Java实现验证码的小工具类

public class VerifyCodeUtil {
    public static void main(String[] args) throws IOException {
        String str = "123456789abdefghijkmnopqrstuvwxyzABCDEFHJKLMNPQRSTUVWXYZ";
        String code = drawVerifyCode(new FileOutputStream("F:\\1.jpg"),str);
        //当用在servlet或者jsp中时，一般需要将这个方法返回的code保存到session中，用来和用户提交的验证码进行比较判断
        System.out.println(code);
    }
    public static final String drawVerifyCode(OutputStream os,String str) throws IOException {
        if(str == null || str.trim().length() == 0){
            str = "123456789abdefghijkmnopqrstuvwxyzABCDEFHJKLMNPQRSTUVWXYZ";
        }
        int width = 120;
        int height = 40;
        // 创建一个画布
        BufferedImage bi = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_RGB);
        // 获取一个画笔
        Graphics2D g = bi.createGraphics();
        // 画图过程
        // 设置画笔的颜色为白色
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, width, height);
        Random random = new Random();
        // 画干扰线
        for (int i = 0; i < 30; i++) {
            g.setColor(new Color(100 + random.nextInt(105),100 + random.nextInt(105), 100 + random.nextInt(105)));
            g.drawLine(random.nextInt(width), random.nextInt(height), random.nextInt(width),
                    random.nextInt(height));
        }
        // 绘制黑色边框；先画干扰线，后画边框，是为了避免干扰先覆盖到边框
        g.setColor(Color.BLACK);
        g.drawRect(0, 0, width - 1, height - 1);
        //设置画笔的字体
        g.setFont(new Font("微软雅黑", Font.BOLD, 22));
        StringBuilder sb = new StringBuilder();
        // 向画布中随机输出几个字符
        for (int i = 1; i < 5; i++) {
            // 为字 生成旋转角度
            double jiaodu = random.nextInt(40) - 30;
            // 将旋转角度 换算弧度
            double theta = jiaodu / 180 * Math.PI;
            g.rotate(theta, 20 * i, 0);
            int index = random.nextInt(str.length());
            char c = str.charAt(index);
            sb.append(c);
            // 随机设置画笔颜色
            g.setColor(new Color(random.nextInt(100), random.nextInt(100), random.nextInt(100)));
            //画出字符
            g.drawString(c + "", 20 * i, 30);
            g.rotate(-theta, 20 * i, 0);
        }
        // 内存中资源 释放
        g.dispose();
        // 将画布输出到文件中
        ImageIO.write(bi, "JPG", os);
        return sb.toString();
    }
}