* There exist different variants of these global identifiers. The methods of * this class are for manipulating the Leach-Salz variant, although the * constructors allow the creation of any variant of UUID (described below). * *
* The layout of a variant 2 (Leach-Salz) UUID is as follows: * * The most significant long consists of the following unsigned fields: * *
* 0xFFFFFFFF00000000 time_low * 0x00000000FFFF0000 time_mid * 0x000000000000F000 version * 0x0000000000000FFF time_hi ** * The least significant long consists of the following unsigned fields: * *
* 0xC000000000000000 variant * 0x3FFF000000000000 clock_seq * 0x0000FFFFFFFFFFFF node ** *
* The variant field contains a value which identifies the layout of the * UUID. The bit layout described above is valid only for a * UUID with a variant value of 2, which indicates the Leach-Salz * variant. * *
* The version field holds a value that describes the type of this UUID. * There are four different basic types of UUIDs: time-based, DCE security, * name-based, and randomly generated UUIDs. These types have a version value of * 1, 2, 3 and 4, respectively. * *
* For more information including algorithms used to create UUIDs,
* see the Internet-Draft UUIDs
* and GUIDs or the standards body definition at ISO/IEC 11578:1996.
*
* @version 1.14, 07/12/04
* @since 1.5
*/
public final class UUID implements java.io.Serializable {
/**
* Explicit serialVersionUID for interoperability.
*/
private static final long serialVersionUID = -4856846361193249489L;
/*
* The most significant 64 bits of this UUID.
*
* @serial
*/
private final long mostSigBits;
/*
* The least significant 64 bits of this UUID.
*
* @serial
*/
private final long leastSigBits;
/*
* The version number associated with this UUID. Computed on demand.
*/
private transient int version = -1;
/*
* The variant number associated with this UUID. Computed on demand.
*/
private transient int variant = -1;
/*
* The timestamp associated with this UUID. Computed on demand.
*/
private transient volatile long timestamp = -1;
/*
* The clock sequence associated with this UUID. Computed on demand.
*/
private transient int sequence = -1;
/*
* The node number associated with this UUID. Computed on demand.
*/
private transient long node = -1;
/*
* The hashcode of this UUID. Computed on demand.
*/
private transient int hashCode = -1;
/*
* The random number generator used by this class to create random based
* UUIDs.
*/
private static volatile SecureRandom numberGenerator = null;
// Constructors and Factories
/*
* Private constructor which uses a byte array to construct the new UUID.
*/
private UUID(byte[] data) {
long msb = 0;
long lsb = 0;
for (int i = 0; i < 8; i++)
msb = (msb << 8) | (data[i] & 0xff);
for (int i = 8; i < 16; i++)
lsb = (lsb << 8) | (data[i] & 0xff);
this.mostSigBits = msb;
this.leastSigBits = lsb;
}
/**
* Constructs a new UUID using the specified data.
* mostSigBits is used for the most significant 64 bits of the
* UUID and leastSigBits becomes the least significant
* 64 bits of the UUID.
*
* @param mostSigBits
* @param leastSigBits
*/
public UUID(long mostSigBits, long leastSigBits) {
this.mostSigBits = mostSigBits;
this.leastSigBits = leastSigBits;
}
/**
* Static factory to retrieve a type 4 (pseudo randomly generated) UUID.
*
* The UUID is generated using a cryptographically strong
* pseudo random number generator.
*
* @return a randomly generated UUID.
*/
public static UUID randomUUID() {
SecureRandom ng = numberGenerator;
if (ng == null) {
numberGenerator = ng = new SecureRandom();
}
byte[] randomBytes = new byte[16];
ng.nextBytes(randomBytes);
randomBytes[6] &= 0x0f; /* clear version */
randomBytes[6] |= 0x40; /* set to version 4 */
randomBytes[8] &= 0x3f; /* clear variant */
randomBytes[8] |= 0x80; /* set to IETF variant */
return new UUID(randomBytes);
}
/**
* Static factory to retrieve a type 3 (name based) UUID based on
* the specified byte array.
