[bv-dev] Value extraction open issue #5: Should value extractors be discoverable via the service loader?

[Michael Nascimento]

Gunnar,

Agreed.

Regards,
Michael

On Mon, Feb 20, 2017 at 12:54 PM, Gunnar Morling <gunnar at hibernate.org>
wrote:

> Hi,
>
> I think there already was agreement essentially that value extractors
> should be discoverable using the service loader mechanism.
>
> This will allow providers of custom collection types (e.g. Google
> Guava) to bundle a value extractor with their library and have it
> being picked up automatically, allowing application developer to put
> @Valid to these types without any further configuration.
>
> So I've prepared a change for that:
>
>     https://github.com/beanvalidation/beanvalidation-spec/pull/140
>
> The open question was how value extractors should be
> overridden/disabled. I've foreseen the following sources for value
> extractors, in descending order of precedence:
>
> * ValidatorContext#addValueExtractor(ValueExtractor<?>)
> * Configuration#addValueExtractor(ValueExtractor<?>)
> * META-INF/validation.xml
> * META-INF/services/javax.validation.valueextraction.ValueExtractor
>
> If an extractor for a specific type (e.g. java.util.List) and type
> parameter (e.g. "E") is given at one level (e.g. ValidatorContext) it
> will override any extractors for the same type and type parameter
> given at the lower levels and the built-in extractor for that type and
> type parameter, if any.
>
> I don't think there's a way needed to explicitly disable an extractor
> without providing an alternative implementation. I.e. I cannot see a
> use case why one would want to disable cascaded validation let's say
> for List. Hence the proposed overriding scheme.
>
> Can you please let me know what you think of this by the end of the week?
>
> Thanks,
>
> --Gunnar
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