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From mvangeert...@comcast.net
Subject Re: A better life: quick webapp deploy
Date Tue, 10 May 2011 16:26:24 GMT


Danielle, 



What you are trying to do is best accomplished by using services.  In my application, we
have a database connection and JMS connections that are used by multiple bundles.  So, for
my database connection (since that's what we're talking about), I created my bundle, and then
in the context file that uses the osgi and osgix namespaces, I simple attached the bundle
to the service registry.  Then any other bundle that needed to consume the database connection
was able to grab a reference to the database service from the service registry, and then inject
it via the database connections interface. 



v/r, 



Mike Van 


----- Original Message ----- 
From: "Daniele Dellafiore" <daniele@dellafiore.net> 
To: users@felix.apache.org 
Sent: Tuesday, May 10, 2011 11:37:22 AM 
Subject: Re: A better life: quick webapp deploy 

On Tue, May 10, 2011 at 3:17 PM, Peter Kriens <peter.kriens@aqute.biz>wrote: 

> In OSGi the idea is that you get a bunch of bundles that collaborate 
> through services. The bundle is a module and is therefore supposed to be 
> impenetrable. Just like a class has private fields so does a bundle have 
> private classes and resources. It would not be very modular if you could use 
> the XML from other bundles, this Spring XML is supposed to be an 
> implementation detail of the bundle. As long as you do the collaboration 
> with services you can use many different techniques: Spring, DS, iPOJO, 
> dependency manager, etc. 
> 

Another way to say is that I use the XML from other bundles as I use a class 
from another bundle, I do not see any violation here. 
A spring xml is an implementation detail? For me is like a class, nothing 
more, I load it using <import> like instantiate a class with a new. 

Example. 
If I've defined some beans that manage storage and search in a bundle A and 
want to load them in a bundle B changing just some properties (database 
connections and some search tuning), the only way I know now, in OSGI, is to 
copy-paste the spring XML into bundle A, cause import classpath*: does not 
work. 
Copy paste is always bad so I figure out that alternatives are: 

1. importing beans from bundle A in the  context of B, using a sort of 
osgi:classpath 
2. exporing those beans as osgi services, but as long that properties are 
chosen by bundle B, I need something more sophisticated like 
ManagedServiceFactory to get a new instance with the actual parameters. I've 
never dig into that but it seems to be the case. This solution, that I do 
not find easy, is OSGI specific while I'd like to stay on spring and avoid 
to couple with OSGI mechanism 
3. i can raise the level of abstraction. If I need a DatabaseTemplate 
configured with some property that definese database connection, i can 
export as osgi service a DatabaseTemplateFactory from bundle B and ask the 
template to the factory from A. But here I loose advantages of spring IOC: 
in my classes I will have an instance of the factory, and I've to ask for a 
new class everytime and who keeps the control that the new template instance 
is a singleton now? 
4. bundle A do the persistence and that's it. I export a DatabaseTemplate 
that can write on different databases, and I tell which one using a 
parameter or some more sophisticated mechanism (ThreadLocal? wonder how it 
works on OSGI). 

Maybe is not that important but sometime it happens I have a bundle that 
offer some classes. In a typical app that use that bundle, one or more 
classes are candidate to become spring beans, in every app that will use the 
classes. So I provide a ready to use spring xml so that you do not need to 
copy-paste the spring definition but you can just import the file as a 
resource. 

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