使用Random生成随机数

public static String getStringRandom() {
    Random random = new Random();
    String str = String.valueOf(random.nextInt(9));
    for (int i = 0; i < 5; i++) {
        str += random.nextInt(9);
    }
    return str;
}

使用Math生成随机数

public static String getStringRandom() {
    return String.valueOf(Math.random()).substring(2, 8);
}

使用ThreadLocalRandom生成随机数

public static String getStringRandom() {
    ThreadLocalRandom random = ThreadLocalRandom.current();
    String str = String.valueOf(random.nextInt(10));
    for (int i = 0; i < 5; i++) {
        str += random.nextInt(10);
    }
    return str;
}

使用SecureRandom生成随机数

public static String getStringRandom() throws NoSuchAlgorithmException {
    SecureRandom random = SecureRandom.getInstance("SHA1PRNG");
    String str = String.valueOf(random.nextInt(10));
    for (int i = 0; i < 5; i++) {
        str += random.nextInt(10);
    }
    return str;
}