Odtnhj

If I make a POJO class and convert the whole objects to Json using the mapper.writeValueAsString() method, or let Spring handle the conversion, the JavaTimeModule is used appropriately and If my POJO had an OffsetDateTime in it, it will get converted to a string like 2018-10-16T13:49:34.564748+02:00.

For some scenarios, I need to use the mapper's T convertValue(Object fromValue, Class<T> toValueType) method and build an ObjectNode by hand. The method does not convert the OffsetDateTime objects the same way as the writeValueAsString.

I construct my Jackson mapper like this:

ObjectMapper defaultMapperObj = new ObjectMapper();
defaultMapperObj.registerModule(new GuavaModule());
defaultMapperObj.registerModule(new Jdk8Module());
defaultMapperObj.registerModule(new JavaTimeModule());
defaultMapperObj.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

Using the mapper, I can easily convert even Lists to their Json strings:

mapper.convertValue(
 Arrays.asList(1,2,23), JsonNode.class
)

Results in:

ArrayNode: [1,2,23]

But If I call this:

mappper.convertValue(OffsetDateTime.now(), JsonNode.class)

I get a DecimalNode: 1542287917.2141993

From the JavaTimeModule documentation:

Most java.time types are serialized as numbers (integers or decimals as appropriate) if the SerializationFeature.WRITE_DATES_AS_TIMESTAMPS feature is enabled, and otherwise are serialized in standard ISO-8601 string representation. [...]

So, to achieve the desired result, disable the SerializationFeature.WRITE_DATES_AS_TIMESTAMPS feature in your ObjectMapper instance:

mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);