[ScopedValue] best way to conditionally bind a value ?

[Benoit LEFEVRE -CAMPUS-]

Hi Alan

Thanks for your advice !


As mentioned in my latest reply to Davor, the goal of this badly chosen
example of mine is to point out the edge case where there is only a single,
optional, ScopedValue to manage :p

*Is there any reason why the caller can't bind ACCEPT_LANGUAGE to
A_DEFAULT_LOCALE so that the callee doesn't need to handle it? :*


Yes, there is one :

This code sample is inspired from an actual Tomcat's Filter, which is
general purpose.

I.E. it's only there to extract certain generic header parameters from
calls to a REST API server, and it's used in each use cases

So it's a very technical oriented piece of code, and that's why from my
point of view its purpose is not to choose which is the default accept
language to be used.

Sounds better to me to hand over this functional responsibility to each
endpoints.

Best regards

Benoit

Le jeu. 31 juil. 2025 à 08:16, Alan Bateman <alan.bateman at oracle.com> a
écrit :

>
>
> On 30/07/2025 19:16, Benoit LEFEVRE -CAMPUS- wrote:
>
> Hello
>
> After using the ScopedValue for a few days, I'm wondering if there is a
> better way to conditionally bind a value than doing the following :
>
>
> public static final ScopedValue< Locale > ACCEPT_LANGUAGE =
> ScopedValue.newInstance();
> public static final ScopedValue< String > USER_ID =
> ScopedValue.newInstance();
>
> final Locale acceptLanguage = getAcceptLanguageFromHeader( httpRequest );
>
>
> if( acceptLanguage == null ) {
>     ScopedValue
>         .where( USER_ID, uid )
>         .call( MyClass::myStaticCallableMethod );
> } else {
>     ScopedValue
>         .where( USER_ID, uid )
>         .where( ACCEPT_LANGUAGE, acceptLanguage )
>         .call( MyClass::myStaticCallableMethod );
> }
>
>
> The point for me of doing so, instead of simply setting a null
> acceptLanguage, is to have a more readable code afterward :
>
>
> private String myStaticCallableMethod() {
>     final Local localToUse = ACCEPT_LANGUAGE.orElse( A_DEFAULT_LOCAL );
>
>
>     ...
> }
>
>
> What is your advise about it ?
>
>
> If the user ID and accept language were (explicit) method parameters then
> you might write:
>
> if (acceptLanguage == null) {
>     MyClass.myStaticCallableMethod(uid);
> } else {
>     MyClass.myStaticCallableMethod(uid, acceptLanguage);
> }
>
> With implicit method parameters you've got the same if-then-else so I
> don't think it is terrible.
>
> Is there any reason why the caller can't bind ACCEPT_LANGUAGE to
> A_DEFAULT_LOCALE so that the callee doesn't need to handle it? That would
> change the usage to:
>
> ScopedValue
>     .where(USER_ID, uid)
>     .where(ACCEPT_LANGUAGE, (acceptLanguage != null) ? acceptLanguage :
> A_DEFAULT_LOCALE)
>     .call(...);
>
> It would then be a bug f myStaticCallableMethod were called without
> bindings for either.
>
> -Alan
>
>
>

-- 
Benoit Lefèvre
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