j2ee中如何拦截jsp页面？

public class RightFilter implements Filter { public void init(FilterConfig filterConfig) throws ServletException { } public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest; HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse; User user = (User) httpServletRequest.getSession(true).getAttribute("user"); if (!isExcludePages(httpServletRequest.getRequestURI())) { if (user == null) { httpServletResponse.sendRedirect(httpServletRequest.getContextPath() + "/login.jsp"); return; } } filterChain.doFilter(servletRequest, servletResponse); } private boolean isExcludePages(String url) { return url.indexOf("login.dhtml") != -1
                || url.indexOf("logout.dhtml") != -1
                || url.indexOf("login.jsp") != -1
                || url.endsWith(".css") || url.endsWith(".js") || url.endsWith(".gif") || url.endsWith(".jpg") || url.endsWith(".png"); } public void destroy() { } }

<filter>
  <filter-name>rightFilter</filter-name> 
  <filter-class>com.xxx.filter.RightFilter</filter-class> 
  </filter>

<filter-mapping>
        <filter-name>rightFilter</filter-name>
        <url-pattern>*.dhtml</url-pattern>
    </filter-mapping>