    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.event;
    018
    019import java.util.Collection;
    020import java.util.Collections;
    021import java.util.LinkedList;
    022import java.util.List;
    023
    024/**
    025 * <p>
    026 * A base class for objects that can generate configuration events.
    027 * </p>
    028 * <p>
    029 * This class implements functionality for managing a set of event listeners that can be notified when an event occurs.
    030 * It can be extended by configuration classes that support the event mechanism. In this case these classes only need to
    031 * call the {@code fireEvent()} method when an event is to be delivered to the registered listeners.
    032 * </p>
    033 * <p>
    034 * Adding and removing event listeners can happen concurrently to manipulations on a configuration that cause events.
    035 * The operations are synchronized.
    036 * </p>
    037 * <p>
    038 * With the {@code detailEvents} property the number of detail events can be controlled. Some methods in configuration
    039 * classes are implemented in a way that they call other methods that can generate their own events. One example is the
    040 * {@code setProperty()} method that can be implemented as a combination of {@code clearProperty()} and
    041 * {@code addProperty()}. With {@code detailEvents} set to <b>true</b>, all involved methods will generate events (i.e.
    042 * listeners will receive property set events, property clear events, and property add events). If this mode is turned
    043 * off (which is the default), detail events are suppressed, so only property set events will be received. Note that the
    044 * number of received detail events may differ for different configuration implementations.
    045 * {@link org.apache.commons.configuration2.BaseHierarchicalConfiguration BaseHierarchicalConfiguration} for instance
    046 * has a custom implementation of {@code setProperty()}, which does not generate any detail events.
    047 * </p>
    048 * <p>
    049 * In addition to &quot;normal&quot; events, error events are supported. Such events signal an internal problem that
    050 * occurred during access of properties. They are handled via the regular {@link EventListener} interface, but there are
    051 * special event types defined by {@link ConfigurationErrorEvent}. The {@code fireError()} method can be used by derived
    052 * classes to send notifications about errors to registered observers.
    053 * </p>
    054 *
    055 * @since 1.3
    056 */
    057public class BaseEventSource implements EventSource {
    058    /** The list for managing registered event listeners. */
    059    private EventListenerList eventListeners;
    060
    061    /** A lock object for guarding access to the detail events counter. */
    062    private final Object lockDetailEventsCount = new Object();
    063
    064    /** A counter for the detail events. */
    065    private int detailEvents;
    066
    067    /**
    068     * Creates a new instance of {@code BaseEventSource}.
    069     */
    070    public BaseEventSource() {
    071        initListeners();
    072    }
    073
    074    /**
    075     * Gets a collection with all event listeners of the specified event type that are currently registered at this
    076     * object.
    077     *
    078     * @param eventType the event type object
    079     * @param <T> the event type
    080     * @return a collection with the event listeners of the specified event type (this collection is a snapshot of the
    081     *         currently registered listeners; it cannot be manipulated)
    082     */
    083    public <T extends Event> Collection<EventListener<? super T>> getEventListeners(final EventType<T> eventType) {
    084        final List<EventListener<? super T>> result = new LinkedList<>();
    085        eventListeners.getEventListeners(eventType).forEach(result::add);
    086        return Collections.unmodifiableCollection(result);
    087    }
    088
    089    /**
    090     * Gets a list with all {@code EventListenerRegistrationData} objects currently contained for this event source. This
    091     * method allows access to all registered event listeners, independent on their type.
    092     *
    093     * @return a list with information about all registered event listeners
    094     */
    095    public List<EventListenerRegistrationData<?>> getEventListenerRegistrations() {
    096        return eventListeners.getRegistrations();
    097    }
    098
    099    /**
    100     * Returns a flag whether detail events are enabled.
    101     *
    102     * @return a flag if detail events are generated
    103     */
    104    public boolean isDetailEvents() {
    105        return checkDetailEvents(0);
    106    }
    107
    108    /**
    109     * Determines whether detail events should be generated. If enabled, some methods can generate multiple update events.
    110     * Note that this method records the number of calls, i.e. if for instance {@code setDetailEvents(false)} was called
    111     * three times, you will have to invoke the method as often to enable the details.
    112     *
    113     * @param enable a flag if detail events should be enabled or disabled
    114     */
    115    public void setDetailEvents(final boolean enable) {
    116        synchronized (lockDetailEventsCount) {
    117            if (enable) {
    118                detailEvents++;
    119            } else {
    120                detailEvents--;
    121            }
    122        }
    123    }
    124
    125    @Override
    126    public <T extends Event> void addEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
    127        eventListeners.addEventListener(eventType, listener);
    128    }
    129
    130    @Override
    131    public <T extends Event> boolean removeEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
    132        return eventListeners.removeEventListener(eventType, listener);
    133    }
    134
    135    /**
    136     * Removes all registered event listeners.
    137     */
    138    public void clearEventListeners() {
    139        eventListeners.clear();
    140    }
    141
    142    /**
    143     * Removes all registered error listeners.
    144     *
    145     * @since 1.4
    146     */
    147    public void clearErrorListeners() {
    148        eventListeners.getRegistrationsForSuperType(ConfigurationErrorEvent.ANY).forEach(eventListeners::removeEventListener);
    149    }
    150
    151    /**
    152     * Copies all event listener registrations maintained by this object to the specified {@code BaseEventSource} object.