*
* @param name
* a byte array to be used to construct a UUID.
* @return a UUID generated from the specified array.
*/
public static UUID nameUUIDFromBytes(byte[] name) {
MessageDigest md;
try {
md = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException nsae) {
throw new InternalError("MD5 not supported");
}
byte[] md5Bytes = md.digest(name);
md5Bytes[6] &= 0x0f; /* clear version */
md5Bytes[6] |= 0x30; /* set to version 3 */
md5Bytes[8] &= 0x3f; /* clear variant */
md5Bytes[8] |= 0x80; /* set to IETF variant */
return new UUID(md5Bytes);
}
/**
* Creates a UUID from the string standard representation as
* described in the {@link #toString} method.
*
* @param name
* a string that specifies a UUID.
* @return a UUID with the specified value.
* @throws IllegalArgumentException
* if name does not conform to the string representation as
* described in {@link #toString}.
*/
public static UUID fromString(String name) {
String[] components = name.split("-");
if (components.length != 5)
throw new IllegalArgumentException("Invalid UUID string: " + name);
for (int i = 0; i < 5; i++)
components[i] = "0x" + components[i];
long mostSigBits = Long.decode(components[0]).longValue();
mostSigBits <<= 16;
mostSigBits |= Long.decode(components[1]).longValue();
mostSigBits <<= 16;
mostSigBits |= Long.decode(components[2]).longValue();
long leastSigBits = Long.decode(components[3]).longValue();
leastSigBits <<= 48;
leastSigBits |= Long.decode(components[4]).longValue();
return new UUID(mostSigBits, leastSigBits);
}
// Field Accessor Methods
/**
* Returns the least significant 64 bits of this UUID's 128 bit value.
*
* @return the least significant 64 bits of this UUID's 128 bit value.
*/
public long getLeastSignificantBits() {
return leastSigBits;
}
/**
* Returns the most significant 64 bits of this UUID's 128 bit value.
*
* @return the most significant 64 bits of this UUID's 128 bit value.
*/
public long getMostSignificantBits() {
return mostSigBits;
}
/**
* The version number associated with this UUID. The version
* number describes how this UUID was generated.
*
* The version number has the following meaning:
*
*
*
* The 60 bit timestamp value is constructed from the time_low, time_mid, * and time_hi fields of this UUID. The resulting timestamp is * measured in 100-nanosecond units since midnight, October 15, 1582 UTC. *
* * The timestamp value is only meaningful in a time-based UUID, which has * version type 1. If this UUID is not a time-based UUID then * this method throws UnsupportedOperationException. * * @throws UnsupportedOperationException * if this UUID is not a version 1 UUID. */ public long timestamp() { if (version() != 1) { throw new UnsupportedOperationException("Not a time-based UUID"); } long result = timestamp; if (result < 0) { result = (mostSigBits & 0x0000000000000FFFL) << 48; result |= ((mostSigBits >> 16) & 0xFFFFL) << 32; result |= mostSigBits >>> 32; timestamp = result; } return result; } /** * The clock sequence value associated with this UUID. * *
* The 14 bit clock sequence value is constructed from the clock sequence * field of this UUID. The clock sequence field is used to guarantee * temporal uniqueness in a time-based UUID. *
* * The clockSequence value is only meaningful in a time-based UUID, which * has version type 1. If this UUID is not a time-based UUID then this * method throws UnsupportedOperationException. * * @return the clock sequence of this UUID. * @throws UnsupportedOperationException * if this UUID is not a version 1 UUID. */ public int clockSequence() { if (version() != 1) { throw new UnsupportedOperationException("Not a time-based UUID"); } if (sequence < 0) { sequence = (int) ((leastSigBits & 0x3FFF000000000000L) >>> 48); } return sequence; } /** * The node value associated with this UUID. * *
* The 48 bit node value is constructed from the node field of this UUID. * This field is intended to hold the IEEE 802 address of the machine that * generated this UUID to guarantee spatial uniqueness. *
*
* The node value is only meaningful in a time-based UUID, which has version
* type 1. If this UUID is not a time-based UUID then this method throws
* UnsupportedOperationException.
