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【JAVA】Session

彭维盛 2022-06-23 阅读 47
java验证码用户名Linux系统/运维

Session

【JAVA】Session_验证码

1. 概念：服务器端会话技术，在一次会话的多次请求间共享数据，将数据保存在服务器端的对象中。HttpSession
2. 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)  

3. 原理
  * Session的实现是依赖于Cookie的。

示例代码，两个servlet之间，一个填写Session，另一个获得Session

以下是用于获得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","hello session");
    }

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

另一个是用于打印session里的数据

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);
    }
}

Session的注意事项

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);

示例代码

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

@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 c = new Cookie("JSESSIONID",session.getId());
        c.setMaxAge(60*60);
        response.addCookie(c);

    }

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

另一个servlet用于查看，验证是否关闭客户端也是获得同一个session

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

@WebServlet("/sessionDemo4")
public class SessionDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //1.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);
    }
}

其余注意事项

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。
      
  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>

 补充： 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

案例，验证码判定

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

【JAVA】Session_用户名_02
前端注册的页面

<%@ 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="/day16_cookie_session_war_exploded/checkCodeServlet?time="+new Date().getTime();
            }
        }


    </script>
    <style>
        div{
            color: red;
        }

    </style>
</head>
<body>

    <form action="/day16_cookie_session_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="/day16_cookie_session_war_exploded/checkCodeServlet"></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>

注意上述路径根据项目工程进行变换，另外包名不是文件夹，所以相对路径上不用写，如/day16_cookie_session_war_exploded/checkCodeServlet，不用写成/day16_cookie_session_war_exploded/servlet/checkCodeServle
t
【JAVA】Session_用户名_03
注册成功页面

<%@ 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>

生成验证码的servlet

package cn.itcast.servlet;

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;

@WebServlet("/checkCodeServlet")
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);
    }
}

点击登录按钮后跳转的servlet

package cn.itcast.servlet;

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("/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);
    }
}


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