Support for BCP 47 `java.util.Locale` serialization/deserialization

Describe the bug

Locale with BCP 47 extensions are not serialized / de-serialized as expected using ObjectMapper.

Version information

Which Jackson version(s) was this for? All Jackson versions.

To Reproduce

If you have a way to reproduce this with:

Brief code sample/snippet: include here in pre-formatted/code section

Locale locale = Locale.forLanguageTag("en-US-x-debug");
// ^^^ above locale will have x-debug as extensions
// This locale is a BCP 47 compliant locale.

ObjectMapper objectMapper = new ObjectMapper();

String serializedLocale = objectMapper.writeValueAsString(locale);
// ^^^ Will be en_US-#x-debug. Conforms to toString() method of Locale.
// This is not correct. There is a rogue # is added before extensions. 

Locale deserializedLocale = objectMapper.readValue(serializedLocale, Locale.class); 
// ^^^ Due to the rogue # before the extensions, when we de-serialize it, the extensions get added as a Variant instead of extensions.

Longer example stored somewhere else (diff repo, snippet), add a link

N/A. Reproducible with the above piece of code.

Textual explanation:

• forLanguageTag locale is used to create a locale object from a BCP 47 compliant locale string. The x-debug gets added as extensions in the Locale.
• However, when we use ObjectMapper to serialize the string, objectMapper uses toString() method of locale to convert it to String.
• As Per Locale Javadocs, for BCP 47 locales, we must be using toLanguageTag() and forLanguageTag() instead to convert to / from String.
• Due to this, when we try to de-serialize this malformed Locale, the x-debug gets added as a Variant instead of extensions, which is not expected.

Expected behavior

• BCP 47 extensions should be added as extensions and not as Variants when serializing and de-serializing.

Additional Details

• Due to this drawback, we are forced to write our own serializer / de-serializer. It would be nice if ObjectMapper provides us a Module which does this for us.

[cowtowncoder]

@praneethjreddy Sure. I do think we have custom (de)serializer already, but it might be part of a multi-type (de)serializer… let me look.

Ok, so:

• for deserialization, it’s FromStringDeserializer
• for serialization, basic ToStringSerializer is used (which as per name only calls Locale.toString())

So, it may be necessary to have separate serializer implementation if deserializer-only handling can not be made to work.

[cowtowncoder]

Uhhhh. Should have remember to link #1600 here; Jackson 3.0 already serializes using “toLanguageTag()”.

So 3.0 (master) will probably need bit different deserializer as all new tests are now failing.