Using Jackson to convert to and from an object with nested JSON

Question

I have an Entity class below with two String fields: name and description. The description field is to contain a raw JSON value e.g. { "abc": 123 }

@Getter
@Setter
public class Entity {
    private String name;

    @JsonRawValue
    private String descriptionJson; 
}

I've got simple test code below using Jackson to serialize and deserialize:

Entity ent = new Entity();
ent.setName("MyName");
ent.setDescriptionJson("{ \"abc\": 123 }");

// Convert Object to JSON string
String json = mapper.writeValueAsString(ent);

// Convert JSON string back to object
Entity ent2 = mapper.readValue(json, Entity.class);

When converting Object -> JSON the description string is nested because the @JsonRawValue is set:

{"name":"MyName","descriptionJson":{ "abc": 123 }}

However, when I call the Jackson mapper.readValue function to read the JSON string back into an entity object I get the exception:

com.fasterxml.jackson.databind.exc.MismatchedInputException:
Cannot deserialize instance of `java.lang.String` out of START_OBJECT token 
at [Source: (String)"{"name":"MyName","descriptionJson":{ "abc": 123 }}"; line: 1, column: 36] (through reference chain: com.test.Entity["descriptionJson"])

Given that the @JsonRawValue annotation exists, how would you recommend marshalling the created JSON string back into to Entity object? Is there another annotation I'm missing?

Thanks

Answer 1

@JsonRawValue is intended for serialization-side only, but in this problem you can do like this:

@Getter
@Setter
public class Entity {

    private String name;

    @JsonRawValue
    private String descriptionJson;

    @JsonProperty(value = "descriptionJson")
    public void setDescriptionJsonRaw(JsonNode node) {
        this.descriptionJson = node.toString();
    }
}

This problem is repeated with How can I include raw JSON in an object using Jackson?.

Answer 2

For one of my requirements I used field type as Map to store Json as it is. This way I was able to read the nested JSOn as Map and when I serialize object to JSON, it came up correctly. Below is the example.

Entity.java

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import lombok.Data;

import java.util.HashMap;
import java.util.Map;

@Data
@JsonIgnoreProperties(ignoreUnknown = true)
public class Entity {
    public int id=0;
    public String itemName="";
    public Map<String,String> owner=new HashMap<>();
}

Temp.java

import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;

public class Temp {

public static void main(String[] args){

    ObjectMapper objectMapper= new ObjectMapper();
    try {
        Entity entity 
=objectMapper.readValue(Temp.class.getResource("sample.json"), Entity.class);
        System.out.println(entity);
        String json=objectMapper.writeValueAsString(entity);
        System.out.println(json);
    } catch (IOException e) {
        e.printStackTrace();
    }


    }
}

Sample.json

{
  "id": 1,
  "itemName": "theItem",
  "owner": {
    "id": 2,
    "name": "theUser"
  }
}