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From Christian Schneider <ch...@die-schneider.net>
Subject Re: Scope of org.apache.camel.spi
Date Wed, 24 Aug 2011 17:55:00 GMT
Actually JDk and spring are two very good examples how to not do it :-)

I guess in the JDK no one cared as you will always have it. Btw. I guess 
everyone agrees that the JDK is a mess architecturally. Btw. he JDK 
extensions ship separate API jars like JAXB api. So they seem to have 
learned.

In spring I suspect it is on purpose. They could provide API jars that 
make you independent of their implementation. By combining API and impl 
they force you into having a hard dependency on spring.
You had to remove the spring JMX annotations as we did not want to have 
their impl. If they had cleanly separated their API from the impl we 
could have kept the one API jar with the annotations and just 
implemented them ourself when running outside of spring.

So having the annotations in the management package is a very bad idea. 
A subpackage would work on a pure simple package perspective but I think 
it would be bad to have a top level package with implementations and a 
subpackage with the API.

We can move around the management stuff at the moment as my commit 
changed it anyway. So before Camel 2.9 comes out we are free to move them.

api.management of course only makes sense if we intend to put more stuff 
there but I think it would be a good idea to do so.
Having a top level api package will also make it easier to create a pure 
API jar for camel 3.0. I think it would be strange if the API jar would 
contain

org.apache.camel
org.apache.camel.spi
org.apache.camel.management.annotation

but not
org.apache.camel.management

Btw management.annotation is not enough anyway as we have more 
management interfaces that have to live in the API space. So 
management.api would be better but I would prefer to have api at the top 
level so the user can clearly see that everything api.* is part of the API.

In any case we need to separate the management API from the management 
impl classes. If we do not do it then we have no chance to avoid cycles. 
Besides that how should we make it possible that the components only 
need to depend on the API if we mix things. For example a component may 
want to use the management annotations or another management interface 
but it should not know the impl.

Btw. the event classes should also be part of the API as they are 
necessary to understand management events. As they live in a separate 
package already the does not depend on the management impl I did not 
move them but they would be better placed in api.management.events.

Christian




Am 24.08.2011 19:12, schrieb Claus Ibsen:
> On Wed, Aug 24, 2011 at 6:17 PM, Christian Schneider
> <chris@die-schneider.net>  wrote:
>> Hi Claus,
>>
>> we can do that but then we have to move the impl classes somewhere else. We
>> may not mix impl and api in the same package. This is what leads to cycles.
>>
> That is actually common. For example look at the JDK
> Map (API) and HashMap (Impl) are both in java.util package.
>
> However these annotations are not regular interfaces, that end users
> is supposed to implement.
> Or for example that we in the Apache Camel provides 2+ different
> implements of those annotations.
>
> As an end user I would feel natural these annotations are in the
> mangement package as they are part of the management
> (end user) API in Camel.
>
>
> The Spring framework put these annotations at
> http://static.springsource.org/spring/docs/3.0.x/javadoc-api/org/springframework/jmx/export/annotation/ManagedOperation.html
>
> We could also have a annotation subpackage
> (org.apache.camel.management.annotation)
> but we usually dont have that, eg there are no annotation package for
> @Consume, @Produce, @EndpointInject etc.
>
> Alternatively we could move them in the root package, but as you said
> there is already plenty of APIs in that package.
>
> Putting them in org.apache.camel.api seems a bit weird, as they would
> be the only pieces in there.
> And for Camel 2.x we should keep the API stable and not move around
> stuff all the time.
>
>
>
>> Christian
>>
>>
>> Am 24.08.2011 17:53, schrieb Claus Ibsen:
>>> On Wed, Aug 24, 2011 at 3:04 PM, Christian Schneider
>>> <chris@die-schneider.net>    wrote:
>>>> So where do you propose to put them?
>>>>
>>>> 1. org.apache.camel
>>>> 2. org.apache.camel.api.management
>>>>
>>> I propose to put them here, where they where already
>>> 3. org.apache.camel.management
>>>
>>> These annotations are part of the management API in Camel and IMHO
>>> should be in that package.
>>>
>>>
>>>
>>>> I propose to go with 2 and create an api package with subpackages so we
>>>> can
>>>> structure org.apache.camel better. In the long run I would like to also
>>>> move
>>>> the whole camel api into an api package to make it clearer but that will
>>>> probably create too much incompatibility.
>>>>
>>>> Christian
>>>>
>>>>
>>>> Am 24.08.2011 14:13, schrieb Claus Ibsen:
>>>>> On Tue, Aug 23, 2011 at 12:38 PM, Christian Schneider
>>>>> <chris@die-schneider.net>      wrote:
>>>>>> I wonder what our scope for the org.apache.camel.spi package is vs
the
>>>>>> org.apache.camel (API) package.
>>>>>>
>>>>>> I know two valid definitions for API vs SPI:
>>>>>>
>>>>>> 1) API interfaces are called by the user to invoke functionality
of the
>>>>>> framework. So API interfaces are implemented by the framework. SPI
>>>>>> interfaces are implemented by the user to change functionality of
the
>>>>>> framework or for callbacks
>>>>>> 2) SPI interfaces are for third party modules while API interfaces
are
>>>>>> for
>>>>>> users
>>>>>>
>>>>>> So the current case for me is the new JMX annotations. Are they SPI
>>>>>> interfaces or API interfaces?
>>>>>>
>>>>> They are API interfaces. Just like @Consumer, @Produce and any of the
>>>>> other API Camel annotations we have.
>>>>> Its just that these annotations is for management enabling your
>>>>> business logic / custom components or whatnot.
>>>>>
>>>>>
>>>>>
>>>>>> So what is your opinion about the specific and the general case.
>>>>>>
>>>>>> As a side question: The org.apache.camel package has grown quite
large.
>>>>>> I
>>>>>> think we should create specialized packages for it. As we are talking
>>>>>> about
>>>>>> the camel API org.apache.camel.api.* would be a good name in my
>>>>>> opinion.
>>>>>> So
>>>>>> the questions are: Should we create such specialized packages? Should
>>>>>> we
>>>>>> move API parts there? Should we only use the new packages for new
>>>>>> stuff?
>>>>>>
>>>>>> Christian
>>>>>>
>>>>>>
>>>>>> --
>>>>>> --
>>>>>> Christian Schneider
>>>>>> http://www.liquid-reality.de
>>>>>>
>>>>>> Open Source Architect
>>>>>> Talend Application Integration Division http://www.talend.com
>>>>>>
>>>>>>
>>>> --
>>>> --
>>>> Christian Schneider
>>>> http://www.liquid-reality.de
>>>>
>>>> Open Source Architect
>>>> Talend Application Integration Division http://www.talend.com
>>>>
>>>>
>>>
>> --
>> Christian Schneider
>> http://www.liquid-reality.de
>>
>> Open Source Architect
>> http://www.talend.com
>>
>>
>
>

-- 
Christian Schneider
http://www.liquid-reality.de

Open Source Architect
http://www.talend.com


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