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From "Millies, Sebastian" <Sebastian.Mill...@softwareag.com>
Subject Tuscany class loading (was: Re: Using EMF with Tuscany 1.6)
Date Tue, 27 Nov 2012 12:30:40 GMT
Hello there,

I've never been back to talk about this, so here goes.

To re-iterate the problem: I want to set up my contributions, so that they can use
different versions of third-party libraries than the Tuscany runtime. My original example
was using recent versions of EMF (hence the subject line), another example is using
Tuscany with an Apache Solr 4.0 backend, which requires different Apache Http Components.

The standard recommendation is [1], but I have had great trouble to get that to work. (The
reasons have to do with the use of SDOs in the application in question.)

I have therefore decided to try the opposite approach of  including any different versions
of components
used  by Tuscany in nested jars in the contribution itself. Nested jars in a zip contributionget
added into
the contribution classpath.

Here I am working under the assumption that the SCA contribution classloader would work
somewhat like a webapp class loader in that it would not follow the delegation model,
but would look for classes in the following order
1) inside the contribution
2) in the imports
3) in the parent classloader

With this behavior, everything goes well. For example, I can make calls to Apache Solr through
the solr-solrj-4.0.0.jar and its dependents, including httpclient-4.1.3.jar and httpcore-4.1.4.jar,
without impacting HTTP calls made by Tuscany-generated proxies elsewhere.

Here's the snag: As it turned out, org.apache.tuscany.sca.contribution.java.impl.ContributionClassLoader
DID
NOT work the way I expected, but rather looked in the parent classloader first, only then
inside the contribution.
I had to change the coding (in module contribution-java) and the associated test. A patch
is attached.

Would my change break anything, perhaps with respect to OSGi? Is there anything in the SCA
spec that mandates a
certain class loading behavior? I do feel that the alternative behavior is more natural than
the one that is currently
implemented. (There a very few resources on Tuscany classloading, and e. g. [2] does not seem
to mention
this particular issue.)

Unfortunately, I cannot get all the Tuscany 1.6  tests to compile and run with maven.

Please, would anyone be willing to see if Tuscany 1.6 with my patch applied would still pass
all current tests?
(unless my proposal is obviously wrong for other reasons, of course)

Best,
Sebastian

[2] https://cwiki.apache.org/TUSCANYWIKI/classloading.html

-----Ursprüngliche Nachricht-----
Von: Simon Nash [mailto:nash@apache.org]
Gesendet: Samstag, 25. August 2012 09:17
An: user@tuscany.apache.org
Betreff: Re: Using EMF with Tuscany 1.6

It's been over 2 years since I looked into this in detail and put together the list of gudelines
in [1], so I don't recall 100% of the detail of how this works.  See inline below for my impressions
of what may be happening.

 [cut]

I'll be interested to hear how you get on with that.

   Simon

> -- Sebastian
>
>>
>> [1]
>> http://mail-archives.apache.org/mod_mbox/tuscany-user/201006.mbox/%3C
>> 4C164DD3.8090405@apache.org%3E
>>
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