Custom DateTime/Date Pattern uses 'Year of Era' instead of 'Year', which is not (strictly) ISO 8601 compliant

[timvahlbrock]

The default for dateTimePattern is yyyy-MM-dd'T'HH:mm:ss.SSSXXX, which seems to be ISO 8601 compliant, but actually isn't because y means "year of era", not "year". This means that when parsing strictly the year would need additional indication whether the year is before or after christ - which is not ISO compliant. Actually ISO compliant would be uuuu-MM-dd'T'HH:mm:ss.SSSXXX. With the current pattern parsing fails in strict mode.

[joelittlejohn]

Wow, interesting one. My guess is that updating this pattern to uuuu would have no affect on the vast majority of users.

Out of interest, do you have an example where these two patterns result in a differently formatted date?

[joelittlejohn]

For info here:

When using yyyy, the year 11 AD is formatted identically to year 10 BC. They both show as 0011.

When using uuuu, these years are formatted as 0011 and -0010 respectively.

Note, be careful as SimpleDateFormat uses u as day of week. DateTimeFormatter can interpret uuuu correctly.

[timvahlbrock]

By the way: Parsing into PoJos generated by this lib might also be a little faster if the pattern wouldn't be written despite no custom date time pattern being configured. If pattern is set, jackson creates a custom DateTimeFormatter instead of using the default ISO Timestamp parser. Don't know though if this is a new parser each time even for identical patterns, as Jackson seems to be caching objects like these in a lot of similar places.