Exception if an error happens during handling of
the request. Common errors are:
IOException if an input/output error occurs and we are
processing an included servlet (otherwise it is swallowed and
handled by the top level error handler mechanism)
ServletException if a servlet throws an exception and
we are processing an included servlet (otherwise it is swallowed
and handled by the top level error handler mechanism)
Tomcat should be able to handle and log any other exception ( including
runtime exceptions )
