/
FixedUidGenerator.java
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/
FixedUidGenerator.java
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/**
* Copyright (c) 2012, Ben Fortuna
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* o Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* o Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* o Neither the name of Ben Fortuna nor the names of any other contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package net.fortuna.ical4j.util;
import net.fortuna.ical4j.model.TemporalAdapter;
import net.fortuna.ical4j.model.property.Uid;
import java.net.SocketException;
import java.time.Instant;
import java.util.concurrent.TimeUnit;
/**
* $Id$
*
* Created on 11/03/2007
*
* Generates {@link Uid} properties in a similar fashion to that recommended in section 4.8.4.7 of the specification.
* @author Ben Fortuna
*/
public class FixedUidGenerator implements UidGenerator {
private final String pid;
private final String hostName;
private static long lastMillis;
/**
* @param pid a unique process identifier for the host machine
* @throws SocketException where host information cannot be retrieved
*/
public FixedUidGenerator(String pid) throws SocketException {
this(new InetAddressHostInfo(), pid);
}
/**
* @param hostInfo custom host information
* @param pid a unique process identifier for the host machine
*/
public FixedUidGenerator(HostInfo hostInfo, String pid) {
this.hostName = hostInfo == null ? null : hostInfo.getHostName();
this.pid = pid;
}
@Override
public Uid generateUid() {
final StringBuilder b = new StringBuilder();
b.append(uniqueTimestamp());
b.append('-');
b.append(pid);
if (hostName != null) {
b.append('@');
b.append(hostName);
}
return new Uid(b.toString());
}
/**
* Generates a timestamp guaranteed to be unique for the current JVM instance.
* @return a {@link TemporalAdapter<Instant>} instance representing a unique timestamp
*/
private static TemporalAdapter<Instant> uniqueTimestamp() {
long currentMillis;
synchronized (FixedUidGenerator.class) {
currentMillis = System.currentTimeMillis();
// guarantee uniqueness by ensuring timestamp is always greater
// than the previous..
if (currentMillis < lastMillis) {
currentMillis = lastMillis;
}
if (currentMillis - lastMillis < TimeUnit.SECONDS.toMillis(1)) {
currentMillis += TimeUnit.SECONDS.toMillis(1);
}
lastMillis = currentMillis;
}
return new TemporalAdapter<>(Instant.ofEpochMilli(currentMillis));
}
}