一、cookie

cookie：客户端会话管理技术

1. 会话技术

2. 什么是cookie

一个普通的java类

3. cookie的属性

4. cookie方法

5. cookie添加和获取

6. 需求案例

需求：
通过cookie记录最后访问时间，并在浏览器上显示出来
目的：
掌握cookie的基本使用，从创建到添加客户端，再到从服务端获取。
实现步骤：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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.text.SimpleDateFormat;
import java.util.Date;

/**
 * cookie 的使用
 */

@WebServlet("/test")
public class Test extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1. 通过响应对象写出提示信息
        resp.setContentType("text/html;charset=UTF-8");
        PrintWriter pw = resp.getWriter();
        pw.write("欢迎访问本网站，您最后的访问时间为：<br>");
        //2.创建cookie对象，用于记录最后时间
        Cookie cookie=new Cookie("time",System.currentTimeMillis()+"");
        //3.设置最大存活时间 1h
        cookie.setMaxAge(3600);
        //4. 将cookie对象添加到客户端
        resp.addCookie(cookie);
        //5. 获取cookie
        Cookie[] arr = req.getCookies();
        for (Cookie c:arr){
            if ("time".equals(c.getName())){
                //6. 获取cookie对象中的value
                String value = c.getValue();
                SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                pw.write(sdf.format(new Date(Long.parseLong(value))));
            }
        }


    }

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

7. cookie的细节

cookie路径限制：创建cookie的路径 获取要一致 ，/servlet开始创建的话，获取也要以此开头

二、session

1. HttpSession介绍

HttpSession服务器会话管理技术，是一个接口

2. HttpSession常用方法

3. HttpSession获取

4. HttpSession使用

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

/**
 * seesion基本使用
 **/
@WebServlet("/demo01")
public class ServletDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       //1.获取请求的用户名
        String username = req.getParameter("username");
        //2. 获取HttpSession的对象
        HttpSession session = req.getSession();
        System.out.println(session);
        System.out.println(session.getId());
        //3.将用户名信息添加到共享数据中
        session.setAttribute("username",username);
    }

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

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

/**
 * seesion基本使用
 **/
@WebServlet("/demo02")
public class ServletDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //1. 获取HttpSession的对象
        HttpSession session = req.getSession();
        System.out.println(session);
        System.out.println(session.getId());
        //2.获取共享数据
        Object username = session.getAttribute("username");
        //3.将数据响应给浏览器
        resp.getWriter().write(username+"");
    }

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

是同一个session对象

成功：

5. HttpSession使用细节