Cookie原理总结

十二、Cookie的使用

12.1 什么是 Cookie

• Cookie是在浏览器访问Web服务器的某个资源时，由Web服务器在HTTP响应消息头中附带传送给浏览器的一小段数据。

• 一旦Web浏览器保存了某个Cookie,那么它在以后每次访问该Web服务器时，都应在HTTP请求头中将这个Cookie回传给Web服务器。

• —个Cookie主要由标识该信息的名称(name)和值(value)组成。

---

12.2 创建 Cookie

package com.hyqwsq.Cookies;

import com.hyqwsq.servlet1.HttpServlet;

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

@WebServlet("/cs")
public class CookieServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1. 服务器创建Cookie对象
        Cookie cookie = new Cookie("username","gavin");

        // 1.1 设置Cookie的访问路径
        //cookie.setPath("//Servlet_code_demo1_war_exploded");    // 如果是项目名称，代表该项目下所有资源都可以使用这个cookie
        cookie.setPath("//Servlet_code_demo1_war_exploded/get");    //只有该项目里的get或者get下面的资源才可以访问

        // 1.2 设置Cookie的有效期
        cookie.setMaxAge(60*60);

        // 2. 将Cookie响应给客户端
        resp.addCookie(cookie); // 添加一个cookie到resp对象里，并响应给客户端
    }
}

查看创建的cookie

---

12.3 获取Cookie

只需要保证 Cookie 的 key 和 路径(Path) 一致即可修改

package com.hyqwsq.Cookies;

import com.hyqwsq.servlet1.HttpServlet;

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

@WebServlet("/get")
public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1. 通过request对象获取所有的cookie
        Cookie[] cookies = req.getCookies();

        /**
         * 若是客户端没有cookie，则会获取一个空数组
         * 所以要加上判空，避免空指针异常
         */
        if(cookies != null){
            // 2. 因为得到的是cookie数组，不知道有几个cookie
            //      所以通过循环遍历cookie
            for(Cookie cookie : cookies){
                System.out.println(cookie.getName()+"："+cookie.getValue()+"路径：" +cookie .getPath());
            }
        }
    }

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

• 注意：如果改变cookie的name和有效路径会新建cookie，而改变cookie值、有效期会覆盖原有cookie

---

12.4 修改 Cookie

package com.hyqwsq.Cookies;

import com.hyqwsq.servlet1.HttpServlet;

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

@WebServlet("/csc")
public class ChangeCookie extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 修改cookie需要key和路径同时一致
        Cookie cookie = new Cookie("username","mark");
        cookie.setPath("/Servlet_code_demo1_war_exploded/get");

        cookie.setMaxAge(60*24*7);

        resp.addCookie(cookie);
    }
}

当访问cs后通过访问getServlet得到 username = ‘gavin’的cookie，这时候访问csc修改key为username 且Path为/Servlet_code_demo1_war_exploded/get的cookie，最后通过访问get来打印结果：

---

12.5 Cookie编码与解码

Cookie默认不支持中文，只能包含ASCII字符，所以Cookie需要对Unicode字符进行编码，否则会出现乱码

• 编码可以使用java.net.URLEncoder类的encode(String str,String encoding) 方法
• 解码使用java.net.URLEncoder类的decode(String str,String encoding)方法

12.5.1创建带中文Cookie

package com.hyqwsq.URLEncoder;

import com.hyqwsq.servlet1.HttpServlet;

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

@WebServlet("/cs3")
public class URLEncoderServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Cookie cookie = new Cookie("姓名","张三");

        cookie.setPath("/Servlet_code_demo1_war_exploded/get");

        cookie.setMaxAge(600);

        resp.addCookie(cookie);

    }
}

package com.hyqwsq.Cookies;

import com.hyqwsq.servlet1.HttpServlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.net.URLEncoder;

@WebServlet("/cs3")
public class URLEncoderServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Cookie cookie = new Cookie(
                URLEncoder.encode("姓名","UTF-8"),
                URLEncoder.encode("何义竏","UTF-8")
        );

        cookie.setPath("/Servlet_code_demo1_war_exploded/get");

        cookie.setMaxAge(600);

        resp.addCookie(cookie);

    }
}

12.5.2读取带中文Cookie

package com.hyqwsq.Cookies;

import com.hyqwsq.servlet1.HttpServlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.net.URLDecoder;

@WebServlet("/get")
public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1. 通过request对象获取所有的cookie
        Cookie[] cookies = req.getCookies();

        /**
         * 若是客户端没有cookie，则会获取一个空数组
         * 所以要加上判空，避免空指针异常
         */
        if(cookies != null){
            // 2. 因为得到的是cookie数组，不知道有几个cookie
            //      所以通过循环遍历cookie
            for(Cookie cookie : cookies){
                System.out.println(
                        URLDecoder.decode(cookie.getName(),"UTF-8")+
                        "："+URLDecoder.decode(cookie.getValue(),"UTF-8")+
                        "  路径：" +cookie.getPath()
                );
            }
        }
    }

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

---

12.6 Cookie优点和缺点

12.6.1 优点

• 可配置到期规则
• 简单性：Cookie是一种基于文本的轻量结构，包含简单的键值对
• 数据持久性：Cookie默认在过期之前是可以一直存在客户端浏览器上的

12.6.2 缺点

• 大小受到限制：大多数浏览器对Cookie的大小有4K、8K字节的限制。
• 用户配置为禁用：有些用户禁用了浏览器或客户端设备接收Cookie的能力，因此限制了这一功能
• 潜在的安全风险：Cookie可能会被篡改。会对安全性造成潜在风险或者导致依赖于Cookie的应用程序失败