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https://issues.apache.org/jira/browse/CONFIGURATION-363?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Oliver Heger resolved CONFIGURATION-363.
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Resolution: Fixed
The nested interpolation feature is available with Commons Lang 2.6. A unit
test was added to verify that it actually works.
However, in the {{StrSubstitutor}} class of Commons Lang the feature is
disabled by default. In order to stay compatible with older Lang versions, I
did not want to use an API which is available in version 2.6 only.
So the configuration API does not provide a convenience method to enable nested
interpolation. Rather, you have to switch on this mode manually on the
substitutor used by the configuration. This can be done as follows:
{code}
AbstractConfiguration config = ...
config.getSubstitutor().setEnableSubstitutionInVariables(true);
{code}
> Consider enhancing to allow nested variable interpolation
> ---------------------------------------------------------
>
> Key: CONFIGURATION-363
> URL: https://issues.apache.org/jira/browse/CONFIGURATION-363
> Project: Commons Configuration
> Issue Type: Improvement
> Components: Interpolation
> Reporter: Rob Walker
> Assignee: Oliver Heger
> Priority: Minor
> Fix For: 1.7
>
>
> It would be really handy of Commons Configuration 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.
> Care is needed to avoid recursion, which can been handled through use of a
> "Cycle Map" that detects of an inner variable has already been referenced.
> An example of this can be found in the substVars method of the Apache Felix
> org.apache.felix.framework.util.Util class.
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