Как уже упоминалось в предыдущих ответах, то лучше использовать один из популярных кэшей в памяти, как Ehcache, Memcached и т.д.
Но так же, как вы хотели реализовать его на собственном кэше, который имеет объект экспирации функцию и меньше времени, я попытался реализовать его вот так - (любые отзывы об испытаниях/предложения очень ценятся).
public class ObjectCache<K, V> {
private volatile boolean shutdown;
private final long maxObjects;
private final long timeToLive;
private final long removalThreadRunDelay;
private final long objectsToRemovePerRemovalThreadRun;
private final AtomicLong objectsCount;
private final Map<K, CacheEntryWrapper> cachedDataStore;
private final BlockingQueue<CacheEntryReference> queue;
private final Object lock = new Object();
private ScheduledExecutorService executorService;
public ObjectCache(long maxObjects, long timeToLive, long removalThreadRunDelay, long objectsToRemovePerRemovalThreadRun) {
this.maxObjects = maxObjects;
this.timeToLive = timeToLive;
this.removalThreadRunDelay = removalThreadRunDelay;
this.objectsToRemovePerRemovalThreadRun = objectsToRemovePerRemovalThreadRun;
this.objectsCount = new AtomicLong(0);
this.cachedDataStore = new HashMap<K, CacheEntryWrapper>();
this.queue = new LinkedBlockingQueue<CacheEntryReference>();
}
public void put(K key, V value) {
if (key == null || value == null) {
throw new IllegalArgumentException("Key and Value both should be not null");
}
if (objectsCount.get() + 1 > maxObjects) {
throw new RuntimeException("Max objects limit reached. Can not store more objects in cache.");
}
// create a value wrapper and add it to data store map
CacheEntryWrapper entryWrapper = new CacheEntryWrapper(key, value);
synchronized (lock) {
cachedDataStore.put(key, entryWrapper);
}
// add the cache entry reference to queue which will be used by removal thread
queue.add(entryWrapper.getCacheEntryReference());
objectsCount.incrementAndGet();
// start the removal thread if not started already
if (executorService == null) {
synchronized (lock) {
if (executorService == null) {
executorService = Executors.newSingleThreadScheduledExecutor();
executorService.scheduleWithFixedDelay(new CacheEntryRemover(), 0, removalThreadRunDelay, TimeUnit.MILLISECONDS);
}
}
}
}
public V get(K key) {
if (key == null) {
throw new IllegalArgumentException("Key can not be null");
}
CacheEntryWrapper entryWrapper;
synchronized (lock) {
entryWrapper = cachedDataStore.get(key);
if (entryWrapper != null) {
// reset the last access time
entryWrapper.resetLastAccessedTime();
// reset the reference (so the weak reference is cleared)
entryWrapper.resetCacheEntryReference();
// add the new reference to queue
queue.add(entryWrapper.getCacheEntryReference());
}
}
return entryWrapper == null ? null : entryWrapper.getValue();
}
public void remove(K key) {
if (key == null) {
throw new IllegalArgumentException("Key can not be null");
}
CacheEntryWrapper entryWrapper;
synchronized (lock) {
entryWrapper = cachedDataStore.remove(key);
if (entryWrapper != null) {
// reset the reference (so the weak reference is cleared)
entryWrapper.resetCacheEntryReference();
}
}
objectsCount.decrementAndGet();
}
public void shutdown() {
shutdown = true;
executorService.shutdown();
queue.clear();
cachedDataStore.clear();
}
public static void main(String[] args) throws Exception {
ObjectCache<Long, Long> cache = new ObjectCache<>(1000000, 60000, 1000, 1000);
long i = 0;
while (i++ < 10000) {
cache.put(i, i);
}
i = 0;
while(i++ < 100) {
Thread.sleep(1000);
System.out.println("Data store size: " + cache.cachedDataStore.size() + ", queue size: " + cache.queue.size());
}
cache.shutdown();
}
private class CacheEntryRemover implements Runnable {
public void run() {
if (!shutdown) {
try {
int count = 0;
CacheEntryReference entryReference;
while ((entryReference = queue.peek()) != null && count++ < objectsToRemovePerRemovalThreadRun) {
long currentTime = System.currentTimeMillis();
CacheEntryWrapper cacheEntryWrapper = entryReference.getWeakReference().get();
if (cacheEntryWrapper == null || !cachedDataStore.containsKey(cacheEntryWrapper.getKey())) {
queue.poll(100, TimeUnit.MILLISECONDS); // remove the reference object from queue as value is removed from cache
} else if (currentTime - cacheEntryWrapper.getLastAccessedTime().get() > timeToLive) {
synchronized (lock) {
// get the cacheEntryWrapper again just to find if put() has overridden the same key or remove() has removed it already
CacheEntryWrapper newCacheEntryWrapper = cachedDataStore.get(cacheEntryWrapper.getKey());
// poll the queue if -
// case 1 - value is removed from cache
// case 2 - value is overridden by new value
// case 3 - value is still in cache but it is old now
if (newCacheEntryWrapper == null || newCacheEntryWrapper != cacheEntryWrapper || currentTime - cacheEntryWrapper.getLastAccessedTime().get() > timeToLive) {
queue.poll(100, TimeUnit.MILLISECONDS);
newCacheEntryWrapper = newCacheEntryWrapper == null ? cacheEntryWrapper : newCacheEntryWrapper;
if (currentTime - newCacheEntryWrapper.getLastAccessedTime().get() > timeToLive) {
remove(newCacheEntryWrapper.getKey());
}
} else {
break; // try next time
}
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
private class CacheEntryWrapper {
private K key;
private V value;
private AtomicLong lastAccessedTime;
private CacheEntryReference cacheEntryReference;
public CacheEntryWrapper(K key, V value) {
this.key = key;
this.value = value;
this.lastAccessedTime = new AtomicLong(System.currentTimeMillis());
this.cacheEntryReference = new CacheEntryReference(this);
}
public K getKey() {
return key;
}
public V getValue() {
return value;
}
public AtomicLong getLastAccessedTime() {
return lastAccessedTime;
}
public CacheEntryReference getCacheEntryReference() {
return cacheEntryReference;
}
public void resetLastAccessedTime() {
lastAccessedTime.set(System.currentTimeMillis());
}
public void resetCacheEntryReference() {
cacheEntryReference.clear();
cacheEntryReference = new CacheEntryReference(this);
}
}
private class CacheEntryReference {
private WeakReference<CacheEntryWrapper> weakReference;
public CacheEntryReference(CacheEntryWrapper entryWrapper) {
this.weakReference = new WeakReference<CacheEntryWrapper>(entryWrapper);
}
public WeakReference<CacheEntryWrapper> getWeakReference() {
return weakReference;
}
public void clear() {
weakReference.clear();
}
}
}
+1 для Guache's CacheBuilder. Я считаю это наиболее подходящим предложением, поскольку он прост в использовании и облегчен. –
Активировано, потому что OP не запрашивает ферму серверов кеша, но для структуры кэша в памяти. Guava 'Cache' лучше всего подходит. –
Как установить истечение срока действия одного объекта с помощью guava? – sodik