会话跟踪技术（Cookie、Session）

会话：用户打开浏览器，访问Web服务器的资源，会话建立，直到有一方断开连接，会话结束。在一次会话中可以包含多次请求和响应

会话跟踪技术： 一种维护浏览器状态的方法，服务器需要识别多次请求是否来自于同一服务器，以便在同一次会话的多次请求间共享数据

HTTP协议是无状态的，每次浏览器向服务器请求时，服务器都会将请求视为新的请求，因此我们需要会话跟踪技术来实现会话内数据共享

实现方式：

1. 客户端会话跟踪技术：Cookie
2. 服务端会话跟踪技术：Session

Cookie

客户端会话跟踪技术，将数据保存到客户端，以后每次请求都携带Cookie数据进行访问

Cookie的基本使用

发送Cookie

1. 创建Cookie对象，设置数据

 Cookie cookie=new  Cookie("key","value");

2. 发送Cookie到客户端：使用response对象

response.addCookie(cookie);

一、添加pom依赖

    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>4.0.1</version>
      <scope>provided</scope>
    </dependency>

    <!--jsp-->
    <dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>jsp-api</artifactId>
      <version>2.2</version>
      <scope>provided</scope>
    </dependency>

    <!--jstl-->
    <dependency>
      <groupId>jstl</groupId>
      <artifactId>jstl</artifactId>
      <version>1.2</version>
    </dependency>
    <dependency>
      <groupId>taglibs</groupId>
      <artifactId>standard</artifactId>
      <version>1.1.2</version>
    </dependency>

二、创建Servlet

package com.GY;

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

@WebServlet(name = "AServlet", value = "/AServlet")
public class AServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // 发送Cookie
        // 1.创建Cookie对象
        Cookie cookie=new Cookie("username","GY");
        // 2.发送Cookie
        response.addCookie(cookie);
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    }
}

三、启动服务器，在浏览器中查看Cookie数据

数据成功写入客户端！！！

获取Cookie

3. 获取客户端携带的所有Cookie，使用request对象

 Cookie[]  cookies=request.getCookies();

4. 遍历数组，获取每一个Cookie对象：for
5. 使用Cookie对象方法获取数据

cookie.getName();

cookie.getValue();

一、 创建Servlet

package com.GY.cookie;

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(name = "BServlet", value = "/BServlet")
public class BServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // 获取Cookie
        // 1.获取Cookie数组
        Cookie[] cookies = request.getCookies();
        // 2.遍历数组
        for (Cookie cookie : cookies) {
            // 3.获取数据
            String name = cookie.getName();
            if ("username".equals(name)) {
                String value = cookie.getValue();
                System.out.println(name+":"+value);
                break;
            }
        }
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    }
}

二、启动服务器

成功访问到Cookie中的数据！！！

Cookie原理

Cookie的实现是基于HTTP协议的
●  响应头: set-cookie
●  请求头: cookie

Cookie使用细节

● Cookie存活时间

       默认情况下，Cookie存储在浏览器内存中，当浏览器关闭，内存释放，则Cookie被销毁
       setMaxAge(int seconds):设置Cookie存活时间
         1.正数: 将Cookie写入浏览器所在电脑的硬盘,持久化存储。到时间自动删除（不会随浏览器的关闭而被销毁）
         2.负数: 默认值,Cookie在当前浏览器内存中,当浏览器关闭,则Cookie被销毁
         3.零: 删除对应Cookie
       
● Cookie存储中文
      Cookie不能直接存储中文
      如需要存储,则需要进行转码: URL编码   

① Cookie存活时间

// 设置存活时间   ,  一周(七天)
        cookie.setMaxAge(60*60*24*7);

② Cookie存储中文

URL编码

package com.GY.cookie;

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

@WebServlet(name = "AServlet", value = "/AServlet")
public class AServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // 发送Cookie
        // 1.创建Cookie对象
        String value="张三";
        // URl编码
        value=URLEncoder.encode(value,"UTF-8");
        System.out.println("存储数据:"+value);
        Cookie cookie=new Cookie("username",value);
        // 设置存活时间   ,  一周(七天)
        cookie.setMaxAge(60*60*24*7);

        // 2.发送Cookie
        response.addCookie(cookie);
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    }
}

URL解码

package com.GY.cookie;

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.net.URLDecoder;

@WebServlet(name = "BServlet", value = "/BServlet")
public class BServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // 获取Cookie
        // 1.获取Cookie数组
        Cookie[] cookies = request.getCookies();
        // 2.遍历数组
        for (Cookie cookie : cookies) {
            // 3.获取数据
            String name = cookie.getName();
                if("username".equals(name)) {
                    String value = cookie.getValue();
                    // URL解码
                    value = URLDecoder.decode(value, "UTF-8");
                    System.out.println(name + ":" + value);
                    break;
                }
        }
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    }
}

成功获取中文数据！！！

Session

服务端会话跟踪技术，将数据保存到服务端
JavaEE提供HttpSession接口,来实现一次会话的多次请求间数据共享功能

Session基本使用

1. 获取Session对象

 HttpSession  session=request.getSession();

2. Session的对象功能

void setAttribute（String  name,Object  o）:  存储数据到Session域中
Object  getAttribute（String  name）:  根据key,获取值
void  removeAttribute（String  name):  根据key，删除该键值对

一、创建Servlet（存储数据）

package com.GY.session;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.util.Enumeration;

@WebServlet(name = "A1Servlet", value = "/A1Servlet")
public class A1Servlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //  1.获取Session对象
        HttpSession session = request.getSession();
        //  2.存储数据
        session.setAttribute("username","GY");
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    }
}

