day20-web开发会话技术02

day20-web开发会话技术02

WEB开发会话技术02

6.Cookie的生命周期

默认情况下,Cookie只在浏览器的内存中存活,也就是说,当你关闭浏览器后,Cookie就会消失。但是也可以通过方法设置cookie的生存时间。

cookie的生命周期指的是如何管理cookie,什么时候cookie被销毁。

  • setMaxAge(int expiry):设置 cookie 的最大生存时间,以秒为单位
    • 整数:表示在指定的秒数后过期
    • 负数:表示浏览器关闭,cookie就会被删除(默认值是-1)
    • 0,表示马上删除cookie

6.1cookie生命周期expiry>0

CookieLive:

package com.li.cookie;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(urlPatterns = {"/CookieLive"})
public class CookieLive extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("CookieLive doPost被调用...");
        //创建一个cookie,生命周期为 60s
        Cookie cookie = new Cookie("job", "java");
        //1.从创建改cookie开始计时,60秒后就无效
        //2.由浏览器来根据创建的时间来开始计时,到时间后就认为该cookie无效
        //3.如果该cookie无效了,那么浏览器在发出HTTP请求时,就不会带上该cookie
        cookie.setMaxAge(60);

        //将cookie保存到浏览器
        response.addCookie(cookie);

        //给浏览器返回信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.print("<h1>设置cookie生命周期成功</h1>");
        writer.flush();
        writer.close();
    }
}
  1. 在浏览器中访问该servlet:

    image-20221120221656177

  2. 可以看到该cookie的创建于: “Sun, 20 Nov 2022 14:15:39 GMT”

    真实时间为上述时间再加八小时

    image-20221120221755132

  3. 超过60s后,再去访问Tomcat服务器:

    image-20221120222222568

    可以看到在浏览器发送的HTTP请求中的Cookie字段已经没有了设置的cookie:

说明:由浏览器来根据创建的时间来开始计时,到时间后就认为该cookie无效。如果该cookie无效了,那么浏览器在发出HTTP请求时,就不会带上该cookie。

但是此时cookie没有被删除,在关闭浏览器的时候才会被删除。

6.2演示删除cookie(expiry=0)

删除下图名为username的cookie

image-20221121162351398

package com.li.cookie;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(urlPatterns = {"/cookieLive"})
public class CookieLive extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //演示删除一个cookie
        //1.先得到usernameCookie
        Cookie[] cookies = request.getCookies();
        Cookie usernameCookie =
                CookieUtils.readCookieByName("username", cookies);
        if (usernameCookie != null) {
            //2.将其生命周期设置为0
            usernameCookie.setMaxAge(0);
            //3.重新保存该cookie,因为你将其生命周期设置为0,就等价于让浏览器删除该cookie
            response.addCookie(usernameCookie);//在响应体的Set-Cookie
        } else {
            System.out.println("没有找到该cookie");
        }

        //给浏览器返回信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.print("<h1>设置cookie生命周期成功</h1>");
        writer.flush();
        writer.close();
    }
}

redeployTomcat,浏览器访问该servlet,点击查看HTTP响应包:可以看到响应包中设置了该cookie的过期时间为1970年,这意味着浏览器将立即删除该cookie。

  1. Set-Cookie: username=jack; Expires=Thu, 01-Jan-1970 00:00:10 GMT

    image-20221121163544953

  2. 点击查看cookie存储,可以发现该cookie已经被删除了

    image-20221121163639913

说明:setMaxAge()方法设置参数为零时,当浏览器接收到服务器的响应包时,会立即删除该cookie。

6.3默认生命周期(expiry<0)

如果没有设置setMaxAge,或者setMaxAge的设置参数为负数,那么默认创建的cookie是会话级别的(即关闭浏览器就销毁了)

如下,MaxAge的默认设置值为-1

image-20221121164922368

7.Cookie的有效路径

image-20221121165341353

cookie有效路径Path的设置:

  1. Cookie的path属性,可以有效地过滤哪些Cookie可以发送给服务器,哪些不发。path属性是通过请求的URL地址来进行有效地过滤

  2. 规则如下:

    cookie1.setPath=/工程路径 cookie2.setPath=/工程路径/aaa

    1. 若请求地址为:http://ip:port/工程路径/资源
      cookie1发送给服务器
      cookie2不会发送给服务器
    2. 若请求地址为:http://ip:port/工程路径/aaa/资源
      cookie1发送给服务器
      cookie2发送给服务器

