javaweb验证码

public class myfunction {
    public static String getRandString(int length) {
        String str = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < length; ++i) {
            int number = random.nextInt(62);
            sb.append(str.charAt(number));
        }
        return sb.toString();
    }
}