Session

什么是Session

Session是由服务器产生，保存在服务器中

一个用户 对应一个session( 一个浏览器 对应一个session)

session的原理

JessionId  session是依赖于cookie的

注意：如果服务器关闭 ，那么会产生一个新的session 和 新的session id

session的常用方法

request.getSession().setAttribute()

request.getSession().getAttribute()

request.getSession().removeAttribute()

 

session 的默认有效时间：30分钟

session 失效的方法：

1、配置web.xml 

<session-config>
      <session-timeout>1</session-timeout>
</session-config>

2、手动的干掉session

session.invalidate();

3、代码设置session的保存时间

session.setMaxInactiveInterval(); 单位秒

案例：验证码的获取

验证码的servlet类

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;

/**
 * 验证码
 */
@WebServlet("/checkCodeServlet")
public class CheckCodeServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        
        //服务器通知浏览器不要缓存
        response.setHeader("pragma","no-cache");
        response.setHeader("cache-control","no-cache");
        response.setHeader("expires","0");
        
        //在内存中创建一个长80，宽30的图片，默认黑色背景
        //参数一：长
        //参数二：宽
        //参数三：颜色
        int width = 80;
        int height = 30;
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
        
        //获取画笔
        Graphics g = image.getGraphics();
        //设置画笔颜色为灰色
        g.setColor(Color.GRAY);
        //填充图片
        g.fillRect(0,0, width,height);
        
        //产生4个随机验证码，12Ey
        String checkCode = getCheckCode();
        //将验证码放入HttpSession中
        request.getSession().setAttribute("checkCode_session",checkCode);
        
        //设置画笔颜色为黄色
        g.setColor(Color.YELLOW);
        //设置字体的小大
        g.setFont(new Font("黑体",Font.BOLD,24));
        //向图片上写入验证码
        g.drawString(checkCode,15,25);
        
        //将内存中的图片输出到浏览器
        //参数一：图片对象
        //参数二：图片的格式，如PNG,JPG,GIF
        //参数三：图片输出到哪里去
        ImageIO.write(image,"PNG",response.getOutputStream());
    }
    /**
     * 产生4位随机字符串 
     */
    private String getCheckCode() {
        String base = "0123456789ABCDEFGabcdefg";
        int size = base.length();
        Random r = new Random();
        StringBuffer sb = new StringBuffer();
        for(int i=1;i<=4;i++){
            //产生0到size-1的随机值
            int index = r.nextInt(size);
            //在base字符串中获取下标为index的字符
            char c = base.charAt(index);
            //将c放入到StringBuffer中去
            sb.append(c);
        }
        return sb.toString();
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }
}

登录的servlet类

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.io.IOException;

@WebServlet("/loginServlet")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1、获取参数
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String code = request.getParameter("code");
        //2、获取session中的验证码
        String checkCode_session = (String) request.getSession().getAttribute("checkCode_session");
        //3验证验证码
        if(code.equalsIgnoreCase(checkCode_session)){
            //判断用户名和密码
            if(username.equals("coco") && password.equals("123")){
                request.getSession().setAttribute("msg", "登录成功！");
                request.getSession().setAttribute("user", "coco");
                response.sendRedirect("/success.jsp");
            }else{
                request.getSession().setAttribute("msg", "用户名或者密码有误！！！");
                response.sendRedirect("/login.jsp");
            }
        }else{
            request.getSession().setAttribute("msg", "验证码错误！");
            response.sendRedirect("/login.jsp");
        }

    }

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

前端代码：login.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="utf-8"/>
    <meta http-equiv="X-UA-Compatible" content="IE=edge"/>
    <meta name="viewport" content="width=device-width, initial-scale=1"/>
    <title>管理员登录</title>

    <!-- 1. 导入CSS的全局样式 -->
    <link href="css/bootstrap.min.css" rel="stylesheet">
    <!-- 2. jQuery导入，建议使用1.9以上的版本 -->
    <script src="js/jquery-2.1.0.min.js"></script>
    <!-- 3. 导入bootstrap的js文件 -->
    <script src="js/bootstrap.min.js"></script>
    <script type="text/javascript">
    </script>
</head>
<body>
<div class="container" style="width: 400px;">
    <h3 style="text-align: center;">管理员登录</h3>
    <form action="/loginServlet" method="post">
        <div class="form-group">
            <label for="user">用户名：</label>
            <input type="text" name="username" class="form-control" id="user" placeholder="请输入用户名"/>
        </div>

        <div class="form-group">
            <label for="password">密码：</label>
            <input type="password" name="password" class="form-control" id="password" placeholder="请输入密码"/>
        </div>

        <div class="form-inline">
            <label for="vcode">验证码：</label>
            <input type="text" name="code" class="form-control" id="verifycode" placeholder="请输入验证码" style="width: 120px;"/>
            <a href="javascript:refreshCode()">
                <img src="${pageContext.request.contextPath}/checkCodeServlet" title="看不清点击刷新" id="vcode"/>
            </a>
        </div>
        <hr/>
        <div class="form-group" style="text-align: center;">
            <input class="btn btn btn-primary" type="submit" value="登录">
        </div>
    </form>

    <!-- 出错显示的信息框 -->
    <div class="alert alert-warning alert-dismissible" role="alert">
        <button type="button" class="close" data-dismiss="alert" >
            <span>&times;</span></button>
        <strong>${msg}</strong>
    </div>
</div>
</body>
<script>
    function refreshCode() {
        // 1、获取当前图片对象
        var elementById = document.getElementById("vcode");
        // 2、修改 src 的值
        elementById.src = "${pageContext.request.contextPath}/checkCodeServlet?time=" + new Date().getTime();
    }
</script>
</html>