protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        
        // 判斷cookie是否有登錄信息
        Cookie[] cookies = req.getCookies();
        boolean isLogin = false;
        for(Cookie c : cookies){
            if("loginInfo".equals(c.getName())){
                String v 
 
= c.getValue();
                if(v!=null && !v.equals("")){
                    isLogin = true;
                }
            }
        }
        
        // 有，登錄通過
        // 沒有，登錄驗證，設置登錄信息，設置cookie有效時間
        if(isLogin){
            System.out.println("用戶已登錄");
        }else{
            System.out.println(
 
"用戶未登錄");
            System.out.println("用戶信息驗證通過");
            Cookie c = new Cookie("loginInfo", "loginInfo");
            c.setMaxAge(Integer.parseInt(login_keep+""));
            resp.addCookie(c);
        }
        
    }

java 通過cookie判斷是否登陸