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Session

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。HttpSession2. 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				
   		        
    
     30
    		    
    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

<%@ page contentType="text/html;charset=UTF-8" language="java" %>                
   
        
    
                 
      
                       
用户名
                       
                  
                  
                       
密码
                       
                  
                  
                       
验证码
                       
                  
                  
                       
                  
                  
                       
                  
             
    
    
   
    
   
    <%=request.getAttribute("cc_error") == null ? "" : request.getAttribute("cc_error")%>
   
    
   
    <%=request.getAttribute("login_error") == null ? "" : request.getAttribute("login_error") %>
   

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

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

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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