Java exception unknown source

Sometimes when debugging application we may run into this exception - Java Exception unknown source.
The possible reason could be when compiling the application, javac ant tasks omits debug option by defaut. So we will have to explicity set debug flag to true. See the javac ant task documentation for more info. You can mention some thing like below:

<target name="compile">
  <javac srcdir="${src.dir}" destdir="{dest.dir}." debug="on" debuglevel="lines,vars,source" />
</target>

Hope this helps.