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/* Copyright (c) 2011-2013 GoPivotal, Inc. All Rights Reserved. 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. */
package com.yiboshi.science.utils;
import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.Random;
import java.util.UUID;
import java.util.concurrent.locks.ReentrantLock;
/**
* Helper for creating random and Type 1 (time-based) UUIDs。
*
* @author Jon Brisbin
*/
public class UUIDUtils {
private static boolean IS_THREADLOCALRANDOM_AVAILABLE = false;
private static Random random;
private static final long leastSigBits;
private static final ReentrantLock lock = new ReentrantLock();
private static long lastTime;
static {
try {
IS_THREADLOCALRANDOM_AVAILABLE = null != UUIDUtils.class.getClassLoader().loadClass(
"java.util.concurrent.ThreadLocalRandom");
} catch (ClassNotFoundException e) {
}
byte[] seed = new SecureRandom().generateSeed(8);
leastSigBits = new BigInteger(seed).longValue();
if (!IS_THREADLOCALRANDOM_AVAILABLE) {
random = new Random(leastSigBits);
}
}
private UUIDUtils() {
}
/**
* Create a new random UUID.
*
* @return the new UUID
*/
public static String random() {
byte[] randomBytes = new byte[16];
if (IS_THREADLOCALRANDOM_AVAILABLE) {
java.util.concurrent.ThreadLocalRandom.current().nextBytes(randomBytes);
} else {
random.nextBytes(randomBytes);
}
long mostSigBits = 0;
for (int i = 0; i < 8; i++) {
mostSigBits = (mostSigBits << 8) | (randomBytes[i] & 0xff);
}
long leastSigBits = 0;
for (int i = 8; i < 16; i++) {
leastSigBits = (leastSigBits << 8) | (randomBytes[i] & 0xff);
}
return new UUID(mostSigBits, leastSigBits).toString().replaceAll("-", "");
}
/**
* Create a new time-based UUID.
*
* @return the new UUID
*/
public static String create() {
long timeMillis = (System.currentTimeMillis() * 10000) + 0x01B21DD213814000L;
lock.lock();
try {
if (timeMillis > lastTime) {
lastTime = timeMillis;
} else {
timeMillis = ++lastTime;
}
} finally {
lock.unlock();
}
// time low
long mostSigBits = timeMillis << 32;
// time mid
mostSigBits |= (timeMillis & 0xFFFF00000000L) >> 16;
// time hi and version
mostSigBits |= 0x1000 | ((timeMillis >> 48) & 0x0FFF); // version 1
return new UUID(mostSigBits, leastSigBits).toString().replaceAll("-", "");
}
public static void main(String[] args) {
String uuid = String.valueOf(UUID.randomUUID());
System.out.println (uuid);
}
}