[转载]一个简单的内存缓存实现--一段漂亮的代码

package test;

import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public final class SimpleCache<K,V> {

private final Lock lock = new ReentrantLock();
private final int maxCapacity;
private final Map<K,V> eden;
private final Map<K,V> longterm;

public SimpleCache(int maxCapacity) {
this.maxCapacity = maxCapacity;
this.eden = new ConcurrentHashMap<K,V>(maxCapacity);
this.longterm = new WeakHashMap<K,V>(maxCapacity);
}

public V get(K k) {
V v = this.eden.get(k);
if (v == null) {
lock.lock();
try{
v = this.longterm.get(k);
}finally{
lock.unlock();
}
if (v != null) {
this.eden.put(k, v);
}
}
return v;
}

public void put(K k, V v) {
if (this.eden.size() >= maxCapacity) {
lock.lock();
try{
this.longterm.putAll(this.eden);
}finally{
lock.unlock();
}
this.eden.clear();
}
this.eden.put(k, v);
}
}