Default Date encoder doesn't preserve milliseconds

[BrunoBonacci]

Hi,

I've noticed that the default encoder for dates doesn't preserve the milliseconds precision

  ;; milliseconds are truncated
  (json/write-value-as-string {:date (java.util.Date.)})
  ;;=> "{\"date\":\"2021-01-12T10:19:44Z\"}"

  (json/write-value-as-string {:date (java.util.Date.)}
    (json/object-mapper {:date-format "yyyy-MM-dd'T'HH:mm:ss.SSSX"}))
  ;;=> "{\"date\":\"2021-01-12T10:19:44.596Z\"}"

Is this a deliberate decision? wouldn't be better for the default encoder to preserve data as much as possible rather than truncating it?

[ikitommi]

Can't recall why, but some questions:

• what does Jackson do to dates by default?
• --"-- with java.time things?
• what happens with js?
• what do the standards say about this?

[BrunoBonacci]

The standard ISO 8601 (https://en.wikipedia.org/wiki/ISO_8601) doesn't define a precise format, hence the trouble.
It defines guidelines and a bunch of possibilities and then it is up to the implementor parties to pick and choose.
It doesn't even decide the decimal marker.

According to DZone Jackson default behaviour is to serialize dates as millisecond from epoch.

Interesting, java.time.Instant renders with 6 decimals (microseconds)

  (json/write-value-as-string {:date (java.time.Instant/now)})
  ;;=> "{\"date\":\"2021-01-12T14:53:15.658653Z\"}"

I have no idea what JS default behaviour is.