配置过滤器

配置过滤器，通过mapping的url-pattern将访问页面截住,通过import javax.servlet.Filter来进行一些校验处理，
,实现innt(),doFilter(),destory()然后转向页面
  代码：
  public class AccessFilter extends HttpServlet implements Filter {
      private FilterConfig filterConfig;  //Handle the passed-in FilterConfig
   private String loginPage;
      private String[] pageBeforeLogin;
      private final String[] DEFAULT_LOGIN_PAGE={"/login.jsp"};
      /**
       * 获取InitParameter
       * 登录页、不用登录就可以访问的页
       * @param filterConfig FilterConfig
       * @throws ServletException
       */
      public void init(FilterConfig filterConfig) throws ServletException {
        this.filterConfig = filterConfig;
    try
        {
          loginPage=filterConfig.getInitParameter("loginPage");
        }
        catch(java.lang.Exception e)
        {
          loginPage=DEFAULT_LOGIN_PAGE[0];
        }
        try
        {
          pageBeforeLogin=(loginPage + "," + filterConfig.getInitParameter("pageBeforeLogin")).split(",");
        }
        catch(Exception e)
        {
        }
      }
      //Process the request/response pair
      public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) {
        HttpServletRequest req=(HttpServletRequest) request;
        HttpServletResponse res=(HttpServletResponse) response;
        //先判断是否已经登录
 
           HttpSession session= req.getSession();
           if(session!=null&&session.getAttribute(SystemGlobals.LOGINUSERID)!=null){
                doNext(request, response, filterChain);
               return;
           }

           //clientRequest 记录真正的被请求的 URL 比如 /index.jsp;/login.jsp;/
           String clientRequest = req.getServletPath();
           System.out.println(clientRequest);
           for (int i=0;i<pageBeforeLogin.length;i++)
           {
             if (pageBeforeLogin[i].equalsIgnoreCase(clientRequest))
             {
                doNext(request,response,filterChain);
                return;
             }
           }

      //运行到此处说明必须转到登录界面
        try
        {
           //RequestDispatcher rd = this.filterConfig.getServletContext().getRequestDispatcher(loginPage); // req.getRequestDispatcher(loginPage);
           //rd.forward(request, res);
            res.sendRedirect(req.getContextPath()+ loginPage);
            return;
        }
        catch(Exception e)
        {
          e.printStackTrace();
        }

      }
     private void doNext(ServletRequest request, ServletResponse response, FilterChain filterChain)
     {
       try {
              filterChain.doFilter(request, response);
            }
            catch(ServletException sx) {
              filterConfig.getServletContext().log(sx.getMessage());
            }
            catch(IOException iox) {
              filterConfig.getServletContext().log(iox.getMessage());
            }
     }
      //Clean up resources
      public void destroy() {
      }
}
  web.xml配置：
  <filter>
    <filter-name>sessionloginchecker</filter-name>
    <filter-class>com.itsv.chy.system.permission.AccessFilter</filter-class>
    <init-param>
      <param-name>loginPage</param-name>
      <param-value>/system/login.jsp</param-value>
    </init-param>
    <init-param>
      <param-name>pageBeforeLogin</param-name>
      <param-value>/login.do,/logout.do</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>sessionloginchecker</filter-name>
    <url-pattern>index.jsp</url-pattern>
  </filter-mapping>
  <filter-mapping>
    <filter-name>sessionloginchecker</filter-name>
    <url-pattern>/accessAction.do</url-pattern>
  </filter-mapping>