylight savings)
Mexico Mountain Time (with daylight savings)
Assuming that you know your user's UTC offset you will now have to check whether your timezone uses daylight savings. Create one January and one June date and check these two dates. If their UTC offsets differ, then you are in a timezone that uses daylight savings.
Say that you have determined that your user is -07:00 with daylight savings, that means either US Mountain Time (America/Denver) or Mexico Mountain Time (America/Chihuahua). How to tell them apart? Well, the date they start their daylight savings differ.
US daylight savings starts in 2011 starts 13 March, and in Mexico it 4th April. So start with Denver and check if 13 march is summer time, no? Ok, check if 4th April is summer time. Yes? Bingo.
Check this: Auto detect a time zone with JavaScript.