src/net/fortuna/ical4j/util/UidGenerator.java@fb9019fb1bf7 (annotated)
src/net/fortuna/ical4j/util/UidGenerator.java
Tue, 10 Feb 2015 18:12:00 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Tue, 10 Feb 2015 18:12:00 +0100
- changeset 0
- fb9019fb1bf7
- permissions
- -rw-r--r--
Import initial revisions of existing project AndroidCaldavSyncAdapater,
forked from upstream repository at 27e8a0f8495c92e0780d450bdf0c7cec77a03a55.
| michael@0 | 1 | /** |
| michael@0 | 2 | * Copyright (c) 2012, Ben Fortuna |
| michael@0 | 3 | * All rights reserved. |
| michael@0 | 4 | * |
| michael@0 | 5 | * Redistribution and use in source and binary forms, with or without |
| michael@0 | 6 | * modification, are permitted provided that the following conditions |
| michael@0 | 7 | * are met: |
| michael@0 | 8 | * |
| michael@0 | 9 | * o Redistributions of source code must retain the above copyright |
| michael@0 | 10 | * notice, this list of conditions and the following disclaimer. |
| michael@0 | 11 | * |
| michael@0 | 12 | * o Redistributions in binary form must reproduce the above copyright |
| michael@0 | 13 | * notice, this list of conditions and the following disclaimer in the |
| michael@0 | 14 | * documentation and/or other materials provided with the distribution. |
| michael@0 | 15 | * |
| michael@0 | 16 | * o Neither the name of Ben Fortuna nor the names of any other contributors |
| michael@0 | 17 | * may be used to endorse or promote products derived from this software |
| michael@0 | 18 | * without specific prior written permission. |
| michael@0 | 19 | * |
| michael@0 | 20 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| michael@0 | 21 | * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| michael@0 | 22 | * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| michael@0 | 23 | * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR |
| michael@0 | 24 | * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, |
| michael@0 | 25 | * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
| michael@0 | 26 | * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR |
| michael@0 | 27 | * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF |
| michael@0 | 28 | * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING |
| michael@0 | 29 | * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS |
| michael@0 | 30 | * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| michael@0 | 31 | */ |
| michael@0 | 32 | package net.fortuna.ical4j.util; |
| michael@0 | 33 | |
| michael@0 | 34 | import java.net.SocketException; |
| michael@0 | 35 | |
| michael@0 | 36 | import net.fortuna.ical4j.model.DateTime; |
| michael@0 | 37 | import net.fortuna.ical4j.model.property.Uid; |
| michael@0 | 38 | |
| michael@0 | 39 | /** |
| michael@0 | 40 | * $Id$ |
| michael@0 | 41 | * |
| michael@0 | 42 | * Created on 11/03/2007 |
| michael@0 | 43 | * |
| michael@0 | 44 | * Generates {@link Uid} properties in a similar fashion to that recommended in section 4.8.4.7 of the specification. |
| michael@0 | 45 | * @author Ben Fortuna |
| michael@0 | 46 | */ |
| michael@0 | 47 | public class UidGenerator { |
| michael@0 | 48 | |
| michael@0 | 49 | private final String pid; |
| michael@0 | 50 | |
| michael@0 | 51 | private final HostInfo hostInfo; |
| michael@0 | 52 | |
| michael@0 | 53 | private static long lastMillis; |
| michael@0 | 54 | |
| michael@0 | 55 | /** |
| michael@0 | 56 | * @param pid a unique process identifier for the host machine |
| michael@0 | 57 | * @throws SocketException where host information cannot be retrieved |
| michael@0 | 58 | */ |
| michael@0 | 59 | public UidGenerator(String pid) throws SocketException { |
| michael@0 | 60 | this(new InetAddressHostInfo(), pid); |
| michael@0 | 61 | } |
| michael@0 | 62 | |
| michael@0 | 63 | /** |
| michael@0 | 64 | * @param hostInfo custom host information |
| michael@0 | 65 | * @param pid a unique process identifier for the host machine |
| michael@0 | 66 | */ |
| michael@0 | 67 | public UidGenerator(HostInfo hostInfo, String pid) { |
| michael@0 | 68 | this.hostInfo = hostInfo; |
| michael@0 | 69 | this.pid = pid; |
| michael@0 | 70 | } |
| michael@0 | 71 | |
| michael@0 | 72 | /** |
| michael@0 | 73 | * @return a unique component identifier |
| michael@0 | 74 | */ |
| michael@0 | 75 | public Uid generateUid() { |
| michael@0 | 76 | final StringBuffer b = new StringBuffer(); |
| michael@0 | 77 | b.append(uniqueTimestamp()); |
| michael@0 | 78 | b.append('-'); |
| michael@0 | 79 | b.append(pid); |
| michael@0 | 80 | if (hostInfo != null) { |
| michael@0 | 81 | b.append('@'); |
| michael@0 | 82 | b.append(hostInfo.getHostName()); |
| michael@0 | 83 | } |
| michael@0 | 84 | return new Uid(b.toString()); |
| michael@0 | 85 | } |
| michael@0 | 86 | |
| michael@0 | 87 | /** |
| michael@0 | 88 | * Generates a timestamp guaranteed to be unique for the current JVM instance. |
| michael@0 | 89 | * @return a {@link DateTime} instance representing a unique timestamp |
| michael@0 | 90 | */ |
| michael@0 | 91 | private static DateTime uniqueTimestamp() { |
| michael@0 | 92 | long currentMillis; |
| michael@0 | 93 | synchronized (UidGenerator.class) { |
| michael@0 | 94 | currentMillis = System.currentTimeMillis(); |
| michael@0 | 95 | // guarantee uniqueness by ensuring timestamp is always greater |
| michael@0 | 96 | // than the previous.. |
| michael@0 | 97 | if (currentMillis < lastMillis) { |
| michael@0 | 98 | currentMillis = lastMillis; |
| michael@0 | 99 | } |
| michael@0 | 100 | if (currentMillis - lastMillis < Dates.MILLIS_PER_SECOND) { |
| michael@0 | 101 | currentMillis += Dates.MILLIS_PER_SECOND; |
| michael@0 | 102 | } |
| michael@0 | 103 | lastMillis = currentMillis; |
| michael@0 | 104 | } |
| michael@0 | 105 | final DateTime timestamp = new DateTime(currentMillis); |
| michael@0 | 106 | timestamp.setUtc(true); |
| michael@0 | 107 | return timestamp; |
| michael@0 | 108 | } |
| michael@0 | 109 | } |
