/*
* JEF - Copyright 2009-2010 Jiyi (mr.jiyi@gmail.com)
*
* 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 jef.common;
import java.util.LinkedHashMap;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 用于存放固定大小缓存的Map，线程安全（仅限get,set两个方法）
* @author Administrator
* @param <K>
* @param <V>
*/
public class CacheMap<K, V> extends LinkedHashMap<K, V> {
private static final long serialVersionUID = 2428383992533927687L;
private static final float DEFAULT_LOAD_FACTOR = 1f;
/**
*<B>关于使用互斥锁而不是读写锁的原因</B>
* 这个类作为缓存，为了防止将最近访问过的对象清除出去，所以要记录访问顺序
* 由于缓存表在每次get操作时要记录访问顺序(accessOrder = true)，修改内部链表结构，因此即使是get操作也是不应当并发的。
*
*/
private final Lock lock = new ReentrantLock();
private final int maxCapacity;
public CacheMap(int size) {
super(size, DEFAULT_LOAD_FACTOR, true);
this.maxCapacity = size;
}
protected final boolean removeEldestEntry(java.util.Map.Entry<K, V> eldest) {
return size() > maxCapacity;
}
public V get(Object key) {
try {
lock.lock();
return super.get(key);
} finally {
lock.unlock();
}
}
public V put(K key, V value) {
try {
lock.lock();
return super.put(key, value);
} finally {
lock.unlock();
}
}
}