Filter encoding version 1 uses a randomly generated UUID with - removed:

private String generateShortNameV1() {
	for (int i = 0; i < 10; i++) {
		final String code = "v1" + UUID.randomUUID().toString().replace("-", "");
		// return shortName if unique
		if (shortFilterRepository.findByCode(code) == null) {
			return code;
		}
	}
	throw new RuntimeException("Failed to generate a unique filters short name in several attempts");
}

This generates filter codes like v1a37ad370d9ca4f62b3d9840094aafae9 and they are fairly long.

Shorter filter codes

We can make use of https://hashids.org/java/ to generate shorter codes with a custom salt!

Initial idea is to use the current timestamp (long value, 4b), resulting in drastically smaller unique short filter codes.

private String generateShortNameV2() {
	Hashids hashids = new Hashids("this is my salt");
	for (int i = 0; i < 10; i++) {
		String hash = hashids.encode(System.currentTimeMillis());
		final String code = "v2" + hash;
		// return shortName if unique
		if (shortFilterRepository.findByCode(code) == null) {
			return code;
		}
	}
	throw new RuntimeException("Failed to generate a unique filters short name in several attempts");
}

We could extend this to our use of UUIDs in URLs, and see if that makes a difference in URL code length.