二、创建Servlet（获取数据）

package com.GY.session;

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

@WebServlet(name = "B1Servlet", value = "/B1Servlet")
public class B1Servlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //  从Session中获取数据
        //  1.获取对应的Session对象
        HttpSession session = request.getSession();
        //  2. 获取数据
        Object username = session.getAttribute("username");
        System.out.println(username);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}

二、启动服务器

成功获取数据！！！

Session原理

Session的实现是基于Cookie的

Session使用细节

● Session钝化、活化

     服务器重启后，Session中的数据是否还在？
         钝化: 在服务器正常关闭后,Tomcat会自动将Session数据写入硬盘的文件中 
         活化: 再次启动服务器后，从文件中加载数据到Session中
              
● Session销毁
      默认情况下,无操作，30分钟自动销毁（分钟）【可在web.xml中配置】
      <session-config>
              <session-timeout>30</session-timeout>
         </session-config>
      调用Session对象的invalidate()方法    

小结

Cookie和Session都是来完成一次会话内多次请求间数据共享的

区别：

      ●   存储位置: Cookie是将数据存储在客户端,Session是将数据存储在服务端
      ●   安全性:  Cookie不安全,Session安全
      ●   数据大小: Cookie最大3kb,Session无大小限制
      ●  存储时间: Cookie可以长期存储,Session默认30分钟
      ●  服务器性能:  Cookie不占服务资源,Session占用服务资源

【一般Cookie保证用户未登录的情况下身份识别，Session一般保存用户登录后的数据；不同的需求需具体分析后选择】

登录注册案例

需求说明：
      1. 完成用户登录功能，如果用户勾选 “记住用户” ，
         则下次访问登录页面，自动填充用户名密码
      3. 完成注册功能，并实现验证码验证

数据库表数据——user表

数据库数据——tb_brand表

项目资源
链接：https://pan.baidu.com/s/1CVGnG3bHGdq5dSGHBDin9g
提取码：GY66

Mybatis配置文件

DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    
    <typeAliases>
        <package name="com.GY.pojo"/>
    typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/test?useSSL=false&useServerPrepStmts=true"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            dataSource>
        environment>
    environments>
    <mappers>
        
        <package name="com.GY.mapper"/>
    mappers>
configuration>

Dao层——BrandMapper

import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.ResultMap;
import org.apache.ibatis.annotations.Select;
import java.util.List;

public interface BrandMapper {
    
    @Select("select * from tb_brand")
    @ResultMap("brandResultMap")
    List<Brand> selectAll();
}

Dao层——UserMapper

package com.GY.mapper;

import com.GY.pojo.User;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

public interface UserMapper {

    @Select("select * from user where username = #{username} and password = #{password}")
    User select(@Param("username") String username,@Param("password")  String password);
}

Service层——UserService

package com.GY.service;

import com.GY.mapper.UserMapper;
import com.GY.pojo.User;
import com.GY.util.SqlSessionFactoryUtils;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;


public class UserService {
    SqlSessionFactory factory = SqlSessionFactoryUtils.getSqlSessionFactory();

    public User login(String username,String password){
        //2. 获取SqlSession
        SqlSession sqlSession = factory.openSession();
        //3. 获取UserMapper
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //4. 调用方法
        User user = mapper.select(username, password);

        //释放资源
        sqlSession.close();

        return  user;
    }
}

Service层——BrandService

package com.GY.service;

import com.GY.mapper.BrandMapper;
import com.GY.pojo.Brand;
import com.GY.util.SqlSessionFactoryUtils;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;

import java.util.List;

public class BrandService {
    SqlSessionFactory factory = SqlSessionFactoryUtils.getSqlSessionFactory();

    public List<Brand> selectAll(){
        //调用BrandMapper.selectAll()

        //2. 获取SqlSession
        SqlSession sqlSession = factory.openSession();
        //3. 获取BrandMapper
        BrandMapper mapper = sqlSession.getMapper(BrandMapper.class);
        //4. 调用方法
        List<Brand> brands = mapper.selectAll();
        sqlSession.close();
        return brands;
    }
}

Web层——LoginServlet类

package com.GY.web;

import com.GY.pojo.User;
import com.GY.service.UserService;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;

@WebServlet("/loginServlet")
public class LoginServlet extends HttpServlet {

    private UserService service = new UserService();
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1. 获取用户名和密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        //2. 调用service查询
        User user = service.login(username, password);
        //3. 判断
        if(user != null){
            //登录成功，跳转到查询所有的BrandServlet（重定向）

            // 将登录成功后的User对象，存储到Session
            HttpSession session = request.getSession();
            session.setAttribute("user",user);
            String contextPath = request.getContextPath();
            response.sendRedirect("/selectAllServlet");
        }else {
            // 登录失败,
            
            // 存储错误信息到request
            request.setAttribute("login_msg","用户名或密码错误");
            // 跳转到login.jsp
            request.getRequestDispatcher("/login.jsp").forward(request,response);
        }
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }
}

Web层——SelectAllServlet 类

package com.GY.web;

import com.GY.pojo.Brand;
import com.GY.service.BrandService;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.util.List;

@WebServlet("/selectAllServlet")
public class SelectAllServlet extends HttpServlet {
    private  BrandService service = new BrandService();

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


        //1. 调用BrandService完成查询
        List<Brand> brands = service.selectAll();

        //2. 存入request域中
        request.setAttribute("brands",brands);

        //3. 转发到brand.jsp（请求转发）
        request.getRequestDispatcher("/brand.jsp").forward(request,response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }
}

效果展示