001    // Copyright 2007, 2009, 2011 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    // http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.ioc.internal.services;
016    
017    import org.apache.tapestry5.ioc.ObjectCreator;
018    import org.apache.tapestry5.ioc.internal.EagerLoadServiceProxy;
019    import org.apache.tapestry5.ioc.internal.ServiceActivityTracker;
020    import org.apache.tapestry5.ioc.services.Status;
021    
022    /**
023     * Invoked from a fabricated service delegate to get or realize (instantiate and configure) the service implementation.
024     * This includes synchronization logic, to prevent multiple threads from attempting to realize the same service at the
025     * same time (a service should be realized only once). The additional interfaces implemented by this class support eager
026     * loading of services (at application startup), and orderly shutdown of proxies.
027     */
028    public class JustInTimeObjectCreator<T> implements ObjectCreator<T>, EagerLoadServiceProxy, Runnable
029    {
030        private final ServiceActivityTracker tracker;
031    
032        private ObjectCreator<T> creator;
033    
034        private volatile T object;
035    
036        private final String serviceId;
037    
038        public JustInTimeObjectCreator(ServiceActivityTracker tracker, ObjectCreator<T> creator, String serviceId)
039        {
040            this.tracker = tracker;
041            this.creator = creator;
042            this.serviceId = serviceId;
043        }
044    
045        /**
046         * Checks to see if the proxy has been shutdown, then invokes {@link ObjectCreator#createObject()} if it has not
047         * already done so.
048         *
049         * @throws IllegalStateException if the registry has been shutdown
050         */
051        public T createObject()
052        {
053            if (object == null)
054                obtainObjectFromCreator();
055    
056            return object;
057        }
058    
059        private synchronized void obtainObjectFromCreator()
060        {
061            if (object != null)
062                return;
063    
064            try
065            {
066                object = creator.createObject();
067    
068                // And if that's successful ...
069    
070                tracker.setStatus(serviceId, Status.REAL);
071    
072                creator = null;
073            } catch (RuntimeException ex)
074            {
075                throw new RuntimeException(ServiceMessages.serviceBuildFailure(serviceId, ex), ex);
076            }
077        }
078    
079        /**
080         * Invokes {@link #createObject()} to force the creation of the underlying service.
081         */
082        public void eagerLoadService()
083        {
084            // Force object creation now
085    
086            createObject();
087        }
088    
089        /**
090         * Invoked when the Registry is shutdown; deletes the instantiated object (if it exists) and replaces
091         * the ObjectCreator with one that throws an IllegalStateException.
092         */
093        public synchronized void run()
094        {
095            creator = new ObjectCreator<T>()
096            {
097                public T createObject()
098                {
099                    throw new IllegalStateException(ServiceMessages.registryShutdown(serviceId));
100                }
101            };
102    
103            object = null;
104        }
105    
106    }