UUID generator from http://www1.ics.uci.edu
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.io.IOException;
import java.net.InetAddress;
import java.security.SecureRandom;
import java.util.Random;
import java.util.UUID;
/**
* UUID value generator. Type 1 generator is based on the time-based generator
* in the Apache Commons Id project: http://jakarta.apache.org/commons/sandbox
* /id/uuid.html The type 4 generator uses the standard Java UUID generator.
*
* The type 1 code has been vastly simplified and modified to replace the
* ethernet address of the host machine with the IP, since we do not want to
* require native libs and Java cannot access the MAC address directly.
*
* In spirit, implements the IETF UUID draft specification, found here:<br />
* http://www1.ics.uci.edu/~ejw/authoring/uuid-guid/draft-leach-uuids-guids-01
* .txt
*
* @author Abe White, Kevin Sutter
* @nojavadoc
* @since 0.3.3
*/
public class UUIDGenerator {
// supported UUID types
public static final int TYPE1 = 1;
public static final int TYPE4 = 4;
// indexes within the uuid array for certain boundaries
private static final byte IDX_TIME_HI = 6;
private static final byte IDX_TYPE = 6; // multiplexed
private static final byte IDX_TIME_MID = 4;
private static final byte IDX_TIME_LO = 0;
private static final byte IDX_TIME_SEQ = 8;
private static final byte IDX_VARIATION = 8; // multiplexed
// indexes and lengths within the timestamp for certain boundaries
private static final byte TS_TIME_LO_IDX = 4;
private static final byte TS_TIME_LO_LEN = 4;
private static final byte TS_TIME_MID_IDX = 2;
private static final byte TS_TIME_MID_LEN = 2;
private static final byte TS_TIME_HI_IDX = 0;
private static final byte TS_TIME_HI_LEN = 2;
// offset to move from 1/1/1970, which is 0-time for Java, to gregorian
// 0-time 10/15/1582, and multiplier to go from 100nsec to msec units
private static final long GREG_OFFSET = 0xB1D069B5400L;
private static final long MILLI_MULT = 10000L;
// type of UUID -- time based
private final static byte TYPE_TIME_BASED = 0x10;
// random number generator used to reduce conflicts with other JVMs, and
// hasher for strings.
private static Random RANDOM;
// 4-byte IP address + 2 random bytes to compensate for the fact that
// the MAC address is usually 6 bytes
private static byte[] IP;
// counter is initialized to 0 and is incremented for each uuid request
// within the same timestamp window.
private static int _counter;
// current timestamp (used to detect multiple uuid requests within same
// timestamp)
private static long _currentMillis;
// last used millis time, and a semi-random sequence that gets reset
// when it overflows
private static long _lastMillis = 0L;
private static final int MAX_14BIT = 0x3FFF;
private static short _seq = 0;
/*
* Initializer for type 1 UUIDs. Creates random generator and genenerates
* the node portion of the UUID using the IP address.
*/
private static synchronized void initializeForType1()
{
if (RANDOM != null)
return;
// note that secure random is very slow the first time
// it is used; consider switching to a standard random
RANDOM = new SecureRandom();
_seq = (short) RANDOM.nextInt(MAX_14BIT);
byte[] ip = null;
try {
ip = InetAddress.getLocalHost().getAddress();
} catch (IOException ioe) {
throw new RuntimeException(ioe);
}
IP = new byte[6];
RANDOM.nextBytes(IP);
System.arraycopy(ip, 0, IP, 2, ip.length);
}
/**
* Return a unique UUID value.
*/
public static byte[] next(int type) {
if (type == TYPE4) {
return createType4();
}
return createType1();
}
/*
* Creates a type 1 UUID
*/
public static byte[] createType1() {
if (RANDOM == null)
initializeForType1();
// set ip addr
byte[] uuid = new byte[16];
System.arraycopy(IP, 0, uuid, 10, IP.length);
// Set time info. Have to do this processing within a synchronized
// block because of the statics...
long now = 0;
synchronized (UUIDGenerator.class) {
// Get the time to use for this uuid. This method has the side
// effect of modifying the clock sequence, as well.
