src/main/java/org/apache/sling/adapter/internal/AdapterManagerImpl.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.sling.adapter.internal;

import static org.apache.sling.api.adapter.AdapterFactory.ADAPTABLE_CLASSES;
import static org.apache.sling.api.adapter.AdapterFactory.ADAPTER_CLASSES;

import java.util.ArrayList;
import java.util.Dictionary;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Properties;
import org.apache.felix.scr.annotations.Property;
import org.apache.felix.scr.annotations.Reference;
import org.apache.felix.scr.annotations.ReferenceCardinality;
import org.apache.felix.scr.annotations.ReferencePolicy;
import org.apache.felix.scr.annotations.Service;
import org.apache.sling.api.SlingConstants;
import org.apache.sling.api.adapter.AdapterFactory;
import org.apache.sling.api.adapter.AdapterManager;
import org.apache.sling.api.resource.SyntheticResource;
import org.apache.sling.commons.osgi.PropertiesUtil;
import org.osgi.framework.Constants;
import org.osgi.framework.ServiceReference;
import org.osgi.service.component.ComponentContext;
import org.osgi.service.event.Event;
import org.osgi.service.event.EventAdmin;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * The <code>AdapterManagerImpl</code> class implements the
 * {@link AdapterManager} interface and is registered as a service for that
 * interface to be used by any clients.
 *
 */
@Component(immediate=true)
@Service
@Properties({
    @Property(name=Constants.SERVICE_DESCRIPTION, value="Sling Adapter Manager"),
    @Property(name=Constants.SERVICE_VENDOR, value="The Apache Software Foundation")

})
@Reference(name="AdapterFactory", referenceInterface=AdapterFactory.class,
cardinality=ReferenceCardinality.OPTIONAL_MULTIPLE, policy=ReferencePolicy.DYNAMIC)
public class AdapterManagerImpl implements AdapterManager {

    private final Logger log = LoggerFactory.getLogger(getClass());

    /**
     * The OSGi <code>ComponentContext</code> to retrieve
     * {@link AdapterFactory} service instances.
     */
    private volatile ComponentContext context;

    /**
     * A list of {@link AdapterFactory} services bound to this manager before
     * the manager has been activated. These bound services will be accessed as
     * soon as the manager is being activated.
     */
    private final List<ServiceReference> boundAdapterFactories = new LinkedList<ServiceReference>();

    /**
     * A map of {@link AdapterFactoryDescriptorMap} instances. The map is
     * indexed by the fully qualified class names listed in the
     * {@link AdapterFactory#ADAPTABLE_CLASSES} property of the
     * {@link AdapterFactory} services.
     *
     * @see AdapterFactoryDescriptorMap
     */
    private final Map<String, AdapterFactoryDescriptorMap> descriptors = new HashMap<String, AdapterFactoryDescriptorMap>();

    /**
     * Matrix of {@link AdapterFactoryDescriptor} instances primarily indexed by the fully
     * qualified name of the class to be adapted and secondarily indexed by the
     * fully qualified name of the class to adapt to (the target class).
     * <p>
     * This cache is built on demand by calling the
     * {@link #getAdapterFactories(Class)} method. It is cleared
     * whenever an adapter factory is registered on unregistered.
     */
    private final ConcurrentMap<String, Map<String, List<AdapterFactoryDescriptor>>> factoryCache
    = new ConcurrentHashMap<String, Map<String, List<AdapterFactoryDescriptor>>>();

    /**
     * The service tracker for the event admin
     */
    @Reference(cardinality=ReferenceCardinality.OPTIONAL_UNARY, policy=ReferencePolicy.DYNAMIC)
    private volatile EventAdmin eventAdmin;

    // ---------- AdapterManager interface -------------------------------------

    /**
     * Returns the adapted <code>adaptable</code> or <code>null</code> if
     * the object cannot be adapted.
     *
     * @see org.apache.sling.api.adapter.AdapterManager#getAdapter(java.lang.Object, java.lang.Class)
     */
    public <AdapterType> AdapterType getAdapter(final Object adaptable,
            final Class<AdapterType> type) {

        // get the adapter factories for the type of adaptable object
        final Map<String, List<AdapterFactoryDescriptor>> factories = getAdapterFactories(adaptable.getClass());

        // get the factory for the target type
        final List<AdapterFactoryDescriptor> descList = factories.get(type.getName());

        if (descList != null && descList.size() > 0) {
            for (AdapterFactoryDescriptor desc : descList) {
                final AdapterFactory factory = desc == null ? null : desc.getFactory();

                // have the factory adapt the adaptable if the factory exists
                if (factory != null) {
                    log.debug("Trying adapter factory {} to map {} to {}",
                            new Object [] { factory, adaptable, type });

                    AdapterType adaptedObject = factory.getAdapter(adaptable, type);
                    if (adaptedObject != null) {
                        log.debug("Using adapter factory {} to map {} to {}",
                                new Object [] { factory, adaptable, type });
                        return adaptedObject;
                    }
                }
            }
        }

