Is BeanDeserializerModifier expected to work for immutable Beans?

[herkrath]

Hi @cowtowncoder, all,

Is BeanDeserializerModifier expected to work for immutable Beans? It is not documented otherwise and the BeanDeserializerModifier methods are triggered, so I would assume yes. It doesn't work though. I tested with a mutable (working) and immutable (not working) version of the same Bean with Jackson 2.14 and 2.16.1.

This is not a recently introduced bug, there are multiple older discussions about this topic, e.g. https://stackoverflow.com/questions/54086246/jacksons-beandeserializermodifier-does-not-work-with-final-fields

The suggested solution in there is not always applicable but the reference to BeanDeserializerBase::resolve seems correct. It appears to me that creator properties aren't correctly set based on BeanDeserializerModifier modifications.

I am mainly looking for a confirmation.

Thanks in advance,
Mark

[cowtowncoder]

@herkrath At high level, there is nothing specific wrt mutable/immutable beans wrt BeanDeserializerModifier, as it only operates on definition of POJO, before/during construction of JsonDeserializer. So it should be fully usable in that sense.

If there are problems in actually using it, those may be flaws or limitations, but there is no intent to prevent its use. There are some known problems specifically related to Creator properties of "implicit" Creators (ones that are not annotated with @JsonCreator), in which annotations are not properly merge across Creator and other properties. So this could be what is happening. But that is sort of outside control of BeanDeserializerModifier.

There are plans to try to tackle this problem wrt (some) Creator properties: as a pre-cursor, I am working on #3719 . But full introspection rewrite has been postponed multiple times as it is likely tricky to do. Even if conceptually simple: introspection should start with location Creators, then proceed with other properties.
But existing processing is complicated so it is not necessarily trivial to change this.

[herkrath]

I have written a unit test which is showing the issue. While doing so, I realized that I should make one point more clear: BeanDeserializerModifier seems to work with immutable beans in general (i.e. modify*Deserializer methods). What does not work is custom updateBuilder and possibly updateProperties logic for the properties being using inside the bean.

I will try to fix this next.

[cowtowncoder]

Right, it is possible some aspects won't work well.

[herkrath]

Hi @cowtowncoder, I have created the issue #4356 and the PR #4357 for the point about the serializer. Sorry if I spam your repo, I am not used to GitHub. Should I have simply created the PR without an issue?

I also created failing UTs about another related issue: Changing the property order via BeanDeserializerModifier::updateProperties doesn't seem to work at all, not for mutable, nor for immutable beans. How to pass them best (here, via issue with GitHub link, via PR)?

[cowtowncoder]

No, creating an Issue and PR is pretty standard (although sometimes just PR is fine too; both are fine).

Failing test (under src/test/java/.../failing) would be a good PR to show the problem.
Although I am surprised as I think updateProperties() is definitely used somewhere. But maybe test can show what is going on.

[herkrath]

Alright, BeanDeserializerModifier::updateProperties issue is #4358 and PR #4359 (failing UTs only).