25、Cookie的入门简介

Cookie：
    1. 概念：客户端会话技术，将数据保存到客户端（客户再次和服务器通讯会将以前数据一起发送给服务器 ）

    2. 快速入门：
        * 使用步骤：
            1. 创建Cookie对象，绑定数据
                * new Cookie(String name, String value) 
            2. 通过响应respond来发送Cookie对象
                * response.addCookie(Cookie cookie) ---服务器发送Cookie给浏览器
            3. 浏览器如果再次servlet，可以获取Cookie，拿到数据
                * Cookie[]  request.getCookies()  ---获取浏览器返回的Cookie数据
            注意：如果换一个浏览器获取关闭浏览器重启，回话就结束了，Cookie保存数据就失效。

    3. 实现原理
        * 基于响应头set-cookie和请求头cookie实现

CookieDemo1A.java

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;

@WebServlet("/CookieDemo1A")
public class CookieDemo1A extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Cookie cookie = new Cookie("msg", "lisi");
        response.addCookie(cookie);
    }
}

CookieDemo1B.java

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;

@WebServlet("/CookieDemo1B")
public class CookieDemo1B extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Cookie[] cs = request.getCookies();
        for (Cookie c : cs) {
            String name = c.getName();
            String value = c.getValue();
            System.out.println(""+name+":"+value);
        }
    }
}

测试方法1：

在同一个浏览器地址栏里面先输入：http://localhost/cookie/CookieDemo1A

执行后再在该浏览器输入或者打开一个新页面输入：http://localhost/cookie/CookieDemo1B

输入如下内容：

JSESSIONID:DC1CAE64269A9F82DB7DED9FCB8BC887
msg:lisi
Idea-661643a5:f8768c12-dedd-49c0-abba-72c4a6d2af18
JSESSIONID:5347B7D7C7665B0DDECE5D006D1AF452

测试方法2：

关闭所有浏览器，直接在浏览器中输入：http://localhost/cookie/CookieDemo1B

这次只会输出Idea-661643a5:f8768c12-dedd-49c0-abba-72c4a6d2af18，我们设定的cookie不会输出