Enforce `@JsonProperty.required` when using builder.

[edinardo]

When using @JsonProperty(required = true) with creator/factory (@JsonCreator annotation), an exception is raised if a required field is missing (as expected).

It is possible to have the same feature when using a builder to deserialize?

Sorry if this request is duplicate or already present, but I couldn't find it at issues list, forum, neither as configuration on the ObjectMapper documentation.

Tested with Jackson version 2.10.2, using the following code:

@JsonDeserialize(builder = Person.Builder.class)
public class Person {
    @JsonProperty(required = true)
    private final String name;
    ...
    public static class Builder {
        public Builder withName(String value) {...}
        public Person build() {...}
  }
}

[cowtowncoder]

There is #230 which could be considered to cover this, but leaving this for builders is ok.
I'll tag this as 3.x since it won't be implemented for 2.x (with 3.x many things will be rewritten opening up new possibilities).

[cowtowncoder]

Actually. Will tag 2.12 to maybe have another look, after 2.11 release.

[cowtowncoder]

Note to self: unfortunately support for builders no easier than that for all POJOs as databind does not have much special handling for builders (they just look like odd POJOs where "Setters" may return this for chaining).

[almson]

Hi, could you clarify your plans on including this feature? I opened a feature request for lombok @Jacksonized to generate @JsonProperty(required=true) (use case is JSON Schema generation) but they retort that it's a liability because Jackson is planning to enable validation of required which will be a backward-incompatible change. Will you really make this breaking change? When? Do you have a mitigation plan?

Also a similar question about defaultValue. (I would like it for documentation of JSON Schema, but the threat that Jackson will start using it creates a dangerous situation.)

[cowtowncoder]

@almson I guess Lombok folks are way more optimistic about this getting implemented then: there is no on-going work to make this happen. But even if there was, I'd probably consider having a MapperFeature (or perhaps DeserializationFeature) to specify whether action was taken, to keep existing default behavior unchanged (that is: to make code fail user would have to enable a feature).

It is in fact quite unlikely that required detection would be implemented for Jackson 2.x, either for regular POJOs or Builder-style approach, at least if it is up to my implementation.

Same goes for "defaultValue": nothing currently exists to use that, except for JSON Schema generation (it was requested for that use case).

Having said all that: just because I do not have time to work on either feature does not mean other members of Jackson community might not be working on it, or decide to try it. 3 out of 5 "most wanted" features for 2.12 came as full "external" contributions (from new contributors, without much discussion before contribution).
So I cannot really predict future in that sense: if someone contributed implementation of either feature, I would work with contributor, trying to balance backwards-compatibility aspects (I would definitely suggest gating these features, opt-in style).