/* * Copyright 2002-2004 Sun Microsystems, Inc. All Rights Reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Sun designates this * particular file as subject to the "Classpath" exception as provided * by Sun in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, * CA 95054 USA or visit www.sun.com if you need additional information or * have any questions. */ package java.io; import java.util.Iterator; import java.util.Map; import java.util.LinkedHashMap; import java.util.Set; class ExpiringCache { private long millisUntilExpiration; private Map map; // Clear out old entries every few queries private int queryCount; private int queryOverflow = 300; private int MAX_ENTRIES = 200; static class Entry { private long timestamp; private String val; Entry(long timestamp, String val) { this.timestamp = timestamp; this.val = val; } long timestamp() { return timestamp; } void setTimestamp(long timestamp) { this.timestamp = timestamp; } String val() { return val; } void setVal(String val) { this.val = val; } } ExpiringCache() { this(30000); } ExpiringCache(long millisUntilExpiration) { this.millisUntilExpiration = millisUntilExpiration; map = new LinkedHashMap() { protected boolean removeEldestEntry(Map.Entry eldest) { return size() > MAX_ENTRIES; } }; } synchronized String get(String key) { if (++queryCount >= queryOverflow) { cleanup(); } Entry entry = entryFor(key); if (entry != null) { return entry.val(); } return null; } synchronized void put(String key, String val) { if (++queryCount >= queryOverflow) { cleanup(); } Entry entry = entryFor(key); if (entry != null) { entry.setTimestamp(System.currentTimeMillis()); entry.setVal(val); } else { map.put(key, new Entry(System.currentTimeMillis(), val)); } } synchronized void clear() { map.clear(); } private Entry entryFor(String key) { Entry entry = (Entry) map.get(key); if (entry != null) { long delta = System.currentTimeMillis() - entry.timestamp(); if (delta < 0 || delta >= millisUntilExpiration) { map.remove(key); entry = null; } } return entry; } private void cleanup() { Set keySet = map.keySet(); // Avoid ConcurrentModificationExceptions String[] keys = new String[keySet.size()]; int i = 0; for (Iterator iter = keySet.iterator(); iter.hasNext(); ) { String key = (String) iter.next(); keys[i++] = key; } for (int j = 0; j < keys.length; j++) { entryFor(keys[j]); } queryCount = 0; } }