/*
* Copyright 2005 Thomas Yip, Werner Guttmann, Ralf Joachim
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.castor.cache.simple;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import org.castor.cache.AbstractBaseCache;
import org.castor.cache.CacheAcquireException;
/**
* CountLimited is a count limted least-recently-used <tt>Map</tt>. Every object being
* put in the Map will live until the map is full. If the map is full, the least recently
* used object will be disposed.
* <p>
* The capacity is passed to the cache at initialization by the individual cache property
* <b>capacity</b> which defines the maximum number of objects the cache can hold. If not
* specified a default capacity of 30 objects will be used.
*
* @author <a href="mailto:tyip AT leafsoft DOT com">Thomas Yip</a>
* @author <a href="mailto:werner DOT guttmann AT gmx DOT net">Werner Guttmann</a>
* @author <a href="mailto:ralf DOT joachim AT syscon DOT eu">Ralf Joachim</a>
* @version $Revision$ $Date: 2006-04-25 16:09:10 -0600 (Tue, 25 Apr 2006) $
*/
public final class CountLimited extends AbstractBaseCache {
//--------------------------------------------------------------------------
/** The type of the cache. */
public static final String TYPE = "count-limited";
/** Mapped initialization parameter <code>capacity</code>. */
public static final String PARAM_CAPACITY = "capacity";
/** Default capacity of cache. */
public static final int DEFAULT_CAPACITY = 30;
/** Status of cache entries that can be replaced at next put. */
private static final int LRU_OLD = 0;
/** Status of new cache entries that should not be replaced. */
private static final int LRU_NEW = 1;
/** Map keys to positions. */
private Hashtable<Object, Integer> _mapKeyPos = null;
/** Array of keys. */
private Object[] _keys = null;
/** Array of values. */
private Object[] _values = null;
/** Array with status of the entries. */
private int[] _status = null;
/** Real capacity of this cache. */
private int _capacity = DEFAULT_CAPACITY;
/** Current position to check if value can be replaced at put. */
private int _cur = 0;
//--------------------------------------------------------------------------
// operations for life-cycle management of cache
/**
* {@inheritDoc}
*/
public void initialize(final Properties params) throws CacheAcquireException {
super.initialize(params);
String param = params.getProperty(PARAM_CAPACITY);
try {
if (param != null) { _capacity = Integer.parseInt(param); }
if (_capacity <= 0) { _capacity = DEFAULT_CAPACITY; }
} catch (NumberFormatException ex) {
_capacity = DEFAULT_CAPACITY;
}
_mapKeyPos = new Hashtable<Object, Integer>(_capacity);
_keys = new Object[_capacity];
_values = new Object[_capacity];
_status = new int[_capacity];
}
//--------------------------------------------------------------------------
// getters/setters for cache configuration
/**
* {@inheritDoc}
*/
public String getType() { return TYPE; }
/**
* Get real capacity of this cache.
*
* @return Real capacity of this cache.
*/
public int getCapacity() { return _capacity; }
//--------------------------------------------------------------------------
// query operations of map interface
/**
* {@inheritDoc}
*/
public synchronized int size() { return _mapKeyPos.size(); }
/**
* {@inheritDoc}
*/
public synchronized boolean isEmpty() { return _mapKeyPos.isEmpty(); }
/**
* {@inheritDoc}
*/
public synchronized boolean containsKey(final Object key) {
return _mapKeyPos.containsKey(key);
}
/**
* {@inheritDoc}
*/
public synchronized boolean containsValue(final Object value) {
Iterator<Integer> iter = _mapKeyPos.values().iterator();
while (iter.hasNext()) {
Integer pos = iter.next();
if (pos != null) {
if (value == null) {
if (_values[pos.intValue()] == null) { return true; }
} else {
if (value.equals(_values[pos.intValue()])) { return true; }
}
}
}
return false;
}
/**
* {@inheritDoc}
*/
public synchronized Object get(final Object key) {
Integer pos = _mapKeyPos.get(key);
if (pos == null) { return null; }
int intPos = pos.intValue();
_status[intPos] = LRU_NEW;
return _values[intPos];
}
//--------------------------------------------------------------------------
// modification operations of map interface
/**
* {@inheritDoc}
*/
public synchronized Object put(final Object key, final Object value) {
Integer pos = _mapKeyPos.get(key);
if (pos != null) {
int intPos = pos.intValue();
Object old = _values[intPos];
_values[intPos] = value;
_status[intPos] = LRU_NEW;
return old;
}
// skip to first position with LRU_OLD status.
while (_status[_cur] == LRU_NEW) {
_status[_cur] = LRU_OLD;
_cur++;
if (_cur >= _capacity) { _cur = 0; }
}
if (_keys[_cur] != null) {
pos = _mapKeyPos.remove(_keys[_cur]);
} else {
pos = new Integer(_cur);
}
_keys[_cur] = key;
_values[_cur] = value;
_status[_cur] = LRU_NEW;
_mapKeyPos.put(key, pos);
_cur++;
if (_cur >= _capacity) { _cur = 0; }
return null;
}
/**
* {@inheritDoc}
*/
public synchronized Object remove(final Object key) {
Integer pos = _mapKeyPos.remove(key);
if (pos == null) { return null; }
int intPos = pos.intValue();
Object old = _values[intPos];
_keys[intPos] = null;
_values[intPos] = null;
_status[intPos] = LRU_OLD;
return old;
}
//--------------------------------------------------------------------------
// bulk operations of map interface
/**
* {@inheritDoc}
*/
public void putAll(final Map<? extends Object, ? extends Object> map) {
Iterator<? extends Entry<? extends Object, ? extends Object>> iter;
iter = map.entrySet().iterator();
while (iter.hasNext()) {
Entry<? extends Object, ? extends Object> entry = iter.next();
put(entry.getKey(), entry.getValue());
}
}
/**
* {@inheritDoc}
*/
public synchronized void clear() {
_mapKeyPos.clear();
for (int intPos = 0; intPos < _capacity; intPos++) {
_keys[intPos] = null;
_values[intPos] = null;
_status[intPos] = LRU_OLD;
}
}
//--------------------------------------------------------------------------
// view operations of map interface
/**
* {@inheritDoc}
*/
public synchronized Set<Object> keySet() {
return Collections.unmodifiableSet(_mapKeyPos.keySet());
}
/**
* {@inheritDoc}
*/
public synchronized Collection<Object> values() {
Collection<Object> col = new ArrayList<Object>(_mapKeyPos.size());
Iterator<Integer> iter = _mapKeyPos.values().iterator();
while (iter.hasNext()) {
Integer pos = iter.next();
if (pos != null) {
col.add(_values[pos.intValue()]);
}
}
return Collections.unmodifiableCollection(col);
}
/**
* {@inheritDoc}
*/
public synchronized Set<Entry<Object, Object>> entrySet() {
Map<Object, Object> map = new Hashtable<Object, Object>(_mapKeyPos.size());
Iterator<Entry<Object, Integer>> iter = _mapKeyPos.entrySet().iterator();
while (iter.hasNext()) {
Entry<Object, Integer> entry = iter.next();
Integer pos = entry.getValue();
if (pos != null) {
map.put(entry.getKey(), _values[pos.intValue()]);
}
}
return Collections.unmodifiableSet(map.entrySet());
}
//--------------------------------------------------------------------------
}