随机生成验证码

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本文介绍了如何使用Java来实现随机验证码的生成，包括验证码的显示效果及其在安全验证中的重要作用。通过实例代码，展示了生成随机字符串和绘制验证码图片的过程。

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package com.CodeServle;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CodeServlet extends HttpServlet {
            public void doGet(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
                // 使用java图形界面技术绘制一张图片

                int charNum = 4;
                int width = 30 * 4;
                int height = 30;

                // 1. 创建一张内存图片
                BufferedImage bufferedImage = new BufferedImage(width, height,
                        BufferedImage.TYPE_INT_RGB);

                // 2.获得绘图对象
                Graphics graphics = bufferedImage.getGraphics();

                // 3、绘制背景颜色
                graphics.setColor(Color.YELLOW);
                graphics.fillRect(0, 0, width, height);

                // 4、绘制图片边框
                graphics.setColor(Color.BLUE);
                graphics.drawRect(0, 0, width - 1, height - 1);

                // 5、输出验证码内容
                graphics.setColor(Color.RED);
                graphics.setFont(new Font("宋体", Font.BOLD, 20));

                // 随机输出4个字符
                Graphics2D graphics2d = (Graphics2D) graphics;
                 String s = "ABCDEFGHGKLMNPQRSTUVWXYZ23456789";
                Random random = new Random();
                //session中要用到
                String msg="";
                int x = 5;
                for (int i = 0; i < 4; i++) {
                    int index = random.nextInt(32);
                    String content = String.valueOf(s.charAt(index));
                    msg+=content;
                    double theta = random.nextInt(45) * Math.PI / 180;
                    //让字体扭曲
                    graphics2d.rotate(theta, x, 18);
                    graphics2d.drawString(content, x, 18);
                    graphics2d.rotate(-theta, x, 18);
                    x += 30;
                }

                // 6、绘制干扰线
                graphics.setColor(Color.GRAY);
                for (int i = 0; i < 5; i++) {
                    int x1 = random.nextInt(width);
                    int x2 = random.nextInt(width);

                    int y1 = random.nextInt(height);
                    int y2 = random.nextInt(height);
                    graphics.drawLine(x1, y1, x2, y2);
                }

                // 释放资源
                graphics.dispose();

                // 图片输出 ImageIO
                ImageIO.write(bufferedImage, "jpg", response.getOutputStream());


            }


        public void doPost(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {

        }

    }

> web.xml
xml文件中配置CodeServlet
  <servlet>
    <description></description>
    <display-name>CodeServlet</display-name>
    <servlet-name>CodeServlet</servlet-name>
    <servlet-class>com.CodeServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>CodeServlet</servlet-name>
    <url-pattern>/code</url-pattern>
  </servlet-mapping>

> code.hmtl

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <img alt="验证码" src="/code" title="看不清换一张" onclick="changeImg(this)">
</body>
<!--图片是静态资源，会缓存到本地，每次请求会把最后修改时间带过去，如果没有修改图片名则读缓存，所以，每次生成的验证码图片名，加入一个变化的参数，使参数名发生改变，造成每次请求图片名都修改的假象 -->
<script type="text/javascript">
function changeImg(obj){
    obj.src="/code?i="+Math.random();
}
</script>
</html>

结果展示：
这里写图片描述