Java – Converting ISO 8601-compliant String to java.util.Date

dateiso8601java

I am trying to convert an ISO 8601 formatted String to a java.util.Date.

I found the pattern yyyy-MM-dd'T'HH:mm:ssZ to be ISO8601-compliant if used with a Locale (compare sample).

However, using the java.text.SimpleDateFormat, I cannot convert the correctly formatted String 2010-01-01T12:00:00+01:00. I have to convert it first to 2010-01-01T12:00:00+0100, without the colon.

So, the current solution is

SimpleDateFormat ISO8601DATEFORMAT = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssZ", Locale.GERMANY);
String date = "2010-01-01T12:00:00+01:00".replaceAll("\\+0([0-9]){1}\\:00", "+0$100");
System.out.println(ISO8601DATEFORMAT.parse(date));

which obviously isn't that nice. Am I missing something or is there a better solution?


Answer

Thanks to JuanZe's comment, I found the Joda-Time magic, it is also described here.

So, the solution is

DateTimeFormatter parser2 = ISODateTimeFormat.dateTimeNoMillis();
String jtdate = "2010-01-01T12:00:00+01:00";
System.out.println(parser2.parseDateTime(jtdate));

Or more simply, use the default parser via the constructor:

DateTime dt = new DateTime( "2010-01-01T12:00:00+01:00" ) ;

To me, this is nice.

Best Solution

Unfortunately, the time zone formats available to SimpleDateFormat (Java 6 and earlier) are not ISO 8601 compliant. SimpleDateFormat understands time zone strings like "GMT+01:00" or "+0100", the latter according to RFC # 822.

Even if Java 7 added support for time zone descriptors according to ISO 8601, SimpleDateFormat is still not able to properly parse a complete date string, as it has no support for optional parts.

Reformatting your input string using regexp is certainly one possibility, but the replacement rules are not as simple as in your question:

  • Some time zones are not full hours off UTC, so the string does not necessarily end with ":00".
  • ISO8601 allows only the number of hours to be included in the time zone, so "+01" is equivalent to "+01:00"
  • ISO8601 allows the usage of "Z" to indicate UTC instead of "+00:00".

The easier solution is possibly to use the data type converter in JAXB, since JAXB must be able to parse ISO8601 date string according to the XML Schema specification. javax.xml.bind.DatatypeConverter.parseDateTime("2010-01-01T12:00:00Z") will give you a Calendar object and you can simply use getTime() on it, if you need a Date object.

You could probably use Joda-Time as well, but I don't know why you should bother with that.