Re: [loom] [dna] Properties in component configurations

On Fri, 2003-11-14 at 01:37, Peter Donald wrote:
> On Fri, 14 Nov 2003 12:34 pm, Ryan Hoegg wrote:
> > Wanted to get your thoughts on using properties in component
> > configuration like in maven / jelly.
> >
> > My first thought is that it should be done transparently by the
> > container, but I don't know if that should somehow be mentioned in DNA.
> > Thoughts?
> 
> I definetly prefer this way. If I understand you correctly what you want to be 
> able to do is something like variable interpolation in configuration ala
> 
> <foo>
>   <dir>${loom.home}</dir>
> </foo>
> 
> If you look in the CLIMain class in Loom you will see that we actually do this 
> for kernel.xml. 
> 
> final Properties params = new Properties();
> params.setProperty( "loom.home", home.getAbsolutePath() );
> final Configuration root = ConfigUtil.expandValues( original, params );
> 
> So loom.home will be expanded in config xml. You could easily expand this to 
> work with all components aswell. Maybe expand a set of default properties + 
> any defined in SAR-INF/config.properties or something.
> 
> Alternatively you could use Jexl (http://jakarta.apache.org/commons/jexl) to 
> expand properties (which is what maven uses). Jexl is good in that you get to 
> do manipulation on objects (string caternating or cutting etc) and can invoke 
> methods etc on values.
> 
> The final method would be to treat the whole config.xml as a jelly script and 
> process it. 
> 
> The ConfigUtil post-processes the configuration after parsing but a far better 
> approach would be to write an XMLFilterImpl that expands the variables it 
> finds etc.

I guess I completely missed the boat on that one. I thought you were
talking about directly configuring components ... Wasn't paying
attention.

At any rate now that I actually know what you're talking about here's a
little Reader that does the trick:

http://cvs.codehaus.org/viewcvs.cgi/plexus/plexus-utils/src/java/org/codehaus/plexus/util/InterpolationFilterReader.java?rev=1.1&root=codehaus&view=auto

Just provide a Map of values, a Reader and begin/end token markers and
the values in the Map will be interpolated into the stream. In plexus I
use a an map adapter for the context and interpolate every configuration
that's processed.

-- 
jvz.

Jason van Zyl
[email protected]
http://tambora.zenplex.org

In short, man creates for himself a new religion of a rational
and technical order to justify his work and to be justified in it.
  
  -- Jacques Ellul, The Technological Society