服务器端会话技术：Session(数据存储在服务器端)，与cookie相反

文章目录

1. 快速入门：
2. Session细节
3. Session案例

原理： Session的实现是依赖于Cookie的。
在这里插入图片描述

session的特点
1. session用于存储一次会话的多次请求的数据，存在服务器端
2. session可以存储任意类型，任意大小的数据
session与Cookie的区别：
1. session存储数据在服务器端，Cookie在客户端
2. session没有数据大小限制，Cookie有
3. session数据安全，Cookie相对于不安全

1. 快速入门：

	1. 获取HttpSession对象：
		HttpSession session = request.getSession();
	2. 使用HttpSession对象：
		Object getAttribute(String name)  
		void setAttribute(String name, Object value)
		void removeAttribute(String name)

SessionDemo1与SessionDemo2一起
session共享数据

package comm.Session;
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;
@WebServlet("/SessionDemo1")
public class SessionDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //使用session共享数据
        //1.获取session
        HttpSession session = request.getSession();
        //2.存储数据
        session.setAttribute("msg","session is good");
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

package comm.Session;
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;
@WebServlet("/SessionDemo2")
public class SessionDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //使用session获取数据
        //1.获取session
        HttpSession session = request.getSession();
        //2.获取数据
        Object msg = session.getAttribute("msg");
        System.out.println(msg);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

2. Session细节

细节1. 当客户端关闭后，服务器不关闭，两次获取session是否为同一个？
* 默认情况下。不是。
* 如果需要相同，则可以创建Cookie,键为JSESSIONID，设置最大存活时间，让cookie持久化保存。
Cookie c = new Cookie(“JSESSIONID”,session.getId());
c.setMaxAge(60*60);
response.addCookie©;

package comm.Session;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;
/**
 * 3.细节(1):当客户端关闭后，服务器不关闭，两次获取session是否为同一个？
 * 	   * 默认情况下,不是。
 * 	   * 如果需要相同，则可以创建Cookie,键为JSESSIONID，设置最大存活时间，让cookie持久化保存。
 * 			Cookie c = new Cookie("JSESSIONID",session.getId());
 * 		    c.setMaxAge(60*60);
 		    response.addCookie(c)
 * */
@WebServlet("/SessionDemo3")
public class SessionDemo3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.获取session
        HttpSession session = request.getSession();
        System.out.println(session);
        //期望客户端关闭后，session也能相同
        Cookie cookie = new Cookie("JSESSIONID", session.getId());
        //设置1小时后，Cookie死亡，则客户端关闭后，session就不相同
        cookie.setMaxAge(60*60);
        //发送响应头
        response.addCookie(cookie);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}
/**
* 1小时内结果相同：
org.apache.catalina.session.StandardSessionFacade@2bc765e4
org.apache.catalina.session.StandardSessionFacade@2bc765e4
* */

细节2. 客户端不关闭，服务器关闭后，两次获取的session是同一个吗？
* 不是同一个，但是要确保数据不丢失。tomcat自动完成以下工作
* session的钝化：
* 在服务器正常关闭之前，将session对象系列化到硬盘上
* session的活化：
* 在服务器启动后，将session文件转化为内存中的session对象即可

细节3. session什么时候被销毁？
1. 服务器关闭
2. session对象调用invalidate() 。
3. session默认失效时间 30分钟

  		选择性配置修改	
  		<session-config>
  	        <session-timeout>30</session-timeout>
  	    </session-config>

package comm.Session;
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;
@WebServlet("/SessionDemo4")
public class SessionDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取session
        HttpSession session = request.getSession();
        System.out.println(session);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}
/**
 * 浏览器不动，服务器关闭后，2次获取结果不同(@Hashcode值):
org.apache.catalina.session.StandardSessionFacade@408dcbc7
org.apache.catalina.session.StandardSessionFacade@29175bbb
 * */

