Generate Long ID from UUID

UniqueId.java

    /**
     * Genereate unique ID from UUID in positive space
     * Reference: http://www.gregbugaj.com/?p=587
     * @return long value representing UUID
     */
    private Long generateUniqueId()
    {
        long val = -1;
        do
        {
            final UUID uid = UUID.randomUUID();
            final ByteBuffer buffer = ByteBuffer.wrap(new byte[16]);
            buffer.putLong(uid.getLeastSignificantBits());
            buffer.putLong(uid.getMostSignificantBits());
            final BigInteger bi = new BigInteger(buffer.array());
            val = bi.longValue();
        } 
         // We also make sure that the ID is in positive space, if its not we simply repeat the process
        while (val < 0);
        return val;
    }

Nice :-)
But I believe you will get the same result by doing:

private Long generateUniqueId() {
        long val = -1;
        do {
            val = UUID.randomUUID().getMostSignificantBits();
        } while (val < 0);
        return val;
    }

UUID.randomUUID().getMostSignificantBits() & Long.MAX_VALUE

I try

private static Long generateUniqueId() {
    Long val = -1L;
    final UUID uid = UUID.randomUUID();
    final ByteBuffer buffer = ByteBuffer.wrap(new byte[16]);
    buffer.putLong(uid.getLeastSignificantBits());
    buffer.putLong(uid.getMostSignificantBits());
    final BigInteger bi = new BigInteger(buffer.array());
    val = bi.longValue() & Long.MAX_VALUE;
    return val;
}

but after 50 000 000 keys in a set its posible a collition :(

can I get uuid back from this generated long value?

@uppersnatch no. UUID operates in a bigger space than Long so when you "trim" it down you lose information that could be used to "inflate" it back again into UUID.