1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/net/fortuna/ical4j/util/UidGenerator.java Tue Feb 10 18:12:00 2015 +0100
1.3 @@ -0,0 +1,109 @@
1.4 +/**
1.5 + * Copyright (c) 2012, Ben Fortuna
1.6 + * All rights reserved.
1.7 + *
1.8 + * Redistribution and use in source and binary forms, with or without
1.9 + * modification, are permitted provided that the following conditions
1.10 + * are met:
1.11 + *
1.12 + * o Redistributions of source code must retain the above copyright
1.13 + * notice, this list of conditions and the following disclaimer.
1.14 + *
1.15 + * o Redistributions in binary form must reproduce the above copyright
1.16 + * notice, this list of conditions and the following disclaimer in the
1.17 + * documentation and/or other materials provided with the distribution.
1.18 + *
1.19 + * o Neither the name of Ben Fortuna nor the names of any other contributors
1.20 + * may be used to endorse or promote products derived from this software
1.21 + * without specific prior written permission.
1.22 + *
1.23 + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
1.24 + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
1.25 + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
1.26 + * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
1.27 + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
1.28 + * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
1.29 + * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
1.30 + * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
1.31 + * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
1.32 + * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
1.33 + * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.34 + */
1.35 +package net.fortuna.ical4j.util;
1.36 +
1.37 +import java.net.SocketException;
1.38 +
1.39 +import net.fortuna.ical4j.model.DateTime;
1.40 +import net.fortuna.ical4j.model.property.Uid;
1.41 +
1.42 +/**
1.43 + * $Id$
1.44 + *
1.45 + * Created on 11/03/2007
1.46 + *
1.47 + * Generates {@link Uid} properties in a similar fashion to that recommended in section 4.8.4.7 of the specification.
1.48 + * @author Ben Fortuna
1.49 + */
1.50 +public class UidGenerator {
1.51 +
1.52 + private final String pid;
1.53 +
1.54 + private final HostInfo hostInfo;
1.55 +
1.56 + private static long lastMillis;
1.57 +
1.58 + /**
1.59 + * @param pid a unique process identifier for the host machine
1.60 + * @throws SocketException where host information cannot be retrieved
1.61 + */
1.62 + public UidGenerator(String pid) throws SocketException {
1.63 + this(new InetAddressHostInfo(), pid);
1.64 + }
1.65 +
1.66 + /**
1.67 + * @param hostInfo custom host information
1.68 + * @param pid a unique process identifier for the host machine
1.69 + */
1.70 + public UidGenerator(HostInfo hostInfo, String pid) {
1.71 + this.hostInfo = hostInfo;
1.72 + this.pid = pid;
1.73 + }
1.74 +
1.75 + /**
1.76 + * @return a unique component identifier
1.77 + */
1.78 + public Uid generateUid() {
1.79 + final StringBuffer b = new StringBuffer();
1.80 + b.append(uniqueTimestamp());
1.81 + b.append('-');
1.82 + b.append(pid);
1.83 + if (hostInfo != null) {
1.84 + b.append('@');
1.85 + b.append(hostInfo.getHostName());
1.86 + }
1.87 + return new Uid(b.toString());
1.88 + }
1.89 +
1.90 + /**
1.91 + * Generates a timestamp guaranteed to be unique for the current JVM instance.
1.92 + * @return a {@link DateTime} instance representing a unique timestamp
1.93 + */
1.94 + private static DateTime uniqueTimestamp() {
1.95 + long currentMillis;
1.96 + synchronized (UidGenerator.class) {
1.97 + currentMillis = System.currentTimeMillis();
1.98 + // guarantee uniqueness by ensuring timestamp is always greater
1.99 + // than the previous..
1.100 + if (currentMillis < lastMillis) {
1.101 + currentMillis = lastMillis;
1.102 + }
1.103 + if (currentMillis - lastMillis < Dates.MILLIS_PER_SECOND) {
1.104 + currentMillis += Dates.MILLIS_PER_SECOND;
1.105 + }
1.106 + lastMillis = currentMillis;
1.107 + }
1.108 + final DateTime timestamp = new DateTime(currentMillis);
1.109 + timestamp.setUtc(true);
1.110 + return timestamp;
1.111 + }
1.112 +}