now = getTime();
// Insert the resulting clock sequence into the uuid
uuid[IDX_TIME_SEQ] = (byte) ((_seq & 0x3F00) >>> 8);
uuid[IDX_VARIATION] |= 0x80;
uuid[IDX_TIME_SEQ+1] = (byte) (_seq & 0xFF);
}
// have to break up time because bytes are spread through uuid
byte[] timeBytes = Long.toString(now).getBytes();
// Copy time low
System.arraycopy(timeBytes, TS_TIME_LO_IDX, uuid, IDX_TIME_LO,
TS_TIME_LO_LEN);
// Copy time mid
System.arraycopy(timeBytes, TS_TIME_MID_IDX, uuid, IDX_TIME_MID,
TS_TIME_MID_LEN);
// Copy time hi
System.arraycopy(timeBytes, TS_TIME_HI_IDX, uuid, IDX_TIME_HI,
TS_TIME_HI_LEN);
//Set version (time-based)
uuid[IDX_TYPE] |= TYPE_TIME_BASED; // 0001 0000
return uuid;
}
/*
* Creates a type 4 UUID
*/
private static byte[] createType4() {
UUID type4 = UUID.randomUUID();
byte[] uuid = new byte[16];
longToBytes(type4.getMostSignificantBits(), uuid, 0);
longToBytes(type4.getLeastSignificantBits(), uuid, 8);
return uuid;
}
/*
* Converts a long to byte values, setting them in a byte array
* at a given starting position.
*/
private static void longToBytes(long longVal, byte[] buf, int sPos) {
sPos += 7;
for(int i = 0; i < 8; i++)
buf[sPos-i] = (byte)(longVal >>> (i * 8));
}
/**
* Return the next unique uuid value as a 16-character string.
*/
public static String nextString(int type) {
byte[] bytes = next(type);
try {
return new String(bytes, "ISO-8859-1");
} catch (Exception e) {
return new String(bytes);
}
}
/**
* Return the next unique uuid value as a 32-character hex string.
*/
public static String nextHex(int type) {
return Base16Encoder.encode(next(type));
}
/**
* Get the timestamp to be used for this uuid. Must be called from
* a synchronized block.
*
* @return long timestamp
*/
// package-visibility for testing
static long getTime() {
if (RANDOM == null)
initializeForType1();
long newTime = getUUIDTime();
if (newTime <= _lastMillis) {
incrementSequence();
newTime = getUUIDTime();
}
_lastMillis = newTime;
return newTime;
}
/**
* Gets the appropriately modified timestamep for the UUID. Must be called
* from a synchronized block.
*
* @return long timestamp in 100ns intervals since the Gregorian change
* offset
*/
private static long getUUIDTime() {
if (_currentMillis != System.currentTimeMillis()) {
_currentMillis = System.currentTimeMillis();
_counter = 0; // reset counter
}
// check to see if we have created too many uuid's for this timestamp
if (_counter + 1 >= MILLI_MULT) {
// Original algorithm threw exception. Seemed like overkill.
// Let's just increment the timestamp instead and start over...
_currentMillis++;
_counter = 0;
}
// calculate time as current millis plus offset times 100 ns ticks
long currentTime = (_currentMillis + GREG_OFFSET) * MILLI_MULT;
// return the uuid time plus the artificial tick counter incremented
return currentTime + _counter++;
}
/**
* Increments the clock sequence for this uuid. Must be called from a
* synchronized block.
*/
private static void incrementSequence() {
// increment, but if it's greater than its 14-bits, reset it
if (++_seq > MAX_14BIT) {
_seq = (short) RANDOM.nextInt(MAX_14BIT); // semi-random
}
}
}
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
/**
* Base 16 encoder.
*
* @author Marc Prud'hommeaux
* @nojavadoc
*/
class Base16Encoder {
private final static char[] HEX = new char[]{
'0', '1', '2', '3', '4', '5', '6', '7',
'8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
/**
* Convert bytes to a base16 string.
*/
public static String encode(byte[] byteArray) {
StringBuffer hexBuffer = new StringBuffer(byteArray.length * 2);
for (int i = 0; i < byteArray.length; i++)
for (int j = 1; j >= 0; j--)
hexBuffer.append(HEX[(byteArray[i] >> (j * 4)) & 0xF]);
return hexBuffer.toString();
}
/**
* Convert a base16 string into a byte array.
*/
public static byte[] decode(String s) {
int len = s.length();
byte[] r = new byte[len / 2];
for (int i = 0; i < r.length; i++) {
int digit1 = s.charAt(i * 2), digit2 = s.charAt(i * 2 + 1);
if (digit1 >= '0' && digit1 <= '9')
digit1 -= '0';
else if (digit1 >= 'A' && digit1 <= 'F')
digit1 -= 'A' - 10;
if (digit2 >= '0' && digit2 <= '9')
digit2 -= '0';
else if (digit2 >= 'A' && digit2 <= 'F')
digit2 -= 'A' - 10;
r[i] = (byte) ((digit1 << 4) + digit2);
}
return r;
}
}
Related examples in the same category