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From "Raymond Feng" <enjoyj...@gmail.com>
Subject Re: Using Axis2 Java with OSGi - some help appreciated
Date Mon, 05 Jan 2009 18:29:39 GMT
I agree that DynamicImport-Package: * is evil :-).

In Tuscany, we adopt the extension/extension point pattern (inspired by 
Eclipse) to solve similar problems without a hard dependency on the OSGi 
service registry APIs [1]. We register implementation classes of a service 
provider interface in a file named as META-INF/services/<service provider 
interface name>. The content of the file is the name of the implementation 
class.

If the code is executed without OSGi, we use the classloader to discover the 
META-INF/services/<service provider interface name> resources and then load 
the implementation class by name. With OSGi, we discover bundles that 
contain the META-INF/services/<service provider interface name> resources 
and use the owning bundle to load the implementation class. This way, we 
don't have to export the implementation classes and they are accessed via 
service provider interfaces and the extension points.

There is also an interesting article that compares the Eclipse 
extension/extension point pattern and the OSGi service registry. See [2].

[1] https://svn.apache.org/repos/asf/tuscany/java/sca/modules/extensibility/
[2] http://www.eclipsezone.com/articles/extensions-vs-services/

Thanks,
Raymond
--------------------------------------------------
From: "David Illsley" <davidillsley@gmail.com>
Sent: Monday, January 05, 2009 9:41 AM
To: <axis-dev@ws.apache.org>
Subject: Re: Using Axis2 Java with OSGi - some help appreciated

> Urgh, DynamicImport-Package: * is pretty evil. It is a pretty simple
> way to retrofit existing code into OSGI, but using it essentially
> throws away the potential benefits. I *think* the best way is for the
> Tuscany MessageReceiver objects to be registered as OSGI services. It
> looks like the existing Axis2 osgi module hooks up registered
> MessageReceiver services to act as the default message receiver for a
> given MEP. I don't know if that would be enough for you? If not, I'd
> think that it wouldn't be too hard to extend the existing code in the
> osgi module to register in non-default MessageReceiver objects.
>
> David
>
> On Mon, Jan 5, 2009 at 4:06 AM, Sameera Jayasoma
> <sameera.madushan@gmail.com> wrote:
>>
>>
>> On Sat, Jan 3, 2009 at 12:56 PM, Mike Edwards
>> <mike.edwards.inglenook@gmail.com> wrote:
>>>
>>> Folks,
>>>
>>> I am writing as a developer on the Apache Tuscany project.
>>>
>>> We are building a version of Tuscany that runs on OSGi - and we use 
>>> Axis2
>>> in our codebase.
>>>
>>> We're experiencing some problems associated with running Axis2 with
>>> Tuscany under OSGi and I'd
>>> appreciate any help you can give us.
>>>
>>> The problem we've run into relates to user-provided Message Receiver
>>> classes that are part of the
>>> Tuscany code and which are configured into axis2.xml as follows:
>>>
>>>    <messageReceivers>
>>>
>>>       <!-- Added by Tuscany -->
>>>        <messageReceiver mep="http://www.w3.org/2004/08/wsdl/in-only"
>>>
>>>
>>> class="org.apache.tuscany.sca.binding.ws.axis2.Axis2ServiceInMessageReceiver"/>
>>>
>>>        <messageReceiver mep="http://www.w3.org/2004/08/wsdl/in-only"
>>>
>>> class="org.apache.axis2.receivers.RawXMLINOnlyMessageReceiver"/>
>>>        <messageReceiver mep="http://www.w3.org/2004/08/wsdl/in-out"
>>>
>>> class="org.apache.axis2.receivers.RawXMLINOutMessageReceiver"/>
>>>
>>>       <!-- Added by Tuscany -->
>>>        <messageReceiver mep="http://www.w3.org/2004/08/wsdl/in-out"
>>>
>>>
>>> class="org.apache.tuscany.sca.binding.ws.axis2.Axis2ServiceInOutSyncMessageReceiver"/>
>>>
>>>       <!-- Added by Tuscany -->
>>>        <messageReceiver mep="http://www.w3.org/2006/01/wsdl/in-only"
>>>
>>>
>>> class="org.apache.tuscany.sca.binding.ws.axis2.Axis2ServiceInMessageReceiver"/>
>>>
>>>        <messageReceiver mep="http://www.w3.org/2006/01/wsdl/in-only"
>>>
>>> class="org.apache.axis2.receivers.RawXMLINOnlyMessageReceiver"/>
>>>        <messageReceiver mep="http://www.w3.org/2006/01/wsdl/in-out"
>>>
>>> class="org.apache.axis2.receivers.RawXMLINOutMessageReceiver"/>
>>>
>>>       <!-- Added by Tuscany -->
>>>        <messageReceiver mep="http://www.w3.org/2006/01/wsdl/in-out"
>>>
>>>
>>> class="org.apache.tuscany.sca.binding.ws.axis2.Axis2ServiceInOutSyncMessageReceiver"/>
>>>
>>>    </messageReceivers>
>>>
>>> When we run the code using OSGi, we get class loading exceptions for 
>>> those
>>> Tuscany message receiver
>>> classes, since the code that loads those classes is in the Axis2 code
>>> (AxisConfigBuilder) - but that
>>> code has no declared dependencies on the Tuscany packages containing the
>>> message receivers - so that
>>> we get class not found exceptions.
>>>
>>> Do you have a solution for this problem?
>>
>> Yes.  As you have mentioned the problem here is, The class loader which
>> loads Axis2 classes does not see the Tuscany classes.  You can use
>> DynamicaImport-Package OSGi manifest header for the Axis2 bundle.
>>
>> DynamicImport-Package: *
>>
>> This allows Axis2 bundle to dynamically load classes from other bundles
>> which are not wired during the Resolving process performed by the OSGi
>> framework implementation. At the same time, you need to export the 
>> package
>> in which message receiver classes reside.
>>
>>
>>>
>>>
>>> I got the code working with the Eclipse/Equinox version of OSGi by
>>> patching the following into the
>>> manifest for the axis2-kernel jar:
>>>
>>> Eclipse-BuddyPolicy: dependent
>>>
>>> ...and then declaring the relevant Tuscany jar files as being buddies of
>>> the axis2-kernel bundle in
>>> thier manifests.
>>
>> Seems like your implementation works only with Equinox, since you have 
>> used
>> Equinox specific constructs.
>>
>>>
>>>
>>> However, I know that this is really a sticking-plaster solution and will
>>> only currently work for the
>>> Equinox version of OSGi.  Do you have a nice neat solution that will 
>>> work
>>> for all the OSGi
>>> implementations?
>>
>> Yes.  We, in WSO2 have built WSO2 Carbon [1]  which runs on OSGi. WSO2
>> Carbon is the base platform for all the WSO2 java projects. Carbon uses
>> Axis2 and we have solved most of these problems.
>>
>>>
>>>
>>>
>>> Yours,  Mike.
>>>
>>
>> [1] http://wso2.org/projects/carbon
>>
>> --
>> Sameera Jayasoma
>> Software Engineer
>> WSO2 Inc.
>> Oxygenating the Web Service Platform.
>> http://wso2.org/
>>
>> blog:http://tech.jayasoma.org/
>> 

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