serialize list of dates with Jackson

Question

I'm trying to serialize an Object that contains a List of Dates and i want to serialize to a JSON list of dates (String) in a specific format (yyyy-MM-dd).

private List<Date> executionDates;

will become like:

"executionDates": [
  "2016-07-22",
  "2016-07-23",
  "2016-07-24"
]

It is possible to do it with annotations?

Thanks in advance.

Apeldoorn

What do you mean with annotations? You mean comments? Also, you can't serialise a list, in order to serialise a list, you need to put the data into a hashset, because hashsets are serialisable. – Alnico

Something like this @JsonSerialize(using = JsonDateSerializer.class) on getter of executionDates variable. – Apeldoorn

Answer 1

I found the solution. I had to use property contentUsing instead of using in annotation like this:

@JsonSerialize(contentUsing = JsonDateSerializer.class)

contentUsing property is used for collections. From class documentation:

Serializer class to use for serializing contents (elements of a Collection/array, values of Maps) of annotated property. Can only be used on properties (methods, fields, constructors), and not value classes themselves (as they are typically generic).

Apeldoorn

To everyone watching this: please consider to have consistency between private fields name and getter/setter method: for example if you put an annotation on a private field but its public getter method it's named differently, the final result won't use annotation feature – Josphinejoss

Answer 2

Try something like this:

For serialising:

@Component
public class JsonDateSerializer extends JsonSerializer<Date>
{
    // ISO 8601
    private static final DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");

    @Override
    public void serialize(Date date, JsonGenerator gen, SerializerProvider provider)
            throws IOException, JsonProcessingException
    {
        String formattedDate = dateFormat.format(date);
        gen.writeString(formattedDate);
    }
}

Alnico

I already tried but i get this exception: com.fasterxml.jackson.databind.JsonMappingException: java.util.Arrays$ArrayList cannot be cast to java.util.Date . Is not being applied to each element in List, but to entire collection. – Apeldoorn

Do you have this somewhere in your code? @JsonSerialize(using=JsonDateSerializer.class) EDIT: Have you tried setting the date into a variable type Date, instead of putting the data into an array list? – Alnico

Yes, i have like this: @JsonSerialize(using = JsonDateSerializer.class) public final List<Date> getExecutionDates() { return executionDates; }. With a variable type Date instead of List of Date's, works but i want a list of dates, not just one date... – Apeldoorn

Ok, how about you try and take everything in the list, and iterate through it and for every piece of data, make that data into a Date variable, and then serialise it? – Alnico