How to create an ISO 8601 Date Formatter with milliseconds and timezone in Swift? [duplicate] - swift

Question

How to generate a date time stamp, using the format standards for ISO 8601 and RFC 3339?
The goal is a string that looks like this:
"2015-01-01T00:00:00.000Z"
Format:
year, month, day, as "XXXX-XX-XX"
the letter "T" as a separator
hour, minute, seconds, milliseconds, as "XX:XX:XX.XXX".
the letter "Z" as a zone designator for zero offset, a.k.a. UTC, GMT, Zulu time.
Best case:
Swift source code that is simple, short, and straightforward.
No need to use any additional framework, subproject, cocoapod, C code, etc.
I've searched StackOverflow, Google, Apple, etc. and haven't found a Swift answer to this.
The classes that seem most promising are NSDate, NSDateFormatter, NSTimeZone.
Related Q&A: How do I get an ISO 8601 date on iOS?
Here's the best I've come up with so far:
var now = NSDate()
var formatter = NSDateFormatter()
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
formatter.timeZone = NSTimeZone(forSecondsFromGMT: 0)
println(formatter.stringFromDate(now))

Answer 1

Swift 4 • iOS 11.2.1 or later
extension ISO8601DateFormatter {
convenience init(_ formatOptions: Options) {
self.init()
self.formatOptions = formatOptions
}
}
extension Formatter {
static let iso8601withFractionalSeconds = ISO8601DateFormatter([.withInternetDateTime, .withFractionalSeconds])
}
extension Date {
var iso8601withFractionalSeconds: String { return Formatter.iso8601withFractionalSeconds.string(from: self) }
}
extension String {
var iso8601withFractionalSeconds: Date? { return Formatter.iso8601withFractionalSeconds.date(from: self) }
}
Usage:
Date().description(with: .current) // Tuesday, February 5, 2019 at 10:35:01 PM Brasilia Summer Time"
let dateString = Date().iso8601withFractionalSeconds // "2019-02-06T00:35:01.746Z"
if let date = dateString.iso8601withFractionalSeconds {
date.description(with: .current) // "Tuesday, February 5, 2019 at 10:35:01 PM Brasilia Summer Time"
print(date.iso8601withFractionalSeconds) // "2019-02-06T00:35:01.746Z\n"
}
iOS 9 • Swift 3 or later
extension Formatter {
static let iso8601withFractionalSeconds: DateFormatter = {
let formatter = DateFormatter()
formatter.calendar = Calendar(identifier: .iso8601)
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
return formatter
}()
}
Codable Protocol
If you need to encode and decode this format when working with Codable
protocol you can create your own custom date encoding/decoding strategies:
extension JSONDecoder.DateDecodingStrategy {
static let iso8601withFractionalSeconds = custom {
let container = try $0.singleValueContainer()
let string = try container.decode(String.self)
guard let date = Formatter.iso8601withFractionalSeconds.date(from: string) else {
throw DecodingError.dataCorruptedError(in: container,
debugDescription: "Invalid date: " + string)
}
return date
}
}
and the encoding strategy
extension JSONEncoder.DateEncodingStrategy {
static let iso8601withFractionalSeconds = custom {
var container = $1.singleValueContainer()
try container.encode(Formatter.iso8601withFractionalSeconds.string(from: $0))
}
}
Playground Testing
let dates = [Date()] // ["Feb 8, 2019 at 9:48 PM"]
encoding
let encoder = JSONEncoder()
encoder.dateEncodingStrategy = .iso8601withFractionalSeconds
let data = try! encoder.encode(dates)
print(String(data: data, encoding: .utf8)!)
decoding
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601withFractionalSeconds
let decodedDates = try! decoder.decode([Date].self, from: data) // ["Feb 8, 2019 at 9:48 PM"]

Answer 2

Remember to set the locale to en_US_POSIX as described in Technical Q&A1480. In Swift 3:
let date = Date()
let formatter = DateFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZZZZZ"
print(formatter.string(from: date))
The issue is that if you're on a device which is using a non-Gregorian calendar, the year will not conform to RFC3339/ISO8601 unless you specify the locale as well as the timeZone and dateFormat string.
Or you can use ISO8601DateFormatter to get you out of the weeds of setting locale and timeZone yourself:
let date = Date()
let formatter = ISO8601DateFormatter()
formatter.formatOptions.insert(.withFractionalSeconds) // this is only available effective iOS 11 and macOS 10.13
print(formatter.string(from: date))
For Swift 2 rendition, see previous revision of this answer.

