JAVA UUID 生成
UUID介绍:
GUID是一个128位长的数字,一般用16进制表示。算法的核心思想是结合机器的网卡、当地时间、一个随即数来生成GUID。从理论上讲,如果一台机器每秒产生10000000个GUID,则可以保证(概率意义上)3240年不重复。
UUID是1.5中新增的一个类,在java.util下,用它可以产生一个号称全球唯一的ID。
生成UUID的网站:http://www.uuid.online/
简单示例:
package com.test; import java.util.UUID; public class Test { public static void main(String[] args) { UUID uuid = UUID.randomUUID(); System.out.println(uuid); } }
控制台输出结果:
概念详解:
UUID(Universally Unique Identifier)全局唯一标识符,是指在一台机器上生成的数字,它保证对在同一时空中的所有机器都是唯一的。
按照开放软件基金会(OSF)制定的标准计算,用到了以太网卡地址、纳秒级时间、芯片ID码和许多可能的数字。
由以下几部分的组合:
1.当前日期和时间(UUID的第一个部分与时间有关,如果你在生成一个UUID之后,过几秒又生成一个UUID,则第一个部分不同,其余相同)
2.时钟序列
3.全局唯一的IEEE机器识别号(如果有网卡,从网卡获得,没有网卡以其他方式获得)
UUID的唯一缺陷在于生成的结果串会比较长。
下面就是实现为数据库获取一个唯一的主键ID的代码:
package com.utils; import java.util.UUID; public class UUIDGenerator { /** * 获得一个去掉“-”符号的UUID * @return String UUID */ public static String getUUID(){ String s = UUID.randomUUID().toString(); //去掉“-”符号 return s.substring(0,8)+s.substring(9,13)+s.substring(14,18)+s.substring(19,23)+s.substring(24); } /** * 获得指定数目去掉“-”符号的UUID * @param number int 需要获得的UUID数量 * @return String[] UUID数组 */ public static String[] getUUID(int number){ if(number < 1){ return null; } String[] ss = new String[number]; for(int i=0;i<number;i++){ ss[i] = getUUID(); } return ss; } public static void main(String[] args) { String[] uuids = getUUID(10); for(int i=0;i<uuids.length;i++){ System.out.println(uuids[i]); } } }
main方法输出结果:
GUID:
package com.utils; /** * @author Administrator * * TODO To change the template for this generated type comment go to * Window - Preferences - Java - Code Style - Code Templates */ import java.net.InetAddress; import java.net.UnknownHostException; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.security.SecureRandom; import java.util.Random; public class RandomGUID extends Object { protected final org.apache.commons.logging.Log logger = org.apache.commons.logging.LogFactory .getLog(getClass()); public String valueBeforeMD5 = ""; public String valueAfterMD5 = ""; private static Random myRand; private static SecureRandom mySecureRand; private static String s_id; private static final int PAD_BELOW = 0x10; private static final int TWO_BYTES = 0xFF; /* * Static block to take care of one time secureRandom seed. * It takes a few seconds to initialize SecureRandom. You might * want to consider removing this static block or replacing * it with a "time since first loaded" seed to reduce this time. * This block will run only once per JVM instance. */ static { mySecureRand = new SecureRandom(); long secureInitializer = mySecureRand.nextLong(); myRand = new Random(secureInitializer); try { s_id = InetAddress.getLocalHost().toString(); } catch (UnknownHostException e) { e.printStackTrace(); } } /* * Default constructor. With no specification of security option, * this constructor defaults to lower security, high performance. */ public RandomGUID() { getRandomGUID(false); } /* * Constructor with security option. Setting secure true * enables each random number generated to be cryptographically * strong. Secure false defaults to the standard Random function seeded * with a single cryptographically strong random number. */ public RandomGUID(boolean secure) { getRandomGUID(secure); } /* * Method to generate the random GUID */ private void getRandomGUID(boolean secure) { MessageDigest md5 = null; StringBuffer sbValueBeforeMD5 = new StringBuffer(128); try { md5 = MessageDigest.getInstance("MD5"); } catch (NoSuchAlgorithmException e) { logger.error("Error: " + e); } try { long time = System.currentTimeMillis(); long rand = 0; if (secure) { rand = mySecureRand.nextLong(); } else { rand = myRand.nextLong(); } sbValueBeforeMD5.append(s_id); sbValueBeforeMD5.append(":"); sbValueBeforeMD5.append(Long.toString(time)); sbValueBeforeMD5.append(":"); sbValueBeforeMD5.append(Long.toString(rand)); valueBeforeMD5 = sbValueBeforeMD5.toString(); md5.update(valueBeforeMD5.getBytes()); byte[] array = md5.digest(); StringBuffer sb = new StringBuffer(32); for (int j = 0; j < array.length; ++j) { int b = array[j] & TWO_BYTES; if (b < PAD_BELOW) sb.append('0'); sb.append(Integer.toHexString(b)); } valueAfterMD5 = sb.toString(); } catch (Exception e) { logger.error("Error:" + e); } } /* * Convert to the standard format for GUID * (Useful for SQL Server UniqueIdentifiers, etc.) * Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6 */ public String toString() { String raw = valueAfterMD5.toUpperCase(); StringBuffer sb = new StringBuffer(64); sb.append(raw.substring(0, 8)); sb.append("-"); sb.append(raw.substring(8, 12)); sb.append("-"); sb.append(raw.substring(12, 16)); sb.append("-"); sb.append(raw.substring(16, 20)); sb.append("-"); sb.append(raw.substring(20)); return sb.toString(); } // Demonstraton and self test of class public static void main(String args[]) { for (int i=0; i< 1; i++) { RandomGUID myGUID = new RandomGUID(); System.out.println("Seeding String:\t" + myGUID.valueBeforeMD5); System.out.println("rawGUID:\t" + myGUID.valueAfterMD5); System.out.println("RandomGUID:\t" + myGUID.toString()); } } }
main方法输出结果:
参考自:http://www.cnblogs.com/jdonson/archive/2009/07/22/1528466.html