convert uuid to byte, that works when using UUID.nameUUIDFromBytes(b)

Question

I am converting UUID to byte using this code

public byte[] getIdAsByte(UUID uuid) {     ByteBuffer bb = ByteBuffer.wrap(new byte[16]);     bb.putLong(uuid.getMostSignificantBits());     bb.putLong(uuid.getLeastSignificantBits());     return bb.array(); } 

However, if I try to recreate the UUID using this function,

public UUID frombyte(byte[] b) {     return UUID.nameUUIDFromBytes(b); } 

It is not the same UUID. Converting a randomUUID back and forth returns two different it.

UUID u = UUID.randomUUID(); System.out.println(u.toString()); System.out.println(frombyte(getIdAsByte(u)).toString()); 

prints:

1ae004cf-0f48-469f-8a94-01339afaec41 8b5d1a71-a4a0-3b46-bec3-13ab9ab12e8e 

Answer 1

public class UuidUtils {   public static UUID asUuid(byte[] bytes) {     ByteBuffer bb = ByteBuffer.wrap(bytes);     long firstLong = bb.getLong();     long secondLong = bb.getLong();     return new UUID(firstLong, secondLong);   }    public static byte[] asBytes(UUID uuid) {     ByteBuffer bb = ByteBuffer.wrap(new byte[16]);     bb.putLong(uuid.getMostSignificantBits());     bb.putLong(uuid.getLeastSignificantBits());     return bb.array();   } } 

---

@Test public void verifyUUIDBytesCanBeReconstructedBackToOriginalUUID() {   UUID u = UUID.randomUUID();   byte[] uBytes = UuidUtils.asBytes(u);   UUID u2 = UuidUtils.asUuid(uBytes);   Assert.assertEquals(u, u2); }  @Test public void verifyNameUUIDFromBytesMethodDoesNotRecreateOriginalUUID() {   UUID u = UUID.randomUUID();   byte[] uBytes = UuidUtils.asBytes(u);   UUID u2 = UUID.nameUUIDFromBytes(uBytes);   Assert.assertNotEquals(u, u2); } 

Answer 2

that's because nameUUIDFromBytes constructs a specific kind of UUID (as the javadoc states).

if you want to convert a byte[] back to a UUID, you should use the UUID constructor. Wrap a ByteBuffer around the byte[], read the 2 longs and pass them to the UUID constructor.