Develop Reference

Converting a time String to ISO 8601 format

I am trying to create a String in a format like 2015-08-20T08:26:21.000Z
to 2015-08-20T08:26:21Z
I know it can be done with some String splitting techniques, but i am wondering if there is an elegant solution for that (with minimal code changes).
Both of the above are time strings, the final one which i need is Date in ISO 8601 . https://www.rfc-editor.org/rfc/rfc3339#section-5.6
I have tried a few similar questions like converting a date string into milliseconds in java but they dont actually solve the purpose.
Also tried using :
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mmZ");
String nowAsString = df.format(new Date());
But it still does not do any String to String conversions. Getting the following error:
23:04:13,829 WARN [RuntimeExceptionMapper] caught RuntimeException: {}: java.lang.IllegalArgumentException: Cannot format given Object as a Date
Is there some library which someone can suggest ?
Thanks.

tl;dr
Instant.parse( "2015-08-20T08:26:21.000Z" )
.toString()
2015-08-20T08:26:21Z
Date-Time Formatter
If all you want to do is eliminate the .000, then use date-time objects to parse your input string value, then generate a new string representation of that date-time value in a different format.
ISO 8601
By the way, if that is your goal, the Question’s title make no sense as both strings mentioned in the first sentence are valid ISO 8601 formatted strings.
2015-08-20T08:26:21.000Z
2015-08-20T08:26:21Z
java.time
Java 8 and later has the new java.time package. These new classes supplant the old java.util.Date/.Calendar & java.text.SimpleDateFormat classes. Those old classes were confusing, troublesome, and flawed.
Instant
If all you want is UTC time zone, then you can use the Instant class. This class represents a point along the timeline without regard to any particular time zone (basically UTC).
DateTimeFormatter.ISO_INSTANT
Calling an Instant’s toString generates a String representation of the date-time value using a DateTimeFormatter.ISO_INSTANT formatter instance. This formatter is automatically flexible about the fractional second. If the value has a whole second, no decimal places are generated (apparently what the Question wants). For a fractional second, digits appear in groups of 3, 6, or 9, as needed to represent the value up to nanosecond resolution. Note: this format may exceed ISO 8601 limit of milliseconds (3 decimal places).
Example code
Here is some example code in Java 8 Update 51.
String output = Instant.parse( "2015-08-20T08:26:21.000Z" ).toString( );
System.out.println("output: " + output );
output: 2015-08-20T08:26:21Z
Changing to a fractional second, .08
String output = Instant.parse( "2015-08-20T08:26:21.08Z" ).toString( );
output: 2015-08-20T08:26:21.080Z
If interested in any time zone other than UTC, then make a ZonedDateTime object from that Instant.
ZonedDateTime zdt = ZonedDateTime.ofInstant( instant , ZoneId.of( "America/Montreal" ) ) ;

Your format is just not right try this :-
try {
String s = "2015-08-20T08:26:21.000Z";
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSX");
Date d = df.parse(s);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssX");
System.out.println(sdf.format(d));
} catch (ParseException e) {
e.printStackTrace();
}

