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 * @since 2.0
059 */
060public class EventListenerParameters implements BuilderParameters,
061        EventListenerProvider
062{
063    /** Stores the event listener registrations added to this object. */
064    private final EventListenerList eventListeners;
065
066    /**
067     * Creates a new instance of {@code EventListenerParameters}.
068     */
069    public EventListenerParameters()
070    {
071        eventListeners = new EventListenerList();
072    }
073
074    /**
075     * Adds an event listener of the specified event type to this object.
076     *
077     * @param eventType the event type object
078     * @param listener the event listener
079     * @param <T> the event type
080     * @return a reference to this object for method chaining
081     */
082    public <T extends Event> EventListenerParameters addEventListener(
083            final EventType<T> eventType, final EventListener<? super T> listener)
084    {
085        eventListeners.addEventListener(eventType, listener);
086        return this;
087    }
088
089    /**
090     * Adds the specified {@code EventListenerRegistrationData} instance to this
091     * object.
092     *
093     * @param registrationData the registration object to be added
094     * @param <T> the event type of the contained event listener
095     * @return a reference to this object for method chaining
096     */
097    public <T extends Event> EventListenerParameters addEventListener(
098            final EventListenerRegistrationData<T> registrationData)
099    {
100        eventListeners.addEventListener(registrationData);
101        return this;
102    }
103
104    /**
105     * {@inheritDoc} This implementation returns an empty map.
106     */
107    @Override
108    public Map<String, Object> getParameters()
109    {
110        return Collections.emptyMap();
111    }
112
113    @Override
114    public EventListenerList getListeners()
115    {
116        return eventListeners;
117    }
118}