Java DateTimeFormatter for time zone with an optional colon separator?

Question

I'm trying to build a DateTimeFormatter that can accepts offset with colon or offset without colon.

Is there a way to pass this test :

DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss[X]");
dateTimeFormatter.parse("2015-01-28T10:21:44+0100"); // OK
dateTimeFormatter.parse("2015-01-28T10:21:44+01:00"); // KO

Answer 1

This: yyyy-MM-dd'T'HH:mm:ss[XXX][X] seems to work.

DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss[XXX][X]"); dateTimeFormatter.parse("2015-01-28T10:21:44+0100"); dateTimeFormatter.parse("2015-01-28T10:21:44+01:00"); 

Answer 2

Here is the ultimate pattern matching for pretty everything looking like an ISO string date !

"[yyyyMMdd][yyyy-MM-dd][yyyy-DDD]['T'[HHmmss][HHmm][HH:mm:ss][HH:mm][.SSSSSSSSS][.SSSSSS][.SSS][.SS][.S]][OOOO][O][z][XXXXX][XXXX]['['VV']']" 

It works for the following list of tests except for the two in comments but I still don't know why...

    ZonedDateTime dt = DateTimeUtils.parse("2016-10-27T16:36:08.993+02:00:00[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993+02:00[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993+020000[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993+0200[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993+0000[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993Z[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993GMT+1[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993UTC[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993PST[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993[Europe/Paris]");      dt = DateTimeUtils.parse("2016-10-27T16:36:08+02:00[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08+020000[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08+0200[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08+0000[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08Z[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08GMT+1[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08UTC[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08PST[Europe/Paris]");     dt = DateTimeUtils.parse("2016-10-27T16:36:08[Europe/Paris]");      dt = DateTimeUtils.parse("2016-10-27T16:36:08.993+02:00:00");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993+02:00");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993+020000");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993+0200");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993+0000");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993Z");     //dt = DateTimeUtils.parse("2016-10-27T16:36:08.993GMT+1");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993UTC");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.993PST");      dt = DateTimeUtils.parse("2016-10-27T16:36:08.993");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.000993");     dt = DateTimeUtils.parse("2016-10-27T16:36:08.000000993");      dt = DateTimeUtils.parse("2016-10-27T16:36:08+02:00:00");     dt = DateTimeUtils.parse("2016-10-27T16:36:08+02:00");     dt = DateTimeUtils.parse("2016-10-27T16:36:08+020000");     dt = DateTimeUtils.parse("2016-10-27T16:36:08+0200");     dt = DateTimeUtils.parse("2016-10-27T16:36:08+0000");     dt = DateTimeUtils.parse("2016-10-27T16:36:08Z");     //dt = DateTimeUtils.parse("2016-10-27T16:36:08GMT+1");     dt = DateTimeUtils.parse("2016-10-27T16:36:08UTC");     dt = DateTimeUtils.parse("2016-10-27T16:36:08PST");     dt = DateTimeUtils.parse("2016-10-27T16:36:08");      dt = DateTimeUtils.parse("2016-100T16:36:08Z");     dt = DateTimeUtils.parse("2016-100T16:36.1Z");     dt = DateTimeUtils.parse("2016-10-27");      dt = DateTimeUtils.parse("20161223T163608");     dt = DateTimeUtils.parse("20161223T1636"); 

And the parse method itself :

public static ZonedDateTime parse(CharSequence text) {     TemporalAccessor temporalAccessor = LOOSE_ISO_DATE_TIME_ZONE_PARSER.parseBest(text, ZonedDateTime::from, LocalDateTime::from, LocalDate::from);     if (temporalAccessor instanceof ZonedDateTime) {         return ((ZonedDateTime) temporalAccessor);     }     if (temporalAccessor instanceof LocalDateTime) {         return ((LocalDateTime) temporalAccessor).atZone(ZoneId.systemDefault());     }     return ((LocalDate) temporalAccessor).atStartOfDay(ZoneId.systemDefault()); }