DataCache.java

/**
 * Copyright (C) 2009 eXo Platform SAS.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software 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 software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.exoplatform.portal.pom.config.cache;

import java.io.Serializable;
import java.util.concurrent.atomic.AtomicLong;

import org.exoplatform.container.ExoContainer;
import org.exoplatform.portal.pom.config.POMSession;
import org.exoplatform.portal.pom.config.POMTask;
import org.exoplatform.portal.pom.config.TaskExecutionDecorator;
import org.exoplatform.portal.pom.config.TaskExecutor;
import org.gatein.common.logging.Logger;
import org.gatein.common.logging.LoggerFactory;

/**
 * @author <a href="mailto:julien.viet@exoplatform.com">Julien Viet</a>
 * @version $Revision$
 */
public class DataCache extends TaskExecutionDecorator {

    /** . */
    private final Logger log = LoggerFactory.getLogger(DataCache.class);

    /** . */
    private final AtomicLong readCount = new AtomicLong();

    /** . */
    private boolean cluster = ExoContainer.getProfiles().contains("cluster");

    public DataCache(TaskExecutor next) {
        super(next);
    }

    public <V> V execute(POMSession session, POMTask<V> task) throws Exception {
        if (task instanceof CacheableDataTask) {
            CacheableDataTask<?, V> loadTask = (CacheableDataTask<?, V>) task;
            switch (loadTask.getAccessMode()) {
                case READ:
                    return read(session, loadTask);
                case CREATE:
                    return create(session, loadTask);
                case WRITE:
                    return write(session, loadTask);
                case DESTROY:
                    return remove(session, loadTask);
                default:
                    throw new UnsupportedOperationException();
            }
        } else {
            return super.execute(session, task);
        }
    }

    private <K extends Serializable, V> V remove(POMSession session, CacheableDataTask<K, V> task) throws Exception {
        K key = task.getKey();
        if (log.isTraceEnabled()) {
            log.trace("Schedule " + key + " for eviction");
        }
        session.scheduleForEviction(key);
        return super.execute(session, task);
    }

    private <K extends Serializable, V> V write(POMSession session, CacheableDataTask<K, V> task) throws Exception {
        K key = task.getKey();
        if (log.isTraceEnabled()) {
            log.trace("Schedule " + key + " for eviction");
        }
        session.scheduleForEviction(key);
        return super.execute(session, task);
    }

    private <K extends Serializable, V> V create(POMSession session, CacheableDataTask<K, V> task) throws Exception {
        K key = task.getKey();
        if (log.isTraceEnabled()) {
            log.trace("Schedule " + key + " for eviction");
        }
        session.scheduleForEviction(key);
        return super.execute(session, task);
    }

    private <K extends Serializable, V> V read(POMSession session, CacheableDataTask<K, V> task) throws Exception {
        K key = task.getKey();

        //
        if (!session.isModified()) {
            Object o = session.getFromCache(key);
            if (log.isTraceEnabled()) {
                log.trace("Retrieved " + o + " for key " + key);
            }

            V v = null;
            if (o != null) {
                if (o == NullObject.get()) {
                    if (log.isTraceEnabled()) {
                        log.trace("Returning null as found null object marker");
                    }
                    return null;
                } else {
                    Class<V> type = task.getValueType();
                    if (type.isInstance(o)) {
                        v = type.cast(o);
                    } else {
                        log.error("Object " + o + " was not of the expected type " + type);
                    }
                }
            }

            //
            if (v != null) {
                if (log.isTraceEnabled()) {
                    log.trace("Returning object " + v + " for key " + key);
                }
                return v;
            } else {
                readCount.incrementAndGet();

                //
                if (log.isTraceEnabled()) {
                    log.trace("Object not found in cache for key " + key + " about to retrieve it");
                }

                //
                v = super.execute(session, task);
                if (log.isTraceEnabled()) {
                    log.trace("Retrieved object " + v + " key " + key + " that will be returned");
                }

                //
                if (!session.isModified()) {
                    if (v == null) {
                        if (log.isTraceEnabled()) {
                            log.trace("Updating cache with null object for key " + key);
                        }
                        session.putInCache(key, NullObject.get());
                    } else {
                        if (log.isTraceEnabled()) {
                            log.trace("Updating cache with object " + v + " for key " + key);
                        }
                        session.putInCache(key, v);
                    }
                }

                //
                return v;
            }
        } else {
            if (log.isTraceEnabled()) {
                log.trace("Session was modified, object for key " + key + " is directly retrieved");
            }

            //
            return super.execute(session, task);
        }
    }

    public long getReadCount() {
        return readCount.longValue();
    }
}