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Colton Idle
10/16/2023, 5:15 PMJust need a sanity check. I need to save the last time I fetched something from the server and persist it and then display to the user, formatted. The format should end up showing them what time it was in their current time zone.
Should I just grab System.currentTimeMillis() or Instant.now() or something else?
Any once I have that instance it should be pretty trivial to format it using the device locale right?
I feel like this is straightforward but time scares me. 😂
r
reactormonk
10/16/2023, 5:35 PMISO time is usually a good way to go - time is complicated.
UTC over the wire / db, parse & adjust as required. There's a ridiculous amount of things that can go wrong with milis.
e
ephemient
10/16/2023, 5:48 PMit kind of depends on what you want to do
System.currentTimeMillis()there are a variety of other clocks (see java.time.Clock, android.os.SystemClock) with different properties
formatting requires platform APIs but is mostly straightforward, with the exception that on Android, the desugared java.time APIs don't have access to all the same locale data across all Android versions
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Colton Idle
10/16/2023, 7:27 PMSo I'm doing
val date = Date(System.currentMillis())
val format = SimpleDateFormat("yyyy.MM.dd HH:mm")
format.format(date)
and it works. It gives me my time. I was expecting it to give me the time set to UTC. Wonder why I didn't have to give it a time zone.
e
ephemient
10/16/2023, 7:30 PMbecause it defaults to SDF defaults to Calendar.getInstance() which defaults to Locale.getDefault() and TimeZone.getDefault()
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t
Ties
10/17/2023, 7:44 AMIf dealing with timezones, I would suggest the Instant.now() and use the new time api
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r
Rob Elliot
10/17/2023, 4:39 PMLikewise, you should use
java.time.format.DateTimeFormatterjava.text.SimpleDateFormatAlso, if you habitually get hold of the current time like this:
Copy code
class MyClass(
private val clock: Clock = Clock.systemUTC()
) {
...
val now = clock.instant()
...
}e
ephemient
10/17/2023, 4:56 PMabsolutely yes, on JVM and new enough Android. on multiplatform you'll have to use something like https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.time/-time-source/ or roll your own
on old Android (which includes new Android if you're using desugaring to target old Android), you should use java.time, but be careful about formatting. https://issuetracker.google.com/issues/157926127 https://issuetracker.google.com/issues/160113376 https://issuetracker.google.com/issues/300128109 etc.
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Colton Idle
10/18/2023, 4:19 PMI wonder why I should use DateTimeFormatter over SDF?
r
reactormonk
10/18/2023, 4:19 PMBecause java.time is the new non-screwy Java time API
r
Rob Elliot
10/18/2023, 4:22 PMI mean, there's stuff on this all over the internet, but quickly:
•
SimpleDateFormatDateDateTimeFormatterInstantSimpleDateFormatc
Colton Idle
10/18/2023, 8:03 PMGotcha. I didn't realize that SDF was piled into that entire package that should be avoided. I thought the formatting lived outside of that. But that makes sense. thanks all for teaching!
k
Klitos Kyriacou
10/19/2023, 3:07 PM•Yep, that was me, 10 years ago!is not threadsafe, and anyone who worked for very long on the JVM more than a decade ago will have at some point found someone thinking "may as well make this format a static constant" and only found out when it failed under heavy loadSimpleDateFormat
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Colton Idle
10/19/2023, 4:57 PMi wish i could just have a denylist of packages that i should never use. 😅
e
ephemient
10/19/2023, 5:03 PMcan't, the old datetime api is in
java.util.*java.text.*👍 1
also you might still need to interoperate with them sometimes… particularly on android, if you need to format in ways that don't work in the desugared java.time, but have workarounds in the old api or in
android.icu.*👍 1
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