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八、会话跟踪技术 ​

一、实现方式 ​

  • 客户端会话跟踪技术：Cookie
  • 服务端会话跟踪技术：Session

二、Cookie ​

1、介绍 ​

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

2、基本使用 ​


（1）创建Cookie对象 ​

java
Cookie cookie = new Cookie("key","value");

（2）携带Cookie响应 ​

java
response.addCookie(cookie);

（3）解析携带Cookie的请求 ​

java
Cookie[] cookie = request.getCookies();

（4）设置Cookie存活时间 ​

java
setMaxAge(int seconds)
  • 正数：将Cookie写入硬盘，持久化存储，到时间删除
  • 负数：默认值，当浏览器关闭，Cookie销毁
  • 零：删除对应Cookie

（5）Cookie值设置中文 ​

  1. 转码

    java
    URLDecoder.encode(value,"UTF-8")

  2. 解码

    java
    URLDecoder.decode(value,"UTF-8")

三、Session ​

1、介绍 ​

Session：服务端跟踪技术，将数据保存到服务端

2、基本使用 ​

（1）获取Session对象 ​

java
HttpSession session = request.getSession();

（2）存储数据 ​

存储数据到session域中

java
void setAttribute(String name , Object o)

（3）获取值 ​

根据key，获取值

java
Object getAttribute(String name)

（4）根据key，删除键值对 ​

java
void removeAttribute(String name)

（5）销毁 ​

默认情况下，无操作，30分钟自动销毁

web.xml

xml
<session-config>
	<session-timeout>30</session-timeout>  <!-- 单位：分钟 -->
</session-config>
java
session.invalidate();

四、验证码 ​

1、CheckCodeUtil工具类 ​

java
package org.example.utils;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.*;
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();


    public static void main(String[] args) throws IOException {
        String property = System.getProperty("user.dir");
        OutputStream fos = new FileOutputStream(property + "/src/main/resources/verifycode/a.jpg");
        String checkCode = CheckCodeUtil.outputVerifyImage(100, 50, fos, 4);
    }


    /**
     * 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 width      图片宽度
     * @param height     图片高度
     * @param os         输出流
     * @param verifySize 数据长度
     * @return 验证码数据
     * @throws IOException
     */
    public static String outputVerifyImage(int width, int height, OutputStream os, int verifySize) throws IOException {
        String verifyCode = generateVerifyCode(verifySize);
        outputImage(width, height, 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);
            }

        }

    }
}

2、生成验证码 ​

/verifycode

java
@WebServlet("/verifycode")
public class VerifyCodeDemo extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        生成验证码
        ServletOutputStream os = resp.getOutputStream();
        String verify_code = CheckCodeUtil.outputVerifyImage(100, 50, os, 4);

        HttpSession session = req.getSession();
        session.setAttribute("verify_code",verify_code);
    }

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

3、跳转前端页面 ​

java
@WebServlet("/login")
public class LoginDemo extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String contextPath = req.getContextPath();
        req.getRequestDispatcher(contextPath+"/login.jsp").forward(req,resp);
    }

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

4、渲染前端页面 ​

html
<%--
  Created by IntelliJ IDEA.
  User: 31190
  Date: 2024/5/4
  Time: 22:42
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
    <style>
        * {
            padding: 0;
            margin: 0;
            box-sizing: border-box;
        }

        html, body {
            width: 100%;
            height: 100%;
            display: flex;
            justify-content: center;
            align-items: center;
        }

        .verifyCode {
            width: 600px;
            border: 1px solid chartreuse;
        }

        .verifyCode img {
            width: 100%;
            height: 300px;

        }
    </style>
</head>
<body>
<div class="verifyCode">
    <button id="changeCode">切换验证码</button>
    <img id="verifyCode" src="/verifycode"/>
</div>
<script>
    document.getElementById("changeCode").onclick = function () {
        let src = "/verifycode?" + new Date().getTime();
        document.getElementById("verifyCode").src = src
    }
</script>
</body>
</html>

5、效果 ​