I want to implement timezone in my web application. I researched and saw most web app use a GMT dropdown, here is the link to that dropdown http://www.attackwork.com/BlogEntry/6/Time-Zone-Dropdown-Select-List/Default.aspx
Then I saw this article suggesting UTC is the way to go when it comes to implement timezone. https://web.archive.org/web/20210513223048/http://aspnet.4guysfromrolla.com/articles/081507-1.aspx Basically it's saying don't use DateTime.Now instead use DateTime.UtcNow
My questions are,
Is there a dropdown of the timezones in UTC, like the first link I showed there is one on GMT?
Should I really use UTC or GMT?
.NET 3.5 provides the TimeZoneInfo class which should make it relatively simple for you to populate a dropdown with time zones. GMT came before UTC and UTC was officially instituted on January 1, 1972. See this link for more information. For today's purposes, the two are pretty much synonymous, though they have different historical origins. Use whichever looks and functions better for your purposes.
I'm not sure if this is what you intended to ask, but in your database you should always store timestamps in UTC/GMT (as noted by others they mean essentially the same thing). For each user of your web app, store the time zone preference.
Then whenever you display the timestamp for something to a user, convert the UTC time in the database to the user's timezone.
GMT (Greenwich Mean Time) is the same as UTC (Universal Coordinated Time). This isn't an either/or choice - use it :)
Use Localization settings, functions and features anywhere possible.
If you aren't running against SQL Server 2008 or don't want to abstract timezone management to the database, you should store all times as UTC/GMT and apply the timezone difference based off the user's profile setting, so that users from all around the world can see timestamps on events in their local time.
The distinction between UTC and GMT is probably too fine to bother with in your code. However, it's probably a good idea to always save and process times internally with zero timezone offset, and deal with it as a presentation concern.
It's also possible to use JavaScript to determine the user's probable timezone: examine the timezone offsets for some pair of Date objects reasonably close to the solstices (even January 1 and July 1 makes a suitable approximation) to obtain a coarse timezone identification. Feel free to use this information to determine a default timezone, but do allow it to be changed by the user: JavaScript doesn't provide sufficient detail to select the exact timezone with national and regional historical shifts, and it may not be enabled by the user anyway.
Related
I have a simple mobile app that schedules future events between people at a specified location. These events may be physical or virtual, so the time specified for the event may or may not be in the same timezone as the 'location' of the event. For example, a physical meeting may be scheduled for two people in London at local time 10am on a specified date. Alternatively, a Skype call may be scheduled for two people in different timezones at 4pm (in one person's timezone) on a specified date though the 'location' of the event is simply 'office' which means two different places in different timezones.
I wonder the following design is going to work for this application:
On the client, it asks user to input the local date and time and specify the timezone local to the event.
On the server, it converts the local date and time with the provided timezone into UTC timestamp, and store this timestamp only.
When a client retrieves these details, it receives the UTC timestamp only and converts it into local time in the same timezone as the client's current timezone. The client's current timezone is determined by the current system timezone setting, which I think is automatically adjusted based on the client's location (of course, assuming the client is connected to a mobile network).
My main motivations for this design are:
UTC is an absolute and universal time standard, and you can convert to/from it from/to any timezone.
Users only care about the local date and time in the timezone they are currently in.
Is this a feasible design? If not, what specific scenarios would break the application or severely affect user experience? Critiques welcome.
For a single event, knowing the UTC instant on which it occurs is usually enough, so long as you have the right UTC instant (see later).
For repeated events, you need to know the time zone in which it repeats... not just the UTC offset, but the actual time zone. For example, if I schedule a weekly meeting at 5pm in Europe/London with colleagues in America/Los_Angeles, then for most of the year it will occur at 9am for them... but for a couple of weeks in the year it will occur at 8am and for a couple of weeks in the year it will occur at 10am, due to differences in when DST is observed.
Even for a single event, you might want to consider what happens if time zone rules change. Suppose I schedule a meeting for 4pm on March 20th 2018, in the Europe/London time zone. Currently that will occur with a UTC offset of 0... but suppose between now and the meeting, the time zone rules change to bring British Summer Time in one hour earlier. If I've written it in my diary as 4pm, I probably don't want the software to think that it's actually at 5pm because that's the UTC instant we originally predicted.
