java 验证用户是否已经登录与实现自动登录方法详解

package cn.hongxin.filter;
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{
 public void init(FilterConfig filterConfig) throws ServletException {
 }
 public void doFilter(ServletRequest request, ServletResponse response,
  FilterChain chain) throws IOException, ServletException {
 //将request强转成htt...
 HttpServletRequest req = (HttpServletRequest) request;
 //获取session
 HttpSession ss = req.getSession();
 //从session中获取user
 if(ss.getAttribute("user")==null){
  System.err.println("你还没有登录");
  req.getSession().setAttribute("msg", "请你先登录");
  //重定向到登录
  HttpServletResponse resp = (HttpServletResponse) response;
  resp.sendRedirect(req.getContextPath()+"/index.jsp");[W2] 
 }else{
  //放行
  chain.doFilter(request, response);
 }
 }
 public void destroy() {
 }
}

<filter>
 <filter-name>login</filter-name>
 <filter-class>cn.itcast.filter.LoginFilter</filter-class>
 </filter>
 <filter-mapping>
 <filter-name>login</filter-name>
 <url-pattern>/jsps/*</url-pattern>
 <url-pattern>/views/*</url-pattern>
 </filter-mapping>

<c:choose>
 <c:when test="${empty sessionScope.name}">
 <form name="x" method="post" action="<c:url value='/LoginServlet'/>">
  Name:<input type="text" name="name"/><br/>
  auto:
  <input type="radio" name="auto" value="-1">不自动登录
  <br/>
  <input type="radio" name="auto" value="1">1天<br/>
  <input type="radio" name="auto" value="7">1周<br/>
  <input type="submit"/>
 </form>
 </c:when>
 <c:otherwise>
 你已经登录了:${name}<br/>
 <a href="<c:url value='/LoginServlet'/>">退出</a>
 </c:otherwise>
</c:choose>

public void doPost(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 //接收用户姓名
 String name = request.getParameter("name");
 String auto = request.getParameter("auto");
 //将用户信息放到session
 request.getSession().setAttribute("name",name);
 //判断auto是否是-1
 if(!auto.equals("-1")){
  int day = Integer.parseInt(auto);//1|7
  int seconds = 60*60*24*day;
  //声明cookie
  Cookie c = new Cookie("autoLogin",name);
  c.setMaxAge(seconds);
  c.setPath(request.getContextPath());
  //保存cookie
  response.addCookie(c);
 }
 }

public void doFilter(ServletRequest request, ServletResponse response,
  FilterChain chain) throws IOException, ServletException {
 //在这儿读取cookie
 HttpServletRequest req = (HttpServletRequest) request;
 //获取所的有cookie
 Cookie[] cs = req.getCookies();
 if(cs!=null){
  for(Cookie c:cs){
  if(c.getName().equals("autoLogin")){//如果存在自动登录的cookie
   String value = c.getValue();//用户名称
   //登录成功是指
   req.getSession().setAttribute("name", value);
   break;
  }
  }
 }
 //不管是否自动登录成
 chain.doFilter(request, response);
 }

<filter>
 <filter-name>auto</filter-name>
 <filter-class>cn.itcast.filter.AutoFilter</filter-class>
 </filter>
 <filter-mapping>
 <filter-name>auto</filter-name>
 <url-pattern>/*</url-pattern>
 </filter-mapping>

System.err.println("用户退出");
 //删除整个session
 request.getSession().invalidate();
 Cookie c = new Cookie("autoLogin", "ddd");
 c.setMaxAge(0);
 c.setPath(request.getContextPath());
 response.addCookie(c);
// request.getSession().removeAttribute("name");
 response.sendRedirect(request.getContextPath()+"/index.jsp");