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 > _______________________________________________ > OSGi Developer Mail List > osgi-dev@mail.osgi.org > https://mail.osgi.org/mailman/listinfo/osgi-dev -- *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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