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 *     http://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}
031 * which allows for a convenient event listener initialization.
032 * </p>
033 * <p>
034 * This class offers a fluent interface for registering event listeners. A fully
035 * initialized instance can be passed to the
036 * {@link BasicConfigurationBuilder#configure(BuilderParameters...)} method. All
037 * event listeners which have been registered at the instance are then copied
038 * over to the configuration builder.
039 * </p>
040 * <p>
041 * The code fragment below shows a typical usage scenario:
042 * </p>
043 *
044 * <pre>
045 * BasicConfigurationBuilder&lt;Configuration&gt; builder =
046 *         new BasicConfigurationBuilder&lt;Configuration&gt;(
047 *                 PropertiesConfiguration.class)
048 *                 .configure(new EventListenerParameters().addEventListener(
049 *                         ConfigurationEvent.ANY, myListener));
050 * </pre>
051 *
052 * <p>
053 * In order to support a configuration builder's {@code configure()} method,
054 * this class implements the {@code BuilderParameters} interface. However, this
055 * is just a dummy implementation; no parameters are propagated to the builder.
056 * </p>
057 *
058 * @version $Id: EventListenerParameters.java 1842194 2018-09-27 22:24:23Z ggregory $
059 * @since 2.0
060 */
061public class EventListenerParameters implements BuilderParameters,
062        EventListenerProvider
063{
064    /** Stores the event listener registrations added to this object. */
065    private final EventListenerList eventListeners;
066
067    /**
068     * Creates a new instance of {@code EventListenerParameters}.
069     */
070    public EventListenerParameters()
071    {
072        eventListeners = new EventListenerList();
073    }
074
075    /**
076     * Adds an event listener of the specified event type to this object.
077     *
078     * @param eventType the event type object
079     * @param listener the event listener
080     * @param <T> the event type
081     * @return a reference to this object for method chaining
082     */
083    public <T extends Event> EventListenerParameters addEventListener(
084            final EventType<T> eventType, final EventListener<? super T> listener)
085    {
086        eventListeners.addEventListener(eventType, listener);
087        return this;
088    }
089
090    /**
091     * Adds the specified {@code EventListenerRegistrationData} instance to this
092     * object.
093     *
094     * @param registrationData the registration object to be added
095     * @param <T> the event type of the contained event listener
096     * @return a reference to this object for method chaining
097     */
098    public <T extends Event> EventListenerParameters addEventListener(
099            final EventListenerRegistrationData<T> registrationData)
100    {
101        eventListeners.addEventListener(registrationData);
102        return this;
103    }
104
105    /**
106     * {@inheritDoc} This implementation returns an empty map.
107     */
108    @Override
109    public Map<String, Object> getParameters()
110    {
111        return Collections.emptyMap();
112    }
113
114    @Override
115    public EventListenerList getListeners()
116    {
117        return eventListeners;
118    }
119}