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From Craig L Russell <Craig.Russ...@Sun.COM>
Subject Re: OSGi confusion...
Date Wed, 20 May 2009 23:33:30 GMT
Sorry, correcting email address.

On May 20, 2009, at 4:27 PM, Craig L Russell wrote:

Hi Felix Devs,

I'm curious about the issue contained in this thread.

My understanding of the issue is this:

If an application is running in an OSGi environment and declares a  
dependency (its OSGI manifest imports the java mail packages) does its  
context class loader see the javax.mail jar in its entirety? My guess  
is: not. The OSGi class loader implements the getResources call and  
filters for exported artifacts.

So, in order for the application to see the META-INF/mailcap.default  
resource, this file would need to be exported explicitly and then the  
getResources as implemented by OSGi container would find it.

Similarly, if an OSGi bundle wants to makes its META-INF/services/ 
some.implemented.Interface file available, the OSGi manifest would  
have to explicitly export it.

Does the user then need to explicitly name the META-INF/services/ 
some.exported.Interface in order to access all the implementations via  
getResources?

Thanks,

Craig

Begin forwarded message:

> From: Peter Williams <Pete.Williams@Sun.COM>
> Date: May 20, 2009 1:08:15 PM PDT
> To: dev@glassfish.dev.java.net
> Subject: Re: OSGi confusion...
> Reply-To: dev@glassfish.dev.java.net
>
>
>
> Bill Shannon wrote:
>> Richard S. Hall wrote:
>>>
>>>
>>> On 5/19/09 4:08 PM, Peter Williams wrote:
>>>> I'm investigating a JavaMail failure in V3 that is caused by the  
>>>> current OSGi configuration and I'm trying to figure out how to  
>>>> fix it.
>>>>
>>>> The issue is this:  Code in the JDK (JAF in this case) is calling  
>>>> getResources() on the current context classloader (web app  
>>>> classloader in my test case, but probably could another one) to  
>>>> locate any available mailcap files.  It's trying to find META-INF/ 
>>>> mailcap.default in javax.mail.jar.  This fails, the code breaks.   
>>>> Outside of OSGi, this all works fine.
>>>>
>>>> So what needed to happen here to make this work?  Should  
>>>> javax.mail.jar be exporting META-INF?  How?  Does the JDK have to  
>>>> import this?  (how?!)
>>>
>>> If I understand correctly, it sounds like JAF expects to be able  
>>> to access every available JAR file by accessing the context class  
>>> loader. This is a recipe for failure in OSGi.
> I don't know that JAF was expecting to access *EVERY* available jar  
> file (perhaps), but certainly most of them and very likely any of  
> them that actually contained "META-INF/mailcap" would be in the  
> "most of them" list (e.g they won't be in weird agent jars or  
> bootloader stuff, just plain application or library jars).
>
> Anyway, see below.
>
>>>
>>> Typically, these sorts of situations involve some sort of extender  
>>> listening for bundles with mailcap files and then the information  
>>> in them can be injected where appropriate.
>>>
>>> Unfortunately, I don't know enough about JAF to say in detail how  
>>> this might work.
> I can help with JAF if you can help me interpret OSGi.
>
> Can you tell me why, even though JAF accessed a classloader that  
> knew about javax.mail.jar, the file at META-INF/mailcap in that jar  
> was not accessible.  Is this because javax.mail.jar does not export  
> META-INF?  (I had problems attempting this, but I don't have the  
> errors handy right now -- glassfish build issued a bunch of split  
> package warnings though, I'm guessing because META-INF is present in  
> all jars).
>
> Assuming the file can be located and processed though, it will  
> contain fully qualified class names for the implementations of a  
> particular public interface.  The implementations will be in private  
> packages of javax.mail.jar.
>
> Do you think JAF be able to instantiate these classes?  If not,  
> they'll need to be exported (e.g. public) too, correct?
>
> FWIW, it looks like another company (guess :)) using OSGi is having  
> similar problems, as I ran across their (unresolved) bugs on this  
> issue while research solutions.
>
> Thanks
> -Peter
>
>>
>> This is a fairly common pattern in the JDK, and one we've recommended
>> in Java EE for quite a few years.  This is essentially the same as
>> java.util.ServiceLoader.
>>
>> It's fine if an OSGi bundle has to explicitly export these classes so
>> they can be loaded by (e.g.) JAF, but JAF needs to be able to load  
>> these
>> classes using the context class loader.
>>
>>
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>
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Craig L Russell
Architect, Sun Java Enterprise System http://db.apache.org/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!


Craig L Russell
Architect, Sun Java Enterprise System http://db.apache.org/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!


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