        // no factory has been found, so we cannot adapt
        log.debug("No adapter factory found to map {} to {}", adaptable, type);

        return null;
    }

    // ----------- SCR integration ---------------------------------------------

    /**
     * Activate the manager.
     * Bind all already registered factories
     * @param context Component context
     */
    protected void activate(final ComponentContext context) {
        this.context = context;

        // register all adapter factories bound before activation
        final List<ServiceReference> refs;
        synchronized ( this.boundAdapterFactories ) {
            refs = new ArrayList<ServiceReference>(this.boundAdapterFactories);
            boundAdapterFactories.clear();
        }
        for (final ServiceReference reference : refs) {
            registerAdapterFactory(context, reference);
        }

        // final "enable" this manager by setting the instance
        SyntheticResource.setAdapterManager(this);
    }

    /**
     * Deactivate
     * @param context Not used
     */
    protected void deactivate(final ComponentContext context) {
        SyntheticResource.unsetAdapterManager(this);
        this.context = null;
    }

    /**
     * Bind a new adapter factory.
     */
    protected void bindAdapterFactory(final ServiceReference reference) {
        boolean create = true;
        if (context == null) {
            synchronized ( this.boundAdapterFactories ) {
                if (context == null) {
                    boundAdapterFactories.add(reference);
                    create = false;
                }
            }
        }
        if ( create ) {
            registerAdapterFactory(context, reference);
        }
    }

    /**
     * Unbind a adapter factory.
     */
    protected void unbindAdapterFactory(final ServiceReference reference) {
        unregisterAdapterFactory(reference);
    }

    // ---------- unit testing stuff only --------------------------------------

    /**
     * Returns the active adapter factories of this manager.
     * <p>
     * <strong><em>THIS METHOD IS FOR UNIT TESTING ONLY. IT MAY BE REMOVED OR
     * MODIFIED WITHOUT NOTICE.</em></strong>
     */
    Map<String, AdapterFactoryDescriptorMap> getFactories() {
        return descriptors;
    }

    /**
     * Returns the current adapter factory cache.
     * <p>
     * <strong><em>THIS METHOD IS FOR UNIT TESTING ONLY. IT MAY BE REMOVED OR
     * MODIFIED WITHOUT NOTICE.</em></strong>
     */
    Map<String, Map<String, List<AdapterFactoryDescriptor>>> getFactoryCache() {
        return factoryCache;
    }

    /**
     * Unregisters the {@link AdapterFactory} referred to by the service
     * <code>reference</code> from the registry.
     */
    private void registerAdapterFactory(final ComponentContext context,
            final ServiceReference reference) {
        final String[] adaptables = PropertiesUtil.toStringArray(reference.getProperty(ADAPTABLE_CLASSES));
        final String[] adapters = PropertiesUtil.toStringArray(reference.getProperty(ADAPTER_CLASSES));

        if (adaptables == null || adaptables.length == 0 || adapters == null
                || adapters.length == 0) {
            return;
        }

        final AdapterFactoryDescriptor factoryDesc = new AdapterFactoryDescriptor(context,
                reference, adapters);

        for (final String adaptable : adaptables) {
            AdapterFactoryDescriptorMap adfMap = null;
            synchronized ( this.descriptors ) {
                adfMap = descriptors.get(adaptable);
                if (adfMap == null) {
                    adfMap = new AdapterFactoryDescriptorMap();
                    descriptors.put(adaptable, adfMap);
                }
            }
            synchronized ( adfMap ) {
                adfMap.put(reference, factoryDesc);
            }
        }

        // clear the factory cache to force rebuild on next access
        this.factoryCache.clear();

        // send event
        final EventAdmin localEA = this.eventAdmin;
        if ( localEA != null ) {
            final Dictionary<String, Object> props = new Hashtable<String, Object>();
            props.put(SlingConstants.PROPERTY_ADAPTABLE_CLASSES, adaptables);
            props.put(SlingConstants.PROPERTY_ADAPTER_CLASSES, adapters);
            localEA.postEvent(new Event(SlingConstants.TOPIC_ADAPTER_FACTORY_ADDED,
                    props));
        }
    }

    /**
     * Unregisters the {@link AdapterFactory} referred to by the service
     * <code>reference</code> from the registry.
     */
    private void unregisterAdapterFactory(final ServiceReference reference) {
        synchronized ( this.boundAdapterFactories ) {
            boundAdapterFactories.remove(reference);
        }
        final String[] adaptables = PropertiesUtil.toStringArray(reference.getProperty(ADAPTABLE_CLASSES));
        final String[] adapters = PropertiesUtil.toStringArray(reference.getProperty(ADAPTER_CLASSES));

        if (adaptables == null || adaptables.length == 0 || adapters == null
                || adapters.length == 0) {
            return;
        }

        boolean factoriesModified = false;
        AdapterFactoryDescriptorMap adfMap = null;
        for (final String adaptable : adaptables) {
            synchronized ( this.descriptors ) {
                adfMap = this.descriptors.get(adaptable);
            }
            if (adfMap != null) {
                synchronized ( adfMap ) {
                    factoriesModified |= (adfMap.remove(reference) != null);
                }
            }
        }

