Cookie

1、Cookie是服务端向客户端响应的一小段数据，最终存放在客户端中；之后客户端每次向服务端发送请求，都会在请求头中携带cookie
2、cookie是有时效性的，默认是Session级别（整个浏览器关闭才会消失，内存释放掉了）；也可以手动设置过期时间（存储在磁盘中）

1. 服务端向客户端发送cookie

   @WebServlet("/controllerA")
   public class controllerA extends HttpServlet {public void service(HttpServletRequest req, HttpServletResponse resp) {// 创建cookieCookie cookieA = new Cookie("keyA", "valueA");Cookie cookieB = new Cookie("keyB", "valueB");// 为cookieA设置过期时间，单位：秒cookieA.setMaxAge(60);// 为bookieA设置提交路径（只有访问此路径才会携带该cookie）cookieA.setPath("/demo/controllerC");// 将cookie放入响应头中resp.addCookie(cookieA);resp.addCookie(cookieB);}
   }
   

2. 服务端接收客户端发送过来的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());}}}
   }