Re: Declarative Services vs Spring

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I recommend we move this discussion
to the osgi-dev-mPdqGMcIfZjsYSj8pfqilw@xxxxxxxxxxxxxxxx mailing list.  You can subscribe
to this mailing list at http://bundles.osgi.org/mailman/listinfo/osgi-dev

This way we can get the rest of the
osgi community involved in any future specification work to Declarative
Services.

Thanks.

Tom

"Neil Bartlett" <neil-eu3/G5jNAhBOSnsfY10OVw@xxxxxxxxxxxxxxxx>
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03/02/2006 07:53 AM

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Subject	Re: [equinox-dev] Declarative Services vs Spring

Subbarao,

I think you're probably right. Having played with Declarative Services
in the last few days, I really miss the flexibility and expressiveness
of Spring's DI capabilities.

I've just been to a seminar given by Rod Johnson where he mentioned that
they are working on OSGi integration with Spring, ie making Spring more
dynamic so that it will work properly within an OSGi runtime. That's very
exciting for me because I think that OSGi combined with Spring's rich framework
and AOP features would be an incredible platform for enterprise services.
It would blow away anything previously possible with J2EE and EJB. 

Unfortunately Rod said that this functionality is probably something that
will be in Spring 3.0, where Spring is currently in 2.0 M1. As an alternative
from the OSGi side, DS could be made more powerful so it could replace
Spring's DI capabilities, while still making use of the other two sides
of the "Spring triangle". 

Neil


On 3/1/06, Subbarao Meduri <mkv-r/Jw6+rmf7HQT0dZR+AlfA@xxxxxxxxxxxxxxxx>
wrote:
Agreed that OSGi is a more dynamic platform, and thus
could say constructor injection is not the best thing that components should
implement. However, if you take the view that OSGi is also a integration
platform for components (where you don't necessarily have control over
how a component is designed), it would make sense to me that declarative
services support constructor injection. Obviously, it would not be a best
practice, but it at least it will not inhibit a component that is not designed
to leverage OSGi dynamic features from being integrated into the framework.

Thoughts ?
Subbarao

"Neil Bartlett" <
neil-eu3/G5jNAhBOSnsfY10OVw@xxxxxxxxxxxxxxxx>

"Neil Bartlett" <neil-eu3/G5jNAhBOSnsfY10OVw@xxxxxxxxxxxxxxxx>
Sent by: equinox-dev-bounces-j9T/66MeVpFAfugRpC6u6w@xxxxxxxxxxxxxxxx

03/01/2006 10:21 AM

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Subject	Re: [equinox-dev] Declarative Services vs Spring

I think that's intentional. With OSGi you always have to be aware that
the services you depend on might go away, and possibly come back again
later. That's the essence of OSGi - it's dynamic. In this context an
"immutable final service reference" is an oxymoron.

Spring lives in a comfortable static world where dependencies, once
supplied, will live for at least as long as the things that depend on
them. In OSGi, that kind of assumption is only really valid for
intra-bundle dependencies. DS on the other can handle dynamic
inter-bundle dependencies, which IMHO makes it much more powerful.

On the other hand Spring has much more to it than dependency
injection. It also has a number of very powerful libraries, eg for
developing DAOs using JDBC or O/R mappers, an AOP library, remoting
libraries, etc. Because Spring is wonderfully modular, you can use as
much or as little of it as you like (just like Eclipse!).

- Neil


On 3/1/06, Subbarao Meduri <mkv-r/Jw6+rmf7HQT0dZR+AlfA@xxxxxxxxxxxxxxxx> wrote:
>
>
> How does declarative services fare when compared with Spring framework in
> terms of its injection capabilities ? My apologies if this is already
> discussed on this forum.
>
>  Is there a reason why declarative services does not support constructor
> injection, for example ? It seems constructor injection is the only way to
> initialize a component that holds a immutable (final) service reference
> injected via its constructor.
>
>  Appreciate your thoughts.
>
>  Regards,
>  Subbarao



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