    即如果请求的url的地址包含了cookie设置的有效路径,则这个cookie就会被发送给服务器。

    说明:如果没有设置cookie的有效路径,默认就是 /工程路径

演示Cookie的有效路径的使用

package com.li.cookie;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(urlPatterns = {"/cookiePath"})
public class CookiePath extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("cookiePath doPost被调用");
        //1.创建两个cookie
        Cookie cookie = new Cookie("address", "beijing");
        Cookie cookie2 = new Cookie("salary", "20000");
        //2.设置不同的有效路径
        //request.getContextPath()=/application context
        cookie.setPath(request.getContextPath());//有效路径=/cs
        cookie2.setPath(request.getContextPath() + "/aaa");//有效路径=/cs/aaa

        //3.保存到浏览器
        response.addCookie(cookie);
        response.addCookie(cookie2);

        //4.给浏览器回送提示信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.print("<h1>设置cookie有效路径成功</h1>");
        writer.flush();
        writer.close();
    }
}

如下,访问http://localhost:8080/cs/cookiePath,创建了address和salary两个cookie并设置了不同的有效路径

image-20221121172033653

现在来访问http://localhost:8080/cs/xxx,抓包如下:

image-20221121172428294

在来访问http://localhost:8080/cs/aaa/xxx

image-20221121172527454

8.练习

完成自动填写登录账户案例,如果用户登录成功,则下次登录自动填写登录账户。

  1. 如果用户名是olien,密码是1234。则认为该用户合法,登录成功,否则失败。
  2. 要求实现:如果登录成功,则该用户在三天内登录可以自动填写其登录名。

CookieUtils:

package com.li.cookie;

import javax.servlet.http.Cookie;

public class CookieUtils {
    //编写一个方法,返回指定名字的cookie值
    public static Cookie readCookieByName(String name, Cookie[] cookies) {
        //判断传入的参数是否正确
        if (name == null || "".equals(name) || cookies == null || cookies.length == 0) {
            return null;
        }
        //否则,就遍历cookies
        for (Cookie cookie : cookies) {
            if (name.equals(cookie.getName())) {
                return cookie;
            }
        }
        return null;
    }
}

loginServlet:

package com.li.cookie;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(urlPatterns = {"/login"})
public class Login extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("login doPost被调用...");
        //编写servlet(以实现自动填写登录名和密码)
        String usernameVal = "";
        String pwdVal = "";
        //访问servlet时,首先获取浏览器的cookie数组
        Cookie[] cookies = request.getCookies();
        //判断得到的cookie数组是否存在
        if (cookies != null && cookies.length != 0) {//如果存在,且长度不为0
            //获取cookie的值
            Cookie usernameCookie = CookieUtils.readCookieByName("username", cookies);
            Cookie pwdCookie = CookieUtils.readCookieByName("pwd", cookies);
            if (usernameCookie != null && pwdCookie != null) {//如果存在指定的cookie
                //获取指定的cookie的值
                usernameVal = usernameCookie.getValue();
                pwdVal = pwdCookie.getValue();
            }
        }

        //绘制html页面
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        if (usernameVal != null && pwdVal != null) {
            writer.print("<!DOCTYPE html>
" +
                    "<html lang="en">
" +
                    "<head>
" +
                    "    <meta charset="UTF-8">
" +
                    "    <title>登录页面</title>
" +
                    "</head>
" +
                    "<body>
" +
                    "<form action="/cs/loginSuccess" method="post">
" +
                    "    用户名:<input type="text" name="username" value="" + usernameVal + ""/><br/>
" +
                    "    密码:<input type="password" name="pwd" value="" + pwdVal + ""/><br/>
" +
                    "    <input type="submit" value="登录"/>
" +
                    "</form>
" +
                    "</body>
" +
                    "</html>");
        }
        writer.flush();
        writer.close();
    }
}

LoginSuccess:

package com.li.cookie;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * 接收用户输入,判断该用户是否合法,并返回提示信息
 */
@WebServlet(urlPatterns = {"/loginSuccess"})
public class LoginSuccess extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("loginServlet doPost 被调用...");
        //1.接收表单用户名和密码
        String username = request.getParameter("username");
        String pwd = request.getParameter("pwd");

        //给浏览器返回提示信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();

