创建简单的验证码

<!-- Servlet -->
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>

/**
* 创建验证码
*/
public static String createCaptcha(HttpServletResponse response) {
StringBuilder captcha = new StringBuilder();
try {
// 参数初始化
int width = 60;                      // 验证码图片的宽度
int height = 25;                     // 验证码图片的高度
int codeCount = 4;                   // 验证码字符个数
int codeX = width / (codeCount + 1); // 字符横向间距
int codeY = height - 4;              // 字符纵向间距
int fontHeight = height - 2;         // 字体高度
int randomSeed = 10;                 // 随机数种子
char[] codeSequence = {              // 验证码中可出现的字符
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'
};
// 创建图像
BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g = bi.createGraphics();
// 将图像填充为白色
g.setColor(Color.WHITE);
g.fillRect(0, 0, width, height);
// 设置字体
g.setFont(new Font("Courier New", Font.BOLD, fontHeight));
// 绘制边框
g.setColor(Color.BLACK);
g.drawRect(0, 0, width - 1, height - 1);
// 产生随机干扰线（160条）
g.setColor(Color.WHITE);
// 创建随机数生成器
Random random = new Random();
for (int i = 0; i < 160; i++) {
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(12);
int yl = random.nextInt(12);
g.drawLine(x, y, x + xl, y + yl);
}
// 生成随机验证码
int red, green, blue;
for (int i = 0; i < codeCount; i++) {
// 获取随机验证码
String validateCode = String.valueOf(codeSequence[random.nextInt(randomSeed)]);
// 随机构造颜色值
red = random.nextInt(255);
green = random.nextInt(255);
blue = random.nextInt(255);
// 将带有颜色的验证码绘制到图像中
g.setColor(new Color(red, green, blue));
g.drawString(validateCode, (i + 1) * codeX - 6, codeY);
// 将产生的随机数拼接起来
captcha.append(validateCode);
}
// 禁止图像缓存
response.setHeader("Cache-Control", "no-store");
response.setHeader("Pragma", "no-cache");
response.setDateHeader("Expires", 0);
// 设置响应类型为 JPEG 图片
response.setContentType("image/jpeg");
// 将缓冲图像写到 Servlet 输出流中
ServletOutputStream sos = response.getOutputStream();
ImageIO.write(bi, "jpeg", sos);
sos.close();
} catch (Exception e) {
logger.error("创建验证码出错！", e);
throw new RuntimeException(e);
}
return captcha.toString();
}