J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2002-2004 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | /* |
| 27 | */ |
| 28 | |
| 29 | package java.io; |
| 30 | |
| 31 | import java.util.Iterator; |
| 32 | import java.util.Map; |
| 33 | import java.util.LinkedHashMap; |
| 34 | import java.util.Set; |
| 35 | |
| 36 | class ExpiringCache { |
| 37 | private long millisUntilExpiration; |
| 38 | private Map map; |
| 39 | // Clear out old entries every few queries |
| 40 | private int queryCount; |
| 41 | private int queryOverflow = 300; |
| 42 | private int MAX_ENTRIES = 200; |
| 43 | |
| 44 | static class Entry { |
| 45 | private long timestamp; |
| 46 | private String val; |
| 47 | |
| 48 | Entry(long timestamp, String val) { |
| 49 | this.timestamp = timestamp; |
| 50 | this.val = val; |
| 51 | } |
| 52 | |
| 53 | long timestamp() { return timestamp; } |
| 54 | void setTimestamp(long timestamp) { this.timestamp = timestamp; } |
| 55 | |
| 56 | String val() { return val; } |
| 57 | void setVal(String val) { this.val = val; } |
| 58 | } |
| 59 | |
| 60 | ExpiringCache() { |
| 61 | this(30000); |
| 62 | } |
| 63 | |
| 64 | ExpiringCache(long millisUntilExpiration) { |
| 65 | this.millisUntilExpiration = millisUntilExpiration; |
| 66 | map = new LinkedHashMap() { |
| 67 | protected boolean removeEldestEntry(Map.Entry eldest) { |
| 68 | return size() > MAX_ENTRIES; |
| 69 | } |
| 70 | }; |
| 71 | } |
| 72 | |
| 73 | synchronized String get(String key) { |
| 74 | if (++queryCount >= queryOverflow) { |
| 75 | cleanup(); |
| 76 | } |
| 77 | Entry entry = entryFor(key); |
| 78 | if (entry != null) { |
| 79 | return entry.val(); |
| 80 | } |
| 81 | return null; |
| 82 | } |
| 83 | |
| 84 | synchronized void put(String key, String val) { |
| 85 | if (++queryCount >= queryOverflow) { |
| 86 | cleanup(); |
| 87 | } |
| 88 | Entry entry = entryFor(key); |
| 89 | if (entry != null) { |
| 90 | entry.setTimestamp(System.currentTimeMillis()); |
| 91 | entry.setVal(val); |
| 92 | } else { |
| 93 | map.put(key, new Entry(System.currentTimeMillis(), val)); |
| 94 | } |
| 95 | } |
| 96 | |
| 97 | synchronized void clear() { |
| 98 | map.clear(); |
| 99 | } |
| 100 | |
| 101 | private Entry entryFor(String key) { |
| 102 | Entry entry = (Entry) map.get(key); |
| 103 | if (entry != null) { |
| 104 | long delta = System.currentTimeMillis() - entry.timestamp(); |
| 105 | if (delta < 0 || delta >= millisUntilExpiration) { |
| 106 | map.remove(key); |
| 107 | entry = null; |
| 108 | } |
| 109 | } |
| 110 | return entry; |
| 111 | } |
| 112 | |
| 113 | private void cleanup() { |
| 114 | Set keySet = map.keySet(); |
| 115 | // Avoid ConcurrentModificationExceptions |
| 116 | String[] keys = new String[keySet.size()]; |
| 117 | int i = 0; |
| 118 | for (Iterator iter = keySet.iterator(); iter.hasNext(); ) { |
| 119 | String key = (String) iter.next(); |
| 120 | keys[i++] = key; |
| 121 | } |
| 122 | for (int j = 0; j < keys.length; j++) { |
| 123 | entryFor(keys[j]); |
| 124 | } |
| 125 | queryCount = 0; |
| 126 | } |
| 127 | } |