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/*
* Copyright 2014 Harlan Noonkester
*
* Licensed 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.
*/
package org.tiogasolutions.dev.common.id;
import java.io.Serializable;
import java.time.*;
import java.util.*;
import org.tiogasolutions.dev.common.StringUtils;
/**
* User: harlan
* Date: 3/20/12
* Time: 12:00 AM
*
* Considerations -
* prefixLifeInSeconds should not be greater than the time it takes to reset the server.
* REVIEW - consider having the generator ensure it has existed at a minimum of prefixLifeInSeconds before generating the first sequence.
* REVIEW - concurrency
*/
/**
* User: harlan
* Date: 3/20/12
* Time: 12:00 AM
* Considerations -
* prefixLifeInSeconds should not be greater than the time it takes to reset the server.
* REVIEW - consider having the generator ensure it has existed at a minimum of prefixLifeInSeconds before generating the first sequence.
* REVIEW - concurrency
*/
public class TwoPartIdGenerator implements IdGenerator, Serializable {
private static final long serialVersionUID = 1L;
private static final int MAX_ATTEMPTS = 10000000; // 10 million
private final Object idLock = new Object();
private final Set rememberedRandomSet = new TreeSet<>();
private final Random random = new Random(System.currentTimeMillis());
private final String idFormat;
private final ZoneId zoneId;
private final ZonedDateTime prefixBegin;
private final char[] prefixChars;
private final int prefixLifeInSeconds;
private final int minPrefixLength;
private final int suffixLength;
private final int suffixMaxInt;
private String currentPrefix;
private int currentPrefixNumber;
private String lastId;
public TwoPartIdGenerator(String idFormat, ZonedDateTime prefixBegin, String prefixChars, int prefixLifeInSeconds, int minPrefixLength, int suffixLength) {
this.idFormat = idFormat;
this.prefixBegin = prefixBegin;
this.zoneId = prefixBegin.getZone();
this.prefixLifeInSeconds = prefixLifeInSeconds;
this.prefixChars = prefixChars.toCharArray();
this.minPrefixLength = minPrefixLength;
this.suffixLength = suffixLength;
this.suffixMaxInt = Integer.valueOf(StringUtils.padRight("", suffixLength, '9'));
this.currentPrefix = "";
}
public TwoPartIdGenerator() {
this("%s-%s",
ZonedDateTime.of(2013, 1, 1, 0, 0, 0, 0, ZoneId.of("UTC")),
"ABCDFGHJKLMNPQRSTVWXYZ",
20,
5,
7);
}
/**
* Generate a new sequence.
*
* @return generated sequence
*/
// CRITICAL should this method be synchronized since we use idLock
@Override
public synchronized String newId() {
// We perform this in a loop so that if we find a duplicate we can regenerate the entire number.
int attempts = 0;
while (attempts++ < MAX_ATTEMPTS) {
// Generate the prefix.
String lastPrefix = currentPrefix;
String prefix = generatePrefix();
// If our prefix has changed we need to clear the rememberedRandomSet
if (!lastPrefix.equals(prefix)) {
rememberedRandomSet.clear();
}
// Create the suffixInt and ensure it's unique.
int suffixInt = random.nextInt(suffixMaxInt);
if (rememberedRandomSet.contains(suffixInt)) {
// This is not a unique number, generate another.
continue;
}
// We have a unique randomInt, so generate the suffix which needs to be padded to suffixLength.
rememberedRandomSet.add(suffixInt);
String suffix = StringUtils.padRight(String.valueOf(suffixInt), suffixLength, '0');
// Return the sequence.
String sequence = String.format(idFormat, prefix, suffix);
synchronized (idLock) {
lastId = sequence;
}
return sequence;
}
// We reached max attempts but never successfully generated sequence, throw exception.
throw new RuntimeException("Exceeded number of attempts at generating a sequence.");
}
public String getLastId() {
synchronized (idLock) {
return lastId;
}
}
private String generatePrefix() {
// Duration will be used to generate the prefix characters, which are time based.
Duration duration = Duration.between(prefixBegin, ZonedDateTime.now(zoneId));
// Safe to cast to int here as will never exceed MAX_INT.
int newPrefixNumber = (int) duration.getSeconds() / prefixLifeInSeconds;
if (newPrefixNumber == currentPrefixNumber) {
// Our prefix number has not changed so just return the previous prefix.
return currentPrefix;
}
// We have a new currentPrefixNumber;
currentPrefixNumber = newPrefixNumber;
// Construct prefix, which is representation of prefixNumber based on the prefix chars.
int base = prefixChars.length;
StringBuilder prefixSb = new StringBuilder();
while (newPrefixNumber != 0) {
int mod = newPrefixNumber % base;
prefixSb.insert(0, prefixChars[mod]);
newPrefixNumber = newPrefixNumber / base;
}
currentPrefix = StringUtils.padLeft(prefixSb.toString(), minPrefixLength, this.prefixChars[0]);
return currentPrefix;
}
}
