How to Leverage Jackson's Default Deserializer within a Custom Deserializer?

How to Call Default Deserializer from a Custom Deserializer in Jackson

When customizing deserialization in Jackson, you may encounter the need to access the default deserializer to populate your object. This can be achieved by employing a BeanDeserializerModifier and registering it via a SimpleModule.

Here's an example implementation:

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;
  }

  @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);
  }
}

By registering this modifier, you can access the default deserializer and pre-populate your object within your custom deserializer without causing an exception.

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