question: @ Override protected void doGet ( HttpServletRequest request , HttpServletResponse response ) throws IOException , ServletException { QueryCommand cmd = QueryCommand . UNKNOWN ; String param = request . getParameter ( "param" ) ; String value = request . getParameter ( "value" ) ; PrintWriter out = response . getWriter ( ) ; String cmdStr = request . getParameter ( "cmd" ) ; if ( cmdStr != null ) { cmd = QueryCommand . valueOf ( cmdStr ) ; } HttpSession session ; switch ( cmd ) { case SET : session = request . getSession ( ) ; session . setAttribute ( param , value ) ; break ; case GET : session = request . getSession ( ) ; String val = ( String ) session . getAttribute ( param ) ; if ( val != null ) { out . write ( val ) ; } break ; case INVALIDATE : session = request . getSession ( ) ; session . invalidate ( ) ; break ; case CALLBACK : Callback c = ( Callback ) context . getAttribute ( "callback" ) ; c . call ( request , response ) ; break ; } }
target:  The standard servlet method overridden.