Pass DeserializationContext to JsonDeserializer.getObjectIdReader

[reda-alaoui]

I want to create a custom deserializer which have the sole purpose of providing a default value via Pageable getNullValue(DeserializationContext ctxt).

PageRequest class implements interface Pageable.

The deserializer:

class PageableDeserializer extends JsonDeserializer<Pageable> {
  @Override
  public Pageable deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
    return p.getCodec().readValue(p, PageRequest.class);
  }

  @Override
  public Pageable getNullValue(DeserializationContext ctxt) throws JsonMappingException {
    return Pageable.unpaged();
  }

 @Override
  public ObjectIdReader getObjectIdReader() {
    return super.getObjectIdReader();
  }
}

The deserializer must be able to keep working with @JsonCreator.
Now correct me if I am wrong but I have no way to retrieve the default ObjectIdReader without having the DeserializationContext in getObjectIdReader?

[cowtowncoder]

Correct, you probably do need DeserializationContext for that.

But I am not 100% sure I follow from custom deserializer to need for access to object id reader?
I don't remember how one is constructed and passed to BeanDeserializer, but similar approach should probably be needed with custom handlers.

[reda-alaoui]

Maybe my conclusion wasn't good.

I was using a mixin for Pageable.

@JsonDeserialize(as = PageRequest.class)
public class PageableMixIn {

}

And another for PageRequest

public class PageRequestMixIn {
  public PageRequestMixIn() {}

  @JsonCreator
  public PageRequestMixIn(
      @JsonProperty("pageNumber") int page,
      @JsonProperty("pageSize") int size,
      @JsonProperty("sort") Sort sort) {}

}

I have this mixin also for PageImpl:

public class PageImplMixIn {

  @JsonUnwrapped @JsonProperty private Pageable pageable;
}

My issue is that when I replace the Pageable mixin with the custom deserializer shown in the first comment, jackson does not deserialize pageable property in PageImpl anymore.

I thought that the issue would come from a missing ObjectIdReader in the deserializer.

[reda-alaoui]

So ObjectIdReader had nothing to do with it.
In fact, I needed to create a delegating deserializer and delegate unwrappingDeserializer method.
Nevertheless, I kept the PR open for master branch.

[cowtowncoder]

Ah ok. Yes, contextualization is... tricky. I wish I could simplify things, but there is a reason why this delegation model is used and I haven't been able to figure out simpler means to separate configuration by class configuration (from class annotations, by-type overrides) and by property overrides.

But I am glad you were able to handle things without change for your current needs.