FileInputStream in = new FileInputStream("configFile");
this will work only if the file is in your current working directory.
i believe the file should be in your WEB-INF/classes folder.
or the other way...
you can specify the real path of the file using..
this will return your servlet context path eg.. http://host/contextPath/,
where contextPath is the context path of this ServletContext.
then append the file name with the path.. in your case it should be
String fPath = this.getServletContext().getRealPath("/") + "WEB-INF/configFile";
Think experts will come out with more suggestions...