官方文档：http://www.jfaster.org/
我这个是基于2.0.1版本~
package org.jfaster.mango.util.local;
/**
* @author ash
*/
public interface LoadingCache<K, V> {
public V get(K key);
}
package org.jfaster.mango.util.local;
import java.util.concurrent.ConcurrentHashMap;
/**
* @author ash
*/
public class DoubleCheckCache<K, V> implements LoadingCache<K, V> {
private final CacheLoader<K, V> loader;
private final ConcurrentHashMap<K, V> cache = new ConcurrentHashMap<K, V>();
private final ConcurrentHashMap<K, Object> locks = new ConcurrentHashMap<K, Object>();
public DoubleCheckCache(CacheLoader<K, V> loader) {
this.loader = loader;
}
@Override
public V get(K key) {
V value = cache.get(key);
if (value == null) {
synchronized (getLock(key)) {
value = cache.get(key);
if (value == null) {
value = loader.load(key);
if (value != null) {
cache.put(key, value);
}
}
}
}
return value;
}
private Object getLock(K key) {
Object lock = locks.get(key);
if (lock == null) {
lock = new Object();
Object old = locks.putIfAbsent(key, lock);
if (old != null) { // 已经存在lock
lock = old;
}
}
return lock;
}
}
