How to convert two longs to a byte array = how to convert UUID to byte array?

Question

I am using Javas UUID and need to convert a UUID to a byte Array. Strangely the UUID Class does not provide a "toBytes()" method.

I already found out about the two methods:

UUID.getMostSignificantBits()
and
UUID.getLeasSignificantBits()

But how to get this into a byte array? the result should be a byte[] with those tow values. I somehow need to do Bitshifting but, how?

update:

I found:

 ByteBuffer byteBuffer = MappedByteBuffer.allocate(2);
 byteBuffer.putLong(uuid.getMostSignificantBits());
 byteBuffer.putLong(uuid.getLeastSignificantBits());

Is this approach corret?

Are there any other methods (for learning purposes)?

Thanks very much!! Jens

The code in the update is not correct: it only allocates two bytes in the buffer but you need 16. The code in the answer below is however correct. — Jon Tirsen, Jan 31 '12 at 12:17

score 16 · Accepted Answer · edited May 21 '13 at 21:14

16

You can use ByteBuffer

 byte[] bytes = new byte[16];
 ByteBuffer bb = ByteBuffer.wrap(bytes);
 bb.order(ByteOrder.LITTLE_ENDIAN or ByteOrder.BIG_ENDIAN);
 bb.putLong(UUID.getMostSignificantBits());
 bb.putLong(UUID.getLeastSignificantBits());

 // to reverse
 bb.flip();
 UUID uuid = new UUID(bb.getLong(), bb.getLong());

edited May 21 '13 at 21:14

Felix GV

167
1
9

answered Jul 30 '11 at 07:06

Peter Lawrey

525,659
79
751
1,130

score 5 · Answer 2 · edited Nov 05 '13 at 08:13

5

One option if you prefer "regular" IO to NIO:

ByteArrayOutputStream baos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(baos);
dos.write(uuid.getMostSignificantBits());
dos.write(uuid.getLeastSignificantBits());
dos.flush(); // May not be necessary
byte[] data = dos.toByteArray();

edited Nov 05 '13 at 08:13

Marius Soutier

11,184
1
38
48

answered Jul 30 '11 at 07:10

Jon Skeet

1,421,763
867
9,128
9,194

score 0 · Answer 3 · answered Sep 11 '13 at 19:23

For anyone trying to use this in Java 1.7, I found the following to be necessary:

<!-- language: lang-java -->
ByteArrayOutputStream baos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(baos);
dos.writeLong(password.getMostSignificantBits());
dos.writeLong(password.getLeastSignificantBits());
dos.flush(); // May not be necessary
return baos.toByteArray();

How to convert two longs to a byte array = how to convert UUID to byte array?

3 Answers3

For anyone trying to use this in Java 1.7, I found the following to be necessary:

Linked