uuidv7.java

import java.nio.ByteBuffer;
import java.security.SecureRandom;
import java.util.UUID;

public class UUIDv7 {
    private static final SecureRandom random = new SecureRandom();

    public static UUID randomUUID() {
        byte[] value = randomBytes();
        ByteBuffer buf = ByteBuffer.wrap(value);
        long high = buf.getLong();
        long low = buf.getLong();
        return new UUID(high, low);
    }

    public static byte[] randomBytes() {
        // random bytes
        byte[] value = new byte[16];
        random.nextBytes(value);

        // current timestamp in ms
        long timestamp = System.currentTimeMillis();

        // timestamp
        value[0] = (byte) ((timestamp >> 40) & 0xFF);
        value[1] = (byte) ((timestamp >> 32) & 0xFF);
        value[2] = (byte) ((timestamp >> 24) & 0xFF);
        value[3] = (byte) ((timestamp >> 16) & 0xFF);
        value[4] = (byte) ((timestamp >> 8) & 0xFF);
        value[5] = (byte) (timestamp & 0xFF);

        // version and variant
        value[6] = (byte) ((value[6] & 0x0F) | 0x70);
        value[8] = (byte) ((value[8] & 0x3F) | 0x80);

        return value;
    }

    public static void main(String[] args) {
        var uuid = UUIDv7.randomUUID();
        System.out.println(uuid);
    }
}