将uuid转换为字节，这在使用UUID.nameUUIDFromBytes（b）时有效

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();  }}

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