How to identify different types automatically using Jackson mapper

Question

I have a simple situation. I have a main DTO class with the following fields: AnimalDTO

public class AnimalDTO {
    @JsonCreator
    public AnimalDTODTO(@JsonProperty("error") boolean error,
                                       @JsonProperty("errorMessage") String errorMessage,
                                       @JsonProperty("cat") CatDTO cat,
                                       @JsonProperty("dog") DogDTO dog) {
        this.error = error;
        this.errorMessage = errorMessage;
        this.cat = cat;
        this.dog = dog;
    }

    private boolean error;
    private String errorMessage;
    private CatDTO cat;
    private DogDTO dog;
}

CatDTO:

public class CatDTO {
    @JsonCreator
    public CatDTO(@JsonProperty("catNumber") String catNumber,
                  @JsonProperty("catState") String catState) {
        this.catNumber = catNumber;
        this.catState = catState;
    }

    private String catNumber;
    private String catState;
}

DogDTO:

public class DogDTO {
    @JsonCreator
    public DogDTO(@JsonProperty("dogNumber") String dogNumber,
                  @JsonProperty("dogState") String dogState
                  @JsonProperty("dogColor") String dogColor
                  @JsonProperty("dogBalance") BigDecimal dogBalance) {
        this.dogNumber = dogNumber;
        this.dogState = dogState;
        this.dogColor = dogColor;
        this.dogBalance = dogBalance;
    }

    private String dogNumber;
    private String dogState;
    private String dogColor;
    private BigDecimal dogBalance;

}

and from external API I have responses (and I can't change it) for dog like:

{
   "dogNumber": "23",
   "dogState": "good",
   "dogColor": "pink",
   "dogBalance": 5
}

and for Cat:

{
   "catNumber": "1",
   "catState": "good"
}

And I want to use Jackson mapper like this: objectMapper.readValue(stringJson, AnimalDTO.class);

I was thinking to add in AnimalDTO:

@JsonTypeInfo(
  use = JsonTypeInfo.Id.NAME, 
  include = JsonTypeInfo.As.PROPERTY, 
  property = "type")
@JsonSubTypes({ 
  @Type(value = CatDTO.class, name = "cat"), 
  @Type(value = DogDTO.class, name = "dog") 
})

but it's not working.

How to handle my case in best way?

You showed us the cat json and the dog json...do you have a an animal json? Or are these 2 JSONS completely independent?? — JCompetence, Nov 25 '21 at 08:14
@SMA - No, I dont have an animal json...these 2 JSONS completely independent — FPerez, Nov 25 '21 at 08:22
then if I am not mistaken, you need to create a DTO for each and you can't use `JsonTypeInfo`. Based on my understand `JsonTypeInfo` and `JsonSubTypes` are used when you have inheritance in your JSONs. In your case each JSON has completely different variables.... — JCompetence, Nov 25 '21 at 08:26
Since two classes are independent (no inheritance hierachy) you don't need `@JsonTypeInfo` nor `@JsonSubTypes`. You can directly serialize/deserialize **animal json** to `AnimalDTO` which will have `CatDTO` and `DogDTO` respectively. — Ruwanka De Silva, Nov 25 '21 at 10:23

score 0 · Accepted Answer · answered Nov 25 '21 at 17:09

Your code will work just fine (without any @JsonTypeInfo or @JsonSubTypes annotations) if the JSON that you get from the external API is as follows:

{
  "dog": {
    "dogNumber": "23",
    "dogState": "good",
    "dogColor": "pink",
    "dogBalance": 5
  },
  "cat": {
    "catNumber": "1",
    "catState": "good"
  }
}

If this does not look similar to the JSON you receive then you need to add it to your answer so that we can help you further.

How to identify different types automatically using Jackson mapper

1 Answers1