Java web过滤器验证登录防止未登录进入界面

import java.io.IOException;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;public class LoginFilter implements Filter { @Override public void init(FilterConfig filterConfig) throws ServletException {  // TODO Auto-generated method stub } @Override public void doFilter(ServletRequest request, ServletResponse response,   FilterChain chain) throws IOException, ServletException {  // 获得在下面代码中要用的request,response,session对象  HttpServletRequest servletRequest = (HttpServletRequest) request;  HttpServletResponse servletResponse = (HttpServletResponse) response;  HttpSession session = servletRequest.getSession();  // 获得用户请求的URI  String path = servletRequest.getRequestURI();  //System.out.println(path);  // 从session里取员工工号信息  String empId = (String) session.getAttribute("empId");  /*创建类Constants.java，里面写的是无需过滤的页面  for (int i = 0; i < Constants.NoFilter_Pages.length; i++) {   if (path.indexOf(Constants.NoFilter_Pages[i]) > -1) {    chain.doFilter(servletRequest, servletResponse);    return;   }  }*/  // 登陆页面无需过滤  if(path.indexOf("/login.jsp") > -1) {   chain.doFilter(servletRequest, servletResponse);   return;  }  // 判断如果没有取到员工信息,就跳转到登陆页面  if (empId == null || "".equals(empId)) {   // 跳转到登陆页面   servletResponse.sendRedirect("/JingXing_OA/login.jsp");  } else {   // 已经登陆,继续此次请求   chain.doFilter(request, response);  } } @Override public void destroy() {  // TODO Auto-generated method stub }}

<!-- 配置登陆过滤器 --><filter>  <filter-name>login</filter-name>  <filter-class>com.jingxing.oa.filter.LoginFilter</filter-class> </filter> <filter-mapping>  <filter-name>login</filter-name>  <url-pattern>/*</url-pattern></filter-mapping>

<!-- 配置登陆过滤器 --> <filter>  <filter-name>login</filter-name>  <filter-class>com.jingxing.oa.filter.LoginFilter</filter-class> </filter> <filter-mapping>  <filter-name>login</filter-name>  <url-pattern>/a/*</url-pattern> </filter-mapping>