Let me see if I can take a crack at it! Though I'm often told I also don't
understand when I try to explain it. :D
Suppose you have an API like so:
interface DataHandler {
void processData(DataContext context);
}
This API has 2 interfaces `DataHandler` and `DataContext`
Now you happen to know there is a library data.machine-1.2.3.jar which is a
data processing engine and to use it all you need to do is publish an OSGi
service of type `DataHandler` and it will do some magic.
Since you implement `DataHandler` this interface is sensitive to you as a
consumer. If the API were to add a method if would break your code. In this
case DataHandler is effectively @ConsumerType. It is a type which is
implemented in order to _use_ the API.
Now, DataContext is not so sensitive for you in this scenario because you
only _recieve_ instances of it. You never have to implement it in your
_use_ of the API. In this case DataContext is @ProviderType since it's an
interface which only _providers_ implement. Therefore if a new method was
added to it, it would _not_ break your code, it _would_ however force the
implementers of data.machine-1.2.3.jar to make a new release since they are
a _provider_ of the API.
So you see, both interfaces are part of the same API, yet one is
@ConsumerType (DataHandler) and the other is @ProviderType (DataContext).
I hope that helps. Others feel free to correct my understanding and
hopefully, I'll finally grok it myself.
- Ray
On Wed, Oct 16, 2019 at 3:34 PM Milen Dyankov via osgi-dev <
osgi-dev@mail.osgi.org> wrote:
> Welcome to the club ;) I struggled with that myself for a long time.
>
> I think I finally got to understand it couple of years ago. Here is how I
> explained it during one of my talks:
> https://www.youtube.com/watch?v=hGNrZmr0zz8&feature=youtu.be&t=1569
> I hope this helps better than me trying to write it all down here.
>
> Best,
> Milen
>
> On Wed, Oct 16, 2019 at 9:15 PM Leschke, Scott via osgi-dev <
> osgi-dev@mail.osgi.org> wrote:
>
>> I’m trying to wrap my head around these two annotations and I’m
>> struggling a bit. Is the perspective of the provider and consumer roles
>> from a bundle perspective or an application perspective?
>>
>> I’ve read the Semantic Versioning whitepaper a number of times and it
>> doesn’t really clear things up for me definitely.
>>
>>
>>
>> If an application has an API bundle that only exposes Interfaces and
>> Abstract classes, and those interfaces are implemented by other bundles in
>> the app, are those bundles providers or consumers? My inclination is that
>> they’re providers but then when does a bundle become a consumer? Given
>> that API bundles are compile only (this is the rule right?), would a good
>> rule be that if you implement the interface and export the package it’s in,
>> that type would be @ProviderType, if you don’t implement it it’s
>> @ConsumeType?
>>
>>
>>
>> It would seem to me that @ProviderType would be the default using this
>> logic, as opposed to @ConsumerType, which leads me to believe that I’m
>> thinking about this wrong.
>>
>>
>>
>> Any help appreciated as always.
>>
>>
>>
>> Regards,
>>
>>
>>
>> Scott Leschke
>> _______________________________________________
>> OSGi Developer Mail List
>> osgi-dev@mail.osgi.org
>> https://mail.osgi.org/mailman/listinfo/osgi-dev
>
>
>
> --
> http://about.me/milen
> _______________________________________________
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--
*Raymond Augé* <http://www.liferay.com/web/raymond.auge/profile>
(@rotty3000)
Senior Software Architect *Liferay, Inc.* <http://www.liferay.com>
(@Liferay)
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