Cookie基本使用：

Cookie:客户端会话技术，将数据保存到客户端，以后每次请求都携带Cookie数据进行访问
Cookie基本使用

1.创建Cookie对象，设置数据
1
Cookie cookie = new Cookie("key","value");
2.发送Cookie到客户端: 使用response对象
1
response.addCookie(cookie):
3.获取客户端所携带的所有Cookie，使用request对象
1
Cookie[] cookies = request.getCookies();
4.遍历数组，获取每一个Cookie对象: for

5.使用Cookie对象防火获取数据
Cookie存储时间设置

cookie.setMaxAge( time ) 其中time以秒为单位，例如一周表示为60 * 60 * 24 * 7

Session

服务器绘画跟踪技术：将数据保存到服务器
JavaEE提供HttpSession接口，来实现一次会话的多次请求间数据共享功能
使用：

1。获取Session对象
1
HttpSession session = request.getSession();
2.Session对象功能：
- void setArribute(String name,Object o) 存储数据到Session域中
- Object getAttribute(String name) 根据key获取值
- void removeArrtibute(String name) 根据key，删除该键值对。

Cookie和Session对比:

Cookie 和Session都是来完成一次会话内多次请求间数据共享的
区别：
- 存储位置：Cookie是将数据存储在客户端，Session将数据存储在服务器段
- 安全性：Cookie不安全，Session安全
- 数据大小：Cookie最大3KB，Session无大小限制
- 存储时间：Cookie可以长期存储，Session默认30分钟
- 服务性能：Cookie不占服务器资源，Session占用服务器资源

页面登录样例：

1.采用三层架构开发思想，

dao层创建映射文件UserMapper，并配置select

1 2	@Select("select * from tb_user where username = #{username} and password = #{password}") User select(@Param("username") String username,@Param("password") String password);

service层创建UserService，并创建login函数

public User login(String username, String password)
   {
       //获取Sqlsession
       SqlSession sqlSession = factory.openSession();
       //获取UserMapper
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);

       User user = mapper.select(username,password);

       sqlSession.close();

       return user;
   }

web层创建LoginServlet，

private UserService service = new UserService();
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       //获取用户名和密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        //调用Service方法login
        User user = service.login(username, password);
        System.out.println(user);

        //获取复选框数据
        String remember = request.getParameter("remember");


        //判断
        if(user != null)  //登录成功
        {
            //判断用户是否记住我
            if("1".equals(remember))
            {
                //勾选了，发送Cookie
                Cookie c_username  = new Cookie("username",username);
                Cookie c_password  = new Cookie("password",password);

                //设置Cookie存储时间为一周
                c_username.setMaxAge(60 * 60 * 24 * 7);
                c_password.setMaxAge(60 * 60 * 24 * 7);

                //发送
                response.addCookie(c_username);
                response.addCookie(c_password);
            }

            //将登录成功后的user存储到session中
            HttpSession session = request.getSession();
            session.setAttribute("user",user);
            //登陆成功，跳转到查询所有的Brand的SellectAllServlet去
            String contextPath = request.getContextPath();
            System.out.println(contextPath);
            response.sendRedirect(contextPath + "/selectAllServlet");
        }
        else     //登录失败
        {
            //存储错误信息到request
            request.setAttribute("login_msg","用户名或密码错误");

            //跳转到login.jsp
            request.getRequestDispatcher("/login.jsp").forward(request,response);
        }

    }

<%--
  Created by IntelliJ IDEA.
  User: xyh
  Date: 2022/1/14
  Time: 11:09
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>login</title>
    <link href="css/login.css" rel="stylesheet">
</head>

<body>
<div id="loginDiv" style="height: 350px">
    <form action="/brand/loginServlet" id="form" method="post">
        <h1 id="loginMsg">LOGIN IN</h1>
        <div id="errorMsg">${login_msg}</div>
        <p>Username:<input id="username" name="username"  value = "${cookie.username.value}" type="text"></p>
            
			//EL表达式获取存放的cookie的username
            
        <p>Password:<input id="password" name="password" value = "${cookie.password.value}" type="password"></p>
            
            //EL表达式获取存放的cookie的password
            
        <p>Remember:<input id="remember" name="remember" value = "1" type="checkbox"></p>                                                   
            //value = 1 表示勾选了remember
            