Conversion of a date String of unknown formatting into a date String that uses known formatting can be accomplished using two DateFormat objects- one dynamically configured to parse the format of the input String, and one configured to generate the formatted output String. For your situation the input String formatting is unspecified and must be provided by the caller, however, the output String formatting can be configured to use ISO 8601 formatting without additional input. Essentially, generating an ISO 8601 formatted date String output requires two inputs provided by the caller- a String containing the formatted date and another String that contains the SimpleDateFormat format.
Here is the described conversion as Java code (I deliberately have left out null checks and validations, add these as appropriate for your code):
private String formatDateAsIso8601(final String inputDateAsString, final String inputStringFormat) throws ParseException {
final DateFormat iso8601DateFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm'Z'", Locale.ENGLISH);
iso8601DateFormatter.setTimeZone(TimeZone.getTimeZone("UTC"));
final DateFormat inputDateFormatter = new SimpleDateFormat(inputStringFormat, Locale.ENGLISH);
final Date inputDate = inputDateFormatter.parse(inputDateAsString);
return iso8601DateFormatter.format(inputDate);
}
If you want to modify that method please note that SimpleDateFormat is not thread-safe, and that you should not use it from a static context without a workaround for multi-threaded code (ThreadLocal is commonly used to do just such a workaround for SimpleDateFormat).
An additional "gotcha" is the use of a Locale during the construction of the SimpleDateFormat objects- do not remove the Locale configuration. It is not safe to allow the system to choose to use the default Locale because that is user/machine specific. If you do allow it to use the default Locale, you run the risk of transient bugs because your development machine uses a Locale different than the Locale of your end-user. You do not have to use my selected ENGLISH Locale, it is perfectly fine to use a different Locale (you should understand the rules of that Locale and modify the code as appropriate however). Specification of no Locale and utilization of the system default is incorrect however, and likely will lead to many frustrating hours trying to diagnose an elusive bug.
Please understand this solution is not ideal as of Java 8 and the inclusion of the JodaTime based classes, like Instant. I chose to answer using the outdated API's because those were what you seemed concerned with in your question. If you are using Java 8 I strongly urge to learn and utilize the new classes as they are an improvement in almost every conceivable way.

Java printf with date and month

System.out.printf("Time: %d-%d %02d:%02d" +
calendar.get(Calendar.DAY_OF_MONTH),
calendar.get(Calendar.MONTH),
calendar.get(Calendar.HOUR_OF_DAY),
calendar.get(Calendar.MINUTE);
That is the code a friend showed me, but how do I get the date to appear in a Format like November 1?

This is how to do it:
DateFormat dateFormat = new SimpleDateFormat( "MMMMM d" );
Calendar calendar = new GregorianCalendar(); // The date you want to format
Date dateToFormat = calendar.getTime();
String formattedDate = dateFormat.format( dateToFormat );
System.out.println( formattedDate );

Date d = new Date();
System.out.printf("%s %tB %<td", "Today", d);
// output :
// Today november 01
%tB for Locale-specific full month name, e.g. "January", "February".
%<td d for Day of month, formatted as two digits with leading zeros as necessary, < for reuse the last parameter.

The DateFormat answer is the way to do this. The printf answer is also good although does not provide locale-specific formats (it provides language-specific names but does not use e.g. the day/month/year ordering that the current locale uses).
You asked in a comment:
Can I do it with the calendar.get(Calendar.MONTH) etc method? Or do I have to use date format?
You don't have to use the other methods here, but if you want to use the Calender fields, it is up to you to convert the numeric values they provide to strings like "Tuesday" or "November". For that you can use the built in DateFormatSymbols, which provides internationalized strings from numbers for dates, in the form of String arrays, which you can use the Calendar fields to index in to. See How can I convert an Integer to localized month name in Java? for example.
Note you can use DateFormat.getDateInstance() to retrieve a pre-made format for the current locale (see the rest of those docs, there are also methods for getting pre-made time-only or date+time formats).
Basically you have the following options:
DateFormat (SimpleDateFormat for custom formats)
Locale-specific format (e.g. day/month/year ordering): Yes
Language-specific names (e.g. English "November" vs. Spanish "Noviembre"): Yes
Does the work for you: Yes. This is the best way and will provide a format that the user is used to working with, with no logic needed on your end.
printf date fields
Locale-specific format: No
Language-specific names: Yes
Does the work for you: Partly (up to you to determine field ordering)
Calendar fields with DateFormatSymbols
Locale-specific format: No
Language-specific names: Yes
Does the work for you: No
Calendar fields with your own string conversions (like a big switch statement):
Locale-specific format: No
Language-specific names: No
Does the work for you: No
Another advantage of DateFormat-based formats vs printf date fields is you can still define your own field ordering and formats with the SimpleDateFormat (just like printf) but you can stick to the DateFormat interface which makes it easier to pass around and combine with stock date formats like DateFormat.getDateInstance(DateFormat.MEDIUM).
Check out the documentation for DateFormat for info on the things you can do with it. Check out the documentation for SimpleDateFormat for info on creating custom date formats. Check out this nice example of date formats (archive) for some example output if you want instant gratification.

