From your ant buildfile, I assume that what you want is to create a single JAR archive that will contain not only your application classes, but also the contents of other JARs required by your application.
However your build-jar
file is just putting required JARs inside your own JAR; this will not work as explained here (see note).
Try to modify this:
<jar destfile="${jar.file}"
basedir="${build.dir}"
manifest="${manifest.file}">
<fileset dir="${classes.dir}" includes="**/*.class" />
<fileset dir="${lib.dir}" includes="**/*.jar" />
</jar>
to this:
<jar destfile="${jar.file}"
basedir="${build.dir}"
manifest="${manifest.file}">
<fileset dir="${classes.dir}" includes="**/*.class" />
<zipgroupfileset dir="${lib.dir}" includes="**/*.jar" />
</jar>
More flexible and powerful solutions are the JarJar or One-Jar projects. Have a look into those if the above does not satisfy your requirements.