build.xml

<?xml version="1.0"?>
<project basedir="." default="compile">

  <taskdef name="jscomp" classname="com.google.javascript.jscomp.ant.CompileTask"
           classpath="build/closure-compiler.jar"/>

  <target name="compile">

    <filelist id="sources" dir="${basedir}/src/js">
      <file name="main.js"/>
    </filelist>

    <concat destfile="war/js/main_uncompiled.js" append="false">
      <filelist refid="sources" />
    </concat>

    <jscomp compilationLevel="whitespace" warning="quiet"
            debug="true" output="war/js/main_debug.js">
      <sources refid="sources" />
    </jscomp>

    <jscomp compilationLevel="simple" warning="verbose" 
            debug="false" output="war/js/main_optimized.js">
      <sources refid="sources" />
    </jscomp>

  </target>

  <target name="clean">

    <delete>
      <fileset dir="war/js">
        <include name="*.js"/>
      </fileset>
    </delete>

  </target>

</project>