        <div id="subDiv">
            <input type="submit" class="button" value="login up">
            <input type="reset" class="button" value="reset">&nbsp;&nbsp;&nbsp;
            <a href="register.html">没有账号？</a>
        </div>
    </form>
</div>

</body>
</html>

页面注册样例：

1.同样采用三层架构：

dao层配置mapper

@Select("select * from tb_user where username = #{username}")       //查询是否存在改用户名
User selectByUsername(String username);
    
@Insert("insert into tb_user values(null,#{username},#{password})") //若不存在则注册
void add(User user);

service层中创建register函数

public boolean register(User user)
   {
       //获取Sqlsession
       SqlSession sqlSession = factory.openSession();
       //获取UserMapper
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);

       //判断用户名是否存在
        User u = mapper.selectByUsername(user.getUsername());
       if(u == null)  //用户名不存在
       {
           mapper.add(user);
           sqlSession.commit();
       }
       sqlSession.close();
       return u == null;      //用户存在
       
   }

web层创建RegisterServlet，

private UserService service = new UserService();
   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
      //获取用户名和密码
       String username = request.getParameter("username");
       String password = request.getParameter("password");

       User user = new User();
       user.setUsername(username);
       user.setPassword(password);

       //调用service注册
       boolean flag = service.register(user);

       //判断注册成功与否
       if(flag)
       {
           //注册成功，跳转登录页面
           request.setAttribute("register_msg","注册成功,请登录");
           request.getRequestDispatcher("/login.jsp").forward(request,response);
       }
       else
       {
           //注册失败，跳转当前页面
           request.setAttribute("register_msg","用户名已存在");
           request.getRequestDispatcher("/register.jsp").forward(request,response);
       }
   }

2.验证码实现

验证码工具类CheckCodeUtil.java ：

package util;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Arrays;
import java.util.Random;

/**
 * 生成验证码工具类
 */
public class CheckCodeUtil {

    public static final String VERIFY_CODES = "123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private static Random random = new Random();



    /**
     * 输出随机验证码图片流,并返回验证码值（一般传入输出流，响应response页面端，Web项目用的较多）
     *
     * @param w
     * @param h
     * @param os
     * @param verifySize
     * @return
     * @throws IOException
     */
    public static String outputVerifyImage(int w, int h, OutputStream os, int verifySize) throws IOException {
        String verifyCode = generateVerifyCode(verifySize);
        outputImage(w, h, os, verifyCode);
        return verifyCode;
    }

    /**
     * 使用系统默认字符源生成验证码
     *
     * @param verifySize 验证码长度
     * @return
     */
    public static String generateVerifyCode(int verifySize) {
        return generateVerifyCode(verifySize, VERIFY_CODES);
    }

    /**
     * 使用指定源生成验证码
     *
     * @param verifySize 验证码长度
     * @param sources    验证码字符源
     * @return
     */
    public static String generateVerifyCode(int verifySize, String sources) {
        // 未设定展示源的字码，赋默认值大写字母+数字
        if (sources == null || sources.length() == 0) {
            sources = VERIFY_CODES;
        }
        int codesLen = sources.length();
        Random rand = new Random(System.currentTimeMillis());
        StringBuilder verifyCode = new StringBuilder(verifySize);
        for (int i = 0; i < verifySize; i++) {
            verifyCode.append(sources.charAt(rand.nextInt(codesLen - 1)));
        }
        return verifyCode.toString();
    }

    /**
     * 生成随机验证码文件,并返回验证码值 (生成图片形式，用的较少)
     *
     * @param w
     * @param h
     * @param outputFile
     * @param verifySize
     * @return
     * @throws IOException
     */
    public static String outputVerifyImage(int w, int h, File outputFile, int verifySize) throws IOException {
        String verifyCode = generateVerifyCode(verifySize);
        outputImage(w, h, outputFile, verifyCode);
        return verifyCode;
    }



