[opencms-dev] Different version jars in lib folder

Fri Apr 15 17:12:12 CEST 2011

Update:

Confirmed that redeployment of the particular OpenCms webapp 
causes ClassCastExceptions to re-appear.

Paul

> -----Original Message-----
> From: opencms-dev-bounces at opencms.org 
> [mailto:opencms-dev-bounces at opencms.org] On Behalf Of 
> Paul-Inge Flakstad
> Sent: 15. april 2011 11:59
> To: The OpenCms mailing list
> Subject: Re: [opencms-dev] Different version jars in lib folder
> 
> Hi again Achim,
> 
> I should clearify that it isn't Tomcat that's throwing 
> exceptions around, it's a JSP I wrote that's parsing XML 
> files.
> 
> The JSP is fine until [something] happens (possibly a redeploy 
> of the OpenCms webapp it resides in), then it starts throwing 
> ClassCastExceptions. The first time I experienced this, I 
> found differing jars in the lib/ folder of the OpenCms webapp. 
> I took care of this, and thought that would be the end of it. 
> This time, however, I cannot seem to find any "version 
> conflict".
> 
> This is the reason I asked if different versions of a library 
> can cause conflict when the versions reside in two different 
> webapp/WEB-INF/lib folders/. I'm not sure if you noticed in 
> my first e-mail that they were _different_ webapps?
> webapp_one/WEB-INF/lib/mylibrary-v1.0.jar  <-- one webapp
> webapp_two/WEB-INF/lib/mylibrary-v2.0.jar  <-- another webapp
> 
> I have 3 OpenCms instances running on the same Tomcat, they're 
> version 7.5.2 and 7.5.3 (so not a huge difference). I 
> restarted Tomcat last night, and everything was fine after 
> that, but I don't know what will happen when I redeploy the 
> webapp. 
> 
> I'll have a look at the link you gave me. Maybe I can make 
> sense of things.
> 
> Thanks for your time and help, Achim - much appreciated! :)
> 
> Cheers,
> Paul
> 
> > -----Original Message-----
> > From: opencms-dev-bounces at opencms.org 
> > [mailto:opencms-dev-bounces at opencms.org] On Behalf Of Achim 
> Westermann
> > Sent: 15. april 2011 10:10
> > To: The OpenCms mailing list
> > Subject: Re: [opencms-dev] Different version jars in lib folder
> > 
> > Hi Paul,
> > 
> > > You're absolutely right, and memory serves you well - they 
> > were 334 bytes indeed.
> > 
> > Uuuuh.... Yesssss!
> > 
> > >  From what you say, I gather it's risky to have different 
> > versions of OpenCms on the same Tomcat, then? (Since they may 
> > employ different version jars, which could cause conflict?)
> > 
> > I'd consider it a bug if tomcat runs into Classloading errors 
> > if several 
> > OpenCms versions are deployed to different webapplications. 
> > But I am not 
> > sure now if there might be a special case where this might 
> > happen. The 
> > mechanism of classloading is explained here: 
> > http://tomcat.apache.org/tomcat-6.0-doc/class-loader-howto.html
> > 
> > HTH,
> > Achim
> > 
> > > Cheers,
> > > Paul
> > >
> > >> -----Original Message-----
> > >> From: opencms-dev-bounces at opencms.org
> > >> [mailto:opencms-dev-bounces at opencms.org] On Behalf Of 
> > Achim Westermann
> > >> Sent: 14. april 2011 22:41
> > >> To: The OpenCms mailing list
> > >> Subject: Re: [opencms-dev] Different version jars in lib folder
> > >>
> > >> Hi Paul,
> > >>
> > >>> For example, all of these:
> > >>> lucene-core-1.9.1.jar
> > >>> lucene-core-2.1.0.jar
> > >>> lucene-core-2.2.0.jar
> > >>> lucene-core-2.3.1.jar
> > >>> lucene-core-2.3.2.jar
> > >>> lucene-core-2.4.1.jar
> > >>
> > >> Most often this is the case for OpenCms installations that have
> > >> undergone at least one update. The setup routine will
> > >> overwrite previous
> > >> libraries with an empty jar file (size something like 334
> > >> bytes, don't
> > >> have this in memory) because in the past deletion of jar 
> > files failed
> > >> under some circumstances. It's OK to delete all the tiny 
> jar files.
> > >>
> > >>> (Most of the commons-xxx jars, and a bunch of others as
> > >> well, are also
> > >>> present in multiple versions.)
> > >>> What could be the cause of all these multiple versions? Is
> > >> it safe to
> > >>> delete the older versions and just keep the most recent?
> > >>> On a side-note:
> > >>> Can two different versions of the "same" jar cause
> > >> conflicts, if they
> > >>> reside in the separate webapps' lib folder?
> > >>> For example:
> > >>> webapp_one/WEB-INF/lib/mylibrary-v1.0.jar
> > >>> webapp_two/WEB-INF/lib/mylibrary-v2.0.jar
> > >>
> > >> Indeed this can cause ClassCastExceptions. It's a matter 
> of luck in
> > >> which order the jar files are loaded by the 
> ClassLoaders. Duplicate
> > >> non-empty jar files have to be deleted as you described.
> > >>
> > >> HTH,
> > >>
> > >> Achim
> > >>
> > >>
> > >> _______________________________________________
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> > >> please visit
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> > >>
> > >
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> 
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