/*
* @(#)UUID.java 1.18 06/06/02
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.util;
import java.security.*;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
/**
*
* A class that represents an immutable universally unique identifier (UUID).
* A UUID represents a 128-bit value.
*
* <p>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).
*
* <p>The layout of a variant 2 (Leach-Salz) UUID is as follows:
*
* The most significant long consists of the following unsigned fields:
* <pre>
* 0xFFFFFFFF00000000 time_low
* 0x00000000FFFF0000 time_mid
* 0x000000000000F000 version
* 0x0000000000000FFF time_hi
* </pre>
* The least significant long consists of the following unsigned fields:
* <pre>
* 0xC000000000000000 variant
* 0x3FFF000000000000 clock_seq
* 0x0000FFFFFFFFFFFF node
* </pre>
*
* <p>The variant field contains a value which identifies the layout of
* the <tt>UUID</tt>. The bit layout described above is valid only for
* a <tt>UUID</tt> with a variant value of 2, which indicates the
* Leach-Salz variant.
*
* <p>The version field holds a value that describes the type of this
* <tt>UUID</tt>. 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.
*
* <p>For more information including algorithms used to create <tt>UUID</tt>s,
* see <a href="http://www.ietf.org/rfc/rfc4122.txt">
* <i>RFC 4122: A Universally Unique IDentifier (UUID) URN
* Namespace</i></a>, section 4.2 "Algorithms for Creating a Time-Based
* UUID".
*
* @version 1.18, 06/02/06
* @since 1.5
*/
public final class UUID
implements java.io.Serializable, Comparable<UUID> {
/**
* 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;
assert data.length == 16;
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 <tt>UUID</tt> using the specified data.
* <tt>mostSigBits</tt> is used for the most significant 64 bits
* of the <tt>UUID</tt> and <tt>leastSigBits</tt> becomes the
* least significant 64 bits of the <tt>UUID</tt>.
*
* @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 <code>UUID</code> is generated using a cryptographically strong
* pseudo random number generator.
*
* @return a randomly generated <tt>UUID</tt>.
*/
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) <tt>UUID</tt> based on
* the specified byte array.
*
* @param name a byte array to be used to construct a <tt>UUID</tt>.
* @return a <tt>UUID</tt> 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 <tt>UUID</tt> from the string standard representation as
* described in the {@link #toString} method.
*
* @param name a string that specifies a <tt>UUID</tt>.
* @return a <tt>UUID</tt> 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 <tt>UUID</tt>. The version
* number describes how this <tt>UUID</tt> was generated.
*
* The version number has the following meaning:<p>
* <ul>
* <li>1 Time-based UUID
* <li>2 DCE security UUID
* <li>3 Name-based UUID
* <li>4 Randomly generated UUID
* </ul>
*
* @return the version number of this <tt>UUID</tt>.
*/
public int version() {
if (version < 0) {
// Version is bits masked by 0x000000000000F000 in MS long
version = (int)((mostSigBits >> 12) & 0x0f);
}
return version;
}
/**
* The variant number associated with this <tt>UUID</tt>. The variant
* number describes the layout of the <tt>UUID</tt>.
*
* The variant number has the following meaning:<p>
* <ul>
* <li>0 Reserved for NCS backward compatibility
* <li>2 The Leach-Salz variant (used by this class)
* <li>6 Reserved, Microsoft Corporation backward compatibility
* <li>7 Reserved for future definition
* </ul>
*
* @return the variant number of this <tt>UUID</tt>.
*/
public int variant() {
if (variant < 0) {
// This field is composed of a varying number of bits
if ((leastSigBits >>> 63) == 0) {
variant = 0;
} else if ((leastSigBits >>> 62) == 2) {
variant = 2;
} else {
variant = (int)(leastSigBits >>> 61);
}
}
return variant;
}
/**
* The timestamp value associated with this UUID.
*
* <p>The 60 bit timestamp value is constructed from the time_low,
* time_mid, and time_hi fields of this <tt>UUID</tt>. The resulting
* timestamp is measured in 100-nanosecond units since midnight,
* October 15, 1582 UTC.<p>
*
* The timestamp value is only meaningful in a time-based UUID, which
* has version type 1. If this <tt>UUID</tt> 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.
*
* <p>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.<p>
*
* 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 <tt>UUID</tt>.
* @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.
*
* <p>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.<p>
*
* 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 <tt>UUID</tt>.
* @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 <code>String</code> object representing this
* <code>UUID</code>.
*
* <p>The UUID string representation is as described by this BNF :
* <blockquote><pre>
* {@code
* 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"
* }</pre></blockquote>
*
* @return a string representation of this <tt>UUID</tt>.
*/
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 <code>UUID</code>.
*
* @return a hash code value for this <tt>UUID</tt>.
*/
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
* <tt>true</tt> if and only if the argument is not
* <tt>null</tt>, is a <tt>UUID</tt> object, has the same variant,
* and contains the same value, bit for bit, as this <tt>UUID</tt>.
*
* @param obj the object to compare with.
* @return <code>true</code> if the objects are the same;
* <code>false</code> 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.
*
* <p>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 <tt>UUID</tt> to which this <tt>UUID</tt> is to be compared.
* @return -1, 0 or 1 as this <tt>UUID</tt> is less than, equal
* to, or greater than <tt>val</tt>.
*/
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 <tt>UUID</tt> 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;
}
}
|