    /**
     * 生成指定验证码图像文件
     *
     * @param w
     * @param h
     * @param outputFile
     * @param code
     * @throws IOException
     */
    public static void outputImage(int w, int h, File outputFile, String code) throws IOException {
        if (outputFile == null) {
            return;
        }
        File dir = outputFile.getParentFile();
        //文件不存在
        if (!dir.exists()) {
            //创建
            dir.mkdirs();
        }
        try {
            outputFile.createNewFile();
            FileOutputStream fos = new FileOutputStream(outputFile);
            outputImage(w, h, fos, code);
            fos.close();
        } catch (IOException e) {
            throw e;
        }
    }

    /**
     * 输出指定验证码图片流
     *
     * @param w
     * @param h
     * @param os
     * @param code
     * @throws IOException
     */
    public static void outputImage(int w, int h, OutputStream os, String code) throws IOException {
        int verifySize = code.length();
        BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        Random rand = new Random();
        Graphics2D g2 = image.createGraphics();
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

        // 创建颜色集合，使用java.awt包下的类
        Color[] colors = new Color[5];
        Color[] colorSpaces = new Color[]{Color.WHITE, Color.CYAN,
                Color.GRAY, Color.LIGHT_GRAY, Color.MAGENTA, Color.ORANGE,
                Color.PINK, Color.YELLOW};
        float[] fractions = new float[colors.length];
        for (int i = 0; i < colors.length; i++) {
            colors[i] = colorSpaces[rand.nextInt(colorSpaces.length)];
            fractions[i] = rand.nextFloat();
        }
        Arrays.sort(fractions);
        // 设置边框色
        g2.setColor(Color.GRAY);
        g2.fillRect(0, 0, w, h);

        Color c = getRandColor(200, 250);
        // 设置背景色
        g2.setColor(c);
        g2.fillRect(0, 2, w, h - 4);

        // 绘制干扰线
        Random random = new Random();
        // 设置线条的颜色
        g2.setColor(getRandColor(160, 200));
        for (int i = 0; i < 20; i++) {
            int x = random.nextInt(w - 1);
            int y = random.nextInt(h - 1);
            int xl = random.nextInt(6) + 1;
            int yl = random.nextInt(12) + 1;
            g2.drawLine(x, y, x + xl + 40, y + yl + 20);
        }

        // 添加噪点
        // 噪声率
        float yawpRate = 0.05f;
        int area = (int) (yawpRate * w * h);
        for (int i = 0; i < area; i++) {
            int x = random.nextInt(w);
            int y = random.nextInt(h);
            // 获取随机颜色
            int rgb = getRandomIntColor();
            image.setRGB(x, y, rgb);
        }
        // 添加图片扭曲
        shear(g2, w, h, c);

        g2.setColor(getRandColor(100, 160));
        int fontSize = h - 4;
        Font font = new Font("Algerian", Font.ITALIC, fontSize);
        g2.setFont(font);
        char[] chars = code.toCharArray();
        for (int i = 0; i < verifySize; i++) {
            AffineTransform affine = new AffineTransform();
            affine.setToRotation(Math.PI / 4 * rand.nextDouble() * (rand.nextBoolean() ? 1 : -1), (w / verifySize) * i + fontSize / 2, h / 2);
            g2.setTransform(affine);
            g2.drawChars(chars, i, 1, ((w - 10) / verifySize) * i + 5, h / 2 + fontSize / 2 - 10);
        }

        g2.dispose();
        ImageIO.write(image, "jpg", os);
    }

    /**
     * 随机颜色
     *
     * @param fc
     * @param bc
     * @return
     */
    private static Color getRandColor(int fc, int bc) {
        if (fc > 255) {
            fc = 255;
        }
        if (bc > 255) {
            bc = 255;
        }
        int r = fc + random.nextInt(bc - fc);
        int g = fc + random.nextInt(bc - fc);
        int b = fc + random.nextInt(bc - fc);
        return new Color(r, g, b);
    }

    private static int getRandomIntColor() {
        int[] rgb = getRandomRgb();
        int color = 0;
        for (int c : rgb) {
            color = color << 8;
            color = color | c;
        }
        return color;
    }

    private static int[] getRandomRgb() {
        int[] rgb = new int[3];
        for (int i = 0; i < 3; i++) {
            rgb[i] = random.nextInt(255);
        }
        return rgb;
    }

