Make JsonPointer java.io.Serializable

[egalpin]

Noting that Instances [of JsonPointer] are fully immutable and can be cached, shared between threads it would be nice to be able to pass these between workers that require object serialization to pass instances around.

[cowtowncoder]

Seems reasonable, I like the idea. However, I wonder if this could be optimized to actually serialize as String, re-parse? (implement Externalizable)
I think this would be much more efficient, space-wise, than relying on JDK serialization.

[egalpin]

@cowtowncoder good call. I ran into an issue where class properties that need to be set via readExternal cannot be declared final. I made 2 commits, each with a different approach to maintaining the final properties of JsonPointer as finals. The 3rd option, not implemented here but very easy to do, is to change the 4 properties (_nextSegment, _matchingPropertyName, _matchingElementIndex, _asString) to not be final; I assumed that was less preferable but I'll leave that up to you.

[cowtowncoder]

Ok thank you. One thing I also need to consider is that I hope implement fix for #736 which will probably change internal layout of things anyway.

[cowtowncoder]

Does Externalizable really require that? TIL

[egalpin]

Does Externalizable really require that? TIL

It turns out it's not 😅 It requires a no-argument constructor, which is already present. It does! I forgot that the second implementation has the JsonPointer class implementing serializable rather than Externalizable. In f53ef84 you would find that having the access be protected would yield the following error:

java.io.InvalidClassException: com.fasterxml.jackson.core.JsonPointer; no valid constructor

[cowtowncoder]

Ok, this looks good. One last thing, CLA: unless you have already sent one, we'd need this:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

(the usual way is to print, fill & sign, scan/photo, email to info at fasterxml dot com)

If you have already sent one already let me know (sometimes I forget as there are quite a few).

Once there's CLA I'll merge this. CLA works for any and all future contributions too so it's just a one-time hassle.

Looking forward to merging this PR!

[egalpin]

Signed and sent 🙂

[cowtowncoder]

Merged to be included in 2.14.0. Thank you very much for contributing this, @egalpin !

[egalpin]

Thanks @cowtowncoder for the prompt and welcoming review! 🙏