Register custom TypeIdResolver on ObjectMapper without using JsonTypeIdResolver annotation

[Paolo Bazzi]

Hi,

I have a question regarding a custom TypeIdResolver. Is there a possibility to register a custom TypeIdResolver class or instance on the used ObjectMapper instance, without having to annotate the serialized beans with @JsonTypeIdResolver annotation?

Background information: We use the serialized beans as interface between multiple systems and do not wan't to have a dependency to jackson-databind on the maven module providing the interface beans. Instead we would prefer to have the dependendy to jackson-databind only within the code, which actually performs the serialization/deserialization.

A rather hacky workaround would be to intercept the AnnotationIntrospector as follow. But a programmatic way to register the custom TypeIdResolver would be preferred.

    ObjectMapper mapper = new ObjectMapper();

    mapper = mapper.setAnnotationIntrospector(new JacksonAnnotationIntrospector() {

      private static final long serialVersionUID = 1L;

      @SuppressWarnings("unchecked")

      @Override

      protected <A extends Annotation> A _findAnnotation(Annotated annotated, Class<A> annoClass) {

        A annotation = super._findAnnotation(annotated, annoClass);

        if (JsonTypeIdResolver.class.equals(annoClass) && annotation == null) {

          return (A) new JsonTypeIdResolver() {

            @Override

            public Class<? extends Annotation> annotationType() {

              return JsonTypeIdResolver.class;

            }

            @Override

            public Class<? extends TypeIdResolver> value() {

              return CustomTypeNameIdResolver.class;

            }

          };

        }

        return annotation;

      }

    });

Regards,

Paolo

[Tatu Saloranta]

Unfortunately handling of TypeIdResolver is quite strongly coupled
with that of `TypeResolverBuilder`, and your best route would probably
be via annotation introspector. Although I actually like your approach
above: did not know it would actually work (I spent some time back in
the day trying to figure out if implementing annotation types via
non-annotation declaration works... didn't think it did).

Anyway, method to override would be

public TypeResolverBuilder<?> findTypeResolver(MapperConfig<?> config,
AnnotatedClass ac, JavaType baseType) { }

and you should be able to just use base implementation, but call
`init(...)` on builder instance if one found, to override default
resolver.

This is not optimal of course.

One more existing facility is method

public ObjectMapper setDefaultTyping(TypeResolverBuilder<?> typer) { ... }

in ObjectMapper. This does let you control all type id aspects,
including type id resolution, but is quite a bit of work.

-+ Tatu +-

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