/*
* Copyright 1990-2008 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
*
* This program 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.
*
* This program 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 at /legal/license.txt).
*
* 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 or visit www.sun.com if you need additional
* information or have any questions.
*/
/*
* @(#)ExpiringCache.java 1.6 06/10/10
*/
package java.io;
import java.util.Iterator;
import java.util.Map;
import java.util.HashMap;
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;
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 HashMap();
}
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;
}
}