A. public void valueUnbound（HttpSessionEvent ev）{...}
B. public void sessionPassivated（HttpSessionEvent ev）{...}
C. public void sessionDidActivate（HttpSessionEvent ev）{...}
D. public void sessionWillPassivate（HttpSessionEvent ev）{...}

A. A filter must implement the destroy method
B. A filter must implement the doFilter method
C. A servlet may have multiple filters associated with it
D. A servlet that is to have a filter applied to it must implement the javax.servlet.FilterChain  interface
E. A filter that is part of a filter chain passes control to the next filter in the chain by invoking the filterChain forward method
F. For each  element in the web application deployment descriptor， multiple instances of a filter may be created by the web container