Source Code Cross Referenced for SoftHashMap.java in  » Portal » uPortal_rel-2-6-1-GA » org » jasig » portal » utils » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Portal » uPortal_rel 2 6 1 GA » org.jasig.portal.utils 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /* Copyright 2001 The JA-SIG Collaborative.  All rights reserved.
002:         *  See license distributed with this file and
003:         *  available online at http://www.uportal.org/license.html
004:         */
005:
006:        package org.jasig.portal.utils;
007:
008:        import java.lang.ref.ReferenceQueue;
009:        import java.lang.ref.SoftReference;
010:        import java.util.AbstractMap;
011:        import java.util.LinkedList;
012:        import java.util.Set;
013:
014:        import edu.emory.mathcs.backport.java.util.concurrent.ConcurrentHashMap;
015:
016:        /**
017:         * A HashMap implementation that uses soft references, 
018:         * leaving memory management up to the gc.
019:         * 
020:         * @author Peter Kharchenko (thanks to Dr. Kabutz on whose article the code is based)
021:         * @version $Revision: 36157 $
022:         */
023:        public class SoftHashMap extends AbstractMap {
024:
025:            private final ConcurrentHashMap map = new ConcurrentHashMap();
026:            private final LinkedList fifo = new LinkedList();
027:            private final ReferenceQueue removeQueue = new ReferenceQueue();
028:
029:            private int minSize;
030:
031:            /**
032:             * Construct a SoftHashMap
033:             * @param minSize minimum number of objects to keep (approximate)
034:             */
035:            public SoftHashMap(int minSize) {
036:                this .minSize = minSize;
037:            }
038:
039:            public SoftHashMap() {
040:                this (10);
041:            }
042:
043:            public Object put(Object key, Object value) {
044:                cleanMap();
045:                if (key == null) {
046:                    return (null);
047:                }
048:                KeyReferencePair pair = new KeyReferencePair(value, key,
049:                        removeQueue);
050:                // place the object into fifo
051:                addToFIFO(value);
052:                return map.put(key, pair);
053:            }
054:
055:            public Object get(Object key) {
056:                if (key == null) {
057:                    return (null);
058:                }
059:                SoftReference soft_ref = (SoftReference) map.get(key);
060:                if (soft_ref != null) {
061:                    Object obj = soft_ref.get();
062:                    if (obj == null) {
063:                        // object has been consumed by gc
064:                        map.remove(key);
065:                    } else {
066:                        // place the object into fifo
067:                        addToFIFO(obj);
068:                    }
069:                    return obj;
070:                }
071:                return null;
072:            }
073:
074:            public Object remove(Object key) {
075:                cleanMap();
076:                if (key == null) {
077:                    return (null);
078:                }
079:                SoftReference soft_ref = (SoftReference) map.remove(key);
080:                if (soft_ref != null) {
081:                    return soft_ref.get();
082:                } else {
083:                    return null;
084:                }
085:            }
086:
087:            public int size() {
088:                cleanMap();
089:                return map.size();
090:            }
091:
092:            public void clear() {
093:                synchronized (fifo) {
094:                    fifo.clear();
095:                }
096:                map.clear();
097:            }
098:
099:            public Set entrySet() {
100:                throw new UnsupportedOperationException();
101:            }
102:
103:            /**
104:             * An extension of a SoftReference that contains a key
105:             * by which it was mapped.
106:             */
107:            private final static class KeyReferencePair extends SoftReference {
108:                private final Object key;
109:
110:                public KeyReferencePair(Object value, Object key,
111:                        ReferenceQueue queue) {
112:                    super (value, queue);
113:                    this .key = key;
114:                }
115:            }
116:
117:            private void addToFIFO(Object o) {
118:                synchronized (fifo) {
119:                    fifo.addFirst(o);
120:                    if (fifo.size() > minSize) {
121:                        fifo.removeLast();
122:                    }
123:                }
124:            }
125:
126:            private void cleanMap() {
127:                KeyReferencePair pair;
128:                while ((pair = (KeyReferencePair) removeQueue.poll()) != null) {
129:                    map.remove(pair.key);
130:                }
131:            }
132:        }
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