AbstractProvider.java

/**
 * Copyright (c) 2014-2017 by the respective copyright holders.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 */
package org.eclipse.smarthome.core.common.registry;

import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * {@link AbstractProvider} can be used as base class for {@link Provider} implementations. It supports the registration
 * and notification of listeners.
 *
 * @author Dennis Nobel - Initial contribution
 *
 * @param <E>
 *            type of the provided elements
 */
public abstract class AbstractProvider<E> implements Provider<E> {

    private enum EventType {
        ADDED,
        REMOVED,
        UPDATED;
    }

    protected final Logger logger = LoggerFactory.getLogger(AbstractProvider.class);
    protected List<ProviderChangeListener<E>> listeners = new CopyOnWriteArrayList<ProviderChangeListener<E>>();

    @Override
    public void addProviderChangeListener(ProviderChangeListener<E> listener) {
        listeners.add(listener);
    }

    @Override
    public void removeProviderChangeListener(ProviderChangeListener<E> listener) {
        listeners.remove(listener);
    }

    private void notifyListeners(E oldElement, E element, EventType eventType) {
        for (ProviderChangeListener<E> listener : this.listeners) {
            try {
                switch (eventType) {
                    case ADDED:
                        listener.added(this, element);
                        break;
                    case REMOVED:
                        listener.removed(this, element);
                        break;
                    case UPDATED:
                        listener.updated(this, oldElement, element);
                        break;
                    default:
                        break;
                }
            } catch (Exception ex) {
                logger.error("Could not inform the listener '" + listener + "' about the '" + eventType.name()
                        + "' event!: " + ex.getMessage(), ex);
            }
        }
    }

    private void notifyListeners(E element, EventType eventType) {
        notifyListeners(null, element, eventType);
    }

    protected void notifyListenersAboutAddedElement(E element) {
        notifyListeners(element, EventType.ADDED);
    }

    protected void notifyListenersAboutRemovedElement(E element) {
        notifyListeners(element, EventType.REMOVED);
    }

    protected void notifyListenersAboutUpdatedElement(E oldElement, E element) {
        notifyListeners(oldElement, element, EventType.UPDATED);
    }

}