Answer 3

If you want to use the ISO8601DateFormatter() with a date from a Rails 4+ JSON feed (and don't need millis of course), you need to set a few options on the formatter for it to work right otherwise the the date(from: string) function will return nil. Here's what I'm using:
extension Date {
init(dateString:String) {
self = Date.iso8601Formatter.date(from: dateString)!
}
static let iso8601Formatter: ISO8601DateFormatter = {
let formatter = ISO8601DateFormatter()
formatter.formatOptions = [.withFullDate,
.withTime,
.withDashSeparatorInDate,
.withColonSeparatorInTime]
return formatter
}()
}
Here's the result of using the options versus not in a playground screenshot:

Answer 4

Swift 5
If you're targeting iOS 11.0+ / macOS 10.13+, you simply use ISO8601DateFormatter with the withInternetDateTime and withFractionalSeconds options, like so:
let date = Date()
let iso8601DateFormatter = ISO8601DateFormatter()
iso8601DateFormatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
let string = iso8601DateFormatter.string(from: date)
// string looks like "2020-03-04T21:39:02.112Z"

Answer 5

To further compliment Andrés Torres Marroquín and Leo Dabus, I have a version that preserves fractional seconds. I can't find it documented anywhere, but Apple truncate fractional seconds to the microsecond (3 digits of precision) on both input and output (even though specified using SSSSSSS, contrary to Unicode tr35-31).
I should stress that this is probably not necessary for most use cases. Dates online do not typically need millisecond precision, and when they do, it is often better to use a different data format. But sometimes one must interoperate with a pre-existing system in a particular way.
Xcode 8/9 and Swift 3.0-3.2
extension Date {
struct Formatter {
static let iso8601: DateFormatter = {
let formatter = DateFormatter()
formatter.calendar = Calendar(identifier: .iso8601)
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(identifier: "UTC")
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSSSSXXXXX"
return formatter
}()
}
var iso8601: String {
// create base Date format
var formatted = DateFormatter.iso8601.string(from: self)
// Apple returns millisecond precision. find the range of the decimal portion
if let fractionStart = formatted.range(of: "."),
let fractionEnd = formatted.index(fractionStart.lowerBound, offsetBy: 7, limitedBy: formatted.endIndex) {
let fractionRange = fractionStart.lowerBound..<fractionEnd
// replace the decimal range with our own 6 digit fraction output
let microseconds = self.timeIntervalSince1970 - floor(self.timeIntervalSince1970)
var microsecondsStr = String(format: "%.06f", microseconds)
microsecondsStr.remove(at: microsecondsStr.startIndex)
formatted.replaceSubrange(fractionRange, with: microsecondsStr)
}
return formatted
}
}
extension String {
var dateFromISO8601: Date? {
guard let parsedDate = Date.Formatter.iso8601.date(from: self) else {
return nil
}
var preliminaryDate = Date(timeIntervalSinceReferenceDate: floor(parsedDate.timeIntervalSinceReferenceDate))
if let fractionStart = self.range(of: "."),
let fractionEnd = self.index(fractionStart.lowerBound, offsetBy: 7, limitedBy: self.endIndex) {
let fractionRange = fractionStart.lowerBound..<fractionEnd
let fractionStr = self.substring(with: fractionRange)
if var fraction = Double(fractionStr) {
fraction = Double(floor(1000000*fraction)/1000000)
preliminaryDate.addTimeInterval(fraction)
}
}
return preliminaryDate
}
}

Answer 6

Uses ISO8601DateFormatter on iOS10 or newer.
Uses DateFormatter on iOS9 or older.
Swift 4
protocol DateFormatterProtocol {
func string(from date: Date) -> String
func date(from string: String) -> Date?
}
extension DateFormatter: DateFormatterProtocol {}
#available(iOS 10.0, *)
extension ISO8601DateFormatter: DateFormatterProtocol {}
struct DateFormatterShared {
static let iso8601: DateFormatterProtocol = {
if #available(iOS 10, *) {
return ISO8601DateFormatter()
} else {
// iOS 9
let formatter = DateFormatter()
formatter.calendar = Calendar(identifier: .iso8601)
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
return formatter
}
}()
}

Answer 7

In my case I have to convert the DynamoDB - lastUpdated column (Unix Timestamp) to Normal Time.
The initial value of lastUpdated was : 1460650607601 - converted down to 2016-04-14 16:16:47 +0000 via :
if let lastUpdated : String = userObject.lastUpdated {
let epocTime = NSTimeInterval(lastUpdated)! / 1000 // convert it from milliseconds dividing it by 1000
let unixTimestamp = NSDate(timeIntervalSince1970: epocTime) //convert unix timestamp to Date
let dateFormatter = NSDateFormatter()
dateFormatter.timeZone = NSTimeZone()
dateFormatter.locale = NSLocale.currentLocale() // NSLocale(localeIdentifier: "en_US_POSIX")
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ssZZZZZ"
dateFormatter.dateFromString(String(unixTimestamp))
let updatedTimeStamp = unixTimestamp
print(updatedTimeStamp)
}

