public static String getRandomString(Integer length) {
    String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    Random random = new Random();
    StringBuilder builder = new StringBuilder();
    for (Integer i = 0; i < length; ++i) {
        builder.append(str.charAt(random.nextInt(62)));
    }
    return builder.toString();
}