基本上和前面的那个差不多，但是稍微复杂一点

    CaptcahCode.java

    1. package com.imooc.code;
    3. import javax.imageio.ImageIO;
    4. import javax.servlet.http.HttpServletRequest;
    5. import javax.servlet.http.HttpServletResponse;
    6. import java.awt.*;
    7. import java.awt.font.FontRenderContext;
    8. import java.awt.geom.Rectangle2D;
    9. import java.awt.image.BufferedImage;
    10. import java.io.IOException;
    11. import java.util.Random;
    12. public class CaptcahCode {
    15. /**
    16.      * 算术表达式验证码
    17.      * 1、干扰线的产生
    18.      * 2、范围随机颜色，随机数
    19.      * @param response
    20.      * @return
    21.      */
    22.     public static String drawImageVericate(HttpServletResponse response){
    23.         //定义验证码的宽度和高度
    24.         int width = 100,height = 30;
    25.         //在内存中创建图片
    26.         BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_3BYTE_BGR);
    27.         //创建图片的上下文
    28.         Graphics2D g = image.createGraphics();
    30.         //产生随机对象，此随机对象主要用户算术表达式的数字
    31.         Random random = new Random();
    33.         //设置背景
    34.         g.setColor(getRandomColor(240,250));
    36.         //设置字体
    37.         g.setFont(new Font("微软雅黑",Font.PLAIN,22));
    39.         //开始绘制
    40.         g.fillRect(0,0,width,height);
    42.         //干扰线的绘制，绘制线条到图片中
    43.         g.setColor(getRandomColor(180,230));
    44.         for (int i = 0; i < 100; i++) {
    45.             int x = random.nextInt(width);
    46.             int y = random.nextInt(height);
    47.             int x1 = random.nextInt(60);
    48.             int y1 = random.nextInt(60);
    49.             //使用drawLine画线
    50.             g.drawLine(x,y,x1,y1);
    51.         }
    53.         //开始进行对算输验证码表达式的拼接
    55.         //这里注意，math的括号要包住后面的*10，不然会先计算(int)Math.random()，因为这个值介于0，1，一直都会是0
    56.         int num1 = (int)(Math.random()*10) +1;
    57.         int num2 = (int)(Math.random()*10) +1;
    58.         System.out.println(num1);
    59.         System.out.println(num2);
    61.         //符号，产生一个[0,2]之间的随机数，0，1，2用于表示加减乘
    62.         int symbol = random.nextInt(3);
    63.         String symbolstr = "";
    65.         int result =0;
    66.         switch (symbol){
    67.             case 0:symbolstr = "+";result = num1 + num2;break;
    68.             case 1:symbolstr = "-";result = num1 - num2;break;
    69.             case 2:symbolstr = "*";result = num1 * num2;break;
    70.         }
    72.         //拼接计算表达式，用于图片显示
    73.         String calc = num1 + " " + symbolstr +" "+num2 + "=" +"?";
    75.         //设置随机颜色
    76.         g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
    77.         //绘制表达式
    78.         g.drawString(calc,5,23);
    80.         //结束绘制
    81.         g.dispose();
    83.         try {
    84.             //输出图片到页面
    85.             ImageIO.write(image,"jpg",response.getOutputStream());
    86.             return  String.valueOf(result);
    87.         }catch (Exception ex){
    88.             ex.printStackTrace();
    89.             return null;
    90.         }
    91.     }
    95.     /**
    96.      * 获取随机颜色
    97.      * @param fc
    98.      * @param bc
    99.      * @return
    100.      */
    102.     public static  Color getRandomColor(int fc,int bc){
    103.         Random random = new Random();
    104.         //随机颜色，颜色的组成有三个参数，red，green和blue
    105.         if(fc>255)fc = 255;
    106.         if(bc>255)bc = 255;
    107.         int r = fc + random.nextInt(bc-fc);
    108.         int g = fc + random.nextInt(bc-fc);
    109.         int b = fc + random.nextInt(bc-fc);
    110.         Color random_color = new Color(r,g,b);
    111.         return random_color;
    112.     }
    113. }

    code.jsp

    1. <%@ page import="com.imooc.code.CaptcahCode" %>
    2. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    3. <%
    4.     //1、清空浏览器缓存，保证验证码图片来自服务器而不是本地缓存
    5.     response.setHeader("pragma","no-cache");
    6.     response.setHeader("cache-control","no-cache");
    7.     response.setHeader("expires","0");
    9.     //2、调用编写的生成验证码的工具
    10.     String code = CaptcahCode.drawImageVericate(response);
    11.     session.setAttribute("code",code);
    12.     //我这里遇到一个问题，在firefox和ie没问题，用chrome就打不开，而且还报错ERR_INCOMPLETE_CHUNKED_ENCODING,然后执行下面的第三步操作，chrome就可以了...，
    14.     //3、解决getOutputStream异常问题,但是不知道为啥这么些
    15.     out.clear();
    16.     out = pageContext.pushBody();
    18. %>

    index.jsp

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: msi
    4.   Date: 2020/7/4
    5.   Time: 8:47
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    9. <html>
    10.   <head>
    11.     <title>验证码</title>
    12.   </head>
    13.   <body>
    14.     <img src="code.jsp" alt="oops" id = "code">
    15.     <a href="javascript:void(0);" onclick="changeCode()">换一张</a>
    16.     <script>
    17.       function changeCode() {
    18.         //这里加?time=是为了避免浏览器缓存而导致加载不出验证码
    19.         document.getElementById("code").src = "code.jsp"+"?time="+new Date().getTime();
    20.       }
    21.     </script>
    22.   </body>
    23. </html>