Ibatis源码阅读LRU (least recently used) 之LruCacheController

/*

 *  Copyright 2004 Clinton Begin

 *

 *  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 com.ibatis.sqlmap.engine.cache.lru;

 

import java.util.Collections;

import java.util.HashMap;

import java.util.LinkedList;

import java.util.List;

import java.util.Map;

import java.util.Properties;

 

import com.ibatis.sqlmap.engine.cache.CacheController;

import com.ibatis.sqlmap.engine.cache.CacheModel;

 

/**

 * LRU (least recently used) cache controller implementation

 */

public class LruCacheController implements CacheController {

 

  private int cacheSize;

  private Map cache;

  private List keyList;

 

  /**

   * Default constructor

   */

  public LruCacheController() {

    this.cacheSize = 100;

    this.cache = Collections.synchronizedMap(new HashMap());

    this.keyList = Collections.synchronizedList(new LinkedList());

  }

 

  public int getCacheSize() {

    return cacheSize;

  }

 

  public void setCacheSize(int cacheSize) {

    this.cacheSize = cacheSize;

  }

 

  /**

   * Configures the cache

   *

   * @param props Optionally can contain properties [reference-type=WEAK|SOFT|STRONG]

   */

  public void setProperties(Properties props) {

    String size = props.getProperty("cache-size");

    if (size == null) {

      size = props.getProperty("size");

    }

    if (size != null) {

      cacheSize = Integer.parseInt(size);

    }

  }

 

  /**

   * Add an object to the cache

   *

   * @param cacheModel The cacheModel

   * @param key        The key of the object to be cached

   * @param value      The object to be cached

   */

  public void putObject(CacheModel cacheModel, Object key, Object value) {

    cache.put(key, value);

    keyList.add(key);

    if (keyList.size() > cacheSize) {

      try {

        Object oldestKey = keyList.remove(0);

        cache.remove(oldestKey);

      } catch (IndexOutOfBoundsException e) {

        //ignore

      }

    }

  }

 

  /**

   * Get an object out of the cache.

   *

   * @param cacheModel The cache model

   * @param key        The key of the object to be returned

   * @return The cached object (or null)

   */

  public Object getObject(CacheModel cacheModel, Object key) {

    Object result = cache.get(key);

    keyList.remove(key);

    if (result != null) {

      keyList.add(key);

    }

    return result;

  }

 

  public Object removeObject(CacheModel cacheModel, Object key) {

    keyList.remove(key);

    return cache.remove(key);

  }

 

  /**

   * Flushes the cache.

   *

   * @param cacheModel The cache model

   */

  public void flush(CacheModel cacheModel) {

    cache.clear();

    keyList.clear();

  }

 

}