*
* @return the node value of this UUID.
* @throws UnsupportedOperationException
* if this UUID is not a version 1 UUID.
*/
public long node() {
if (version() != 1) {
throw new UnsupportedOperationException("Not a time-based UUID");
}
if (node < 0) {
node = leastSigBits & 0x0000FFFFFFFFFFFFL;
}
return node;
}
// Object Inherited Methods
/**
* Returns a String object representing this
* UUID.
*
*
* The UUID string representation is as described by this BNF : * *
* UUID = <time_low> "-" <time_mid> "-"
* <time_high_and_version> "-"
* <variant_and_sequence> "-"
* <node>
* time_low = 4*<hexOctet>
* time_mid = 2*<hexOctet>
* time_high_and_version = 2*<hexOctet>
* variant_and_sequence = 2*<hexOctet>
* node = 6*<hexOctet>
* hexOctet = <hexDigit><hexDigit>
* hexDigit =
* "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
* | "a" | "b" | "c" | "d" | "e" | "f"
* | "A" | "B" | "C" | "D" | "E" | "F"
*
*
* @return a string representation of this UUID.
*/
public String toString() {
return (digits(mostSigBits >> 32, 8) + "-"
+ digits(mostSigBits >> 16, 4) + "-" + digits(mostSigBits, 4)
+ "-" + digits(leastSigBits >> 48, 4) + "-" + digits(
leastSigBits, 12));
}
/** Returns val represented by the specified number of hex digits. */
private static String digits(long val, int digits) {
long hi = 1L << (digits * 4);
return Long.toHexString(hi | (val & (hi - 1))).substring(1);
}
/**
* Returns a hash code for this UUID.
*
* @return a hash code value for this UUID.
*/
public int hashCode() {
if (hashCode == -1) {
hashCode = (int) ((mostSigBits >> 32) ^ mostSigBits
^ (leastSigBits >> 32) ^ leastSigBits);
}
return hashCode;
}
/**
* Compares this object to the specified object. The result is true
* if and only if the argument is not null, is a UUID
* object, has the same variant, and contains the same value, bit for bit,
* as this UUID.
*
* @param obj
* the object to compare with.
* @return true if the objects are the same;
* false otherwise.
*/
public boolean equals(Object obj) {
if (!(obj instanceof UUID))
return false;
if (((UUID) obj).variant() != this.variant())
return false;
UUID id = (UUID) obj;
return (mostSigBits == id.mostSigBits && leastSigBits == id.leastSigBits);
}
// Comparison Operations
/**
* Compares this UUID with the specified UUID.
*
* * The first of two UUIDs follows the second if the most significant field * in which the UUIDs differ is greater for the first UUID. * * @param val * UUID to which this UUID is to be * compared. * @return -1, 0 or 1 as this UUID is less than, equal to, or * greater than val. */ public int compareTo(UUID val) { // The ordering is intentionally set up so that the UUIDs // can simply be numerically compared as two numbers return (this.mostSigBits < val.mostSigBits ? -1 : (this.mostSigBits > val.mostSigBits ? 1 : (this.leastSigBits < val.leastSigBits ? -1 : (this.leastSigBits > val.leastSigBits ? 1 : 0)))); } /** * Reconstitute the UUID instance from a stream (that is, * deserialize it). This is necessary to set the transient fields to their * correct uninitialized value so they will be recomputed on demand. */ private void readObject(java.io.ObjectInputStream in) throws java.io.IOException, ClassNotFoundException { in.defaultReadObject(); // Set "cached computation" fields to their initial values version = -1; variant = -1; timestamp = -1; sequence = -1; node = -1; hashCode = -1; } }