Source code
Description: source: package: org.apache.commons.configuration2.event, class: BaseEventSource

    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.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 <strong>true</strong>, 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
    059    /** The list for managing registered event listeners. */
    060    private EventListenerList eventListeners;
    061
    062    /** A lock object for guarding access to the detail events counter. */
    063    private final Object lockDetailEventsCount = new Object();
    064
    065    /** A counter for the detail events. */
    066    private int detailEvents;
    067
    068    /**
    069     * Creates a new instance of {@code BaseEventSource}.
    070     */
    071    public BaseEventSource() {
    072        initListeners();
    073    }
    074
    075    @Override
    076    public <T extends Event> void addEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
    077        eventListeners.addEventListener(eventType, listener);
    078    }
    079
    080    /**
    081     * Helper method for checking the current counter for detail events. This method checks whether the counter is greater
    082     * than the passed in limit.
    083     *
    084     * @param limit the limit to be compared to
    085     * @return <strong>true</strong> if the counter is greater than the limit, <strong>false</strong> otherwise
    086     */
    087    private boolean checkDetailEvents(final int limit) {
    088        synchronized (lockDetailEventsCount) {
    089            return detailEvents > limit;
    090        }
    091    }
    092
    093    /**
    094     * Removes all registered error listeners.
    095     *
    096     * @since 1.4
    097     */
    098    public void clearErrorListeners() {
    099        eventListeners.getRegistrationsForSuperType(ConfigurationErrorEvent.ANY).forEach(eventListeners::removeEventListener);
    100    }
    101
    102    /**
    103     * Removes all registered event listeners.
    104     */
    105    public void clearEventListeners() {
    106        eventListeners.clear();
    107    }
    108
    109    /**
    110     * Overrides the {@code clone()} method to correctly handle so far registered event listeners. This implementation ensures that the clone will have empty
    111     * event listener lists, i.e. the listeners registered at an {@code BaseEventSource} object will not be copied.
    112     *
    113     * @return the cloned object
    114     * @throws CloneNotSupportedException if the object's class does not support the {@code Cloneable} interface. Subclasses that override the {@code clone}
    115     *                                    method can also throw this exception to indicate that an instance cannot be cloned.
    116     * @since 1.4
    117     */
    118    @Override
    119    protected Object clone() throws CloneNotSupportedException {
    120        final BaseEventSource copy = (BaseEventSource) super.clone();
    121        copy.initListeners();
    122        return copy;
    123    }
    124
    125    /**
    126     * Copies all event listener registrations maintained by this object to the specified {@code BaseEventSource} object.
    127     *
    128     * @param source the target source for the copy operation (must not be <strong>null</strong>)
    129     * @throws IllegalArgumentException if the target source is <strong>null</strong>
    130     * @since 2.0
    131     */
    132    public void copyEventListeners(final BaseEventSource source) {
    133        if (source == null) {
    134            throw new IllegalArgumentException("Target event source must not be null.");
    135        }
    136        source.eventListeners.addAll(eventListeners);
    137    }
    138
    139    /**
    140     * Creates a {@code ConfigurationErrorEvent} object based on the passed in parameters. This is called by
    141     * {@code fireError()} if it decides that an event needs to be generated.
    142     *
    143     * @param type the event's type
    144     * @param opType the operation type related to this error
    145     * @param propName the name of the affected property (can be <strong>null</strong>)
    146     * @param propValue the value of the affected property (can be <strong>null</strong>)
    147     * @param ex the {@code Throwable} object that caused this error event
    148     * @return the event object
    149     */
    150    protected ConfigurationErrorEvent createErrorEvent(final EventType<? extends ConfigurationErrorEvent> type, final EventType<?> opType,
    151        final String propName, final Object propValue, final Throwable ex) {
    152        return new ConfigurationErrorEvent(this, type, opType, propName, propValue, ex);
    153    }
    154
    155    /**
    156     * Creates a {@code ConfigurationEvent} object based on the passed in parameters. This method is called by
    157     * {@code fireEvent()} if it decides that an event needs to be generated.
    158     *
    159     * @param type the event's type
    160     * @param propName the name of the affected property (can be <strong>null</strong>)
    161     * @param propValue the value of the affected property (can be <strong>null</strong>)
    162     * @param before the before update flag
    163     * @param <T> the type of the event to be created
    164     * @return the newly created event object
    165     */
    166    protected <T extends ConfigurationEvent> ConfigurationEvent createEvent(final EventType<T> type, final String propName, final Object propValue,
    167        final boolean before) {
    168        return new ConfigurationEvent(this, type, propName, propValue, before);
    169    }
    170
    171    /**
    172     * Creates an error event object and delivers it to all registered error listeners of a matching type.
