Jackson Java 8 DateTime serialisation

Question

Jackson operates java.time.Instant with WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS (READ_ as well) enabled by default. jackson-datatype-jsr310

It produces JSON like this

{ "createDate":1421261297.356000000, "modifyDate":1421261297.356000000 }

In JavaScript it's much easier to get Date from traditional millis timestamp (not from seconds/nanos as above), like new Date(1421261297356).

I think there should be some reason to have the nanos approach by default, so what is that reason?

The reason is probably that Jackson tries not to lose the precision the Instant has. The receiver might not be JavaScript. — JB Nizet, Jan 14 '15 at 22:05
Yes, most likely you right. But nonos are really zeros here. Perhaps this is more to Java 8 java.time. — Andrii Karaivanskyi, Jan 15 '15 at 19:40

score 5 · Answer 1 · edited May 23 '17 at 12:25

One way is to create your own Jackson module and do the serialization you way need.

You can even do a simple Jackson8Module which extends the Jackson SimpleModule and provides some lambda friendly methods.

ObjectMapper jacksonMapper = new ObjectMapper();
Jackson8Module module = new Jackson8Module();
module.addStringSerializer(LocalDate.class, (val) -> val.toString());
module.addStringSerializer(LocalDateTime.class, (val) -> val.toString());
jacksonMapper.registerModule(module);

Here is the code for the Jackson8Module:

Is there a way to use Java 8 lambda style to add custom Jackson serializer?

score 5 · Answer 2 · answered Sep 05 '16 at 16:16

I have found this weird to, since using JSR310Module classes like Calendar or Date are still serialized in milliseconds. It's not logical.

In the JSR310Module documentation (https://github.com/FasterXML/jackson-datatype-jsr310) they have a referenced this:

For serialization, timestamps are written as fractional numbers (decimals), where the number is seconds and the decimal is fractional seconds, if WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS is enabled (it is by default), with resolution as fine as nanoseconds depending on the underlying JDK implementation. If WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS is disabled, timestamps are written as a whole number of milliseconds.

So, a simple solution for what you want to achieve it's configure your mapper like they say:

  mapper.configure( SerializationFeature.WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS, false );
  mapper.configure( SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, true );

`WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS` is really confusing name because what it really does: it writes timestamps as SECONDS (not NANOSECONDS) with fractional part. And that fractional part contains up to 6 digits after dot, so it can be interpreted as NANOSECONDS part, but the whole value is still in seconds. — Ruslan Stelmachenko, Dec 15 '18 at 09:41
mapper.configure() - where should this be done? Do you know how to do this in XML? — veritas, Jan 10 '21 at 16:53

Jackson Java 8 DateTime serialisation

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