Question

I have a structure of objects representing a Questionnaire and I need to serialize to JSON.
One class of the structure is a OpenQuestion and this class use generics with two parameters.
The problem starts when one of types used was Date, the date is serialized wrong, like a long.

Class code:

public class OpenQuestion <valueType,validationType> extends AbstractQuestion implements    Serializable {
    private valueType value;
    private validationType minValue;
    private validationType maxValue;
    ...
}

I saw how to serialize a date in a hash map if the hash map always uses a Date, but in this case I use the class with String, Integer or Date.

Any idea to solve it?
Thanks

Answer 1

As pointed out by @MiserableVariable, Jackson serializes (most) date fields as (numeric long) timestamps by default. You can override this behavior in a number of ways.

If using your own instance of ObjectMapper, override a property to write dates as ISO-8601:

objectMapper.configure(SerializationConfig.Feature.WRITE_DATES_AS_TIMESTAMPS, false);

If using your own instance of ObjectMapper, to have dates written in your own custom format:

objectMapper.setDateFormat(myDateFormat); // 1.8 and above
objectMapper.getSerializationConfig().setDateFormat(myDateFormat); // for earlier versions (deprecated for 1.8+)

To leave the default serialization behavior for most fields, but override it for certain fields on certain objects, use a custom serializer:

public class MyBean implements Serializable {
    private Date postDate;

    // ... constructors, etc

    @JsonSerialize(using = MyCustomDateSerializer.class)
    public Date getPostDate() {
        return postDate;
    }
}

public class MyCustomDateSerializer extends JsonSerializer<Date> {

    @Override
    public void serialize(final Date date, final JsonGeneraror generator,
          final SerializerProvider provider) throws IOException,
          JSONProcessingException {

        generator.writeString(yourRepresentationHere);
    }
}

All of this information is available in the Jackson Documentation, with the bulk of it in the section dealing with date handling.