Here’s an example from a project I am currently working on. I suspect you can modify it to work for your situation.
<path id="master-classpath">
<fileset dir="${web.dir}/WEB-INF/lib">
<include name="*.jar"/>
</fileset>
<fileset dir="${appserver.lib}">
<include name="servlet*.jar"/>
</fileset>
<pathelement path="${build.dir}"/>
</path>
...
<javac destdir="${build.dir}">
<src path="${src.dir}"/>
<classpath refid="master-classpath"/>
</javac>