JAVA生成验证码（字母+数字）

/**
 * 验证码、邀请码工具类
 */
@Component
public class VerificationCodeUtil {


    /**
     * 生成验证码：字母+数字
     * @param length 验证码长度
     * @return 验证码字符串
     */
     public static String getVerificationCode(int length) {
         String characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
         StringBuilder verificationCode = new StringBuilder();
         Random random = new Random();

         for (int i = 0; i < length; i++) {
             int index = random.nextInt(characters.length());
             verificationCode.append(characters.charAt(index));
         }

         return verificationCode.toString();
     }


    /**
     * 生成验证码：只有数字
     * @param length 验证码长度
     * @return 验证码字符串
     */
    public static String getVerificationCodeOnlyNumber(int length) {
        String characters = "0123456789";
        StringBuilder verificationCode = new StringBuilder();
        Random random = new Random();

        for (int i = 0; i < length; i++) {
            int index = random.nextInt(characters.length());
            verificationCode.append(characters.charAt(index));
        }

        return verificationCode.toString();
    }

}