    173     *
    174     * @param eventType the event's type
    175     * @param operationType the type of the failed operation
    176     * @param propertyName the name of the affected property (can be <strong>null</strong>)
    177     * @param propertyValue the value of the affected property (can be <strong>null</strong>)
    178     * @param cause the {@code Throwable} object that caused this error event
    179     * @param <T> the event type
    180     */
    181    public <T extends ConfigurationErrorEvent> void fireError(final EventType<T> eventType, final EventType<?> operationType, final String propertyName,
    182        final Object propertyValue, final Throwable cause) {
    183        final EventListenerList.EventListenerIterator<T> iterator = eventListeners.getEventListenerIterator(eventType);
    184        if (iterator.hasNext()) {
    185            final ConfigurationErrorEvent event = createErrorEvent(eventType, operationType, propertyName, propertyValue, cause);
    186            while (iterator.hasNext()) {
    187                iterator.invokeNext(event);
    188            }
    189        }
    190    }
    191
    192    /**
    193     * Creates an event object and delivers it to all registered event listeners. The method checks first if sending an
    194     * event is allowed (making use of the {@code detailEvents} property), and if listeners are registered.
    195     *
    196     * @param type the event's type
    197     * @param propName the name of the affected property (can be <strong>null</strong>)
    198     * @param propValue the value of the affected property (can be <strong>null</strong>)
    199     * @param before the before update flag
    200     * @param <T> the type of the event to be fired
    201     */
    202    protected <T extends ConfigurationEvent> void fireEvent(final EventType<T> type, final String propName, final Object propValue, final boolean before) {
    203        if (checkDetailEvents(-1)) {
    204            final EventListenerList.EventListenerIterator<T> it = eventListeners.getEventListenerIterator(type);
    205            if (it.hasNext()) {
    206                final ConfigurationEvent event = createEvent(type, propName, propValue, before);
    207                while (it.hasNext()) {
    208                    it.invokeNext(event);
    209                }
    210            }
    211        }
    212    }
    213
    214    /**
    215     * Gets a list with all {@code EventListenerRegistrationData} objects currently contained for this event source. This
    216     * method allows access to all registered event listeners, independent on their type.
    217     *
    218     * @return a list with information about all registered event listeners
    219     */
    220    public List<EventListenerRegistrationData<?>> getEventListenerRegistrations() {
    221        return eventListeners.getRegistrations();
    222    }
    223
    224    /**
    225     * Gets a collection with all event listeners of the specified event type that are currently registered at this
    226     * object.
    227     *
    228     * @param eventType the event type object
    229     * @param <T> the event type
    230     * @return a collection with the event listeners of the specified event type (this collection is a snapshot of the
    231     *         currently registered listeners; it cannot be manipulated)
    232     */
    233    public <T extends Event> Collection<EventListener<? super T>> getEventListeners(final EventType<T> eventType) {
    234        final List<EventListener<? super T>> result = new LinkedList<>();
    235        eventListeners.getEventListeners(eventType).forEach(result::add);
    236        return Collections.unmodifiableCollection(result);
    237    }
    238
    239    /**
    240     * Initializes the collections for storing registered event listeners.
    241     */
    242    private void initListeners() {
    243        eventListeners = new EventListenerList();
    244    }
    245
    246    /**
    247     * Returns a flag whether detail events are enabled.
    248     *
    249     * @return a flag if detail events are generated
    250     */
    251    public boolean isDetailEvents() {
    252        return checkDetailEvents(0);
    253    }
    254
    255    @Override
    256    public <T extends Event> boolean removeEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
    257        return eventListeners.removeEventListener(eventType, listener);
    258    }
    259
    260    /**
    261     * Determines whether detail events should be generated. If enabled, some methods can generate multiple update events.
    262     * Note that this method records the number of calls, i.e. if for instance {@code setDetailEvents(false)} was called
    263     * three times, you will have to invoke the method as often to enable the details.
    264     *
    265     * @param enable a flag if detail events should be enabled or disabled
    266     */
    267    public void setDetailEvents(final boolean enable) {
    268        synchronized (lockDetailEventsCount) {
    269            if (enable) {
    270                detailEvents++;
    271            } else {
    272                detailEvents--;
    273            }
    274        }
    275    }
    276}