There's a direct way how to do it using printf, but it's a pain, too:
String.printf("Time: %1$td-%1$tm %1$tH:%1$tM", new Date());
One problem with it is that it uses 4 formatting strings with the same object, so it needs the 1$ prefix to always access the first argument. The other is that I can never remember what letter means what (but maybe that's just me).
Speed could actually be another problem, if you care.
This is documented in the underlying class Formatter.
My preffered way would be something like
myFormatter.format("Time: [d-m HH:MM]", new Date())
where the braces would save us from repeating $1 and make clear where the argument ends.

Portable way to guarantee that the year field of a DateFormat is only two digits

Currently, I'm having
private ThreadLocal<DateFormat> shortDateFormat = new ThreadLocal<DateFormat>() {
#Override protected DateFormat initialValue() {
final DateFormat format = DateFormat.getDateInstance(DateFormat.SHORT);
return format;
}
};
Using my Android 4.1, this provides me date in format (In my localization. It may look different for other countries)
19/07/2013
However, sometimes I would like to have a much shorter version like 19/07/13
I do not want to hard code as
dd/MM/yy
As the above way would not portable across different countries. Some countries, their month come before date.
Is there any portable way to achieve so?
p/s Not only month/date order. There might be other problem as well. For instance, China is using 19-07-13 or 19-07-2013. There might be more edge cases for other countries, but I don't know.

SimpleDateFormat dateFormat= (SimpleDateFormat) DateFormat.getDateInstance();
dateFormat.applyPattern(dateFormat.toPattern().replaceAll("y{4}", "yy"));
Explanation:
applyPattern(String pattern) applies the given pattern string to this date format.
dateFormat.toPattern() gets the current pattern
dateFormat.toPattern().replaceAll(String regex, String replacement) returns the current pattern, with regex replaced by replacement.
"y{4}" looks through the date format pattern for a series of 4 y's, and
"yy" says that if you see 4 y's, replace them with 2 instead.
Hope that helped. Good luck.
EDIT:
As MH pointed out, since this is for android, it is probably more appropriate to use:
SimpleDateFormat dateFormat = (SimpleDateFormat)
android.text.format.DateFormat.getDateFormat(getApplicationContext());
This should work fine, since the above method call returns a DateFormat of java.text.DateFormat, not of android.text.format.DateFormat.

You should take a look at the functionality android.text.format.DateFormat provides, on top of the java.text.DateFormat.
In particular, the following method will be of interest:
getDateFormatOrder(Context context)
Javadoc:
Gets the current date format stored as a char array. The array will
contain 3 elements (DATE, MONTH, and YEAR) in the order specified by
the user's format preference. Note that this order is only appropriate
for all-numeric dates; spelled-out (MEDIUM and LONG) dates will
generally contain other punctuation, spaces, or words, not just the
day, month, and year, and not necessarily in the same order returned
here.
In other words, the method allows you to determine what order the day, month and year fields are in, according to the user's preference (which triumphs the user's locale, if you ask me). From there it should easy enough to figure out what 'short' format to use; i.e. dd/MM/yy or MM/dd/yy.
As pointed out by the documentation, the return value of the method is only useful in the context of all-numeric date representations. That should be fine in your case.

