    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *     https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.configuration2.builder;
    018
    019import java.util.Collections;
    020import java.util.Map;
    021
    022import org.apache.commons.configuration2.event.Event;
    023import org.apache.commons.configuration2.event.EventListener;
    024import org.apache.commons.configuration2.event.EventListenerList;
    025import org.apache.commons.configuration2.event.EventListenerRegistrationData;
    026import org.apache.commons.configuration2.event.EventType;
    027
    028/**
    029 * <p>
    030 * A specialized parameters implementation for {@link BasicConfigurationBuilder} which allows for a convenient event
    031 * listener initialization.
    032 * </p>
    033 * <p>
    034 * This class offers a fluent interface for registering event listeners. A fully initialized instance can be passed to
    035 * the {@link BasicConfigurationBuilder#configure(BuilderParameters...)} method. All event listeners which have been
    036 * registered at the instance are then copied over to the configuration builder.
    037 * </p>
    038 * <p>
    039 * The code fragment below shows a typical usage scenario:
    040 * </p>
    041 *
    042 * <pre>
    043 * BasicConfigurationBuilder&lt;Configuration&gt; builder = new BasicConfigurationBuilder&lt;Configuration&gt;(PropertiesConfiguration.class)
    044 *     .configure(new EventListenerParameters().addEventListener(ConfigurationEvent.ANY, myListener));
    045 * </pre>
    046 *
    047 * <p>
    048 * In order to support a configuration builder's {@code configure()} method, this class implements the
    049 * {@code BuilderParameters} interface. However, this is just a dummy implementation; no parameters are propagated to
    050 * the builder.
    051 * </p>
    052 *
    053 * @since 2.0
    054 */
    055public class EventListenerParameters implements BuilderParameters, EventListenerProvider {
    056
    057    /** Stores the event listener registrations added to this object. */
    058    private final EventListenerList eventListeners;
    059
    060    /**
    061     * Creates a new instance of {@code EventListenerParameters}.
    062     */
    063    public EventListenerParameters() {
    064        eventListeners = new EventListenerList();
    065    }
    066
    067    /**
    068     * Adds the specified {@code EventListenerRegistrationData} instance to this object.
    069     *
    070     * @param registrationData the registration object to be added
    071     * @param <T> the event type of the contained event listener
    072     * @return a reference to this object for method chaining
    073     */
    074    public <T extends Event> EventListenerParameters addEventListener(final EventListenerRegistrationData<T> registrationData) {
    075        eventListeners.addEventListener(registrationData);
    076        return this;
    077    }
    078
    079    /**
    080     * Adds an event listener of the specified event type to this object.
    081     *
    082     * @param eventType the event type object
    083     * @param listener the event listener
    084     * @param <T> the event type
    085     * @return a reference to this object for method chaining
    086     */
    087    public <T extends Event> EventListenerParameters addEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
    088        eventListeners.addEventListener(eventType, listener);
    089        return this;
    090    }
    091
    092    @Override
    093    public EventListenerList getListeners() {
    094        return eventListeners;
    095    }
    096
    097    /**
    098     * {@inheritDoc} This implementation returns an empty map.
    099     */
    100    @Override
    101    public Map<String, Object> getParameters() {
    102        return Collections.emptyMap();
    103    }
    104}