How can I prevent Jackson from serializing a polymorphic type's annotation property?

Question

I have polymorphic types and deserializing from JSON to POJO works. I followed the documentation here, in fact. When serializing POJOs into JSON I'm getting an unwanted attribute, specifically the logical type name.

import static org.codehaus.jackson.annotate.JsonTypeInfo.*;

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

public class Dog extends Animal { ... }
public class Cat extends Animal { ... }

When Jackson serializes into JSON it provides the type information which I don't want to expose.

{"type":"dog", ... }
{"type":"cat", ... }

Can I prevent this somehow? I only want to ignore type when deserializing.

Answer 1

A simple solution would be to just move the @JsonTypeInfo and @JsonSubTypes configs to a MixIn, and then only register the MixIn for deserialization.

mapper.getDeserializationConfig().addMixInAnnotations(MyClass.class, MyMixIn.class)

Answer 2

This took me a long time to solve so I thought I'd share.

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY,
visible = false, property = "type")

visible=false ensures that if the property type exists on the class, it will not be populated with the value of type during deserialization.

include = JsonTypeInfo.As.EXISTING_PROPERTY dictates that if the property type exists, use that value during serialization otherwise do nothing.

So putting it all together:

import static org.codehaus.jackson.annotate.JsonTypeInfo.*;

@JsonTypeInfo(use = Id.NAME, include = As.EXISTING_PROPERTY, visible = false, property = "type")
@JsonSubTypes({
    @JsonSubTypes.Type(value=Dog.class, name="dog"),
    @JsonSubTypes.Type(value=Cat.class, name="cat")
})    
public class Animal { ... }

public class Dog extends Animal { ... }
public class Cat extends Animal { ... }