        // only remove cache if some adapter factories have actually been
        // removed
        if (factoriesModified) {
            this.factoryCache.clear();
        }

        // send event
        final EventAdmin localEA = this.eventAdmin;
        if ( localEA != null ) {
            final Dictionary<String, Object> props = new Hashtable<String, Object>();
            props.put(SlingConstants.PROPERTY_ADAPTABLE_CLASSES, adaptables);
            props.put(SlingConstants.PROPERTY_ADAPTER_CLASSES, adapters);
            localEA.postEvent(new Event(SlingConstants.TOPIC_ADAPTER_FACTORY_REMOVED,
                    props));
        }
    }

    /**
     * Returns the map of adapter factories index by adapter (target) class name
     * for the given adaptable <code>clazz</code>. If no adapter exists for
     * the <code>clazz</code> and empty map is returned.
     *
     * @param clazz The adaptable <code>Class</code> for which to return the
     *            adapter factory map by target class name.
     * @return The map of adapter factories by target class name. The map may be
     *         empty if there is no adapter factory for the adaptable
     *         <code>clazz</code>.
     */
    private Map<String, List<AdapterFactoryDescriptor>> getAdapterFactories(final Class<?> clazz) {
        final String className = clazz.getName();
        Map<String, List<AdapterFactoryDescriptor>> entry = this.factoryCache.get(className);
        if (entry == null) {
            // create entry
            entry = createAdapterFactoryMap(clazz);
            this.factoryCache.put(className, entry);
        }

        return entry;
    }

    /**
     * Creates a new target adapter factory map for the given <code>clazz</code>.
     * First all factories defined to support the adaptable class by
     * registration are taken. Next all factories for the implemented interfaces
     * and finally all base class factories are copied.
     *
     * @param clazz The adaptable <code>Class</code> for which to build the
     *            adapter factory map by target class name.
     * @return The map of adapter factories by target class name. The map may be
     *         empty if there is no adapter factory for the adaptable
     *         <code>clazz</code>.
     */
    private Map<String, List<AdapterFactoryDescriptor>> createAdapterFactoryMap(final Class<?> clazz) {
        final Map<String, List<AdapterFactoryDescriptor>> afm = new HashMap<String, List<AdapterFactoryDescriptor>>();

        // AdapterFactories for this class
        AdapterFactoryDescriptorMap afdMap = null;
        synchronized ( this.descriptors ) {
            afdMap = this.descriptors.get(clazz.getName());
        }
        if (afdMap != null) {
            final List<AdapterFactoryDescriptor> afdSet;
            synchronized ( afdMap ) {
                afdSet = new ArrayList<AdapterFactoryDescriptor>(afdMap.values());
            }
            for (final AdapterFactoryDescriptor afd : afdSet) {
                final String[] adapters = afd.getAdapters();
                for (final String adapter : adapters) {
                    // to handle service ranking, we add to the end of the list or create a new list
                    List<AdapterFactoryDescriptor> factoryDescriptors = afm.get(adapter);
                    if (factoryDescriptors == null) {
                        factoryDescriptors = new ArrayList<AdapterFactoryDescriptor>();
                        afm.put(adapter, factoryDescriptors);
                    }
                    factoryDescriptors.add(afd);
                }
            }
        }

        // AdapterFactories for the interfaces
        final Class<?>[] interfaces = clazz.getInterfaces();
        for (final Class<?> iFace : interfaces) {
            copyAdapterFactories(afm, iFace);
        }

        // AdapterFactories for the super class
        final Class<?> superClazz = clazz.getSuperclass();
        if (superClazz != null) {
            copyAdapterFactories(afm, superClazz);
        }

        return afm;
    }

    /**
     * Copies all adapter factories for the given <code>clazz</code> from the
     * <code>cache</code> to the <code>dest</code> map except for those
     * factories whose target class already exists in the <code>dest</code>
     * map.
     *
     * @param dest The map of target class name to adapter factory into which
     *            additional factories are copied. Existing factories are not
     *            replaced.
     * @param clazz The adaptable class whose adapter factories are considered
     *            for adding into <code>dest</code>.
     */
    private void copyAdapterFactories(final Map<String, List<AdapterFactoryDescriptor>> dest,
            final Class<?> clazz) {

        // get the adapter factories for the adaptable clazz
        final Map<String, List<AdapterFactoryDescriptor>> scMap = getAdapterFactories(clazz);

        // for each target class copy the entry to dest and put it in the list or create the list
        for (Map.Entry<String, List<AdapterFactoryDescriptor>> entry : scMap.entrySet()) {

            List<AdapterFactoryDescriptor> factoryDescriptors = dest.get(entry.getKey());

            if (factoryDescriptors == null) {
                factoryDescriptors = new ArrayList<AdapterFactoryDescriptor>();
                dest.put(entry.getKey(), factoryDescriptors);
            }
            for (AdapterFactoryDescriptor descriptor : entry.getValue()) {
                factoryDescriptors.add(descriptor);
            }
        }
    }
}