public class LoginFilter implements Filter {      private String permitUrls[] = null;      private String gotoUrl = null;      public void destroy() {          // TODO Auto-generated method stub          permitUrls = null;          gotoUrl = null;      }      public void doFilter(ServletRequest request, ServletResponse response,              FilterChain chain) throws IOException, ServletException {          // TODO Auto-generated method stub          HttpServletRequest res=(HttpServletRequest) request;          HttpServletResponse resp=(HttpServletResponse)response;          if(!isPermitUrl(request)){              if(filterCurrUrl(request)){                  System.out.println("--->请登录");                  resp.sendRedirect(res.getContextPath()+gotoUrl);                  return;              }          }          System.out.println("--->允许访问");          chain.doFilter(request, response);      }      public boolean filterCurrUrl(ServletRequest request){          boolean filter=false;          HttpServletRequest res=(HttpServletRequest) request;          User user =(User) res.getSession().getAttribute("user");          if(null==user)              filter=true;          return filter;      }            public boolean isPermitUrl(ServletRequest request) {          boolean isPermit = false;          String currentUrl = currentUrl(request);          if (permitUrls != null && permitUrls.length > 0) {              for (int i = 0; i < permitUrls.length; i++) {                  if (permitUrls[i].equals(currentUrl)) {                      isPermit = true;                      break;                  }              }          }          return isPermit;      }             //请求地址      public String currentUrl(ServletRequest request) {            HttpServletRequest res = (HttpServletRequest) request;          String task = request.getParameter("task");          String path = res.getContextPath();          String uri = res.getRequestURI();          if (task != null) {// uri格式 xx/ser              uri = uri.substring(path.length(), uri.length()) + "?" + "task="                     + task;          } else {              uri = uri.substring(path.length(), uri.length());          }          System.out.println("当前请求地址:" + uri);          return uri;      }      public void init(FilterConfig filterConfig) throws ServletException {          // TODO Auto-generated method stub          String permitUrls = filterConfig.getInitParameter("permitUrls");          String gotoUrl = filterConfig.getInitParameter("gotoUrl");             this.gotoUrl = gotoUrl;             if (permitUrls != null && permitUrls.length() > 0) {              this.permitUrls = permitUrls.split(",");          }      }  }

<filter>      <filter-name>loginFilter</filter-name>      <filter-class>filter.LoginFilter</filter-class>         <init-param>          <param-name>ignore</param-name>          <param-value>false</param-value>      </init-param>      <init-param>          <param-name>permitUrls</param-name>          <param-value>/,/servlet/Loginservlet?task=login,/public.jsp,/login.jsp</param-value>      </init-param>      <init-param>          <param-name>gotoUrl</param-name>          <param-value>/login.jsp</param-value>      </init-param>  </filter>  <filter-mapping>      <filter-name>loginFilter</filter-name>      <url-pattern>/*</url-pattern>  </filter-mapping>