/**
* DataCleaner (community edition)
* Copyright (C) 2014 Neopost - Customer Information Management
*
* This copyrighted material is made available to anyone wishing to use, modify,
* copy, or redistribute it subject to the terms and conditions of the GNU
* Lesser General Public License, as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this distribution; if not, write to:
* Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA 02110-1301 USA
*/
package org.datacleaner.components.remote;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Cache for single key value. If a value retrieval throws an exception, this exception is cached instead of
* the value and will be thrown each time the value is requested.
* The cached value never expires, but the exception expires after 1 second.
*<p>
* This class is NOT thread-safe.
*/
public abstract class SingleValueErrorAwareCache<K, V> {
private static final Logger logger = LoggerFactory.getLogger(SingleValueErrorAwareCache.class);
private static final long EXCEPTION_EXPIRATION_TIME = 1000;
private Exception cachedException;
private long cachedExceptionTimestamp;
private V cachedValue;
private K cachedValueKey;
/** The actual value retrieval procedure */
protected abstract V fetch(K key) throws Exception;
/**
* Returns the cached value/exception. If nothing cached, calls {@link #fetch},
* caches the value/exception and returns/throws it.
*/
public V getCachedValue(final K key) throws Exception {
if (cachedValueKey != null) {
if (key.equals(cachedValueKey)) {
if (cachedValue != null) {
logger.debug("Reusing cached output columns, nothing changed");
return cachedValue;
} else if (cachedException != null && System.currentTimeMillis() < (cachedExceptionTimestamp
+ EXCEPTION_EXPIRATION_TIME)) {
logger.debug("Retrowing last exception, nothing changed in last seconds");
throw cachedException;
}
}
}
cachedValueKey = key;
cachedException = null;
cachedValue = null;
try {
return cachedValue = fetch(key);
} catch (final Exception e) {
cachedException = e;
cachedExceptionTimestamp = System.currentTimeMillis();
throw e;
}
}
}