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List:       tuscany-user
Subject:    Re: FW: Q: Best practice for making service references available
From:       Mike Edwards <mike.edwards.inglenook () gmail ! com>
Date:       2011-07-07 15:50:13
Message-ID: 4E15D5B5.3090408 () gmail ! com
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Folks,

I completely missed this discussion when it was raised originally. Very late to the party now :-(

One point I can make is that it is possible for the reference(s) to be propogated using the Context 
and retrieved anywhere using the ComponentContext API.

Agreed, this is not as neat as using injection, but it is probably neater than creating a whole load 
of extra APIs of the type discussed in this email thread.

It also does require that everything is running on one thread - but if you're going to spin off 
extra threads for the reference calls, then you need to build your app carefully to pass over 
whatever context is required on the new thread.


Yours,  Mike.

On 22/09/2010 08:36, Millies, Sebastian wrote:
> yes, I see. However, I still think that sometimes propagating the
> references in application code can be clumsy, especially with references
> to infrastructure services such as logging, which then clutter the
> business interfaces.
>
> A simpler idea might be to provide an SCAInjector utility, and do something like
> SCAInjector.injectReferences(String serviceName, Object new_app_object)
> after having created a new application object instance. The SCAInjector should be
> able to discover the required implementation of the reference proxy from
> the service definition in the domain and the type of the reference variable.
>
> -- Sebastian
>
>> -----Original Message-----
>> From: Simon Nash [mailto:nash@apache.org]
>> Sent: Tuesday, September 21, 2010 11:52 PM
>> To: user@tuscany.apache.org
>> Subject: Re: Q: Best practice for making service references available
>> in a component?
>>
>> Millies, Sebastian wrote:
>>> Hello there,
>>>
>>> I have an idea for a Tuscany extension. Would it not be possible to
>>> introduce an additional attribute "package" on the
>> implementation.java
>>> element, the purpose of which would be to specify all classes in
>>> one (or more) Java package(s) as collectively making up the component
>>> implementation. Tuscany could then inject proxies for the referenced
>>> services at any point where the @Reference annotation is used in any
>>> class of the packages. Similarly for @Context etc. (The value of the
>>> "class" attribute would still denote the main class, which provides
>>> the component's external interface.)
>>>
>>> Would this make sense in your opinion? Would it be hard to implement?
>>>
>> I think it would be hard to implement because:
>>    1. Tuscany would need a way to enumerate all the classes in the
>>       package so that it could find all the @Reference annotations.
>>    2. Tuscany would need to discover the runtime instance relationships
>>       between all these application classes so that it could find the
>>       right instance objects on which to perform the injections.
>>       This is just about impossible because the "non-main" objects are
>>       instantiated by the application and not by Tuscany.
>>    3. When Tuscany creates the instance of the "main" class, the other
>>       application instance objects that need to be injected might not
>>       exist at that time.
>>
>> I think the current SCA mechanisms are sufficient to allow application
>> classes to propagate these references to wherever they are needed, and
>> I think that handling such propagation is best left to application
>> code.
>>
>>     Simon
>>
>>> -- Sebastian
>>>
>>>
>>>> -----Original Message-----
>>>> From: Simon Nash [mailto:nash@apache.org]
>>>> Sent: Tuesday, September 21, 2010 8:26 PM
>>>> To: user@tuscany.apache.org
>>>> Subject: Re: Q: Best practice for making service references
>> available
>>>> in a component?
>>>>
>>>> Millies, Sebastian wrote:
>>>>> Hello there,
>>>>>
>>>>> this is a question about coding style. SCA components are coarse
>>>> grained,
>>>>> i. e. the actual component implementation can consist of many
>>>> classes, only
>>>>> one of which is defined as _the_ component implementation class in
>>>> the composite
>>>>> XML. It is only on this class that annotations like @Reference can
>> be
>>>> used to
>>>>> inject dependencies to other services. It is likely, however, that
>>>> the referenced
>>>>> services really need to be called from one of the other classes in
>>>> the component
>>>>> implementation.
>>>>>
>>>>> How do you pass the values of these reference variables to those
>>>> ordinary Java
>>>>> classes? Is there a special "SCA way" of doing this, perhaps making
>>>> these References
>>>>> globally available in a component, or do you just use normal Java
>>>> programming idioms
>>>>> like property setters, or constructor/method parameters?
>>>>>
>>>>> -- Sebastian
>>>>>
>>>> There isn't any specific SCA way of doing this.  You can treat
>>>> the injected proxy as a regular Java object and pass it around
>>>> however you wish.  However it's useful to bear in mind that SCA
>>>> offers 3 different ways to obtain the reference proxy:
>>>>     as a constructor parameter
>>>>     as a setter parameter
>>>>     as an injected field
>>>>
>>>> Depending on how you want to pass the value around, one or other
>>>> of these might be more appropriate.
>>>>
>>>>     Simon
>>>
>

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