怎样用java生成GUID与UUID
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
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)。
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