    private static void shear(Graphics g, int w1, int h1, Color color) {
        shearX(g, w1, h1, color);
        shearY(g, w1, h1, color);
    }

    private static void shearX(Graphics g, int w1, int h1, Color color) {

        int period = random.nextInt(2);

        boolean borderGap = true;
        int frames = 1;
        int phase = random.nextInt(2);

        for (int i = 0; i < h1; i++) {
            double d = (double) (period >> 1)
                    * Math.sin((double) i / (double) period
                    + (6.2831853071795862D * (double) phase)
                    / (double) frames);
            g.copyArea(0, i, w1, 1, (int) d, 0);
            if (borderGap) {
                g.setColor(color);
                g.drawLine((int) d, i, 0, i);
                g.drawLine((int) d + w1, i, w1, i);
            }
        }

    }

    private static void shearY(Graphics g, int w1, int h1, Color color) {

        int period = random.nextInt(40) + 10; // 50;

        boolean borderGap = true;
        int frames = 20;
        int phase = 7;
        for (int i = 0; i < w1; i++) {
            double d = (double) (period >> 1)
                    * Math.sin((double) i / (double) period
                    + (6.2831853071795862D * (double) phase)
                    / (double) frames);
            g.copyArea(i, 0, 1, h1, 0, (int) d);
            if (borderGap) {
                g.setColor(color);
                g.drawLine(i, (int) d, i, 0);
                g.drawLine(i, (int) d + h1, i, h1);
            }

        }

    }
}

3.最终实现：

1.Register.jsp

<%--
  Created by IntelliJ IDEA.
  User: xyh
  Date: 2022/1/14
  Time: 18:20
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>欢迎注册</title>
    <link href="css/register.css" rel="stylesheet">
</head>
<body>

<div class="form-div">
    <div class="reg-content">
        <h1>欢迎注册</h1>
        <span>已有帐号？</span> <a href="login.html">登录</a>
    </div>
    <form id="reg-form" action="/brand/registerServlet" method="post">

        <table>

            <tr>
                <td>用户名</td>
                <td class="inputs">
                    <input name="username" type="text" id="username">
                    <br>
                    <span id="username_err" class="err_msg" >${register_msg}</span>                              //style="display: none本来存在，要去掉,
                         //${register_msg}需要放到login里id为msg的标签里去
                </td>

            </tr>

            <tr>
                <td>密码</td>
                <td class="inputs">
                    <input name="password" type="password" id="password">
                    <br>
                    <span id="password_err" class="err_msg" style="display: none">密码格式有误</span>
                </td>
            </tr>


            <tr>
                <td>验证码</td>
                <td class="inputs">
                    <input name="checkCode" type="text" id="checkCode">
                    <img src="/brand/CheckCodeServlet">
                    <a href="#" id="changeImg">看不清？</a>
                </td>
            </tr>

        </table>

        <div class="buttons">
            <input value="注 册" type="submit" id="reg_btn">
        </div>
        <br class="clear">
    </form>

</div>
            
 <script>
    document.getElementById("changeImg").src = "/brand/checkCodeServlet?" + new Date().getMilliseconds();         //增加更改图片的单击事件，并且因为浏览器会缓存掉图片，所以后面加上								  永远不可能与之前相等的值，用time可以满足。
</script>
    
</body>
</html>

2.CheckCodeServlet

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //生成图片
        ServletOutputStream os = response.getOutputStream();
        String checkCode = CheckCodeUtil.outputVerifyImage(100,50,os,4);

        //存入Session
        HttpSession session = request.getSession();
        session.setAttribute("checkCodeGen",checkCode);
    }

3.在RegisterServlet中增添以下代码

该部分代码放在注册之前，即验证码若错误不去访问数据库判断用户名和密码。

//获取用户输入的验证码
        String checkCode = request.getParameter("checkCode:");

        //从Session中获取程序生成的验证码
        HttpSession session = request.getSession();
        String checkCodeGen = (String) session.getAttribute("checkCodeGen");

        //比对
        if(!checkCodeGen.equals(checkCode)) //比对不成功，验证码错误
        {
            request.setAttribute("register_msg","验证码错误");
            request.getRequestDispatcher("/register.jsp").forward(request,response);
            
            //不允许注册
            return;
        }