JavaWeb学习(12)--Session快速入门

1）Session快速入门

代码：https://gitee.com/jianghaok/Login.git
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
2.1 ) 获取HttpSession对象

HttpSession session = request.getSession();

2.2) 使用HttpSession对象

Object getAttribute(String name)
void setAttribute(String name, Object value)
void removeAttribute(String name)

例：SessionDemo1.java

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

SessionDemo2.java

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

输出：先访问http://localhost:8080/Cookie/sessionDemo1，再访问http://localhost:8080/Cookie/sessionDemo2,结果如下所示：

2.3) 原理：Session的实现是依赖于Cookie的

2）Session细节

2.1 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);

例：SessionDemo3.java

package cn.itcast.session;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;
@WebServlet("/sessionDemo3")
public class SessionDemo3 extends HttpServlet {
    @Override
    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());
        //设置最大存活时间【在1小时内访问的session将是同一个】
        c.setMaxAge(60*60);
        response.addCookie(c);
    }
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

2.2 客户端不关闭，服务器关闭后，两次获取的session是同一个吗？

例：SessionDemo4,java

package cn.itcast.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 {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.获取session
        HttpSession session = request.getSession();
        System.out.println(session);
    }
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

输出：先访问 http://localhost:8080/Cookie/sessionDemo4，重启工程后再次访问http://localhost:8080/Cookie/sessionDemo4，结果如下，客户端未关闭，可见不是同一个

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对象序列化到硬盘上；
• 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 【IDEA中不能活化】

2.3 session什么时候被销毁？

• 服务器关闭
• session对象调用invalidate()
• session默认失效时间 30分钟
  在tomcat安装目录：\apache-tomcat-8.5.31-windows-64位\apache-tomcat-8.5.31\conf中的 web.xml 中配置

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

如图所示：

2.4 session的特点

• session用于存储一次会话的多次请求的数据，存在服务器端
• 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

3）案例：验证码

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

分析：

代码实现：
LoginServlet.java

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

CheckCodeServlet.java

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

完整代码：https://gitee.com/jianghaok/Login.git
输出：访问http://localhost:8080/Cookie/login.jsp

内容来源：《学习传智播客的课程《JavaWeb+黑马旅游网》》
代码：https://gitee.com/jianghaok/Login.git
关注公众号，回复 【算法】，获取高清算法书！