How to transform property into multiple arguments to <exec> task - ant

Question

I have a property that contains multiple values, and I want to execute a command with a separate "-j" argument for each value in the property.
E.g. <property name="arguments" value="foo bar hello world"/>
Should execute: mycommand -j foo -j bar -j hello -j world
I'm using Ant 1.7.1, so I can't use the "prefix" attribute (Ant 1.8) on the <arg> element of an <exec> task.
One workaround is to insert the "-j" directly into the property by hand and then use the "line" attribute of <arg>:
<property name="args" value="-j foo -j bar -j hello -j world"/>
<exec executable="mycommand">
<arg line="${args}"/>
</exec>
...But I prefer to have the property be a simple list without the embedded arguments.
Edit: Actually, my arguments are paths within an XML file, so a more accurate argument list would be:
<property name="arguments" value="/foo/bar /hello/world /a/very/long/path"/>
I would like the command to then execute with arguments: "-j /foo/bar -j /hello/world -j /a/very/long/path". Note that the slashes remain forward slashes even under Windows (these are arguments to a command, not filenames).

Answer 1

You can use Ant resource tools for this.
<property name="arg_list" value="foo bar hello world"/>
<resources id="arguments">
<mappedresources>
<string value="${arg_list}" />
<filtermapper>
<replacestring from=" " to=" -j "/>
</filtermapper>
</mappedresources>
</resources>
<property name="arguments" value="-j ${toString:arguments}" />
The above will result in property arguments having the value -j foo -j bar -j hello -j world, which can then be used in the exec arg line.
Alternatively a pathconvert task can help in this regard:
<property name="arg_list" value="foo bar hello world"/>
<pathconvert property="arguments" pathsep=" ">
<chainedmapper>
<flattenmapper />
<regexpmapper from="(.*)" to="-j \1" />
</chainedmapper>
<filelist files="${arg_list}" />
</pathconvert>
If you have absolute paths, rather than just strings in the list, then remove the flattenmapper.
If you have relative paths, replace the flattenmapper line with:
<globmapper from="${basedir}/*" to="*" />
to prevent the paths being converted to absolute.
In the event that you have UNIX-like paths in the arg_list on a Windows system the default settings for pathconvert won't work - the paths get converted to Windows style. Instead, to process the list use:
<pathconvert property="arguments" pathsep=" " targetos="unix">
<chainedmapper>
<regexpmapper from="C:(.*)" to="-j \1" />
</chainedmapper>
<filelist files="${arg_list}" />
</pathconvert>
Note the targetos setting and the revised regexmapper from argument.

Answer 2

Use some for loop, here's a solution based on Ant Addon Flaka :
<project name="demo" xmlns:fl="antlib:it.haefelinger.flaka">
<!-- make standard ant tasks like i.e. exec understand EL expressions -->
<fl:install-property-handler/>
<property name="arguments" value="foo bar hello world"/>
<fl:for var="arg" in="split('${arguments}',' ')">
<exec executable="mycommand">
<arg line="#{arg} -j"/>
</exec>
</fl:for>
</project>

Answer 3

Not sure your comfort with scripting languages, but you can also embed script to do the parsing/reassembling:
http://ant.apache.org/manual/Tasks/script.html
I will say, I think it's a bit fragile because you have an explicit reference to the ANT project's name, but up to you:
<?xml version="1.0" encoding="utf-8"?>
<project name="ScriptProj" basedir=".">
<property name="arguments" value="foo bar hello world"/>
<target name="test">
<script language="javascript">
<![CDATA[
argsParm = ScriptProj.getProperty("arguments");
argsParmAmend = "";
args = argsParm.split(" ");
for (i = 0; i < args.length; i++)
argsParmAmend = argsParmAmend + "-j " + args[i] + " ";
// remove trailing string
ScriptProj.setProperty("arguments.amended", argsParmAmend.substr(0, argsParmAmend.length-1));
]]>
</script>
<echo>${arguments}</echo>
<echo>${arguments.amended}</echo>
</target>
</project>