question: public boolean isValid ( ) { if ( ! isValid ) { return false ; } if ( getMaxInactiveInterval ( ) >= 0 ) { long now = System . currentTimeMillis ( ) ; if ( now - attributes . getLastAccessedTime ( ) >= getMaxInactiveInterval ( ) * 1000 ) { return false ; } } return true ; }
target:  Determine whether the session is still valid or whether it has expired.