A lovely little Ant task that not only makes one jar out of many (merge), it can also change package names of certain classes in byte-code! Ant Task using jarjar to rebuild jar packages https://code.google.com/p/jarjar

build.xml

<project name="generate-jarjar">
    <property name="jarjarfile" value="elfadili.jar"/>
    <path id="classpath">
      <pathelement location="jarjar-1.4.jar"/>
      <pathelement location="asm-2.2.3.jar"/>
    </path>
    <taskdef name="jarjar" classname="com.tonicsystems.jarjar.JarJarTask"   classpathref="classpath"/>
    <delete file="${jarjarfile}"/>
    <jarjar destfile="${jarjarfile}">
    <zipfileset src="xyz.jar"/>
    <rule pattern="com.xyz.**" result="com.elfadili.@1"/>
    </jarjar>
</project>