I want my ant script to execute the command

java -cp libs/a.jar:libs/b.jar org.stack.class1 --package pName --out classes new.wsdl

How can I do it with an Ant script? The following does not work

<?xml version="1.0" encoding="UTF-8"?>
project name="class" default="compile">
<target name="compile">
    <java classname="org.stack.class1" fork="true">
    <classpath>
        <pathelement location="libs/a.jar"/>
        <pathelement location="libs/b.jar"/>

    </classpath>
    <arg value="--package pName --out classes new.wsdl"/>

    </java>
</target>