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1   /**
2   The contents of this file are subject to the Mozilla Public License Version 1.1 
3   (the "License"); you may not use this file except in compliance with the License. 
4   You may obtain a copy of the License at http://www.mozilla.org/MPL/ 
5   Software distributed under the License is distributed on an "AS IS" basis, 
6   WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the 
7   specific language governing rights and limitations under the License. 
8   
9   The Original Code is "HiLoGenerator.java".  Description: 
10  "Abstract base class for HiLo ID Generators" 
11  
12  The Initial Developer of the Original Code is University Health Network. Copyright (C) 
13  2001.  All Rights Reserved. 
14  
15  Contributor(s): ______________________________________. 
16  
17  Alternatively, the contents of this file may be used under the terms of the 
18  GNU General Public License (the  "GPL"), in which case the provisions of the GPL are 
19  applicable instead of those above.  If you wish to allow use of your version of this 
20  file only under the terms of the GPL and not to allow others to use your version 
21  of this file under the MPL, indicate your decision by deleting  the provisions above 
22  and replace  them with the notice and other provisions required by the GPL License.  
23  If you do not delete the provisions above, a recipient may use your version of 
24  this file under either the MPL or the GPL. 
25   */
26  package ca.uhn.hl7v2.util.idgenerator;
27  
28  import java.io.IOException;
29  
30  import org.slf4j.Logger;
31  import org.slf4j.LoggerFactory;
32  
33  /**
34   * Abstract base class for a HiLo-style generator that cheaply generates "lo"
35   * IDs in memory but only seldomly increments (potentially more expensive) a
36   * "hi" ID, e.g. in a persistent store. The combination of "lo" and "hi" ID
37   * becomes the final ID returned to the caller.
38   * 
39   * @author Christian Ohr
40   */
41  public abstract class HiLoGenerator extends IDGenerator.OrderedSupport {
42  
43  	private static final Logger LOG = LoggerFactory
44  			.getLogger(HiLoGenerator.class.getName());
45  
46  	private long lo = 0L;
47  	private long base = -1L;
48  
49  	public synchronized String getID() throws IOException {
50  		if (base < 0) {
51  			LOG.debug("Obtain next hi ID");
52  			base = nextBase();
53  		}
54  		if (getNextLoId() >= getMaxLo()) {
55  			LOG.debug("Obtain next hi ID");
56  			base = nextBase();
57  		}
58  		return Long.toString(base + lo);
59  	}
60  
61  	private long nextBase() throws IOException {
62          long base = getNextHiId();
63  		lo = 0;
64  		return base;
65  	}
66  
67      /**
68       * Returns the next Hi ID
69       * @return the next Hi ID
70       * @throws IOException
71       */
72  	protected abstract long getNextHiId() throws IOException;
73  
74      /**
75       * Resets the Hi ID
76       */
77  	protected abstract void resetHiId();
78  
79      /**
80       * Returns then next Lo ID
81       * @return
82       */
83  	protected long getNextLoId() {
84  		return ++lo;
85  	}
86  
87      /**
88       * Resets the generator
89       */
90  	public void reset() {
91  		lo = 0;
92  		base = -1;
93  		resetHiId();
94  	}
95  
96      /**
97       * Returns the maximum Lo ID (expect the Hi ID be incremented afterwards)
98       * @return the maximum Lo ID
99       */
100 	abstract public long getMaxLo();
101 
102 }