Support for canonical JSON output in Jackson.

[digulla]

Support for canonical JSON output in Jackson.

I kept all classes in the tests folder since there will be many more changes and it's easier when everything is in a single place.

[cowtowncoder]

Ok cool! Couple of notes/suggestions:

First, master is for Jackson 3.0; we probably would want this for 2.x, so maybe developing against 2.16 would make sense.

Second: it might be possible to package this as Module (3.x JacksonModule); modules can register serializers, change various Features? Registering something like CanonicalJSONModule would be nice way to add on this functionality.
I guess there are parts that wouldn't work (override/delegation for number writing), but maybe majority.

Also: while SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS works for Maps (and different MapperFeature for POJO properties), there'd also be need for a JsonNodeFeature for sorting properties of ObjectNodes on output -- that would be useful in general; I'll file an issue for that.

[digulla]

Okay. I'll rebase the code to 2.16 and try to move every config that I can to a new CanonicalJSONModule so we can see what's left.

[cowtowncoder]

Thank you @digulla ! I am starting to think this would be a great addition to 2.16 if we can figure out how to package things.

Sounds like there are at least these things to tackle:

1. Sorting of Object properties alphabetically (although not 100% sure what specific sorting semantics needed; is configurability needed)
2. Pretty-printing using settings slightly different than Jackson default one (but achievable with what PrettyPrinter allows)
3. Limiting format of BigDecimal serialization (and maybe magnitude/scale?)

of which first 2 seem easier to achieve.

[JooHyukKim]

Is there an existing reference to this implementation or newly created? I think we can use some methods within BigDecimal itself, or JDK methods like java.text.DecimalFormat to simplify the conversion.

[digulla]

I created this from scratch since I couldn't find anything suitable on the classpath.

The toString() methods in BigDecimal itself don't work (they either don't print an exponent or print only some numbers with exponent) and DecimalFormat has weird quirks (like being not thread safe which might or might not cause problems). There are other implementations of DecimalFormat in some Apache commons library but I didn't want to add new dependencies.

This class only exists because https://gibson042.github.io/canonicaljson-spec/ requires it. Personally, I would always print the number in a readable form without exponent OR as an integer with a negative exponent (so it can always be parsed without any rounding errors).

I would be grateful for advice how to proceed here.

[JooHyukKim]

True, this whole class seems like it could be all done with a (for example) Builder.
Improvement idea, @cowtowncoder ?

[digulla]

Actually, I would add a new option to Separators like beforeColon. Then I can configure it without any overrides and the code doesn't change much.

[digulla]

I've created a new MR which is based off Jackson 2.16: #3967

Feel free to close this one.