subscriptionservice.java

一个工作流设计及定义的系统,可以直接与数据库结合进行系统工作流程的定义及应用.

/*
 * Copyright (c) 2005, John Mettraux, OpenWFE.org
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 * 
 * . Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.  
 * 
 * . Redistributions in binary form must reproduce the above copyright notice, 
 *   this list of conditions and the following disclaimer in the documentation 
 *   and/or other materials provided with the distribution.
 * 
 * . Neither the name of the "OpenWFE" nor the names of its contributors may be
 *   used to endorse or promote products derived from this software without
 *   specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * $Id$
 */

//
// SubscriptionService.java
//
// [e-mail]
//
// generated with 
// jtmpl 1.1.01 2004/05/19 ([e-mail])
//

package openwfe.org.sub;

import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;

import openwfe.org.AbstractService;
import openwfe.org.ApplicationContext;


/**
 * This service will wait for registrations : other service subscribing for
 * topics by indicating their own service name and giving the Method they
 * want to be notified if anything is posted for the given topic.
 * This allows for an 'event system' or some multiplexing...
 *
 * <p><font size=2>CVS Info :
 * <br>$Author$
 * <br>$Id$ </font>
 *
 * @author [e-mail]
 */
public class SubscriptionService

    extends AbstractService

{

    /*
     * this class was imagined in Schiphol gate F3 and written on 
     * KL 835 to Singapore, near Bob, an english bricklayer heading to
     * Bali. I had seat 21H on a Boeing 747-400.
     */

    private final static org.apache.log4j.Logger log = org.apache.log4j.Logger
        .getLogger(SubscriptionService.class.getName());

    //
    // CONSTANTS & co

    /**
     * This service should be stored in the application context
     * as "subscriptionService" (that's the value that this constant
     * is carrying).
     */
    public final static String S_SUBSCRIPTION_SERVICE
        = "subscriptionService";

    //
    // FIELDS

    private java.util.Map topicMap = new java.util.HashMap();

    //
    // CONSTRUCTORS

    //
    // METHODS

    /**
     * Any service may used to method to 'subscribe' to a given topic.
     * The service has to give its serviceName in the applicationContext 
     * (this is how it will be reached) and the Method instance that as
     * to be used for the notification.
     */
    public void subscribe 
        (final String topicName, 
         final String subscriberServiceName, 
         final Method method)
    {
        java.util.List subscribers = (java.util.List)this.topicMap
            .get(topicName);
        if (subscribers == null)
        {
            subscribers = new java.util.ArrayList(10);
            this.topicMap.put(topicName, subscribers);
        }

        subscribers.add(new TopicMapEntry(subscriberServiceName, method));

        log.debug
            ("subscribe() topic:'"+topicName+"' method:'"+method.getName()+"'");
    }

    /**
     * Emitting services use this method to 'multiplex' the event to
     * the topic. The subscribed services will get notified by this 
     * SubscriptionService.
     */
    public void post
        (final String topicName,
         final Object[] arguments)
    throws
        Throwable
    {
        log.debug("post() topic:'"+topicName+"'");

        java.util.List subscribers = (java.util.List)this.topicMap
            .get(topicName);

        if (subscribers == null) return;

        final java.util.Iterator it = subscribers.iterator();
        while (it.hasNext())
        {
            final TopicMapEntry entry = (TopicMapEntry)it.next();

            final Object service = getContext()
                .lookup(entry.subscriberServiceName);

            try
            {
                entry.method.invoke(service, arguments);
            }
            catch (final IllegalArgumentException iae)
            {
                log.warn
                    ("post() failure for topic:'"+topicName+
                     "' subscriber:'"+entry.subscriberServiceName+"'", 
                     iae);
            }
            catch (final IllegalAccessException iae)
            {
                log.warn
                    ("post() failure for topic:'"+topicName+
                     "' subscriber:'"+entry.subscriberServiceName+"'", 
                     iae);
            }
            catch (final InvocationTargetException ite)
            {
                log.debug
                    ("post() invocation exception for topic:'"+topicName+
                     "' subscriber:'"+entry.subscriberServiceName+"'", 
                     ite.getCause());
                throw ite.getCause();
            }
        }
    }

    //
    // STATIC METHODS

    /**
     * Given an applicationContext, this static method will return 
     * the subscription service (if any) stored in it under the
     * name given by S_SUBSCRIPTION_SERVICE.
     */
    public static SubscriptionService getSubcriptionService 
        (final ApplicationContext context)
    {
        return (SubscriptionService)context.lookup(S_SUBSCRIPTION_SERVICE);
    }

    //
    // INNER CLASSES

    /**
     * Just a struct[ure] class.
     */
    protected static class TopicMapEntry
    {
        public String subscriberServiceName = null;
        public Method method = null;

        public TopicMapEntry 
            (final String subscriberServiceName, final Method method)
        {
            this.subscriberServiceName = subscriberServiceName;
            this.method = method;
        }
    }

}