JacksonPolymorphismIssueTests.java

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.Assert;
import org.junit.Test;

import java.io.IOException;
import java.util.Collections;
import java.util.Map;

public class JacksonPolymorphismIssueTests {

    @Test
    public void testUnsuccessfulSerialization() throws IOException
    {
        ObjectMapper mapper = new ObjectMapper();
        Dog dog = new Dog();
        Map<String, Map<String, Object>> incorrectSerialization = mapper.readValue(mapper.writeValueAsString(Collections.singletonMap("value", dog)), Map.class);
        Map<String, Object> unwrappedObject = incorrectSerialization.get("value");
        Assert.assertTrue(unwrappedObject.containsKey("type"));
    }

    @Test
    public void testSuccessfulSerialization() throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        Dog dog = new Dog();
        Map<String, Object> correctSerialization = mapper.readValue(mapper.writeValueAsString(dog), Map.class);
        Assert.assertTrue(correctSerialization.containsKey("type"));

    }

    @JsonTypeInfo(use=JsonTypeInfo.Id.NAME, include=JsonTypeInfo.As.PROPERTY, property="type")
    @JsonSubTypes({
            @JsonSubTypes.Type(value= Dog.class,    name="dog")
    })
    interface IPet
    {
        public Long getId();
        public String getPetMakes();
    }

    class Dog implements IPet
    {
        @Override
        public String getPetMakes()
        {
            return "Wuff!";
        }

        @Override
        public Long getId()
        {
            return 777L;
        }
    }

}