Jackson: how to include null value property in JSON serialization

Question

I'm trying to generate a JSON response using my own Java entity classes together with Jackson annotations. Two key values must be null in my JSON response but if I set them to null they disappear from JSON. I'm limited to Jackson version 1.9.13 unfortunately.

I already tried set values to null, using

@JsonSerialize(include = JsonSerialize.Inclusion.ALWAYS)

My response entity:

public class Response {

@JsonProperty("data")
private Data data;

@JsonProperty("error")
private Error error;

public Data getData() {
    return data;
}

public void setData(PgSoftAuthData data) {
    this.data = data;
}

public Error getError() {
    return error;
}

public void setError(PgSoftError error) {
    this.error = error;
}
}

I'm trying to generate response like this:

Data data = new Data();
data.setName("Name");
data.setTime(null); // This key dissappear from JSON

Response responseSuccess = Response();
responseSuccess.setData(data);
responseSuccess.setError(null); // Error object disappear from JSON

I would like to get following response:

{
    "data" : {
        "name" : "Name",
        "time" : null
    },
    "error" : null
}

Solution 1

Add JsonInclude to relevant classes Response and Data

(updated using @ThomasFritsch comment)

@JsonInclude(JsonInclude.Include.ALWAYS)

Value that indicates that property is to be always included, independent of value of the property.

Solution 2

Thank you for your answers! As I mentioned I'm limited to Jackson 1.9.13 and I tried multiple combinations with following Jackson annotation but unsuccessfully:

@JsonSerialize(include = JsonSerialize.Inclusion.ALWAYS)

Then I used following:

@XmlElement(nillable = true)

annotation on error and name attributes and it works. Now I get proper JSON response.

Error attribute solution:

@XmlElement(nillable = true)
@JsonProperty("error")
private Error error;

Comments

[Thomas Fritsch]

and add it also to Data class

[pbjerry10]

I can use only @JsonSerialize(include = JsonSerialize.Inclusion.ALWAYS) and it doesn't work.

[softwarevamp]

How can i do the same to a HashMap?

[Radhesh Khanna]

Somehow not working in Jackson version 2.11.0 as well