Jackson: is it possible to include property of parent object into nested object?

Question

I'm using Jackson to serialize/deserialize JSON objects.

I have the following JSON for a Study object:

{
    "studyId": 324,
    "patientId": 12,
    "patient": {
        "name": "John",
        "lastName": "Doe"
    }
}

UPDATE: Unfortunately the JSON structure cannot be modified. It's part of the problem.

I would like to deserialize the object to the following classes:

public class Study {
    Integer studyId;
    Patient patient;
}

and

public class Patient {
    Integer patientId;
    String name;
    String lastName;
}

Is it possible to include the patientId property in the Patient object?

I am able to deserialize the patient object into the Patient class (with the corresponding name and lastName properties), but unable to include the patientId property.

Any ideas?

Answer 1

You can use a custom deserializer for your use case. Here is what it will look like:

import java.io.IOException;

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonNode;

public class StudyDeserializer extends JsonDeserializer<Study>
{
    @Override
    public Study deserialize(JsonParser parser, DeserializationContext context)
        throws IOException, JsonProcessingException
    {
        JsonNode studyNode = parser.readValueAsTree();

        Study study = new Study();
        study.setStudyId(studyNode.get("studyId").asInt());

        Patient patient = new Patient();
        JsonNode patientNode = studyNode.get("patient");
        patient.setPatientId(studyNode.get("patientId").asInt());
        patient.setName(patientNode.get("name").asText());
        patient.setLastName(patientNode.get("lastName").asText());
        study.setPatient(patient);

        return study;
    }
}

Specify the above class as your deserializer in the Study class:

import com.fasterxml.jackson.databind.annotation.JsonDeserialize;

@JsonDeserialize(using = StudyDeserializer.class)
public class Study
{
    Integer studyId;
    Patient patient;

    // Getters and setters
}

Now, the JSON input you have specified should get deserialized as expected.

Answer 2

There is no declarative way to do such object transformation: you are transforming structure between JSON and POJOs. Jackson's support in this area is limited by design: two things are out of scope: validation (use external validation; Bean Validation API or JSON Schema validator) and transformations (can use JsonNode or external libraries).