001/**
002The contents of this file are subject to the Mozilla Public License Version 1.1 
003(the "License"); you may not use this file except in compliance with the License. 
004You may obtain a copy of the License at http://www.mozilla.org/MPL/ 
005Software distributed under the License is distributed on an "AS IS" basis, 
006WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the 
007specific language governing rights and limitations under the License. 
008
009The Original Code is "HiLoGenerator.java".  Description: 
010"Abstract base class for HiLo ID Generators" 
011
012The Initial Developer of the Original Code is University Health Network. Copyright (C) 
0132001.  All Rights Reserved. 
014
015Contributor(s): ______________________________________. 
016
017Alternatively, the contents of this file may be used under the terms of the 
018GNU General Public License (the  "GPL"), in which case the provisions of the GPL are 
019applicable instead of those above.  If you wish to allow use of your version of this 
020file only under the terms of the GPL and not to allow others to use your version 
021of this file under the MPL, indicate your decision by deleting  the provisions above 
022and replace  them with the notice and other provisions required by the GPL License.  
023If you do not delete the provisions above, a recipient may use your version of 
024this file under either the MPL or the GPL. 
025 */
026package ca.uhn.hl7v2.util.idgenerator;
027
028import java.io.IOException;
029
030import org.slf4j.Logger;
031import org.slf4j.LoggerFactory;
032
033/**
034 * Abstract base class for a HiLo-style generator that cheaply generates "lo"
035 * IDs in memory but only seldomly increments (potentially more expensive) a
036 * "hi" ID, e.g. in a persistent store. The combination of "lo" and "hi" ID
037 * becomes the final ID returned to the caller.
038 * 
039 * @author Christian Ohr
040 */
041public abstract class HiLoGenerator extends IDGenerator.OrderedSupport {
042
043        private static final Logger LOG = LoggerFactory
044                        .getLogger(HiLoGenerator.class.getName());
045
046        private long lo = 0L;
047        private long base = -1L;
048
049        public synchronized String getID() throws IOException {
050                if (base < 0) {
051                        LOG.debug("Obtain next hi ID");
052                        base = nextBase();
053                }
054                if (getNextLoId() >= getMaxLo()) {
055                        LOG.debug("Obtain next hi ID");
056                        base = nextBase();
057                }
058                return Long.toString(base + lo);
059        }
060
061        private long nextBase() throws IOException {
062        long base = getNextHiId();
063                lo = 0;
064                return base;
065        }
066
067    /**
068     * Returns the next Hi ID
069     * @return the next Hi ID
070     * @throws IOException
071     */
072        protected abstract long getNextHiId() throws IOException;
073
074    /**
075     * Resets the Hi ID
076     */
077        protected abstract void resetHiId();
078
079    /**
080     * Returns then next Lo ID
081     * @return
082     */
083        protected long getNextLoId() {
084                return ++lo;
085        }
086
087    /**
088     * Resets the generator
089     */
090        public void reset() {
091                lo = 0;
092                base = -1;
093                resetHiId();
094        }
095
096    /**
097     * Returns the maximum Lo ID (expect the Hi ID be incremented afterwards)
098     * @return the maximum Lo ID
099     */
100        abstract public long getMaxLo();
101
102}