Cookie

1、Cookie是服務端向客戶端響應的一小段數據，最終存放在客戶端中；之后客戶端每次向服務端發送請求，都會在請求頭中攜帶cookie
2、cookie是有時效性的，默認是Session級別（整個瀏覽器關閉才會消失，內存釋放掉了）；也可以手動設置過期時間（存儲在磁盤中）

1. 服務端向客戶端發送cookie

   @WebServlet("/controllerA")
   public class controllerA extends HttpServlet {public void service(HttpServletRequest req, HttpServletResponse resp) {// 創建cookieCookie cookieA = new Cookie("keyA", "valueA");Cookie cookieB = new Cookie("keyB", "valueB");// 為cookieA設置過期時間，單位：秒cookieA.setMaxAge(60);// 為bookieA設置提交路徑（只有訪問此路徑才會攜帶該cookie）cookieA.setPath("/demo/controllerC");// 將cookie放入響應頭中resp.addCookie(cookieA);resp.addCookie(cookieB);}
   }
   

2. 服務端接收客戶端發送過來的cookie

   @WebServlet("/controllerB")
   public class controllerA extends HttpServlet {public void service(HttpServletRequest req, HttpServletResponse resp) {Cookie[] cookies = req.getCookies();if (cookies != null) {for(Cookie c : cookies) {System.out.println(c.getName() + ":" + c.getValue());}}}
   }