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From "Aaron Mulder" <ammul...@alumni.princeton.edu>
Subject Re: Removing attributes and refs from the config.xml
Date Sat, 25 Feb 2006 20:06:27 GMT
I accidentally followed up to this off-list, but I think Jeff and I
have agreed to disagree.  I prefer to avoid adding extra attributes to
support an empty string value when we don't seem to really have a need
for empty string values.  Jeff (if I can try to summarize) feels that
we ought to support all 3 possibilities (null, empty, not set) for the
benefit of future GBean implementers who might have different needs. 
Additional input would be appreciated.

Thanks,
   Aaron

On 2/24/06, Jeff Genender <jgenender@apache.org> wrote:
>
>
> Aaron Mulder wrote:
> > What's wrong with just listing the attribute or reference with no
> > content but without the new "empty=true"?  As in:
> >
> > <gbean name="TomcatEngine">
> >   <reference name="TomcatValveChain" />
> > </gbean>
> >
>
> This may be fine for references, but an empty string could be a
> reasonable and valid setting for an attribute.  Therefore we need a way
> to designate a difference between an empty string value, a null value,
> and full removal of setting the value.
>
> I also believe that we should be consistent.  So the way we do it for
> one, we probably should do it for the other.
>
> Jeff
>
> > Thanks,
> >     Aaron
> >
> > On 2/24/06, Jeff Genender <jgenender@apache.org> wrote:
> >> The config.xml allows us to declare new GBeans and override references
> >> and attributes of already existing Gbeans. But there is a missing
> >> configuration item here, which is the ability to *remove* a reference or
> >> attribute value from the configuration.  Currently there is no way to do
> >> this.
> >>
> >> Matt Hogstrom and I ran into this when trying to remove a logging
> >> reference in one of the GBeans.
> >>
> >> An example of this is the TomcatValveChain on the TomcatEngine.  As it
> >> stands, our default implementation installs an AccessLogValve into the
> >> TomcatValveChain reference.  We wanted to shut off logging to test
> >> different performance numbers and found that there was no way to "clear"
> >> or remove a reference that was set in the car plan via the config.xml,
> >> without rebuilding the car from the source.
> >>
> >> On further discussion with David J and Dain, we came up with a new xml
> >> attribute to place on refs and attribute tags. You would use:
> >>
> >> empty="true"
> >>
> >> Example:  You want to remove the access logger to improve web container
> >> performance, you would declare the following in the config.xml, which
> >> would remove the TomcatValveChain from the TomcatEngine:
> >>
> >> ...
> >> <configuration name="geronimo/tomcat/1.1-SNAPSHOT/car">
> >>     ...
> >>     <gbean name="FirstValve" load="false"/>
> >>
> >>     <gbean name="TomcatEngine">
> >>         <reference name="TomcatValveChain" empty="true"/>
> >>     </gbean>
> >>     ...
> >> </configuration>
> >> ...
> >>
> >> You would do the same for attributes that needed to be removed.
> >>
> >> I have this all coded up and ready to check in, but wanted to get any
> >> feedback or issues before I went ahead and did it.
> >>
> >> Comments?
> >>
> >> Jeff
> >>
>

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