RandomTools

RandomTools generates ordinary random numbers and strings, exposes a shared SecureRandom, and creates UUID version 7 strings.

int code = RandomTools.generateNumber();          // six digits, 100000–999999
String text = RandomTools.generateRandomString(8); // eight letters/digits

String compactId = RandomTools.uuidV7();          // 32 lowercase hex characters
String standardId = RandomTools.uuidV7(true);     // 8-4-4-4-12 format
Date createdAt = RandomTools.showTime(compactId);

generateNumber(int) accepts 1 through 9 digits, and generateRandomString(int) requires a positive length. Both use ThreadLocalRandom and are not suitable for passwords, authentication codes, tokens, or cryptographic keys.

uuidV7 uses RandomTools.RANDOM (SecureRandom) for its random portion and embeds the current epoch millisecond. UUIDv7 is time-ordered by that timestamp but is not guaranteed monotonic inside the same millisecond or if the system clock moves backward. It is an identifier, not a secret token. showTime accepts hyphenated or 32-character UUIDv7 input and rejects other UUID versions.

Use RandomTools.RANDOM or DoCipher.randomBytes() when cryptographically strong random bytes are needed.

UUIDv7 format and validation

UUIDv7 includes a 48-bit Unix-millisecond timestamp, version bits, RFC UUID variant bits, and 74 random bits. The default uuidV7() is equivalent to uuidV7(false); it returns a compact 32-character lowercase value. Choose the hyphenated form when interoperating with APIs that expect UUID.toString() format.

String id = RandomTools.uuidV7(true);
Date timestamp = RandomTools.showTime(id);

// Either form is accepted by showTime:
Date sameTimestamp = RandomTools.showTime(id.replace("-", ""));

showTime does not trim whitespace and throws IllegalArgumentException for malformed input or a UUID that is not version 7. The returned Date is the timestamp embedded in the identifier; it is not independent proof of the actual creation time.

Randomness choices

None of these APIs keeps a uniqueness registry. Store and enforce uniqueness where the application requires it.

Implementation notes

The numeric and alphanumeric helpers use ThreadLocalRandom, avoiding contention on a shared pseudo-random generator in ordinary concurrent application code. UUIDv7 takes a different path: it fills 16 bytes from a shared SecureRandom, then overwrites the timestamp, version, and variant positions according to UUIDv7 layout before formatting with UUID. The timestamp extraction method reverses that layout from the UUID most-significant bits.

This design gives sortable identifiers and a strong random component, but it does not coordinate calls made in the same millisecond. If strict database ordering is required, store a separate sequence or ordering column.