We don't know your exact application requirements, but the above situations at least provide an argument for potentially storing the local time and time zone instead of the UTC instant... but you'll also need to work out what to do if the local time ends up being skipped or being ambiguous due to DST changes. (When the clocks fall back, some local times occur twice. When the clocks skip forward, some local times are skipped. A time that was unambiguous may become invalid or ambiguous if the rules change between the original planning time and the actual event. You should probably account for this in your design.)
To keep it simple, my answers are:
Timezone info is redundant if you want to define a single moment. A
UTC/Unix timestamp completely defines a moment.
Your design seems feasible but on point 2: i would convert to the UTC/Unix timestamp on the client-side and already give this timestamp
in its final form to the server. Reason: the client-side already has the info necessary to convert (see this time-keeping
client-server-db
architecture
example - it works based exactly on the principles you describe).
One possible problem (as described by Jon Skeet in his answer) are recurring events, but this should be reflected in the way you model
time. The difference between recurring events and fixed events is
that the latter completely define a moment (like a UTC/Unix
timestamp) while the first are only a 'function' which can be applied
to the current time to get the next trigger time of the recurring
event. But this might entirely be a different problem than what
you ask - in any case, somehow distinguishing between recurring
events (if you need them) and fixed events in your model is a good
idea.
One decision to make is: PULL or PUSH? Or both? Do you want the server to be able to send emails for example, when an event comes to
pass? Or do you want client-side alerts only when your client-side
app is running? The answers to these questions will help you come
towards a design suitable for you.
We have a really strange problem in xpages regarding dates, the Notesdocument we have contain a date field and the value is only a date, there is no time portion.
In the xpage I have specified to display the date as a date/time value. the date display correctly on the webpage but we are now getting reports from users who login at night (around midnight) and see the date as adjusted by one day. if the same people login at daytime the date is correct so this only seem to happend around midnight
I have tried to change my clock on my client to around midnight but that does not reproduce it so I assume this is a server issue.
The domino server have correct date/time and we are using the latest version of Domino
any ideas?
we encountered the same problem recently and, I believe, found a very nice solution.
system treats the pure date as a date in UTC time zone. Date value is automatically converted into server's time zone. So the question is how to prevent conversion?
this code prevents conversion:
<xp:this.converter>
<xp:convertDateTime
type="date"
ignoreUserTimeZone="true"
dateStyle="long"
timeZone="UTC">
</xp:convertDateTime>
</xp:this.converter>
pay attention at "timeZone" attribute.
The issue is related to not having the TimeZone specified in the date / time field. We ran into this just yesterday. If you don't have the TZ specified, it seems to assume UTC and will adjust accordingly. Include the time zone and your field will stop adjusting erroneously.
Perhaps it has to do with this ?
http://www-304.ibm.com/support/docview.wss?uid=swg21508734
I've seen some reports about XPages Dates and TimeZone Issues
I suspect your Domino version was 8.5.3, because there were 2 APAR, LO72278 and LO67745, on similar problems against 8.5.3. Fixpack 3 addresses them.
The root cause is that Lotus Notes allows you to save a "Date" with no time or zone and the Notes server has a default Time Zone setting to interpret these incomplete things called dates. XPages doesn't play by the same rules, and its master Java wants to know what zone you're using, and looks to the system for some clue, and generally will use midnight within some TZ to refer to a "Date". There is a whole region on Stack Overflow on the "how to store/represent a date" topic - [datetime] - since languages and DBMS each have their own approach.
Nice legacy Notes focused article about it.
http://www-10.lotus.com/ldd/ddwiki.nsf/dx/05022009100728PMAGU5MB.htm
XPages article about it
http://www-10.lotus.com/ldd/ddwiki.nsf/dx/XPagesTimeZones.htm
Too bad they are not totally on the same page, I assume each release gets closer.
GWT doesn't serialize Java Date properly. When I tried sending Date created in Javascript through the wire, I found out that dates between April 1st (funny) and 25th October for years before year 1983 get subtracted by one day.
That means that, say, both 1982-04-01 and 1982-03-31 become 1982-03-31 on the Java side.
Given the dates in question, I would guess that this is some kind of DST problem. I've tried googling, and found only one other reference that describes similar problem.
I also tried submitting bug to the GWT team, but curiously wasn't able to find bugtracker for GWT.
So, my questions are:
Anyone else run into this? I'm on GWT 1.7, and would like to confirm if this happens on 2.0 as well.
