cookie与seesion的简单用法

1.cookie

客户端技术 （响应，请求）

Servlet代码，主要是用以显示用户上次访问时间

package com.you.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.io.PrintWriter;
import java.util.Date;

public class CookieDemon01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决乱码
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        req.setCharacterEncoding("utf-8");
        PrintWriter out = resp.getWriter();

        //Cookie,服务器端从客户端获取
        Cookie[] cookies = req.getCookies();

        //判断Cookie是否存在
        if (cookies!=null){
            out.write("你上一次访问的时间是：");
            for (int i = 0; i <cookies.length ; i++) {
                Cookie cookie = cookies[i];

                //获取cookie的名字
                if (cookie.getName().equals("lastLoginTime")){
                    //获取Cookie中的值
                    long lastLoginTime = Long.parseLong(cookie.getValue());
                    Date date = new Date(lastLoginTime);
                    out.write(date.toLocaleString());
                }
            }
        }else {
            out.write("这是你第一次访问本网站");
        }

        Cookie cookie = new Cookie("lastLoginTime", System.currentTimeMillis()+"");
        resp.addCookie(cookie);
    }

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

cookie.setMaxAge(60*60);  //设置Cookie的有效时间

细节问题：

• 一个Cookie只能保存一个信息；
• 一个web站点可以给浏览器发送多个cookie，最多存放20个cookie；
• Cookie大小有限制4kb；
• 300个cookie浏览器上限

2.session

服务器技术，利用这个技术，可以保存用户的会话信息，我们可以把信息或者数据放在Session中！

什么是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问！--> 保存用户的信息；保存购物车的信息…..

Session和cookie的区别：

• Cookie是把用户的数据写给用户的浏览器，浏览器保存 （可以保存多个）
• Session把用户的数据写到用户独占Session中，服务器端保存（保存重要的信息，减少服务器资源的浪费）
• Session对象由服务器创建

session的使用：

package com.you.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;

public class SessionDemon01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决乱码问题
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("txt/html;charset=utf-8");

        //得到Session
        HttpSession session = req.getSession();

        //给Session中存东西
        session.setAttribute("name", "李四");

        //获取Session的ID
        String sessionId = session.getId();

        //判断Session是不是新创建的
        if (session.isNew()) {
            resp.getWriter().write("session创建成功"+sessionId);
        }else {
            resp.getWriter().write("session已经在服务器中存在了"+sessionId);
        }

        //session创建的时候做了什么事情
//        Cookie cookie = new Cookie("JSESSIONID", sessionId);
//        resp.addCookie(cookie);
    }

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

从前一个Servlet中获取Session中的数据

package com.you.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 SessionDemon02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决乱码问题
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("txt/html;charset=utf-8");

        //得到Session
        HttpSession session = req.getSession();

        //给Session中存东西
        String  name = (String) session.getAttribute("name");
        System.out.println(name);

    }

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

清除session

package com.you.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 SessionDemon03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决乱码问题
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("txt/html;charset=utf-8");
        //清除Session
        HttpSession session = req.getSession();
        session.removeAttribute("name");
        session.invalidate();
    }

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

cookie与seesion的简单用法

原文：https://www.cnblogs.com/Ydharma/p/13232780.html