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From Ralph Goers <Ralph.Go...@dslextreme.com>
Subject Re: Maven dependency resolution (Re: svn commit: r517439 - /cocoon/trunk/core/cocoon-servlet-service/cocoon-servlet-service-impl/pom.xml)
Date Wed, 14 Mar 2007 06:02:05 GMT
Grzegorz Kossakowski wrote:
> I would suggest to read my mail once again. The problem is that ClassNotFoundException
will not be thrown.
> Let's assume me have A, B, C:
> A depends on B and dependency is declared in A's pom
> B depends on C and dependency is declared in B's pom
> A depends on C but dependency is not declared in A's pom
>
> Now A's dependency on C will be satisfied by transitive dependency. However, transitive
dependencies are really
> vulnerable to the ambiguity of dependency mediation. My main point was that we should
avoid satisfying dependencies by
> transitive dependencies. Given that, we should find a way to find out that we really
rely on transitive dependencies.
>   
My point was that transitive dependencies need not be ambiguous any 
longer. Project A can now specify in it's dependencyManagement section a 
version for C. If C is referenced in a transitive dependency its version 
will be ignored and the version specified in the dependencyManagement 
will be used instead.  I suspect that the reason C isn't in A's pom is 
that it isn't an "explicit" dependency, i.e. it is only referenced 
indirectly through B. In this case a transitive dependency is appropriate.

As a developer you should go through the dependencies you are using in 
your pom and find out what their dependencies are and explicitly define 
them in your dependencyManagement (or a parent's). If you don't do this 
you will eventually end up with a mess.  This is exactly why this patch 
was developed.

Yes, the case above can occur, and is probably likely with the released 
versions of Maven. However, with explicit dependencyManagement it should 
not occur if developers do what they are supposed to.  The real culprit 
in your scenario above wasn't that there was a transitive dependency. It 
was that the way in which you declare the version of the transitive 
dependency.

So ultimately, if there is a single "master" pom it would contain all 
the versions of everything used anywhere in Cocoon. directly or 
indirectly. Since ultimately every other project would extend this you 
could be assured that the versions are in synch.

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