JavaWeb11-Cookie

应用场景：用于自动登录， 浏览记录， 购物车等等。

使用Cookie步骤如下：

1. 首先添加Cookie

   resp.addCookie(new Cookie("name", "张三"));

2. 获取Cookie

   Cookie[] cookies = req.getCookies();

3. 获取Cookie的name以及value

   String name = cookie.getName();
   String value = cookie.getValue();

完整代码如下：

public class CookieServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter out = resp.getWriter();
        // 添加cookie
        resp.addCookie(new Cookie("name", "张三"));
        // 获取cookie， 并将其遍历出来
        Cookie[] cookies = req.getCookies();
        if(cookies != null) {
            for (Cookie cookie : cookies) {
                out.write(cookie.getName() + cookie.getValue() + "<br/>");
            }
        }
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

小案例：获取上一次的访问时间。

 @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter out = resp.getWriter();
        Cookie[] cookies = req.getCookies();
        if(cookies != null) { // 如果cookie不为空输出上一次访问的时间
            for (Cookie cookie : cookies){
                if (cookie.getName().equals("currentTime")){ // 获取下面添加的Cookie：currentTime属性
                    String value = cookie.getValue();
                    long time = Long.parseLong(value);
                    Date date = new Date(time);
                    out.write("上一次访问的时间" + date.toLocaleString());
                }
            }
        }
        Cookie cookie = new Cookie("currentTime", System.currentTimeMillis() + "");// 访问时，添加一个访问的当前时间
        cookie.setMaxAge(10); // 还有一个设置最大有效时间
        resp.addCookie(cookie);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

​