3. Session案例

(1)checkCode

package comm.Test;
import javax.imageio.ImageIO;
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 java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
/**
 * 案例：验证码
 * */
@WebServlet("/checkCode")
public class checkCodeServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int width = 100;
        int height = 50;
        //1.创建一对象，在内存中图片(验证码图片对象)
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
        //2.美化图片
        //2.1 填充背景色
        Graphics g = image.getGraphics();//画笔对象
        g.setColor(Color.PINK);//设置画笔颜色
        g.fillRect(0,0,width,height);
        //2.2画边框
        g.setColor(Color.BLUE);
        g.drawRect(0,0,width - 1,height - 1);
        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789";
        //生成随机角标
        Random ran = new Random();
        StringBuilder sb = new StringBuilder();
        for (int i = 1; i <= 4; i++) {
            int index = ran.nextInt(str.length());
            //获取字符
            char ch = str.charAt(index);//随机字符
            sb.append(ch);
            //2.3写验证码
            g.drawString(ch+"",width/5*i,height/2);
        }
        String checkCode_session = sb.toString();
        //将验证码存入session        request.getSession().setAttribute("checkCode_session",checkCode_session);
        //2.4画干扰线
        g.setColor(Color.GREEN);
        //随机生成坐标点
        for (int i = 0; i < 10; i++) {
            int x1 = ran.nextInt(width);
            int x2 = ran.nextInt(width);
            int y1 = ran.nextInt(height);
            int y2 = ran.nextInt(height);
            g.drawLine(x1,y1,x2,y2);
        }
        //3.将图片输出到页面展示
        ImageIO.write(image,"jpg",response.getOutputStream());
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

(2)loginServlet

package comm.Test;
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;
/**
 ## 案例：验证码
 1. 案例需求：
 1. 访问带有验证码的登录页面login.jsp
 2. 用户输入用户名，密码以及验证码。
 * 如果用户名和密码输入有误，跳转登录页面，提示:用户名或密码错误
 * 如果验证码输入有误，跳转登录页面，提示：验证码错误
 * 如果全部输入正确，则跳转到主页success.jsp，显示：用户名,欢迎您
 * */
@WebServlet("/loginServlet")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.设置request编码
        request.setCharacterEncoding("utf-8");
        //2.获取参数
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String checkCode = request.getParameter("checkCode");
        //3.先获取生成的验证码
        HttpSession session = request.getSession();
        String checkCode_session = (String) session.getAttribute("checkCode_session");
        //删除session中存储的验证码
        session.removeAttribute("checkCode_session");
        //3.先判断验证码是否正确
        if(checkCode_session!= null && checkCode_session.equalsIgnoreCase(checkCode)){
            //忽略大小写比较
            //验证码正确
            //判断用户名和密码是否一致
            if("zhangsan".equals(username) && "123".equals(password)){//需要调用UserDao查询数据库
                //登录成功
                //存储信息，用户信息
                session.setAttribute("user",username);
                //重定向到success.jsp              response.sendRedirect(request.getContextPath()+"/success.jsp");
            }else{
                //登录失败
                //存储提示信息到request
                request.setAttribute("login_error","用户名或密码错误");
                //转发到登录页面          request.getRequestDispatcher("/login.jsp").forward(request,response);
            }
        }else{
            //验证码不一致
            //存储提示信息到request
            request.setAttribute("cc_error","验证码错误");
            //转发到登录页面           request.getRequestDispatcher("/login.jsp").forward(request,response);
        }
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

(3)login.jsp

<%--
  Date: 2020/1/31 0031,Time: 13:22
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>login</title>
    <script>
        window.onload = function(){
            document.getElementById("img").onclick = function(){
                this.src="/Servlet_war_exploded/checkCode?time="+new Date().getTime();
            }
        }
    </script>
    <style>
        div{
            color: red;
        }
    </style>
</head>
<body>
<form action="/Servlet_war_exploded/loginServlet" method="post">
    <table>
        <tr>
            <td>用户名</td>
            <td><input type="text" name="username"></td>
        </tr>
        <tr>
            <td>密码</td>
            <td><input type="password" name="password"></td>
        </tr>
        <tr>
            <td>验证码</td>
            <td><input type="text" name="checkCode"></td>
        </tr>
        <tr>
            <td colspan="2"><img id="img" src="/Servlet_war_exploded/checkCode"></td>
        </tr>
        <tr>
            <td colspan="2"><input type="submit" value="登录"></td>
        </tr>
    </table>
</form>
<div><%=request.getAttribute("cc_error") == null ? "" : request.getAttribute("cc_error")%></div>
<div><%=request.getAttribute("login_error") == null ? "" : request.getAttribute("login_error") %></div>
</body>
</html>

(4)success.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <h1><%=request.getSession().getAttribute("user")%>,欢迎您</h1>
</body>
</html>

结果展示：在这里插入图片描述

灰色头像JH

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