[jira] Resolved: (CONFIGURATION-363) Consider enhancing to allow nested variable interpolation

["Oliver Heger (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CONFIGURATION-363?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Oliver Heger resolved CONFIGURATION-363.
----------------------------------------

    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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