/* | |
* Licensed to the Apache Software Foundation (ASF) under one | |
* or more contributor license agreements. See the NOTICE file | |
* distributed with this work for additional information | |
* regarding copyright ownership. The ASF licenses this file | |
* to you 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.apache.uima.caseditor.editor.util; | |
import java.util.Random; | |
/** | |
* <p> | |
* The IDGenerator generate unique IDs. | |
* </p> | |
* <p> | |
* Attention: The maximal number of generateable IDs is Long.MAX_VALUE. If there are more than | |
* Long.MAX_VALUE calls to nextUniqueID() an IllegalStateException will be thrown. | |
* </p> | |
*/ | |
public class IDGenerator { | |
private long sStartValue; | |
/** | |
* The unique id that will be incremented. | |
*/ | |
private long sUniqueID; | |
/** | |
* The singleton instance. | |
*/ | |
private static IDGenerator sIdGeneratorInstance; | |
/** | |
* Call <code>IDGenerator.getInstance()</code> to retrieve an instance of this class. Must not be | |
* instantiated outside this class, singleton pattern. | |
*/ | |
private IDGenerator() { | |
sStartValue = new Random().nextLong(); | |
sUniqueID = sStartValue + 1; | |
} | |
/** | |
* Retrieve the next unique ID. | |
* | |
* @throws IllegalStateException - | |
* if there are more than Long.MAX_VALUE calls to | |
* <code>IDGenerator.nextUniqueID()</code> | |
* @return - the unique id | |
*/ | |
public byte[] nextUniqueID() { | |
if (sUniqueID == sStartValue) { | |
throw new IllegalStateException("The ID Generator is out of IDs"); | |
} | |
byte[] id = new byte[] { (byte) (sUniqueID >> 56), (byte) (sUniqueID >> 48), | |
(byte) (sUniqueID >> 40), (byte) (sUniqueID >> 32), (byte) (sUniqueID >> 24), | |
(byte) (sUniqueID >> 16), (byte) (sUniqueID >> 8), (byte) sUniqueID, }; | |
sUniqueID++; | |
return id; | |
} | |
/** | |
* Retrieves the only instance of the IDGenerator. | |
* | |
* @return - the instance of the IDGenerator | |
*/ | |
public static IDGenerator getInstance() { | |
if (sIdGeneratorInstance == null) { | |
sIdGeneratorInstance = new IDGenerator(); | |
} | |
return sIdGeneratorInstance; | |
} | |
} |