If you want portable, rather than using the date object, you could instead create an array with month,date, and year. (I would just use the cal object and access each of the three individually)
Calendar cal = Calendar.getInstance();
int year =cal.get(Calendar.YEAR);
int month = cal.get(Calendar.MONTH) + 1;
int day= cal.get(Calendar.DAY);
dateArray[0] = month;
dateArray[1] = year;
dateArray[2] = day;

How about creating a map with localized patterns based on country ISO code and a fallback default pattern in case you don't have a specific country defined?

How do I get localized date pattern string?

It is quite easy to format and parse Java Date (or Calendar) classes using instances of DateFormat.
I could format the current date into a short localized date like this:
DateFormat formatter = DateFormat.getDateInstance(DateFormat.SHORT, Locale.getDefault());
String today = formatter.format(new Date());
My problem is that I need to obtain this localized pattern string (something like "MM/dd/yy").
This should be a trivial task, but I just couldn't find the provider.

For SimpleDateFormat, You call toLocalizedPattern()
EDIT:
For Java 8 users:
The Java 8 Date Time API is similar to Joda-time. To gain a localized pattern we can use class
DateTimeFormatter
DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM);
Note that when you call toString() on LocalDate, you will get date in format ISO-8601
Note that Date Time API in Java 8 is inspired by Joda Time and most solution can be based on questions related to time.

For those still using Java 7 and older:
You can use something like this:
DateFormat formatter = DateFormat.getDateInstance(DateFormat.SHORT, Locale.getDefault());
String pattern = ((SimpleDateFormat)formatter).toPattern();
String localPattern = ((SimpleDateFormat)formatter).toLocalizedPattern();
Since the DateFormat returned From getDateInstance() is instance of SimpleDateFormat.
Those two methods should really be in the DateFormat too for this to be less hacky, but they currently are not.

It may be strange, that I am answering my own question, but I believe, I can add something to the picture.
ICU implementation
Obviously, Java 8 gives you a lot, but there is also something else: ICU4J. This is actually the source of Java original implementation of things like Calendar, DateFormat and SimpleDateFormat, to name a few.
Therefore, it should not be a surprise that ICU's SimpleDateFormat also contains methods like toPattern() or toLocalizedPattern(). You can see them in action here:
DateFormat fmt = DateFormat.getPatternInstance(
DateFormat.YEAR_MONTH,
Locale.forLanguageTag("pl-PL"));
if (fmt instanceof SimpleDateFormat) {
SimpleDateFormat sfmt = (SimpleDateFormat) fmt;
String pattern = sfmt.toPattern();
String localizedPattern = sfmt.toLocalizedPattern();
System.out.println(pattern);
System.out.println(localizedPattern);
}
ICU enhancements
This is nothing new, but what I really wanted to point out is this:
DateFormat.getPatternInstance(String pattern, Locale locale);
This is a method that can return a whole bunch of locale specific patterns, such as:
ABBR_QUARTER
QUARTER
YEAR
YEAR_ABBR_QUARTER
YEAR_QUARTER
YEAR_ABBR_MONTH
YEAR_MONTH
YEAR_NUM_MONTH
YEAR_ABBR_MONTH_DAY
YEAR_NUM_MONTH_DAY
YEAR_MONTH_DAY
YEAR_ABBR_MONTH_WEEKDAY_DAY
YEAR_MONTH_WEEKDAY_DAY
YEAR_NUM_MONTH_WEEKDAY_DAY
ABBR_MONTH
MONTH
NUM_MONTH
ABBR_STANDALONE_MONTH
STANDALONE_MONTH
ABBR_MONTH_DAY
MONTH_DAY
NUM_MONTH_DAY
ABBR_MONTH_WEEKDAY_DAY
MONTH_WEEKDAY_DAY
NUM_MONTH_WEEKDAY_DAY
DAY
ABBR_WEEKDAY
WEEKDAY
HOUR
HOUR24
HOUR_MINUTE
HOUR_MINUTE_SECOND
HOUR24_MINUTE
HOUR24_MINUTE_SECOND
HOUR_TZ
HOUR_GENERIC_TZ
HOUR_MINUTE_TZ
HOUR_MINUTE_GENERIC_TZ
MINUTE
MINUTE_SECOND
SECOND
ABBR_UTC_TZ
ABBR_SPECIFIC_TZ
SPECIFIC_TZ
ABBR_GENERIC_TZ
GENERIC_TZ
LOCATION_TZ
Sure, there are quite a few. What is good about them, is that these patterns are actually strings (as in java.lang.String), that is if you use English pattern "MM/d", you'll get locale-specific pattern in return. It might be useful in some corner cases. Usually you would just use DateFormat instance, and won't care about the pattern itself.
Locale-specific pattern vs. localized pattern
The question intention was to get localized, and not the locale-specific pattern. What's the difference?
In theory, toPattern() will give you locale-specific pattern (depending on Locale you used to instantiate (Simple)DateFormat). That is, no matter what target language/country you put, you'll get the pattern composed of symbols like y, M, d, h, H, M, etc.
On the other hand, toLocalizedPattern() should return localized pattern, that is something that is suitable for end users to read and understand. For instance, German middle (default) date pattern would be:
toPattern(): dd.MM.yyyy
toLocalizedPattern(): tt.MM.jjjj (day = Tag, month = Monat, year = Jahr)
The intention of the question was: "how to find the localized pattern that could serve as hint as to what the date/time format is". That is, say we have a date field that user can fill-out using the locale-specific pattern, but I want to display a format hint in the localized form.
Sadly, so far there is no good solution. The ICU I mentioned earlier in this post, partially works. That's because, the data that ICU uses come from CLDR, which is unfortunately partially translated/partially correct. In case of my mother's tongue, at the time of writing, neither patterns, nor their localized forms are correctly translated. And every time I correct them, I got outvoted by other people, who do not necessary live in Poland, nor speak Polish language...
The moral of this story: do not fully rely on CLDR. You still need to have local auditors/linguistic reviewers.

