src/main/java/org/apache/onami/persist/ContainerManagedEntityManagerFactoryProvider.java

package org.apache.onami.persist;

/*
 * 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.
 */

import javax.inject.Inject;
import javax.inject.Singleton;

import javax.persistence.EntityManagerFactory;

import static org.apache.onami.persist.Preconditions.checkNotNull;

/**
 * Implementation of {@link PersistenceService} and {@link EntityManagerFactoryProvider} for
 * container managed persistence units.
 */
@Singleton
class ContainerManagedEntityManagerFactoryProvider
    implements EntityManagerFactoryProvider, PersistenceService
{

    /**
     * The source for retrieving the entity manager factory instance.
     */
    private final EntityManagerFactorySource emfSource;

    /**
     * Currently active entity manager factory.
     * Is {@code null} when the persistence service is not running.
     */
    private EntityManagerFactory emf;

    /**
     * Constructor.
     *
     * @param emfSource the source for the  {@link EntityManagerFactory}. Must not be {@code null}.
     */
    @Inject
    ContainerManagedEntityManagerFactoryProvider( EntityManagerFactorySource emfSource )
    {
        this.emfSource = checkNotNull( emfSource, "emfSource is mandatory!" );
    }

    /**
     * {@inheritDoc}
     */
    // @Override
    public EntityManagerFactory get()
    {
        if ( isRunning() )
        {
            return emf;
        }

        throw new IllegalStateException( "PersistenceService is not running." );
    }

    /**
     * {@inheritDoc}
     */
    // @Override
    public void start()
    {
        if ( isRunning() )
        {
            throw new IllegalStateException( "PersistenceService is already running." );
        }

        emf = emfSource.getEntityManagerFactory();
    }

    /**
     * {@inheritDoc}
     */
    // @Override
    public boolean isRunning()
    {
        return null != emf;
    }

    /**
     * {@inheritDoc}
     */
    // @Override
    public void stop()
    {
        emf = null;
        // the entity manager factory must NOT be closed:
        // - it was created by the container and it is therefore the responsibility of the container to close it
        // - we cannot know if another part of the application has obtained the same instance
    }

}