java web中用于检测用户是否登陆的过滤器(Filter - 3)

package OSChina;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * 用于检测用户是否登陆的过滤器，如果未登录，则重定向到指的登录页面
 * <p>
 * 配置参数
 * <p>
 * checkSessionKey 需检查的在 Session 中保存的关键字<br/>
 * redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath<br/>
 * notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath<br/>
 */
public class FilterDemoThree implements Filter {

 protected FilterConfig filterConfig = null;
 private String redirectURL = null;
 private List<String> notCheckURLList = new ArrayList<String>();
 private String sessionKey = null;

 public void destroy() {

  notCheckURLList.clear();
 }

 @Override
 public void doFilter(ServletRequest servletRequest,
   ServletResponse servletResponse, FilterChain filterChain)
   throws IOException, ServletException {

  HttpServletRequest request = (HttpServletRequest) servletRequest;
  HttpServletResponse response = (HttpServletResponse) servletResponse;

  HttpSession session = request.getSession();
  if (sessionKey == null) {
   filterChain.doFilter(request, response);
   return;
  }
  if ((!checkRequestURIIntNotFilterList(request))
    && session.getAttribute(sessionKey) == null) {
   response.sendRedirect(request.getContextPath() + redirectURL);
   return;
  }
  filterChain.doFilter(servletRequest, servletResponse);
 }

 public void init(FilterConfig filterconfig) throws ServletException {

  this.filterConfig = filterconfig;
  redirectURL = filterConfig.getInitParameter("redirectURL");
  sessionKey = filterConfig.getInitParameter("checkSessionKey");

  String notCheckURLListStr = filterConfig
    .getInitParameter("notCheckURLList");

  if (notCheckURLListStr != null) {
   StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";");
   notCheckURLList.clear();
   while (st.hasMoreTokens()) {
    notCheckURLList.add(st.nextToken());
   }
  }
 }

 private boolean checkRequestURIIntNotFilterList(HttpServletRequest request) {
  String uri = request.getServletPath()
    + (request.getPathInfo() == null ? "" : request.getPathInfo());
  return notCheckURLList.contains(uri);
 }

}