Guaranteed order of annotations?

[joe darcy]

Hi Gunnar,

Annotations went into the platform way back in Java SE 5.0, with a GA 
during 2004. When working on repeating annotations, I was surprised to 
find there weren't stronger ordering guarantees for annotations from 
core reflection. However, requests to tighten this aspect of the 
platform haven't come up very often in the interim and I don't like it 
is likely to happen at this point.

HTH,

-Joe


On 1/17/2017 11:26 PM, Gunnar Morling wrote:
> Joseph, all,
>
> Thanks for the clarification.
>
> Are there chances to establish such guaranteed ordering in a future
> Java version? As pointed out, it'd be very helpful to Bean Validation
> and I reckon other cases, too.
>
> Thanks,
>
> --Gunnar
>
>
>
> 2017-01-18 3:13 GMT+01:00 Joseph D. Darcy <joe.darcy at oracle.com>:
>> Hello,
>>
>> Following up on Joel's message, IIRC this ordering issue did come up during
>> the design and testing of repeating annotations.
>>
>> As noted previously in the thread, while the ordering of the annotations in
>> a container annotation is guaranteed, there is *not* a general ordering
>> constraint on the annotations returned by the methods of the
>> AnnotatedElement interface.
>>
>> HTH,
>>
>> -Joe
>>
>>
>> On 1/13/2017 1:16 PM, Gunnar Morling wrote:
>>> Hi Yuri,
>>>
>>> Thanks for the pointer.
>>>
>>> But do you see any clear description of an order mandated for
>>> getDeclaredAnnotations()? The only references to an order I can find
>>> there are for repeatable annotations (where source code order is
>>> maintained when retrieving them via the container annotation type).
>>> But I cannot find any guaranteed order when obtaining all declared
>>> annotations from an element.
>>>
>>> The reason why I'm asking is Bean Validation, where we've seen
>>> requests of people that wish to validate the constraints of an element
>>> in a fixed order, aborting after the first failed constraint:
>>>
>>>       @NotNull
>>>       @Email
>>>       String email;
>>>
>>> Here one may want to first validate @NotNull and don't proceed with
>>> validating @Email if the field is null.
>>>
>>> Relying on source order would be a very natural way to express the
>>> order of constraints. Without a guaranteed ordering of annotations
>>> we'd have to add some other means of ordering, e.g. an attribute with
>>> the index (@NotNull(order=0) @Email(order=1)) which is more verbose of
>>> course.
>>>
>>> --Gunnar
>>>
>>>
>>>
>>>
>>>
>>> 2017-01-13 21:15 GMT+01:00 Yuri Gaevsky <ygaevsky at azulsystems.com>:
>>>> Hi Gunnar,
>>>>
>>>> Please take a look at JDK-8010679 'Clarify "present" and annotation
>>>> ordering in Core Reflection for Annotations' [*].
>>>>
>>>> Best regards,
>>>> -Yuri
>>>>
>>>> [*] https://bugs.openjdk.java.net/browse/JDK-8010679
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: core-libs-dev [mailto:core-libs-dev-bounces at openjdk.java.net] On
>>>> Behalf Of Gunnar Morling
>>>> Sent: Friday, January 13, 2017 08:14 PM
>>>> To: core-libs-dev at openjdk.java.net
>>>> Subject: Guaranteed order of annotations?
>>>>
>>>> Hi,
>>>>
>>>> Is there any order guaranteed in which an element's annotations are
>>>> returned by AnnotatedElement#getDeclaredAnnotations()? Specifically,
>>>> is this the order in which the annotations are given in the source
>>>> code?
>>>>
>>>> Section 9.7.5. of the JLS ("Multiple Annotations of the Same Type")
>>>> makes a statement of the source order being considered by the array of
>>>> the implicit container annotation created for a repeatable annotation
>>>> ("[...] all the base annotations in the left-to-right order in which
>>>> they appeared in the context").
>>>>
>>>> But I couldn't find any authoritative description on the ordering
>>>> behaviour of getDeclaredAnnotations(). Should we assume that we cannot
>>>> rely on the order in the source?
>>>>
>>>> Thanks for any pointers,
>>>>
>>>> --Gunnar
>>