[jira] [Commented] (CONFIGURATION-444) SubsetConfiguration does not properly handle interpolation when used on a HierarchicalConfiguration

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

    [ https://issues.apache.org/jira/browse/CONFIGURATION-444?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13016490#comment-13016490 ] 

Oliver Heger commented on CONFIGURATION-444:
--------------------------------------------

You should not create the {{SubsetConfiguration}} manually, but call the {{subset()}} method instead. (Please also refer to my comment on CONFIGURATION-442.) I have added a test case for {{HierarchicalConfiguration}} based on your description. The only difference is that the line
{code}
Configuration subset3 = new SubsetConfiguration(subset2,"prop");
{code}
has been replaced by
{code}
Configuration subset3 = subset2.subset("prop");
{code}

Then interpolation works as expected.

Your remarks about the implementation of {{SubsetConfiguration.interpolate()}} make sense. I don't know why it is implemented in this complicated way. In fact, the specialized configuration returned by the {{subset()}} method of {{HierarchicalConfiguration}} actually just delegates to its parent configuration for doing interpolation. When I find the time I will have a look if this implementation can be simplified.

I am not sure how the interpolation method could be exposed through the {{Configuration}} interface. It is not called directly by a client of a configuration object. Rather, the specific implementations of the various get methods are responsible for handling this feature.

> SubsetConfiguration does not properly handle interpolation when used on a HierarchicalConfiguration
> ---------------------------------------------------------------------------------------------------
>
>                 Key: CONFIGURATION-444
>                 URL: https://issues.apache.org/jira/browse/CONFIGURATION-444
>             Project: Commons Configuration
>          Issue Type: Bug
>          Components: Interpolation
>    Affects Versions: 1.6
>         Environment: all
>            Reporter: Fabien Nisol
>
> Imaging next text files:
> {code:xml}
> <properties>
> 	<var>a_value</var>
> 	<prop2>
> 		<prop
> 			attr1="${var}"
> 			attr2="attr2"
> 		/>
> 	</prop2>
> </properties>
> {code}
> {code:java}
> ...
>   XMLConfiguration config2 = new XMLConfiguration("test/test2.xml");
>   Configuration subset2 = config2.subset("prop2");
>   Configuration subset3 = new SubsetConfiguration(subset2,"prop");
>   System.err.println(subset3.getString("[@attr1]"))
> ...
> {code}
> the result is wrong:
> {code}
> ${var}
> {code}
> it should be:
> {code}
> a_value
> {code}
> I think the problem is related to the _interpolate()_ method in SubsetConfiguration(), which seems to involve some kind of recursive trick that seem overcomplicated (and inefficient, since it's creating unnecessary SubsetConfiguration)..
> But maybe I'm missing something.
> {code}
>     protected Object interpolate(Object base)
>     {
>         if (delimiter == null && "".equals(prefix))
>         {
>             return super.interpolate(base);
>         }
>         else
>         {
>             SubsetConfiguration config = new SubsetConfiguration(parent, "");
>             return config.interpolate(base);
>         }
>     }
> {code}
> I think the code below would be more appropriate:
> {code}
>     protected Object interpolate(Object base)
>     {
>         if(parent instanceof AbstractConfiguration)
>         {
>             return ((AbstractConfiguration)parent).interpolate(base);
>         } else {
>             return base;
>         }
>     }
> {code}
> There's no reason to try interpolation if the parent is not implementing interpolation. 
> This brings other questions about the whole interpolation thing. I really wonder why the _Configuration_ interface does not define that method, leaving or the the option to implementation to actually implement it. But that is another debate.

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