    153     *
    154     * @param source the target source for the copy operation (must not be <b>null</b>)
    155     * @throws IllegalArgumentException if the target source is <b>null</b>
    156     * @since 2.0
    157     */
    158    public void copyEventListeners(final BaseEventSource source) {
    159        if (source == null) {
    160            throw new IllegalArgumentException("Target event source must not be null!");
    161        }
    162        source.eventListeners.addAll(eventListeners);
    163    }
    164
    165    /**
    166     * Creates an event object and delivers it to all registered event listeners. The method checks first if sending an
    167     * event is allowed (making use of the {@code detailEvents} property), and if listeners are registered.
    168     *
    169     * @param type the event's type
    170     * @param propName the name of the affected property (can be <b>null</b>)
    171     * @param propValue the value of the affected property (can be <b>null</b>)
    172     * @param before the before update flag
    173     * @param <T> the type of the event to be fired
    174     */
    175    protected <T extends ConfigurationEvent> void fireEvent(final EventType<T> type, final String propName, final Object propValue, final boolean before) {
    176        if (checkDetailEvents(-1)) {
    177            final EventListenerList.EventListenerIterator<T> it = eventListeners.getEventListenerIterator(type);
    178            if (it.hasNext()) {
    179                final ConfigurationEvent event = createEvent(type, propName, propValue, before);
    180                while (it.hasNext()) {
    181                    it.invokeNext(event);
    182                }
    183            }
    184        }
    185    }
    186
    187    /**
    188     * Creates a {@code ConfigurationEvent} object based on the passed in parameters. This method is called by
    189     * {@code fireEvent()} if it decides that an event needs to be generated.
    190     *
    191     * @param type the event's type
    192     * @param propName the name of the affected property (can be <b>null</b>)
    193     * @param propValue the value of the affected property (can be <b>null</b>)
    194     * @param before the before update flag
    195     * @param <T> the type of the event to be created
    196     * @return the newly created event object
    197     */
    198    protected <T extends ConfigurationEvent> ConfigurationEvent createEvent(final EventType<T> type, final String propName, final Object propValue,
    199        final boolean before) {
    200        return new ConfigurationEvent(this, type, propName, propValue, before);
    201    }
    202
    203    /**
    204     * Creates an error event object and delivers it to all registered error listeners of a matching type.
    205     *
    206     * @param eventType the event's type
    207     * @param operationType the type of the failed operation
    208     * @param propertyName the name of the affected property (can be <b>null</b>)
    209     * @param propertyValue the value of the affected property (can be <b>null</b>)
    210     * @param cause the {@code Throwable} object that caused this error event
    211     * @param <T> the event type
    212     */
    213    public <T extends ConfigurationErrorEvent> void fireError(final EventType<T> eventType, final EventType<?> operationType, final String propertyName,
    214        final Object propertyValue, final Throwable cause) {
    215        final EventListenerList.EventListenerIterator<T> iterator = eventListeners.getEventListenerIterator(eventType);
    216        if (iterator.hasNext()) {
    217            final ConfigurationErrorEvent event = createErrorEvent(eventType, operationType, propertyName, propertyValue, cause);
    218            while (iterator.hasNext()) {
    219                iterator.invokeNext(event);
    220            }
    221        }
    222    }
    223
    224    /**
    225     * Creates a {@code ConfigurationErrorEvent} object based on the passed in parameters. This is called by
    226     * {@code fireError()} if it decides that an event needs to be generated.
    227     *
    228     * @param type the event's type
    229     * @param opType the operation type related to this error
    230     * @param propName the name of the affected property (can be <b>null</b>)
    231     * @param propValue the value of the affected property (can be <b>null</b>)
    232     * @param ex the {@code Throwable} object that caused this error event
    233     * @return the event object
    234     */
    235    protected ConfigurationErrorEvent createErrorEvent(final EventType<? extends ConfigurationErrorEvent> type, final EventType<?> opType,
    236        final String propName, final Object propValue, final Throwable ex) {
    237        return new ConfigurationErrorEvent(this, type, opType, propName, propValue, ex);
    238    }
    239
    240    /**
    241     * Overrides the {@code clone()} method to correctly handle so far registered event listeners. This implementation
    242     * ensures that the clone will have empty event listener lists, i.e. the listeners registered at an
    243     * {@code BaseEventSource} object will not be copied.
    244     *
    245     * @return the cloned object
    246     * @throws CloneNotSupportedException if cloning is not allowed
    247     * @since 1.4
    248     */
    249    @Override
    250    protected Object clone() throws CloneNotSupportedException {
    251        final BaseEventSource copy = (BaseEventSource) super.clone();
    252        copy.initListeners();
    253        return copy;
    254    }
    255
    256    /**
    257     * Initializes the collections for storing registered event listeners.
    258     */
    259    private void initListeners() {
    260        eventListeners = new EventListenerList();
    261    }
    262
    263    /**
    264     * Helper method for checking the current counter for detail events. This method checks whether the counter is greater
    265     * than the passed in limit.
    266     *
    267     * @param limit the limit to be compared to
    268     * @return <b>true</b> if the counter is greater than the limit, <b>false</b> otherwise
    269     */
    270    private boolean checkDetailEvents(final int limit) {
    271        synchronized (lockDetailEventsCount) {
    272            return detailEvents > limit;
    273        }
    274    }
    275}