001 /*
002 * Copyright 2002-2004 Sun Microsystems, Inc. All Rights Reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation. Sun designates this
008 * particular file as subject to the "Classpath" exception as provided
009 * by Sun in the LICENSE file that accompanied this code.
010 *
011 * This code is distributed in the hope that it will be useful, but WITHOUT
012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014 * version 2 for more details (a copy is included in the LICENSE file that
015 * accompanied this code).
016 *
017 * You should have received a copy of the GNU General Public License version
018 * 2 along with this work; if not, write to the Free Software Foundation,
019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020 *
021 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022 * CA 95054 USA or visit www.sun.com if you need additional information or
023 * have any questions.
024 */
025
026 /*
027 * @(#)ExpiringCache.java 1.12 07/05/05
028 */
029
030 package java.io;
031
032 import java.util.Iterator;
033 import java.util.Map;
034 import java.util.LinkedHashMap;
035 import java.util.Set;
036
037 class ExpiringCache {
038 private long millisUntilExpiration;
039 private Map map;
040 // Clear out old entries every few queries
041 private int queryCount;
042 private int queryOverflow = 300;
043 private int MAX_ENTRIES = 200;
044
045 static class Entry {
046 private long timestamp;
047 private String val;
048
049 Entry(long timestamp, String val) {
050 this .timestamp = timestamp;
051 this .val = val;
052 }
053
054 long timestamp() {
055 return timestamp;
056 }
057
058 void setTimestamp(long timestamp) {
059 this .timestamp = timestamp;
060 }
061
062 String val() {
063 return val;
064 }
065
066 void setVal(String val) {
067 this .val = val;
068 }
069 }
070
071 ExpiringCache() {
072 this (30000);
073 }
074
075 ExpiringCache(long millisUntilExpiration) {
076 this .millisUntilExpiration = millisUntilExpiration;
077 map = new LinkedHashMap() {
078 protected boolean removeEldestEntry(Map.Entry eldest) {
079 return size() > MAX_ENTRIES;
080 }
081 };
082 }
083
084 synchronized String get(String key) {
085 if (++queryCount >= queryOverflow) {
086 cleanup();
087 }
088 Entry entry = entryFor(key);
089 if (entry != null) {
090 return entry.val();
091 }
092 return null;
093 }
094
095 synchronized void put(String key, String val) {
096 if (++queryCount >= queryOverflow) {
097 cleanup();
098 }
099 Entry entry = entryFor(key);
100 if (entry != null) {
101 entry.setTimestamp(System.currentTimeMillis());
102 entry.setVal(val);
103 } else {
104 map.put(key, new Entry(System.currentTimeMillis(), val));
105 }
106 }
107
108 synchronized void clear() {
109 map.clear();
110 }
111
112 private Entry entryFor(String key) {
113 Entry entry = (Entry) map.get(key);
114 if (entry != null) {
115 long delta = System.currentTimeMillis() - entry.timestamp();
116 if (delta < 0 || delta >= millisUntilExpiration) {
117 map.remove(key);
118 entry = null;
119 }
120 }
121 return entry;
122 }
123
124 private void cleanup() {
125 Set keySet = map.keySet();
126 // Avoid ConcurrentModificationExceptions
127 String[] keys = new String[keySet.size()];
128 int i = 0;
129 for (Iterator iter = keySet.iterator(); iter.hasNext();) {
130 String key = (String) iter.next();
131 keys[i++] = key;
132 }
133 for (int j = 0; j < keys.length; j++) {
134 entryFor(keys[j]);
135 }
136 queryCount = 0;
137 }
138 }
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