ASF_20_SRC_AUTO/src/blocks/jms/java/org/apache/cocoon/components/jms/JMSEventListener.java

/*
 * Copyright 1999-2004 The Apache Software Foundation.
 * 
 * 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.apache.cocoon.components.jms;

import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.naming.NamingException;

import org.apache.avalon.framework.CascadingException;
import org.apache.avalon.framework.activity.Disposable;
import org.apache.avalon.framework.activity.Initializable;
import org.apache.avalon.framework.logger.AbstractLogEnabled;
import org.apache.avalon.framework.parameters.ParameterException;
import org.apache.avalon.framework.parameters.Parameterizable;
import org.apache.avalon.framework.parameters.Parameters;
import org.apache.avalon.framework.service.ServiceException;
import org.apache.avalon.framework.service.ServiceManager;
import org.apache.avalon.framework.service.Serviceable;
import org.apache.avalon.framework.thread.ThreadSafe;
import org.apache.cocoon.caching.EventAware;
import org.apache.cocoon.caching.validity.Event;
import org.apache.cocoon.caching.validity.NamedEvent;

/**
 * JMS listener will notify an {@link org.apache.cocoon.caching.EventAware} component
 * of external events. This could be used for example to do external cache invalidation.
 * Configuration parameters default to <a href="http://openjms.sf.net">OpenJMS</a> demo
 * installation on localhost using "topic1".
 * 
 * <p>Parameters:</p>
 * <table>
 *  <tbody>
 *   <tr><td>connection      </td><td>(required, no default)</td></tr>
 *   <tr><td>component       </td><td>(required, no default)</td></tr>
 *   <tr><td>message-selector</td><td>("")</td></tr>
 *  </tbody>
 * </table>
 * 
 * @version CVS $Id: JMSEventListener.java,v 1.10 2004/03/05 13:01:57 bdelacretaz Exp $
 * @author <a href="mailto:chaul@apache.org">chaul</a>
 */
public class JMSEventListener
    extends AbstractLogEnabled
    implements Serviceable, Parameterizable, MessageListener, Initializable, Disposable, ThreadSafe {

    protected String selector = "";

    protected ServiceManager manager;

    protected String serviceName = null;
    protected EventAware service = null;
    protected String connectionName = null;
    protected JMSConnection connection = null;

    /*
     * @see org.apache.avalon.framework.service.Serviceable#service(org.apache.avalon.framework.service.ServiceManager)
     */
    public void service(ServiceManager manager) throws ServiceException {
        this.manager = manager;
    }

    /* 
     * @see org.apache.avalon.framework.parameters.Parameterizable#parameterize(org.apache.avalon.framework.parameters.Parameters)
     */
    public void parameterize(Parameters parameters) throws ParameterException {

        this.connectionName = parameters.getParameter("connection");
        this.serviceName = parameters.getParameter("component");
        this.selector = parameters.getParameter("message-selector", this.selector);
    }
    
    public void initialize() {

        try {
			this.connection = (JMSConnection) this.manager.lookup(JMSConnection.ROLE+"/"+this.connectionName);
            this.connection.registerListener(this, this.selector);
        } catch (ServiceException e) {
			if (getLogger().isWarnEnabled()) {
                getLogger().warn("Could not obtain JMSConnection", e);
			}
		} catch (JMSException e) {
            if (getLogger().isWarnEnabled()) {
                getLogger().warn("Could not obtain JMSConnection", e);
            }
		} catch (NamingException e) {
            if (getLogger().isWarnEnabled()) {
                getLogger().warn("Could not obtain JMSConnection", e);
            }
		} catch (CascadingException e) {
            if (getLogger().isWarnEnabled()) {
                getLogger().warn("Could not obtain JMSConnection", e);
            }
		}
    }

    /* (non-Javadoc)
     * @see org.apache.avalon.framework.activity.Disposable#dispose()
     */
    public void dispose() {
        if (this.manager != null){
            this.manager.release(connection);
            this.manager.release(service);
        }
    }
    
    /* 
     * @see javax.jms.MessageListener#onMessage(javax.jms.Message)
     */
    public synchronized void onMessage(Message message) {
        EventAware service = this.service;
        try {
            if (service == null) {
                service = (EventAware) this.manager.lookup(this.serviceName);
            }
            Event[] events = eventsFromMessage(message);
            for (int i = 0; i < events.length; i++) {
                if (this.getLogger().isDebugEnabled())
                    this.getLogger().debug(
                        "Notifying "
                            + this.serviceName
                            + " of "
                            + events[i]);
                service.processEvent(events[i]);
            }
        } catch (ServiceException e) {
            if (this.getLogger().isErrorEnabled()) {
                this.getLogger().error(
                    "Could not obtain " + this.serviceName + " from component manager.",
                    e);
            }
        } finally {
            if (service instanceof ThreadSafe) {
                this.service = service;
            } else {
                this.manager.release(service);
            }
        }
    }
    
    /**
     * Convert the message contents to (a series of) cache event. The default implementation 
     * assumes that the message contains the trigger name, a '|', and a table name. 
     * It extracts the tablename and creates a NamedEvent with it. 
     * Override this method to provide your own message to event mappings.
     * 
     * @param message  the JMS message.
     * @return  the cache event.
     */
    protected Event[] eventsFromMessage(Message message) {
        String name = message.toString();
        int pos = name.indexOf('|');
        return new Event[] { new NamedEvent(name.substring(pos + 1)) };
    }

}