com.b2international.snowowl.datastore.server.CDOChangeProcessorFactoryManager.java Source code

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Here is the source code for com.b2international.snowowl.datastore.server.CDOChangeProcessorFactoryManager.java

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/*
 * Copyright 2011-2015 B2i Healthcare Pte Ltd, http://b2i.sg
 * 
 * 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 com.b2international.snowowl.datastore.server;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Collection;
import java.util.Collections;

import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.Platform;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.Preconditions;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.Multimap;
import com.google.common.collect.Multimaps;

/**
 * Class for loading and managing CDO specific change processor factories via extension points.
 * @see CDOChangeProcessorFactory
 */
public enum CDOChangeProcessorFactoryManager {

    /**
     * The manager instance.
     */
    INSTANCE;

    /**
     * Unique identifier of the change processor factory extension point. <br><br>ID: {@value}
     */
    public static final String CHANGE_PROCESSOR_FACTORY_EXTENSION_POINT_ID = "com.b2international.snowowl.datastore.changeProcessorFactory";

    private static final String CLASS_ATTRIBUTE = "class";
    private static final String ID_ATTRIBUTE = "id";
    private static final String REPOSITORY_NAME_ATTRIBUTE = "repositoryUuid";
    private static final Logger LOGGER = LoggerFactory.getLogger(CDOChangeProcessorFactoryManager.class);

    /**Mapping between the repository names (UUIDs) and the associated CDO change processor factories.*/
    private Multimap<String, CDOChangeProcessorFactory> factories;

    /**
     * Returns with the number of all available and registered CDO change processors.
     * @return the number of CDO change processors registered via Eclipse extension points.
     */
    public int getCDOChangeProcessorCount() {
        return getFactories().size();
    }

    /**
     * Returns with a maps of all available {@link CDOChangeProcessorFactory} instances grouped by the repository UUIDs.
     * @return a collection of change processor factories.
     */
    public Multimap<String, CDOChangeProcessorFactory> getFactories() {
        if (null == factories) {
            synchronized (CDOChangeProcessorFactoryManager.class) {
                if (null == factories) {
                    factories = Multimaps.unmodifiableMultimap(loadFactories());
                }
            }
        }
        return factories;
    }

    /**
     * Returns with a collection of CDO change processor factories working on given repository as a write access handler. 
     * @param repositoryName the unique name (UUID) of the repository.
     * @return a collection of CDO change processor factories.
     */
    public Collection<CDOChangeProcessorFactory> getFactories(final String repositoryName) {
        final Collection<CDOChangeProcessorFactory> $ = getFactories().asMap()
                .get(Preconditions.checkNotNull(repositoryName, "Repository name argument cannot be null."));
        return null == $ ? Collections.<CDOChangeProcessorFactory>emptySet()
                : Collections.unmodifiableCollection($);
    }

    /*loads the change processor factories via extension points*/
    private Multimap<String, CDOChangeProcessorFactory> loadFactories() {
        final Multimap<String, CDOChangeProcessorFactory> factories = HashMultimap.create();
        for (final IConfigurationElement element : getChangeProcessorFactoryExtensions()) {

            final String id = element.getAttribute(ID_ATTRIBUTE);
            final String repositoryName = element.getAttribute(REPOSITORY_NAME_ATTRIBUTE);
            Preconditions.checkNotNull(repositoryName,
                    "Repository name should be specified for CDO change processor factory. ID: " + id);

            final CDOChangeProcessorFactory factory = createFactorySafe(element);
            if (null != factory) {
                factories.put(repositoryName, factory);
            }
        }

        return factories;
    }

    /*returns with the configuration elements to the change processor extension point*/
    private IConfigurationElement[] getChangeProcessorFactoryExtensions() {
        return Platform.getExtensionRegistry()
                .getConfigurationElementsFor(CHANGE_PROCESSOR_FACTORY_EXTENSION_POINT_ID);
    }

    /*creates the executable change processor factories from the specified configuration element. returns with null if error occurred.*/
    private CDOChangeProcessorFactory createFactorySafe(final IConfigurationElement element) {
        checkNotNull(element, "Configuration element argument should not be null.");
        try {
            final Object executableExtension = element.createExecutableExtension(CLASS_ATTRIBUTE);
            if (executableExtension instanceof CDOChangeProcessorFactory) {
                return (CDOChangeProcessorFactory) executableExtension;
            } else {
                throw new Exception("Executable extension should be a CDO change processor but was: "
                        + executableExtension.getClass());
            }
        } catch (final Exception e) {
            final String id = element.getAttribute(ID_ATTRIBUTE);
            LOGGER.error("Error while creating executable CDO change processor factory with ID: '"
                    + String.valueOf(id) + "'.", e);
            return null;
        }
    }

}