You can use DateTimeFormatterBuilder in Java 8. Following example returns localized date only pattern e.g. "d.M.yyyy".
String datePattern = DateTimeFormatterBuilder.getLocalizedDateTimePattern(
FormatStyle.SHORT, null, IsoChronology.INSTANCE,
Locale.GERMANY); // or whatever Locale

The following code will give you the pattern for the locale:
final String pattern1 = ((SimpleDateFormat) DateFormat.getDateInstance(DateFormat.SHORT, locale)).toPattern();
System.out.println(pattern1);

Java 8 provides some useful features out of the box for working with and formatting/parsing date and time, including handling locales. Here is a brief introduction.
Basic Patterns
In the simplest case to format/parse a date you would use the following code with a String pattern:
DateTimeFormatter.ofPattern("MM/dd/yyyy")
The standard is then to use this with the date object directly for formatting:
return LocalDate.now().format(DateTimeFormatter.ofPattern("MM/dd/yyyy"));
And then using the factory pattern to parse a date:
return LocalDate.parse(dateString, DateTimeFormatter.ofPattern("MM/dd/yyyy"));
The pattern itself has a large number of options that will cover the majority of usecases, a full rundown can be found at the javadoc location here.
Locales
Inclusion of a Locale is fairly simple, for the default locale you have the following options that can then be applied to the format/parse options demonstrated above:
DateTimeFormatter.ofLocalizedDate(dateStyle);
The 'dateStyle' above is a FormatStyle option Enum to represent the full, long, medium and short versions of the localized Date when working with the DateTimeFormatter. Using FormatStyle you also have the following options:
DateTimeFormatter.ofLocalizedTime(timeStyle);
DateTimeFormatter.ofLocalizedDateTime(dateTimeStyle);
DateTimeFormatter.ofLocalizedDateTime(dateTimeStyle, timeStyle);
The last option allows you to specify a different FormatStyle for the date and the time. If you are not working with the default Locale the return of each of the Localized methods can be adjusted using the .withLocale option e.g
DateTimeFormatter.ofLocalizedTime(timeStyle).withLocale(Locale.ENGLISH);
Alternatively the ofPattern has an overloaded version to specify the locale too
DateTimeFormatter.ofPattern("MM/dd/yyyy",Locale.ENGLISH);
I Need More!
DateTimeFormatter will meet the majority of use cases, however it is built on the DateTimeFormatterBuilder which provides a massive range of options to the user of the builder. Use DateTimeFormatter to start with and if you need these extensive formatting features fall back to the builder.

