过滤器第一篇【介绍、入门、简单应用】（四）

   public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
        //让Web资源不缓存，很简单，设置http中response的请求头即可了！
        //我们使用的是http协议，ServletResponse并没有能够设置请求头的方法，所以要强转成HttpServletRequest
        //一般我们写Filter都会把他俩强转成Http类型的
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) resp;
        response.setDateHeader("Expires", -1);
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        //放行目标资源的response已经设置成不缓存的了
        chain.doFilter(request, response);
    }

   private String username ;
    private String password;
    public User() {
    }
    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }
    //各种setter和getter

  public class UserDB {
        private static List<User> users = new ArrayList<>();
        static {
            users.add(new User("aaa", "123"));
            users.add(new User("bbb", "123"));
            users.add(new User("ccc", "123"));
        }
        public static List<User> getUsers() {
            return users;
        }
        public static void setUsers(List<User> users) {
            UserDB.users = users;
        }
    }

   public User find(String username, String password) {
        List<User> userList = UserDB.getUsers();
        //遍历List集合，看看有没有对应的username和password
        for (User user : userList) {
            if (user.getUsername().equals(username) && user.getPassword().equals(password)) {
                return user;
            }
        }
        return null;
    }

<form action="${pageContext.request.contextPath}/LoginServlet">
    用户名<input type="text" name="username">
    <br>
    密码<input type="password" name="password">
    <br>
    <input type="radio" name="time" value="10">10分钟
    <input type="radio" name="time" value="30">30分钟
    <input type="radio" name="time" value="60">1小时
    <br>
    <input type="submit" value="登陆">
</form>

  //得到客户端发送过来的数据
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        UserDao userDao = new UserDao();
        User user = userDao.find(username, password);
        if (user == null) {
            request.setAttribute("message", "用户名或密码是错的！");
            request.getRequestDispatcher("/message.jsp").forward(request, response);
        }
        //如果不是为空，那么在session中保存一个属性
        request.getSession().setAttribute("user", user);
        request.setAttribute("message", "恭喜你，已经登陆了！");
        //如果想要用户关闭了浏览器，还能登陆，就必须要用到Cookie技术了
        Cookie cookie = new Cookie("autoLogin", user.getUsername() + "." + user.getPassword());
        //设置Cookie的最大声明周期为用户指定的
        cookie.setMaxAge(Integer.parseInt(request.getParameter("time")) * 60);
        //把Cookie返回给浏览器
        response.addCookie(cookie);
        //跳转到提示页面
        request.getRequestDispatcher("/message.jsp").forward(request, response);

 HttpServletResponse response = (HttpServletResponse) resp;
        HttpServletRequest request = (HttpServletRequest) req;
        //如果用户没有关闭浏览器，就不需要Cookie做拼接登陆了
        if (request.getSession().getAttribute("user") != null) {
            chain.doFilter(request, response);
            return;
        }
        //用户关闭了浏览器，session的值就获取不到了。所以要通过Cookie来自动登陆
        Cookie[] cookies = request.getCookies();
        String value = null;
        for (int i = 0; cookies != null && i < cookies.length; i++) {
            if (cookies[i].getName().equals("autoLogin")) {
                value = cookies[i].getValue();
            }
        }
        //得到Cookie的用户名和密码
        if (value != null) {
            String username = value.split("\\.")[0];
            String password = value.split("\\.")[1];
            UserDao userDao = new UserDao();
            User user = userDao.find(username, password);
            if (user != null) {
                request.getSession().setAttribute("user", user);
            }
        }
        chain.doFilter(request, response);

   public User find(String username) {
        List<User> userList = UserDB.getUsers();
        //遍历List集合，看看有没有对应的username和password
        for (User user : userList) {
            if (user.getUsername().equals(username)) {
                return user;
            }
        }
        return null;
    }

   //得到Cookie的用户名和密码
        if (value != null) {
            String username = value.split("\\.")[0];
            String password = value.split("\\.")[1];
            //在Cookie拿到的密码是md5加密过的，不能直接与数据库中的密码比较
            UserDao userDao = new UserDao();
            User user = userDao.find(username);
            //通过用户名获得用户信息，得到用户的密码，用户的密码也md5一把
            String dbPassword = md5.md5(user.getPassword());
            //如果两个密码匹配了，就是正确的密码了
            if (password.equals(dbPassword)) {
                request.getSession().setAttribute("user", user);
            }
        }