java 生成GUID
全局唯一标识符(GUID,Globally Unique Identifier)是一种由算法生成的二进制长度为128位的数字标识符,一般用16进制表示。在理想情况下,任何计算机和计算机集群都不会生成两个相同的GUID。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
第一种:可以用UUID类来生成GUID
import java.util.UUID; public class GuidTest { public static void main(String[] args) { UUID uuid = UUID.randomUUID(); System.out.println (uuid); } }
输出:
第二种:直接生成
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 GUID { public String valueBeforeMD5 = ""; public String valueAfterMD5 = ""; private static final Random myRand; private static final SecureRandom mySecureRand; private static String s_id; static { mySecureRand = new SecureRandom(); long secureInitializer = mySecureRand.nextLong(); myRand = new Random(secureInitializer); try { s_id = InetAddress.getLocalHost().toString(); } catch (UnknownHostException e) { e.printStackTrace(); } } public GUID() { getRandomGUID(false); } public GUID(boolean secure) { getRandomGUID(secure); } private void getRandomGUID(boolean secure) { MessageDigest md5 = null; StringBuilder sbValueBeforeMD5 = new StringBuilder(); try { md5 = MessageDigest.getInstance("MD5"); } catch (NoSuchAlgorithmException e) { System.out.println("Error: " + e); } try { long time = System.currentTimeMillis(); long rand = myRand.nextLong(); if (secure) { rand = mySecureRand.nextLong(); } sbValueBeforeMD5.append(s_id); sbValueBeforeMD5.append(":"); sbValueBeforeMD5.append(time); sbValueBeforeMD5.append(":"); sbValueBeforeMD5.append(rand); valueBeforeMD5 = sbValueBeforeMD5.toString(); md5.update(valueBeforeMD5.getBytes()); byte[] array = md5.digest(); StringBuilder sb = new StringBuilder(); for (byte value : array) { int b = value & 0xFF; if (b < 0x10) sb.append('0'); sb.append(Integer.toHexString(b)); } valueAfterMD5 = sb.toString(); } catch (Exception e) { System.out.println("Error:" + e); } } public String toString() { String raw = valueAfterMD5.toUpperCase(); return raw.substring(0, 8) + "-" + raw.substring(8, 12) + "-" + raw.substring(12, 16) + "-" + raw.substring(16, 20) + "-" + raw.substring(20); } public static void main(String[] args) { GUID guid = new GUID(); System.out.println(guid); } }
输出:
不积跬步,无以至千里;不积小流,无以成江海