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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