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package com.sun.faces.util;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.logging.Logger;
/**
* A concurrent caching mechanism.
*/
public class Cache<K, V> {
// Log instance for this class
private static final Logger LOGGER = FacesLogger.UTIL.getLogger();
/**
* Factory interface for creating various cacheable objects.
*/
public interface Factory<K,V> {
V newInstance(final K arg) throws InterruptedException;
} // END Factory
private final ConcurrentMap<K,V> cache =
new ConcurrentHashMap<>();
private final Factory<K,V> factory;
// -------------------------------------------------------- Constructors
/**
* Constructs this cache using the specified <code>Factory</code>.
* @param factory
*/
public Cache(Factory<K,V> factory) {
this.factory = factory;
}
// ------------------------------------------------------ Public Methods
/**
* If a value isn't associated with the specified key, a new
* {@link java.util.concurrent.Callable} will be created wrapping the <code>Factory</code>
* specified via the constructor and passed to a {@link java.util.concurrent.FutureTask}. This task
* will be passed to the backing ConcurrentMap. When {@link java.util.concurrent.FutureTask#get()}
* is invoked, the Factory will return the new Value which will be cached
* by the {@link java.util.concurrent.FutureTask}.
*
* @param key the key the value is associated with
* @return the value for the specified key, if any
*/
public V get(final K key) {
V result = cache.get(key);
if (result == null)
{
try
{
result = factory.newInstance(key);
}
catch (InterruptedException ie)
{
// will never happen. Just for testing
throw new RuntimeException(ie);
}
// put could be used instead if it didn't matter whether we replaced
// an existing entry
V oldResult = cache.putIfAbsent(key, result);
if (oldResult != null)
result = oldResult;
}
return result;
}
public V remove(final K key) {
return cache.remove(key);
}
} // END Cache