How to Call Jackson's Default Deserializer from a Custom Deserializer?

Calling the Default Deserializer from a Custom Deserializer in Jackson

Problem:

Creating a custom deserializer in Jackson that allows access to the default deserializer for pre-populating objects before applying custom logic.

Code:

public class UserEventDeserializer extends StdDeserializer<User> {

    public UserEventDeserializer() {
        super(User.class);
    }

    @Override
    public User deserialize(JsonParser jp, DeserializationContext ctxt)
        throws IOException, JsonProcessingException {
        
        // Line causing UnsupportedOperationException:
        User deserializedUser = super.deserialize(jp, ctxt, new User()); 
    }
}

Solution:

Implement a BeanDeserializerModifier to register a custom deserializer for a specific class.

Code:

public class UserEventDeserializer extends StdDeserializer<User> implements ResolvableDeserializer {

    private final JsonDeserializer<?> defaultDeserializer;

    public UserEventDeserializer(JsonDeserializer<?> defaultDeserializer) {
        super(User.class);
        this.defaultDeserializer = defaultDeserializer;
    }

    @Override
    public User deserialize(JsonParser jp, DeserializationContext ctxt)
        throws IOException, JsonProcessingException {
        
        User deserializedUser = (User) defaultDeserializer.deserialize(jp, ctxt);

        // Special logic

        return deserializedUser;
    }

    // Required when modifying BeanDeserializer
    @Override
    public void resolve(DeserializationContext ctxt) throws JsonMappingException {
        ((ResolvableDeserializer) defaultDeserializer).resolve(ctxt);
    }

    public static void main(String[] args) throws Exception {
        SimpleModule module = new SimpleModule();
        module.setDeserializerModifier(new BeanDeserializerModifier() {
            @Override
            public JsonDeserializer<?> modifyDeserializer(DeserializationConfig config, BeanDescription beanDesc, JsonDeserializer<?> deserializer) {
                if (beanDesc.getBeanClass() == User.class)
                    return new UserEventDeserializer(deserializer);
                return deserializer;
            }
        });

        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(module);
        User user = mapper.readValue(new File("test.json"), User.class);
    }
}

The above is the detailed content of How to Call Jackson's Default Deserializer from a Custom Deserializer?. For more information, please follow other related articles on the PHP Chinese website!