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ExpiringCache.java
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127 lines (112 loc) · 2.9 KB
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/*
* Copyright (c) 2002, 2011, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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/*
*/
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<String,Entry> 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);
}
@SuppressWarnings("serial")
ExpiringCache(long millisUntilExpiration) {
this.millisUntilExpiration = millisUntilExpiration;
map = new LinkedHashMap<String,Entry>() {
protected boolean removeEldestEntry(Map.Entry<String,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 = 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<String> keySet = map.keySet();
// Avoid ConcurrentModificationExceptions
String[] keys = new String[keySet.size()];
int i = 0;
for (String key: keySet) {
keys[i++] = key;
}
for (int j = 0; j < keys.length; j++) {
entryFor(keys[j]);
}
queryCount = 0;
}
}