Answer 8

In the future the format might need to be changed which could be a small head ache having date.dateFromISO8601 calls everywhere in an app. Use a class and protocol to wrap the implementation, changing the date time format call in one place will be simpler. Use RFC3339 if possible, its a more complete representation. DateFormatProtocol and DateFormat is great for dependency injection.
class AppDelegate: UIResponder, UIApplicationDelegate {
internal static let rfc3339DateFormat = "yyyy-MM-dd'T'HH:mm:ssZZZZZ"
internal static let localeEnUsPosix = "en_US_POSIX"
}
import Foundation
protocol DateFormatProtocol {
func format(date: NSDate) -> String
func parse(date: String) -> NSDate?
}
import Foundation
class DateFormat: DateFormatProtocol {
func format(date: NSDate) -> String {
return date.rfc3339
}
func parse(date: String) -> NSDate? {
return date.rfc3339
}
}
extension NSDate {
struct Formatter {
static let rfc3339: NSDateFormatter = {
let formatter = NSDateFormatter()
formatter.calendar = NSCalendar(calendarIdentifier: NSCalendarIdentifierISO8601)
formatter.locale = NSLocale(localeIdentifier: AppDelegate.localeEnUsPosix)
formatter.timeZone = NSTimeZone(forSecondsFromGMT: 0)
formatter.dateFormat = rfc3339DateFormat
return formatter
}()
}
var rfc3339: String { return Formatter.rfc3339.stringFromDate(self) }
}
extension String {
var rfc3339: NSDate? {
return NSDate.Formatter.rfc3339.dateFromString(self)
}
}
class DependencyService: DependencyServiceProtocol {
private var dateFormat: DateFormatProtocol?
func setDateFormat(dateFormat: DateFormatProtocol) {
self.dateFormat = dateFormat
}
func getDateFormat() -> DateFormatProtocol {
if let dateFormatObject = dateFormat {
return dateFormatObject
} else {
let dateFormatObject = DateFormat()
dateFormat = dateFormatObject
return dateFormatObject
}
}
}

Answer 9

There is a new ISO8601DateFormatter class that let's you create a string with just one line. For backwards compatibility I used an old C-library. I hope this is useful for someone.
Swift 3.0
extension Date {
var iso8601: String {
if #available(OSX 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *) {
return ISO8601DateFormatter.string(from: self, timeZone: TimeZone.current, formatOptions: .withInternetDateTime)
} else {
var buffer = [CChar](repeating: 0, count: 25)
var time = time_t(self.timeIntervalSince1970)
strftime_l(&buffer, buffer.count, "%FT%T%z", localtime(&time), nil)
return String(cString: buffer)
}
}
}

Answer 10

To complement the version of Leo Dabus, I added support for projects written Swift and Objective-C, also added support for the optional milliseconds, probably isn't the best but you would get the point:
Xcode 8 and Swift 3
extension Date {
struct Formatter {
static let iso8601: DateFormatter = {
let formatter = DateFormatter()
formatter.calendar = Calendar(identifier: .iso8601)
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
return formatter
}()
}
var iso8601: String {
return Formatter.iso8601.string(from: self)
}
}
extension String {
var dateFromISO8601: Date? {
var data = self
if self.range(of: ".") == nil {
// Case where the string doesn't contain the optional milliseconds
data = data.replacingOccurrences(of: "Z", with: ".000000Z")
}
return Date.Formatter.iso8601.date(from: data)
}
}
extension NSString {
var dateFromISO8601: Date? {
return (self as String).dateFromISO8601
}
}

Answer 11

It is now 2022, but I was looking for an answer to this (i.e. how to convert a Date to ISO8601 that includes fractions of seconds). It turns out the answer nowadays is a one-liner:
var somedate: Date = Date.now
var isodate = somedate.ISO8601Format(Date.ISO8601FormatStyle(includingFractionalSeconds: true))
so this will print something like 2022-08-16T17:45:08.548Z

Answer 12

Without some manual String masks or TimeFormatters
import Foundation
struct DateISO: Codable {
var date: Date
}
extension Date{
var isoString: String {
let encoder = JSONEncoder()
encoder.dateEncodingStrategy = .iso8601
guard let data = try? encoder.encode(DateISO(date: self)),
let json = try? JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [String: String]
else { return "" }
return json?.first?.value ?? ""
}
}
let dateString = Date().isoString

Answer 13

Based on the acceptable answer in an object paradigm
class ISO8601Format
{
let format: ISO8601DateFormatter
init() {
let format = ISO8601DateFormatter()
format.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
format.timeZone = TimeZone(secondsFromGMT: 0)!
self.format = format
}
func date(from string: String) -> Date {
guard let date = format.date(from: string) else { fatalError() }
return date
}
func string(from date: Date) -> String { return format.string(from: date) }
}
class ISO8601Time
{
let date: Date
let format = ISO8601Format() //FIXME: Duplication
required init(date: Date) { self.date = date }
convenience init(string: String) {
let format = ISO8601Format() //FIXME: Duplication
let date = format.date(from: string)
self.init(date: date)
}
func concise() -> String { return format.string(from: date) }
func description() -> String { return date.description(with: .current) }
}
callsite
let now = Date()
let time1 = ISO8601Time(date: now)
print("time1.concise(): \(time1.concise())")
print("time1: \(time1.description())")
let time2 = ISO8601Time(string: "2020-03-24T23:16:17.661Z")
print("time2.concise(): \(time2.concise())")
print("time2: \(time2.description())")