JAVA之UUID实现

冷不防 2022-03-20 17:41 325阅读 0赞

UUID：通用唯一识别码 (Universally Unique Identifier)

介绍就不说了，以前写过一个从hibernate源码中获取uuid主键生成器的类：http://blog.csdn.net/lushuaiyin/article/details/8590925

其实java.util.UUID已经有生成uuid的方法。

写个例子看看效果：

package org.test.algo;
 
 import java.util.UUID;
 
 /**
 * @author lushuaiyin
 */
 public class JavaUUIDTest {
 	
 	public static void main(String[] sdfs){
 		
 		for(int i=0;i<10;i++){
 			UUID ranId=UUID.randomUUID();
 			System.out.println(ranId.toString()+" 去除-后的32位UUID "+ranId.toString().replace("-", ""));
 			
 		}
 		
 		
 		
 		System.out.println("--------------------");
 		//或者下面的声明方式
 		//传入一个字符串变量（这个会经过md5加密，所以一个字符串对应一个UUID，从结果看相当于md5加密）
 		UUID ranId2=UUID.nameUUIDFromBytes(new String("abc").getBytes());
 		System.out.println(ranId2.toString()+" 去除-后的32位UUID "+ranId2.toString().replace("-", ""));
 		
 		
 		
 	}
 
 }
 
 /*
 打印：
 a7006664-4ad7-4e88-b441-7d66a7198fa1 去除-后的32位UUID a70066644ad74e88b4417d66a7198fa1
 b4553e52-bd8a-4b18-8479-072028e9f92a 去除-后的32位UUID b4553e52bd8a4b188479072028e9f92a
 8cc7ff8f-47bb-48de-bc9b-260fb546611c 去除-后的32位UUID 8cc7ff8f47bb48debc9b260fb546611c
 ac5265e4-693a-49cd-a7c9-5671ef2c8701 去除-后的32位UUID ac5265e4693a49cda7c95671ef2c8701
 96bbeaf3-699b-4a71-a43a-c5933cda4641 去除-后的32位UUID 96bbeaf3699b4a71a43ac5933cda4641
 9232e365-79e4-4d67-be56-8fad0361eec1 去除-后的32位UUID 9232e36579e44d67be568fad0361eec1
 89339c84-8a89-4070-b703-dbd10ede87c4 去除-后的32位UUID 89339c848a894070b703dbd10ede87c4
 f33ced50-ec97-4434-b507-bdf4b6c46e91 去除-后的32位UUID f33ced50ec974434b507bdf4b6c46e91
 ea4b2a29-b24a-4007-ae0c-ab24a1f48440 去除-后的32位UUID ea4b2a29b24a4007ae0cab24a1f48440
 47bb4ec8-3a6f-4bc9-af9f-203bd4e6160f 去除-后的32位UUID 47bb4ec83a6f4bc9af9f203bd4e6160f
 --------------------
 90015098-3cd2-3fb0-9696-3f7d28e17f72 去除-后的32位UUID 900150983cd23fb096963f7d28e17f72
 
 
 */

\-----------------------下面是UUID的源码----------

想研究UUID算法的可以参考注释中提到的网址：  http://www.ietf.org/rfc/rfc4122.txt

UUID

/*
 * @(#)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.
 *
 * 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:
 * <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>
 *
 * 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.
 *
 * 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.
 * 
 * For more information including algorithms used to create <tt>UUID</tt>s,
 * see <a href="http://www.ietf.org/rfc/rfc4122.txt">
 * RFC 4122: A Universally Unique IDentifier (UUID) URN
 * Namespace</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:
 * <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:
 * <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.
 *
 * 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.
 *
 * 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.
 *
 * 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 <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.
 *
 * 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 <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>.
 * 
 * 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.
 * 
 * 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;
 }
 }