My workaround was to send dates as Strings, and parse them on server. Anyone knows better workaround?
Assuming that you are using a java.util.Date
Question 1: It seems that it is fixed in 2.0. I've created both Dates above (1982-04-01 and 1982-03-31) and they come through correctly to the server (both represent on the server as 1982-04-01 and 1982-03-31 respectively). My setup is:
GWT 2.0
Java 1.6
OSX 10.6.2
Question 2: You could always pass the 'milliseconds since January 1, 1970, 00:00:00 GMT' over the async service-which you can get using getTime() on the date object. On the server side you can then instantiate a new Date passing this value in on the constructor:
Date date = new Date(millis);
This saves fiddling around with formatters and parsers.
Dates and times are a complicated subject. The conversion can depend on the locale that the browser is running in and wether both you JVM on the server and the locales of the clients are up-to-date.
In some cases there can be differences because in some regions they switched timezones in the past.
GWT sends dates using just millis since epoch time. Since it is using Date objects, you are limited in that the Dates on the server side will be automatically modified to the servers timezone. Are you sure that you take into account the possible difference in timezones between client and server ?
David
I'm pretty certain the FTR library has some date emulation in it.
http://code.google.com/p/ftr-gwt-library
If you don't have to do client-side conversions (adapt to user's timezone) or calculations send it in a String from the server.
Never came across your specific problem though.
The possible problems soure is difference in Client/Server time zones.
We have also run into a similar problem. It was long enough ago that I do not remember the exact details but the gist of it was there were some minor differences between java.util.Date and the way dates were handled in Javascript. Our workaround was effectively the same as yours, where the actual value sent over the wire was generally a String.
I would like to be able to display time based on the user's current time zone. I will be storing times in UTC format in my database, but wish to normalize these to the client's time zone. So far the option that seems most viable is to capture the clients time and then deteremine the difference between that and current UTC and use that delta to normalize times when rendering. I would like to know if there are any more straight forward options available to detect and normalize a UTC time to that of the requesting client's machine.
I would use the javascript dateObject.getTimezoneOffset(). Even if their time isn't set accurately, hopefully they've set their timezone:
http://www.w3schools.com/jsref/jsref_getTimezoneOffset.asp
You can use this value to calculate an offset between the server's time and the client's time. (as Jason helpfully pointed out in a comment below)
In addition to, or instead of using getTimezoneOffset, you should consider permitting the user to specify preferred timezone in their profile. For instance, a user may be visiting in one timezone, yet may prefer to see time displayed in his home timezone.
Also, if this were as simple as calling a JavaScript function, then sites would never have to ask for your timezone.
A much better approach is to store per-user the exact time zone the user is in (and optionally) allow them to select if they observe daylight savings time (if it's applicable to their time zone.) You can of course, automatically fill in the DST information (based on the time zone) if you wanted.
You'd have to make this part of the sign-up or possibly in their "options".
I am trying to determine, how I should implement local time in a web-app. All users are logged in, there are no anonymous users. They will need to see all time-values in their local time.
Is this how it should be done?
All DateTime values are saved as UTC-time in database
Each user has a UTC-Offset value stored in his profile
When displaying a datetime-value, I take the value from the database, and apply the users offset.
Is this the way to go? Or am I missing something?
Don't store a UTC offset for the user - that's not enough to know the full time zone information. You should store their Olson time zone ID, e.g. "Europe/London". Then you can display any UTC time in the local time, taking into account historical changes, daylight savings etc.
EDIT: It looks like the TimeZoneInfo ID isn't actually in the normal Olson format - but so long as there's something sensible you can display to the user (as a choice), and an ID you can retrieve the zone from later on, that's probably okay... you may have difficulties if you need to interoperate with other systems later though.
You should ask the user for their time zone (possibly trying to guess it first through JavaScript) - they will have more information than you do.
You should investigate the TimeZoneInfo class for more on this - I can't say I've used it much myself, but it's the way to go as of .NET 3.5. In particular, FindSystemTimeZoneById and GetSystemTimeZones will be important.
Time zones are a pain in general, but at least TimeZoneInfo gives a lot more support than the old TimeZone type.
That sounds like the most straightforward way to me. The only slip ups I could see occurring are some areas (such as parts of Indiana and I think all of Arizona) don't cooperate with daylight savings time, so you'll have to take extra precautions displaying the correct time for them.