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From "Rob Walker (JIRA)" <j...@apache.org>
Subject [jira] Created: (CONFIGURATION-364) Enhance StrSubstitutor to support nested ${var-${subvr}} expansion
Date Fri, 06 Feb 2009 13:23:59 GMT
Enhance StrSubstitutor to support nested ${var-${subvr}} expansion
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                 Key: CONFIGURATION-364
                 URL: https://issues.apache.org/jira/browse/CONFIGURATION-364
             Project: Commons Configuration
          Issue Type: Improvement
            Reporter: Rob Walker


It would be really handy of StrSubstitutor could support nested variable interpolation:

org.osgi.framework.system.packages=org.osgi.framework; version=1.4.0, \
org.osgi.service.packageadmin; version=1.2.0, \
org.osgi.service.startlevel; version=1.1.0, \
org.osgi.service.url; version=1.0.0, \
org.osgi.util.tracker; version=1.3.3 \
${jre-${java.specification.version}}

The process being to expand innermost variable references first and work outwards - this allows
for very advance config, such as the above, which can dynamically detect the Java version
and expand a JRE version specific property into the property being defined.


Looking at the implementation, it seems it might be a fairly straightforward enhancement to:

    private int substitute(StrBuilder buf, int offset, int length, List priorVariables)

The code already has the cyclic map in place. 

I already have code that achieves this within Apache Felix, so I will see if I can retro-fit
a similar model to the above and if so submit  a patch. 

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