【JavaWeb】练习五

1>过滤器实现登录过滤

@WebFilter(urlPatterns = "*.do",initParams = {@WebInitParam(name="driver",value = "com.mysql.jdbc.Driver")})
public class LoginFilter implements Filter {
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;

        String uri = request.getRequestURI();
        if (uri.indexOf("login")!=-1){
            filterChain.doFilter(servletRequest,servletResponse);
        }
        else {
            Object users = request.getSession().getAttribute("users");
            if (users!=null){
                filterChain.doFilter(servletRequest,servletResponse);
            }
            else {
                request.setAttribute("error","请先登录");
                request.getRequestDispatcher("index.jsp").forward(request,response);
            }
        }
    }
}

2>监听器，统计在线人数

public class SessionListener implements HttpSessionListener, HttpSessionAttributeListener {

    @Override
    public void attributeAdded(HttpSessionBindingEvent se) {
        String name = se.getName();
        if ("users".equals(name)){
            ServletContext application = se.getSession().getServletContext();
            Object num  = application.getAttribute("num");
            if (num==null){
                application.setAttribute("num",1);
            }
            else {
                int n = Integer.parseInt(num.toString())+1;
                application.setAttribute("num",n);
            }
        }
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
    	ServletContext application = se.getSession().getServletContext();
       Object num  = application.getAttribute("num");
       if (num==null){
       		application.setAttribute("num",1);
            }
       else {
           int n = Integer.parseInt(num.toString())-1;
           application.setAttribute("num",n);
         }
    }
}