How to Deserialize Polymorphic JSON with Jackson into Polymorphic Types?

Unable to Deserialize JSON with Jackson into Polymorphic Types

Issue:

Upon attempting to deserialize polymorphic JSON data, an error is encountered at compile time:

The method readValue(JsonParser, Class) in the type ObjectMapper is not applicable for the arguments (ObjectNode, Class<capture#6-of ? extends Animal>)

Triggered by the line:

return mapper.readValue(root, animalClass);

Solution:

To resolve this issue, we can employ annotations to indicate the polymorphic relationship between the base class (Animal) and its subclasses (Dog and Cat). By declaring the @JsonTypeInfo, @JsonSubTypes, and @JsonIgnoreProperties annotations in the Animal class, the ObjectMapper will be informed of the polymorphic nature of your classes.

Annotated Animal Class:

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;

@JsonIgnoreProperties(ignoreUnknown = true)
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY)
@JsonSubTypes({
    @JsonSubTypes.Type(value = Dog.class, name = "Dog"),

    @JsonSubTypes.Type(value = Cat.class, name = "Cat") })
public abstract class Animal {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    
}

Subclass Declarations:

Define the Dog and Cat subclasses as follows:

public class Dog extends Animal {

    private String breed;

    public Dog() {

    }

    public Dog(String name, String breed) {
        setName(name);
        setBreed(breed);
    }

    public String getBreed() {
        return breed;
    }

    public void setBreed(String breed) {
        this.breed = breed;
    }
}

public class Cat extends Animal {

    public String getFavoriteToy() {
        return favoriteToy;
    }

    public Cat() {}

    public Cat(String name, String favoriteToy) {
        setName(name);
        setFavoriteToy(favoriteToy);
    }

    public void setFavoriteToy(String favoriteToy) {
        this.favoriteToy = favoriteToy;
    }

    private String favoriteToy;

}

This updated approach utilizing annotations will enable seamless serialization and deserialization of polymorphic JSON.

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