        //2.判断数据是否合法
        if ("olien".equals(username) && "1234".equals(pwd)) {//合法
            //将登陆成功的用户名和密码以cookie形式保存到浏览器中
            //根据用户名和密码创建cookie
            Cookie usernameCookie = new Cookie("username", "olien");
            Cookie pwdCookie = new Cookie("pwd", "1234");
            //设置cookie生命周期
            usernameCookie.setMaxAge(60 * 60 * 24 * 3);//3天
            pwdCookie.setMaxAge(60 * 60 * 24 * 3);//3天
            //给浏览器返回cookie
            response.addCookie(usernameCookie);
            response.addCookie(pwdCookie);
            //给浏览器返回提示信息
            writer.print("<h1>登录OK</h1>");
        } else {//不合法
            writer.print("<h1>登录失败,请重新登录</h1>");
        }
        writer.flush();
        writer.close();
    }
}

redeployTomcat,在浏览器中访问http://localhost:8080/cs/login。 输入正确的用户名密码,成功跳转。

image-20221121204334606
image-20221121204414669

此时,再次访问该页面,可以看到登录页面自动填写登录名:

9.Cookie注意事项和细节

  1. 一个cookie只能标识一种信息,它至少含有一个标识该信息的名称(name)和设置值(value)
  2. 一个web站点可以给一个浏览器发送多个cookie,一个浏览器也可以存储多个web站点提供的cookie
  3. cookie的总数量没有限制,但是每个域名的cookie数量和每个cookie的大小是有限制的(不同的浏览器限制不同),因此cookie不适合存放数据量大的信息
  4. 注意:删除cookie时,path必须一致,否则不会删除
  5. Java Servlet中cookie中文乱码解决。如果cookie存放中文,默认会报错,但可以通过URL编码和解码来解决(尽量不要使用cookie保存中文信息)

例子:解决cookie中文乱码

package com.li.cookie;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLEncoder;

@WebServlet(name = "EncoderCookie", urlPatterns = {"/encoderCookie"})
public class EncoderCookie extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("EncoderCookie doPost被调用...");
        //1.创建一个带有中文的cookie
        //Cookie company = new Cookie("company", "小葵花公司");
        //2.保存到浏览器
        /**
         * 1.如果直接存放带有中文的cookie,Tomcat服务器会报错:
         * 		Control character in cookie value or attribute.
         * 2.解决方法:将中文编码设置成URL编码
         * 3.使用工具类 URLEncode
         * 4.编码后再保存cookie即可
         */
        String company = URLEncoder.encode("小葵花公司", "utf-8");
        Cookie cookie = new Cookie("company", company);
        response.addCookie(cookie);
        //3.给浏览器返回提示信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.print("<h1>设置cookie中文信息成功</h1>");
        writer.flush();
        writer.close();
    }
}
  1. 浏览器访问地址:http://localhost:8080/cs/encoderCookie

    image-20221121211750168

  2. 进行抓包:如下,浏览器在保存中文cookie时,以url编码进行保存

    image-20221121211718026
    image-20221121211942352

  3. 服务器在获取该中文cookie时,也要以url编码形式进行解码,否则得到的cookie的值是url编码。

    ReadCookie2:

    package com.li.cookie;
    
    import javax.servlet.*;
    import javax.servlet.http.*;
    import javax.servlet.annotation.*;
    import java.io.IOException;
    import java.io.PrintWriter;
    import java.net.URLDecoder;
    
    @WebServlet(name = "ReadCookie2", value = "/readCookie2")
    public class ReadCookie2 extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            doPost(request, response);
        }
    
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            //读取中文cookie
            Cookie[] cookies = request.getCookies();
            Cookie companyCookie = CookieUtils.readCookieByName("company", cookies);
            String companyVal = companyCookie.getValue();
            System.out.println("companyVal= " + companyVal);//url编码
            //解码
            companyVal = URLDecoder.decode(companyVal, "utf-8");
            System.out.println("解码后的companyVal= " + companyVal);//中文
    
            //给浏览器返回提示信息
            response.setContentType("text/html;charset=utf-8");
            PrintWriter writer = response.getWriter();
            writer.print("<h1>读取中文cookie并解码成功</h1>");
            writer.flush();
            writer.close();
        }
    }
    

    浏览器访问该资源,后台输出如下:

    image-20221121213440651

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