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From Michael Ludwig <>
Subject Re: IS that a good idea moving all the common libs?
Date Tue, 21 Dec 2010 00:32:47 GMT
Luca Gervasi schrieb am 20.12.2010 um 18:15 (+0100):
> I'm trying to lower the permgen needed by a large amount of webapps
> moving all the commonly used libs to the tomcat common libs.
> My questions is: how good is that idea?
> I read that each *same* lib in WEB-INF/lib is handled as unique, thus
> requiring additional permgen space.

  Keep component libs in components

  Servlet and J2EE containers have a clear purpose: to provide a set
  of services to *independent* and *isolated* components. That set
  of services is defined by the servlet and j2ee specifications.
  These specifications also define a mechanism for components to
  provide any libraries they depend on -- WEB-INF/lib. 

  It is therefore a complete mystery to me why people seem so keen
  to push libraries up out of the components where they belong and
  into the container's library directories. It's like pushing user
  code into the operating system kernel. Just don't do it.

I think the fact that many developers are "keen to push libraries
up out of the components where they belong" is due to conceptions
stemming from other environments, or probably even from their
deeply entrenched desire to remove redundancy from systems, like
avoiding to duplicate code, or striving to normalize tables.

I remember those were my motivations before I had accepted that a
Java application server has been designed to work differently than
I had taken for granted.

Michael Ludwig

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