Mega Code Archive
Cache Map
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/*******************************************************************************
* Copyright (c) 2007, 2008 IBM Corporation and Others
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Hisashi MIYASHITA - initial API and implementation
* Kentarou FUKUDA - initial API and implementation
*******************************************************************************/
import java.util.Iterator;
import java.util.LinkedList;
import java.util.NoSuchElementException;
import java.util.SortedMap;
import java.util.TreeMap;
/**
* Utility class for cache map.
*/
public class CacheMap extends TreeMap<String, Object> {
private static final long serialVersionUID = 6681131647931821052L;
private final int maxSize;
private final int evictSize;
private final LinkedList<Object> accessList = new LinkedList<Object>();
/**
* Constructor of cache map. If the map exceed the maximum size, the
* key/value sets will be removed from map based on specified evict size.
*
* @param maxSize
* maximum size of the map
* @param evictSize
* number of evict object
*/
public CacheMap(int maxSize, int evictSize) {
this.maxSize = maxSize;
this.evictSize = evictSize;
}
private void evict() {
Iterator<Object> it = accessList.iterator();
for (int i = 0; i < evictSize; i++) {
if (!it.hasNext())
return;
Object key = it.next();
this.remove(key);
it.remove();
}
}
private int searchAccessList(Object key) {
return accessList.indexOf(key);
}
private void accessEntry(Object key) {
int idx = searchAccessList(key);
if (idx >= 0) {
accessList.remove(idx);
}
accessList.add(key);
}
public Object put(String key, Object val) {
if (size() >= maxSize)
evict();
accessEntry(key);
return super.put(key, val);
}
public Object get(Object key) {
accessEntry(key);
return super.get(key);
}
/**
* Search a key that starts with the specified prefix from the map, and
* return the value corresponding to the key.
*
* @param prefix
* target prefix
* @return the value whose key starts with prefix, or null if not available
*/
public Object matchStartsWith(String prefix) {
SortedMap<String, Object> smap = super.tailMap(prefix);
Object okey;
try {
okey = smap.firstKey();
} catch (NoSuchElementException e) {
return null;
}
if (!(okey instanceof String))
return null;
String key = (String) okey;
// System.err.println("MSW:" + key + " / " + prefix);
if (!key.startsWith(prefix))
return null;
return super.get(key);
}
}
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