/*
 * Copyright 2005, 2006 Gregory Block
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.castor.cache.hashbelt.reaper;

import java.util.Iterator;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.castor.cache.hashbelt.container.Container;

/**
 * Calls a refresh method on each object in the container; it reinserts any
 * returned object to the front of the expiration system. Useful for any object
 * that needs to be periodically refreshed from source; you are free to return
 * the same object that was called or to replace it with a refreshed version of
 * that object.
 * <p>
 * Note that you must supply the implementation of the refresh method.
 * 
 * @author <a href="mailto:gblock AT ctoforaday DOT com">Gregory Block</a>
 * @version $Revision$ $Date: 2006-04-25 16:09:10 -0600 (Tue, 25 Apr 2006) $
 * @since 1.0
 */
public abstract class RefreshingReaper extends AbstractReaper {
    /** The <a href="http://jakarta.apache.org/commons/logging/">Jakarta Commons
     *  Logging </a> instance used for all logging. */
    private static final Log LOG = LogFactory.getLog(RefreshingReaper.class);

    /**
     * {@inheritDoc}
     */
    public final void handleExpiredContainer(final Container expiredContainer) {
        Iterator<Object> iter = expiredContainer.keyIterator();
        while (iter.hasNext()) {
            Object key = iter.next();
            Object value = expiredContainer.get(key);
            Object refreshed = null;
            
            try {
                refreshed = refresh(value);
            } catch (Throwable t) {
                LOG.error("Caught exception while processing refresh on a cache value; "
                        + "dropping cache value", t);
                if (t instanceof VirtualMachineError) {
                    throw (VirtualMachineError) t;
                }
            }
            
            if (refreshed != null) { getCache().put(key, refreshed); }
        }
    }

    /**
     * Function called to attempt to refresh the object. If refresh was successful,
     * return the refreshed object; if not, return null.
     * 
     * @param objectToBeRefreshed The object to be refreshed.
     * @return The refreshed object, or null if the object could not be refreshed.
     */
    protected abstract Object refresh(final Object objectToBeRefreshed);
}