Jackson, serialize one attribute of a reference

Question

When serializing a Java object which has other object references, I need to serialize only one attribute of the nested object(usual case of foreign key, so serialize the \"i

Answer 1

You can implement custom deserializer for this class and use it in User class. Example implementation:

class AddressInformationIdJsonSerializer extends JsonSerializer<AddressInformation> {
    @Override
    public void serialize(AddressInformation value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
        jgen.writeString(value.getId());
    }
}

And configuration in User class:

@JsonProperty(value = "defaultaddress")
@JsonSerialize(using = AddressInformationIdJsonSerializer.class)
public AddressInformation getDefaultAddress() {
    return defaultAddress;
}

### Generic solution for all classes which implement one interface ###
You can create interface which contains String getId() method:

interface Identifiable {
    String getId();
}

Serializer for this interface could look like that:

class IdentifiableJsonSerializer extends JsonSerializer<Identifiable> {
    @Override
    public void serialize(Identifiable value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
        jgen.writeString(value.getId());
    }
}

And now, you can use this serializer for all Identifiable implementations. For example:

@JsonProperty(value = "defaultaddress")
@JsonSerialize(using = IdentifiableJsonSerializer.class)
public AddressInformation getDefaultAddress() {
    return defaultAddress;
}

of course: AddressInformation have to implement this interface:

class AddressInformation implements Identifiable {
    ....
}

Answer 2

Just Found a way using Jackson 2.1+ .

Annotate object references with(this will pick only the id attribute of AddressInformation):

@JsonProperty(value = "defaultaddressid")
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
@JsonIdentityReference(alwaysAsId = true) 
public AddressInformation getDefaultAddress() {
    return defaultAddress;
}

Serialization works very well.