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Java - How to format and parse dates

16 Oct 2015

Hi guys here comes a very quick and usefull guide of how to parse and format Dates in Java, I hope it helps.

Using the java.text.DateFormat and java.text.SimpleDateFormat

Formatting - from date to string

The simplest way to format a Date in java is to use the java.text.DateFormat, it is an abstract class so we have to use an implementation of it. You can call DateFormat.getInstance methods to get a concrete class and start working.

DateFormat df = DateFormat.getInstance();
System.out.println(df.format(new Date()));

// Output: 10/16/15 3:15 PM
DateFormat df = DateFormat.getTimeInstance();
System.out.println(df.format(new Date()));
// Output: 3:15:03 PM
DateFormat df = DateFormat.getDateInstance();
System.out.println(df.format(new Date()));

// Output: Oct 16, 2015
DateFormat df = DateFormat.getDateTimeInstance();
System.out.println(df.format(new Date()));

// Output: Oct 16, 2015 3:15:03 PM

It works but it is not so usefull, most part of time we want to format a Date using some custom pattern like day month year. We can use java.text.SimpleDateFormat to customize our date pattern:

DateFormat df = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss.SSS");
System.out.println(df.format(date));

// Output: 16/10/2015 15:03:17.396

We can also show week days and month names just changing the pattern:

DateFormat df = new SimpleDateFormat("EEEE dd MMMM yyyy");
System.out.println(df.format(date));
System.out.println(Locale.getDefault());
// Output: Friday 16 October 2015
// Output: en_US

And finally we can change the default locale in order to change the month and week day name, java.util.Locale represents the Locale which will be considered.

Locale.setDefault(Locale.FRENCH);

Now we can show in French

DateFormat df = new SimpleDateFormat("EEEE dd MMMM yyyy");
System.out.println(df.format(date));
System.out.println(Locale.getDefault());

// Output: vendredi 16 octobre 2015
// Output: fr

Parsing - from string to date

To parse a Date to String we use the same Class DateFormat but now calling the parse method, if the String does not match with the pattern a java.text.ParseException will be thrown.

DateFormat df = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss.SSS");
Date date = df.parse("16/10/2015 15:25:07.861");
DateFormat df = new SimpleDateFormat("EEEE dd MMMM yyyy");
Date date = df.parse("Friday 16 October 2015");

Same thing using Locales

Locale.setDefault(Locale.FRENCH);

DateFormat df = new SimpleDateFormat("EEEE dd MMMM yyyy");
Date date = df.parse("jeudi 15 octobre 2015");

With Java 8 - java.time.format.DateTimeFormatter

Java 8 brings a new API to deal with Date and Time, java.time.* fixes some problems related with TimeZones and adds some facilities while using date and time manipulations (adding or substracting days hours minutes).

We can create a java.time.format.DateTimeFormatter using the ofPattern passing the same pattern used by SimpleDateFormat or using any constant of DateTimeFormatter examples (BASIC_ISO_DATE, ISO_LOCAL_DATE, ISO_ZONED_DATE_TIME). See java/time/format/DateTimeFormatter.html for more informations.

Formatting - from date to string

To format a date using this API is very simple, create a java.time.format.DateTimeFormatter and pass to format method of a java.time.LocalDateTime, java.time.ZonedDateTime, java.time.LocalDate or java.time.LocalTime

LocalDateTime now = LocalDateTime.now();
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm:ss.SSS");
System.out.println(now.format(formatter));

// Output: 16/10/2015 16:34:23.532

Beware when working with java.time.LocalDate if you try to format using a pattern that requires any time field it will throw an exception

LocalDate now = LocalDate.now();
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm:ss.SSS");
System.out.println(now.format(formatter));

// Output: Exception in thread "main" java.time.temporal.UnsupportedTemporalTypeException: Unsupported field: HourOfDay

Same using java.time.LocalTime

LocalTime now = LocalTime.now();
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm:ss.SSS");
System.out.println(now.format(formatter));

// Output: Exception in thread "main" java.time.temporal.UnsupportedTemporalTypeException: Unsupported field: DayOfMonth

Parsing - from string to date

To parse we use the same java.time.format.DateTimeFormatter calling its parse method. Parse returns a java.time.temporal.TemporalAccessor so you can create a LocalDateTime using it.

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm:ss.SSS");
TemporalAccessor temporalAccessor = formatter.parse("21/10/2015 11:37:09.702");
LocalDateTime localDateTime = LocalDateTime.from(temporalAccessor);

References