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comparison: src/net/fortuna/ical4j/util/UidGenerator.java
src/net/fortuna/ical4j/util/UidGenerator.java
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| 1 /** | |
| 2 * Copyright (c) 2012, Ben Fortuna | |
| 3 * All rights reserved. | |
| 4 * | |
| 5 * Redistribution and use in source and binary forms, with or without | |
| 6 * modification, are permitted provided that the following conditions | |
| 7 * are met: | |
| 8 * | |
| 9 * o Redistributions of source code must retain the above copyright | |
| 10 * notice, this list of conditions and the following disclaimer. | |
| 11 * | |
| 12 * o Redistributions in binary form must reproduce the above copyright | |
| 13 * notice, this list of conditions and the following disclaimer in the | |
| 14 * documentation and/or other materials provided with the distribution. | |
| 15 * | |
| 16 * o Neither the name of Ben Fortuna nor the names of any other contributors | |
| 17 * may be used to endorse or promote products derived from this software | |
| 18 * without specific prior written permission. | |
| 19 * | |
| 20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |
| 21 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |
| 22 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR | |
| 23 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR | |
| 24 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, | |
| 25 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, | |
| 26 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR | |
| 27 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF | |
| 28 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING | |
| 29 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS | |
| 30 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
| 31 */ | |
| 32 package net.fortuna.ical4j.util; | |
| 33 | |
| 34 import java.net.SocketException; | |
| 35 | |
| 36 import net.fortuna.ical4j.model.DateTime; | |
| 37 import net.fortuna.ical4j.model.property.Uid; | |
| 38 | |
| 39 /** | |
| 40 * $Id$ | |
| 41 * | |
| 42 * Created on 11/03/2007 | |
| 43 * | |
| 44 * Generates {@link Uid} properties in a similar fashion to that recommended in section 4.8.4.7 of the specification. | |
| 45 * @author Ben Fortuna | |
| 46 */ | |
| 47 public class UidGenerator { | |
| 48 | |
| 49 private final String pid; | |
| 50 | |
| 51 private final HostInfo hostInfo; | |
| 52 | |
| 53 private static long lastMillis; | |
| 54 | |
| 55 /** | |
| 56 * @param pid a unique process identifier for the host machine | |
| 57 * @throws SocketException where host information cannot be retrieved | |
| 58 */ | |
| 59 public UidGenerator(String pid) throws SocketException { | |
| 60 this(new InetAddressHostInfo(), pid); | |
| 61 } | |
| 62 | |
| 63 /** | |
| 64 * @param hostInfo custom host information | |
| 65 * @param pid a unique process identifier for the host machine | |
| 66 */ | |
| 67 public UidGenerator(HostInfo hostInfo, String pid) { | |
| 68 this.hostInfo = hostInfo; | |
| 69 this.pid = pid; | |
| 70 } | |
| 71 | |
| 72 /** | |
| 73 * @return a unique component identifier | |
| 74 */ | |
| 75 public Uid generateUid() { | |
| 76 final StringBuffer b = new StringBuffer(); | |
| 77 b.append(uniqueTimestamp()); | |
| 78 b.append('-'); | |
| 79 b.append(pid); | |
| 80 if (hostInfo != null) { | |
| 81 b.append('@'); | |
| 82 b.append(hostInfo.getHostName()); | |
| 83 } | |
| 84 return new Uid(b.toString()); | |
| 85 } | |
| 86 | |
| 87 /** | |
| 88 * Generates a timestamp guaranteed to be unique for the current JVM instance. | |
| 89 * @return a {@link DateTime} instance representing a unique timestamp | |
| 90 */ | |
| 91 private static DateTime uniqueTimestamp() { | |
| 92 long currentMillis; | |
| 93 synchronized (UidGenerator.class) { | |
| 94 currentMillis = System.currentTimeMillis(); | |
| 95 // guarantee uniqueness by ensuring timestamp is always greater | |
| 96 // than the previous.. | |
| 97 if (currentMillis < lastMillis) { | |
| 98 currentMillis = lastMillis; | |
| 99 } | |
| 100 if (currentMillis - lastMillis < Dates.MILLIS_PER_SECOND) { | |
| 101 currentMillis += Dates.MILLIS_PER_SECOND; | |
| 102 } | |
| 103 lastMillis = currentMillis; | |
| 104 } | |
| 105 final DateTime timestamp = new DateTime(currentMillis); | |
| 106 timestamp.setUtc(true); | |
| 107 return timestamp; | |
| 108 } | |
| 109 } |
