UnsafeLocaleUsage
Possible unsafe operation related to the java.util.Locale library.

Severity
WARNING
Has Fix?

The problem

The Java Locale API is broken in a few ways that should be avoided, with some examples of error prone issues below:

Constructors

The constructors don’t validate the parameters at all, they just “trust” it 100%.

For example:

Locale locale = new Locale("en_AU");
toString()        : "en_au"
getLanguage()     : "en_au"
locale.getCountry : ""

locale = new Locale("somethingBad#!34, too long, and clearly not a locale ID");
toString()    : "somethingbad#!34, too long, and clearly not a locale id"
getLanguage() : "somethingbad#!34, too long, and clearly not a locale id"
getCountry()  : ""

As you can see, the full string is interpreted as language, and the country is empty.

For new Locale("zh", "tw", "#Hant") you get:

toString()    : zh_TW_#Hant
getLanguage() : zh
getCountry()  : TW
getScript()   :
getVariant()  : #Hant

And for Locale.forLanguageTag("zh-hant-tw") you get a different result:

toString()    : zh_TW_#Hant
getLanguage() : zh
getCountry()  : TW
getScript()   : Hant
getVariant()  :

We can see that while the toString() value for both locales are equivalent, the individual parts are different. More specifically, the first locale is incorrect since #Hant is supposed to be the script for the locale rather than the variant.
There’s no reliable way of getting a correct result through a Locale constructor, so we should prefer using Locale.forLanguageTag() (and the IETF BCP 47 format) for correctness.

Note: You might see a .replace("_", "-") appended to a suggested fix for the error prone checker for this bug pattern. This is sanitization measure to handle the fact that Locale.forLanguageTag() accepts the “minus form” of a tag (en-US) but not the “underscore form” (en_US). It will silently default to Locale.ROOT if the latter form is passed in.

toString()

This poses the inverse of the constructor problem

Locale myLocale = Locale.forLanguageTag("zh-hant-tw")
String myLocaleStr = myLocale.toString() // zh_TW_#Hant
Locale derivedLocale = ??? // Not clean way to get a correct locale from this string

The toString() implementation for Locale isn’t necessarily incorrect in itself.
It is intended to be “concise but informative representation that is easy for a person to read” (see documentation at Object.toString()).

So it is not intended to produce a value that can be turned back into a Locale. It is not a serialization format.
It often produces a value that looks like a locale identifier, but it is not.

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("UnsafeLocaleUsage") to the enclosing element.