JavaWeb-Cookie和Session

cookie：存放在客户端

session：存放在服务端

cookie

package com.th0r.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Date;

public class Demo1 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");
        
        if (req.getCookies() != null){
            resp.getWriter().print("你上次访问的时间是：");
            for (Cookie cookie : req.getCookies()) {
                if (cookie.getName().equals("lastLogin")){
                    long l = Long.parseLong(cookie.getValue());
                    Date date = new Date(l);
                    resp.getWriter().print(date.toString());
                }
            }
        } else {
            resp.getWriter().println("这是你第一次访问");
        }
        //设置cookie
        Cookie cookie = new Cookie("lastLogin", System.currentTimeMillis() + "");
        //设置cookie有效期
        cookie.setMaxAge(2*60*60);
        resp.addCookie(cookie);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}

第一次访问

第二次访问

• 一个cookie只能保存一个信息
• 一个web站点可以发送多个cookie，最多存放20个
• cookie的大小限制为4kb
• 浏览器的cookie上限为300个

删除cookie的方法

• 不设置有效期，关闭浏览器，自动失效
• 设置有效期为0

Session

• 服务器会给每一个用户（浏览器）创建一个Seesion对象
• 一个Seesion独占一个浏览器，只要浏览器没有关闭，这个Session就存在
• 用户登录之后，整个网站它都可以访向

创建Session

package com.th0r.servlet;

import com.th0r.pro.Person;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class Demo3 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");

        HttpSession session = req.getSession();
        session.setAttribute("name", new Person("Bob", 18));
        String sessionId = session.getId();
        if (session.isNew()){
            resp.getWriter().write("Session 创建成功" + sessionId);
        } else {
            resp.getWriter().write("Session 已存在" + sessionId);
            Person person = (Person)session.getAttribute("name");
            resp.getWriter().print("\n"+person);
        }

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}

销毁session

package com.th0r.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class Demo4 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");

        HttpSession session = req.getSession();
        if (session.getAttribute("name") != null){
            session.removeAttribute("name");
            session.invalidate();
            resp.getWriter().println("注销成功！");
        }else {
            resp.getWriter().println("未登录！");
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}

设置时间

web.xml

<session-config>
    <session-timeout>15</session-timeout>
</session-config>