Weak Cache Map : Cache « Development Class « Java

1. Java
2. Development Class
3. Cache

Weak Cache Map

 
/*
 * This file is part of aion-emu <aion-emu.com>.
 *
 *  aion-emu is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  aion-emu 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 for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with aion-emu.  If not, see <http://www.gnu.org/licenses/>.
 */
//package com.aionemu.gameserver.utils.collections.cachemap;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.Map;



/**
 * This class is a simple map implementation for cache usage.<br>
 * <br>
 * Values from the map will be removed after the first garbage collector run if there isn't any strong reference to the
 * value object.
 * 
 * @author Luno
 * 
 */
class WeakCacheMap<K, V> extends AbstractCacheMap<K, V> implements CacheMap<K, V>
{
  /**
   * This class is a {@link WeakReference} with additional responsibility of holding key object
   * 
   * @author Luno
   */
  private class Entry extends WeakReference<V>
  {
    private K  key;

    Entry(K key, V referent, ReferenceQueue<? super V> q)
    {
      super(referent, q);
      this.key = key;
    }

    K getKey()
    {
      return key;
    }
  }

  WeakCacheMap(String cacheName, String valueName)
  {
    super(cacheName, valueName);
  }

  @SuppressWarnings("unchecked")
  @Override
  protected synchronized void cleanQueue()
  {
    Entry en = null;
    while ((en = (Entry) refQueue.poll()) != null)
    {
      K key = en.getKey();
      cacheMap.remove(key);
    }
  }

  @Override
  protected Reference<V> newReference(K key, V value, ReferenceQueue<V> vReferenceQueue)
  {
    return new Entry(key, value, vReferenceQueue);
  }
}

/**
 * Base class for {@link WeakCacheMap} and {@link SoftCacheMap}
 * 
 * @author Luno
 * 
 * @param <K>
 * @param <V>
 */
abstract class AbstractCacheMap<K, V> implements CacheMap<K, V>
{
  protected final String          cacheName;
  protected final String          valueName;

  /** Map storing references to cached objects */
  protected final Map<K, Reference<V>>  cacheMap  = new HashMap<K, Reference<V>>();

  protected final ReferenceQueue<V>    refQueue  = new ReferenceQueue<V>();

  /**
   * @param cacheName
   * @param valueName
   */
  AbstractCacheMap(String cacheName, String valueName)
  {
    this.cacheName = "#CACHE  [" + cacheName + "]#  ";
    this.valueName = valueName;
  }

  /** {@inheritDoc} */
  @Override
  public void put(K key, V value)
  {
    cleanQueue();

    if (cacheMap.containsKey(key))
      throw new IllegalArgumentException("Key: " + key + " already exists in map");

    Reference<V> entry = newReference(key, value, refQueue);

    cacheMap.put(key, entry);
  }

  /** {@inheritDoc} */
  @Override
  public V get(K key)
  {
    cleanQueue();

    Reference<V> reference = cacheMap.get(key);

    if (reference == null)
      return null;

    V res = reference.get();
    return res;
  }

  @Override
  public boolean contains(K key)
  {
    cleanQueue();
    return cacheMap.containsKey(key);
  }

  protected abstract void cleanQueue();

  @Override
  public void remove(K key)
  {
    cacheMap.remove(key);
  }

  protected abstract Reference<V> newReference(K key, V value, ReferenceQueue<V> queue);
}

interface CacheMap<K, V>
{

  /**
   * Adds a pair <key,value> to cache map.<br>
   * <br>
   * 
   * <font color='red'><b>NOTICE:</b> </font> if there is already a value with given id in the map,
   * {@link IllegalArgumentException} will be thrown.
   * 
   * @param key
   * @param value
   */
  public void put(K key, V value);

  /**
   * Returns cached value correlated to given key.
   * 
   * @param key
   * @return V
   */
  public V get(K key);

  /**
   * Checks whether this map contains a value related to given key.
   * @param key
   * @return true or false
   */
  public boolean contains(K key);

  /**
   * Removes an entry from the map, that has given key.
   * @param key
   */
  public void remove(K key);
}

   
  

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