Jackson: Object Mapper annotations to deserialize a inner collection

Question

I want to convert the following json into a java object, using as much as possible annotations.

{"user":{
  "id":1,
  "diets":[
    {"diet":{
      "name":"...",
      "meals":[]
      }
    }
  ]
 }
}

I'm getting trouble with the collection diets. I tried to use @JsonProperty but it doesn't work properly. Is there a special annotation for map inner aggregates?

Diet.java

    @JsonRootName(value = "diet")
    public class Diet {

        @JsonProperty(value="name")
        private String name;
        @JsonProperty(value="meals")
        private List<Meal> meals;
        private User user;

        // Rest of the class omitted.
}

User.java

@JsonRootName(value = "user")
public class User {

    @JsonProperty("id")
    private long id;
    @JsonProperty("diets")
    private List<Diet> diets = new ArrayList<Diet>();

    // Rest of the class omitted.
}

Thanks!

Answer 1

The diets object in your json is not a List. Its a List of key-value pair with key "diet" and value a diet object. So you have three options here.

One is to create a wrapper object say DietWrapper and use List of diet wrapper in User like

@JsonRootName(value = "user")
class User {

    @JsonProperty(value = "id")
    private long id;
    @JsonProperty(value = "diets")
    private List<DietWrapper> diets;

    //Getter & Setters
}

class DietWrapper {
    @JsonProperty(value = "diet")
    Diet diet;
}

Second option is to keep diest as simple list of maps like List>

@JsonRootName(value = "user")
class User {

    @JsonProperty(value = "id")
    private long id;
    @JsonProperty(value = "diets")
    private List<Map<String, Diet>> diets;

    //Getter & Setters
}

Third option is to use a custom deserializer which would ignore your diet class.

@JsonRootName(value = "user")
class User {

    @JsonProperty(value = "id")
    private long id;
    @JsonProperty(value = "diets")
    @JsonDeserialize(using = DietDeserializer.class)
    private List<Diet> diets;

    //Getter & Setters
}

class DietDeserializer extends JsonDeserializer<List<Diet>> {

    @Override
    public List<Diet> deserialize(JsonParser jsonParser, 
            DeserializationContext deserializationContext) throws IOException {

        ObjectMapper mapper = new ObjectMapper();
        JsonNode node = mapper.readTree(jsonParser);
        List<Diet> diets = mapper.convertValue(node.findValues("diet"), new TypeReference<List<Diet>>() {});
        return diets;
    }
}