ant > map property names into a new set of properties - ant

Question

I'd like to "map" a bunch of ant properties, based on a prefix (sounds simple enough).
I have a solution, but it's not elegant (having to write out to a properties file, then read it back in!)
Question: Is there a quicker/more generic/simpler/out-of-the-box/straight-forward way of doing the below "load-propertyset" within ANT? (... than the example I've provided below)
(Roughly analogous to the Groovy > ConfigSlurper > Special Environment Configuration behaviour.)
For example:
<?xml version="1.0" encoding="UTF-8"?>
<project name="Config">
<!-- Section 1. (These will be loaded from a property file...) -->
<property name="a.yyy" value="foo" />
<property name="a.zzz" value="cat" />
<property name="b.xxx" value="bar" />
<property name="b.zzz" value="dog" />
<macrodef name="load-propertyset">
<attribute name="prefix" />
<attribute name="outfile" default="123" />
<attribute name="propset" default="123" />
<sequential>
<propertyset id="#{propset}">
<propertyref prefix="#{prefix}" />
<globmapper from="#{prefix}.*" to="*" />
</propertyset>
<echo level="debug">Created propertyset - '#{propset}' from prefix='#{prefix}'</echo>
<tempfile property="#{outfile}" suffix=".properties" deleteonexit="true" />
<echo level="debug">Writing propset to temp file - '${#{outfile}}'</echo>
<echoproperties destfile="${#{outfile}}">
<propertyset refid="#{propset}"/>
</echoproperties>
<echo level="debug">Reading props from temp file - '${#{outfile}}'</echo>
<property file="${#{outfile}}" />
<delete file="${#{outfile}}" />
</sequential>
</macrodef>
<load-propertyset prefix="a" />
<load-propertyset prefix="b" />
<echo>>>> Using variables xxx=${xxx} yyy=${yyy} zzz=${zzz}</echo>
</project>
I'm sure I'm missing something simple, for instance:
Can I reference properties within a propertyset? (e.g. ${myprops.yyy} ?)
I'd like to avoid something like ${${filter}.hostname}.

Answer 1

The third-party Ant-Contrib has an <antcallback> task that takes the <antcall> task and adds the ability to return properties to the caller:
<?xml version="1.0" encoding="UTF-8"?>
<project name="Config" default="run">
<taskdef resource="net/sf/antcontrib/antlib.xml" />
<!-- Section 1. (These will be loaded from a property file...) -->
<property name="a.yyy" value="foo" />
<property name="a.zzz" value="cat" />
<property name="b.xxx" value="bar" />
<property name="b.zzz" value="dog" />
<macrodef name="load-propertyset">
<attribute name="prefix" />
<attribute name="return" />
<sequential>
<antcallback target="-empty-target" return="#{return}">
<propertyset>
<propertyref prefix="#{prefix}" />
<globmapper from="#{prefix}.*" to="*" />
</propertyset>
</antcallback>
</sequential>
</macrodef>
<target name="-empty-target"/>
<target name="run">
<property name="properties-to-return" value="xxx,yyy,zzz"/>
<load-propertyset prefix="a" return="${properties-to-return}"/>
<load-propertyset prefix="b" return="${properties-to-return}"/>
<echo>>>> Using variables xxx=${xxx} yyy=${yyy} zzz=${zzz}</echo>
</target>
</project>
The properties-to-return concept is a bit of a maintenance burden. Luckily, <antcallback> doesn't fail when asked to return a property that wasn't set. Only the properties-to-return property needs to be modified when you want a new mapped property.