Please find in the below code which accepts the locale instance and returns the locale specific data format/pattern.
public static String getLocaleDatePattern(Locale locale) {
// Validating if Locale instance is null
if (locale == null || locale.getLanguage() == null) {
return "MM/dd/yyyy";
}
// Fetching the locale specific date pattern
String localeDatePattern = ((SimpleDateFormat) DateFormat.getDateInstance(
DateFormat.SHORT, locale)).toPattern();
// Validating if locale type is having language code for Chinese and country
// code for (Hong Kong) with Date Format as - yy'?'M'?'d'?'
if (locale.toString().equalsIgnoreCase("zh_hk")) {
// Expected application Date Format for Chinese (Hong Kong) locale type
return "yyyy'MM'dd";
}
// Replacing all d|m|y OR Gy with dd|MM|yyyy as per the locale date pattern
localeDatePattern = localeDatePattern.replaceAll("d{1,2}", "dd").replaceAll(
"M{1,2}", "MM").replaceAll("y{1,4}|Gy", "yyyy");
// Replacing all blank spaces in the locale date pattern
localeDatePattern = localeDatePattern.replace(" ", "");
// Validating the date pattern length to remove any extract characters
if (localeDatePattern.length() > 10) {
// Keeping the standard length as expected by the application
localeDatePattern = localeDatePattern.substring(0, 10);
}
return localeDatePattern;
}

Since it's just the locale information you're after, I think what you'll have to do is locate the file which the JVM (OpenJDK or Harmony) actually uses as input to the whole Locale thing and figure out how to parse it. Or just use another source on the web (surely there's a list somewhere). That'll save those poor translators.

You can try something like :
LocalDate fromCustomPattern = LocalDate.parse("20.01.2014", DateTimeFormatter.ofPattern("MM/dd/yy"))

Im not sure about what you want, but...
SimpleDateFormat example:
SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yy");
Date date = sdf.parse("12/31/10");
String str = sdf.format(new Date());

Date display in different locales in Java?

In java how do I display dates in different locales (for e.g. Russian).

Something like:
Locale locale = new Locale("ru","RU");
DateFormat full = DateFormat.getDateInstance(DateFormat.LONG, locale);
out.println(full.format(new Date()));
Should do the trick. However, there was a problem of Russian Date formatting in jdk1.5
The deal with Russian language is that month names have different suffix when they are presented stand-alone (i.e. in a list or something) and yet another one when they are part of a formatted date. So, even though March is "Март" in Russian, correctly formatted today's date would be: "7 Марта 2007 г."
Let's see how JDK formats today's date: 7 Март 2007 г. Clearly wrong.

Use SimpleDateFormat constructor which takes locale. You need to first check if JDK supports the locale you are looking for, if not then you need to implement that.

Use the java.text.DateFormat class, you can construct that's configured to a specific Locale.
DateFormat format = DateFormat.getDateInstance(DateFormat.MEDIUM, theLocaleYouWant);
String text = format.format(new Date());
System.out.println(text);

The DateFormat class can help you. As explained in the Javadoc:
To format a date for a different
Locale, specify it in the call to
getDateInstance().
DateFormat df = DateFormat.getDateInstance(DateFormat.LONG, Locale.FRANCE);
So you just need to adapt this code by using the adequate Locale.

Use a java.util.Calendar with an appropriate time zone and locale.