How do I call the default deserializer from a custom deserializer in Jackson

Question

I have a problem in my custom deserializer in Jackson. I want to access the default serializer to populate the object I am deserializing into. After the population I will do

Answer 1

You are bound to fail if you try to create your custom deserializer from scratch.

Instead, you need to get hold of the (fully configured) default deserializer instance through a custom BeanDeserializerModifier, and then pass this instance to your custom deserializer class:

public ObjectMapper getMapperWithCustomDeserializer() {
    ObjectMapper objectMapper = new ObjectMapper();

    SimpleModule module = new SimpleModule();
    module.setDeserializerModifier(new BeanDeserializerModifier() {
        @Override
        public JsonDeserializer modifyDeserializer(DeserializationConfig config,
                    BeanDescription beanDesc, JsonDeserializer defaultDeserializer) 
            if (beanDesc.getBeanClass() == User.class) {
                return new UserEventDeserializer(defaultDeserializer);
            } else {
                return defaultDeserializer;
            }
        }
    });
    objectMapper.registerModule(module);

    return objectMapper;
}

Note: This module registration replaces the @JsonDeserialize annotation, i.e. the User class or User fields should no longer be annotated with this annotation.

The custom deserializer should then be based on a DelegatingDeserializer so that all methods delegate, unless you provide an explicit implementation:

public class UserEventDeserializer extends DelegatingDeserializer {

    public UserEventDeserializer(JsonDeserializer delegate) {
        super(delegate);
    }

    @Override
    protected JsonDeserializer newDelegatingInstance(JsonDeserializer newDelegate) {
        return new UserEventDeserializer(newDelegate);
    }

    @Override
    public User deserialize(JsonParser p, DeserializationContext ctxt)
            throws IOException {
        User result = (User) super.deserialize(p, ctxt);

        // add special logic here

        return result;
    }
}