简单的UUID类

最近应工程的需要写了个简单的UUID类。

可通过方法 String getUUID(int length) 使用。length是制定返回字符串的长度。

一般最好能20位以上

package test; import java.net.InetAddress; import java.net.UnknownHostException; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.util.Random; public class UUIDGenerator { private static String baseUUID = null; private static long incrementingValue = 0; private static Random myRand = null; public static String getUUID(int length) { if (baseUUID == null) { getInitialUUID(length); } long i = ++incrementingValue; if (i >= Long.MAX_VALUE || i < 0) { incrementingValue = 0; i = 0; } return baseUUID; } protected static synchronized void getInitialUUID(int length) { if (baseUUID != null) { return; } if (myRand == null) { myRand = new Random(); } long rand = myRand.nextLong(); String sid; try { sid = InetAddress.getLocalHost().toString(); } catch (UnknownHostException e) { sid = Thread.currentThread().getName(); } StringBuffer sb = new StringBuffer(); sb.append(sid); sb.append(":"); sb.append(Long.toString(rand)); sb.append(System.currentTimeMillis()); MessageDigest md5 = null; try { md5 = MessageDigest.getInstance("MD5"); } catch (NoSuchAlgorithmException e) { } md5.update(sb.toString().getBytes()); byte[] array = md5.digest(); StringBuffer sb2 = new StringBuffer(); for (int j = 0; j < array.length; ++j) { int b = array[j] & 0xFF; sb2.append(Integer.toHexString(b)); } int begin = 0; baseUUID = sb2.toString().substring(begin, length).toUpperCase(); } public static void main(String[] args) { System.out.println(UUIDGenerator.getUUID(10)); } }