Leave a Comment
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、一个随机数来生成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
import java.util.UUID; public class Test { public static void main(String[] args) { UUID uuid = UUID.randomUUID(); System.out.println (uuid); } }
编译运行输出:
07ca3dec-b674-41d0-af9e-9c37583b08bb两种方式生成guid 与uuid
07ca3dec-b674-41d0-af9e-9c37583b08bb两种方式生成guid 与uuid
需要comm log 库
/** * @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< 100; i++) { RandomGUID myGUID = new RandomGUID(); System.out.println("Seeding String=" + myGUID.valueBeforeMD5); System.out.println("rawGUID=" + myGUID.valueAfterMD5); System.out.println("RandomGUID=" + myGUID.toString()); } } }
同样
UUID uuid = UUID.randomUUID(); System.out.println("{"+uuid.toString()+"}");
UUID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。通常平台会提供生成UUID的API。UUID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: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),时钟序列,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。关于UUID这个标准使用最普遍的是微软的GUID(Globals Unique Identifiers)。