Mega Code Archive
UUID generator
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/*
* Copyright 2004,2005 The Apache Software Foundation.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Random;
/**
* UUID generator
*/
public class UUIDGenerator {
private static String baseUUID = null;
private static long incrementingValue = 0;
private static Random myRand = null;
/**
* MD5 a random string with localhost/date etc will return 128 bits
* construct a string of 18 characters from those bits.
*
* @return string
*/
public static String getUUID() {
if (baseUUID == null) {
getInitialUUID();
}
long i = ++incrementingValue;
if(i >= Long.MAX_VALUE || i < 0){
incrementingValue = 0;
i = 0;
}
return baseUUID + System.currentTimeMillis() + i;
}
protected static synchronized void getInitialUUID() {
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));
MessageDigest md5 = null;
try {
md5 = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException e) {
//todo have to be properly handled
}
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 = myRand.nextInt();
if (begin < 0) begin = begin * -1;
begin = begin % 8;
baseUUID = sb2.toString().substring(begin, begin + 18).toUpperCase();
}
}
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