Example of polymorphic JSON de/serialization in Jackson (1.5+?)

polyjson_Animal.java

package hiam.polyjson;

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

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type")
@JsonSubTypes({@JsonSubTypes.Type(Dog.class), @JsonSubTypes.Type(Cat.class)})
public abstract class Animal {
}

polyjson_Cat.java

package hiam.polyjson;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonTypeName;

import static java.util.Objects.hash;

@JsonTypeName("cat")
public class Cat extends Animal {

    private final boolean likesCream;
    private final int lives;

    @JsonCreator
    public Cat(@JsonProperty("likesCream") boolean likesCream, @JsonProperty("lives") int lives) {
        this.likesCream = likesCream;
        this.lives = lives;
    }

    public boolean isLikesCream() {
        return likesCream;
    }

    public int getLives() {
        return lives;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Cat)) return false;
        Cat other = (Cat) o;
        return likesCream == other.likesCream && lives == other.lives;
    }

    @Override
    public int hashCode() {
        return hash(likesCream, lives);
    }
}

polyjson_Dog.java

package hiam.polyjson;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonTypeName;

import static java.util.Objects.hash;

@JsonTypeName("dog")
public class Dog extends Animal {

    private final double barkVolumeDecibels;

    @JsonCreator
    public Dog(@JsonProperty("barkVolumeDecibels") double barkVolumeDecibels) {
        this.barkVolumeDecibels = barkVolumeDecibels;
    }

    public double getBarkVolumeDecibels() {
        return barkVolumeDecibels;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Dog)) return false;
        return Double.compare(((Dog) o).barkVolumeDecibels, barkVolumeDecibels) == 0;
    }

    @Override
    public int hashCode() {
        return hash(barkVolumeDecibels);
    }
}

polyjson_PolymorphicJsonTest.java

package hiam.polyjson;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.Test;

import java.io.IOException;

import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.instanceOf;
import static org.junit.Assert.assertThat;

public class PolymorphicJsonTest {

    private static final Animal DOG = new Dog(100);
    private static final String DOG_JSON = "{\"type\":\"dog\",\"barkVolumeDecibels\":100.0}";
    private static final Animal CAT = new Cat(true, 9);
    private static final String CAT_JSON = "{\"type\":\"cat\",\"likesCream\":true,\"lives\":9}";

    private ObjectMapper mapper = new ObjectMapper();

    @Test
    public void givenDog_whenWriteValueAsString_thenProducesExpectedJson() throws JsonProcessingException {
        String json = mapper.writeValueAsString(DOG);
        assertThat(json, equalTo(DOG_JSON));
    }

    @Test
    public void givenCat_whenWriteValue_thenReturnsExpectedJson() throws JsonProcessingException {
        String json = mapper.writeValueAsString(CAT);
        assertThat(json, equalTo(CAT_JSON));
    }

    @Test
    public void givenDogJson_whenReadValue_thenReturnsDog() throws IOException {
        Animal animal = mapper.readValue(DOG_JSON, Animal.class);
        assertThat(animal, instanceOf(Dog.class));
    }

    @Test
    public void givenDogJson_whenReadValue_thenReturnsExpectedDog() throws IOException {
        Animal animal = mapper.readValue(DOG_JSON, Animal.class);
        assertThat(animal, equalTo(DOG));
    }

    @Test
    public void givenCatJson_whenReadValue_thenReturnsCat() throws IOException {
        Animal animal = mapper.readValue(CAT_JSON, Animal.class);
        assertThat(animal, instanceOf(Cat.class));
    }

    @Test
    public void givenCatJson_whenReadValue_thenReturnsExpectedCat() throws IOException {
        Animal animal = mapper.readValue(CAT_JSON, Animal.class);
        assertThat(animal, equalTo(CAT));
    }
}