Servlet过滤器和监听器

1，Servlet过滤器

 <filter>
     <filter-name>charset</filter-name>
     <filter-class>org.guangsoft.filter.CharsetFilter</filter-class>
     <init-param>
         <param-name>encoding</param-name>
         <param-value>utf-8</param-value>
     </init-param>
 </filter>

 <filter-mapping>
         <filter-name>encoding</filter-name>
     <url-pattern>/*</url-pattern>
 </filter-mapping>

 Filter:
     package org.guangsoft.filter;

 public class CharsetFilter implements Filter
 {
     private String encoding;
     public void init(FilterConfig filterconfig) throws ServletException
     {
         this.encoding = filterconfig.getInitParameter("endcoding");
     }
     public void doFilter(ServletRequest req, ServletResponse resp,
             FilterChain chain) throws IOException, ServletException
     {
         req.setCharacterEncoding(encoding);
         chain.doFilter(req, resp);
     }
     public void destroy()
     {
     }
 }
         

2,Servlet监听器

Web.xml:
    <listener>
        <listener-class>org.guangsoft.listener.CountListener</listener-class>
</listener>
Listener:
public class CountListener implements HttpSessionListener 
{
    private ServletContext sc = null;
    public void sessionCreated(HttpSessionEvent se) 
　　{
        this.sc = se.getSession().getServletContext();
        Integer i = (Integer) this.sc.getAttribute("online");
        if (i == null)
            i = new Integer(0);
        i = new Integer((i.intValue()) + 1);
        this.sc.setAttribute("online", i);
    }
    public void sessionDestroyed(HttpSessionEvent httpsessionevent) 
　　{
        Integer i = (Integer) this.sc.getAttribute("online");
        if (i == null)
            i = new Integer(1);
        i = new Integer((i.intValue()) - 1);
        this.sc.setAttribute("online", i);
    }
}