BaseEventSource.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.configuration2.event;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
/**
* <p>
* A base class for objects that can generate configuration events.
* </p>
* <p>
* This class implements functionality for managing a set of event listeners that can be notified when an event occurs.
* It can be extended by configuration classes that support the event mechanism. In this case these classes only need to
* call the {@code fireEvent()} method when an event is to be delivered to the registered listeners.
* </p>
* <p>
* Adding and removing event listeners can happen concurrently to manipulations on a configuration that cause events.
* The operations are synchronized.
* </p>
* <p>
* With the {@code detailEvents} property the number of detail events can be controlled. Some methods in configuration
* classes are implemented in a way that they call other methods that can generate their own events. One example is the
* {@code setProperty()} method that can be implemented as a combination of {@code clearProperty()} and
* {@code addProperty()}. With {@code detailEvents} set to <b>true</b>, all involved methods will generate events (i.e.
* listeners will receive property set events, property clear events, and property add events). If this mode is turned
* off (which is the default), detail events are suppressed, so only property set events will be received. Note that the
* number of received detail events may differ for different configuration implementations.
* {@link org.apache.commons.configuration2.BaseHierarchicalConfiguration BaseHierarchicalConfiguration} for instance
* has a custom implementation of {@code setProperty()}, which does not generate any detail events.
* </p>
* <p>
* In addition to "normal" events, error events are supported. Such events signal an internal problem that
* occurred during access of properties. They are handled via the regular {@link EventListener} interface, but there are
* special event types defined by {@link ConfigurationErrorEvent}. The {@code fireError()} method can be used by derived
* classes to send notifications about errors to registered observers.
* </p>
*
* @since 1.3
*/
public class BaseEventSource implements EventSource {
/** The list for managing registered event listeners. */
private EventListenerList eventListeners;
/** A lock object for guarding access to the detail events counter. */
private final Object lockDetailEventsCount = new Object();
/** A counter for the detail events. */
private int detailEvents;
/**
* Creates a new instance of {@code BaseEventSource}.
*/
public BaseEventSource() {
initListeners();
}
@Override
public <T extends Event> void addEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
eventListeners.addEventListener(eventType, listener);
}
/**
* Helper method for checking the current counter for detail events. This method checks whether the counter is greater
* than the passed in limit.
*
* @param limit the limit to be compared to
* @return <b>true</b> if the counter is greater than the limit, <b>false</b> otherwise
*/
private boolean checkDetailEvents(final int limit) {
synchronized (lockDetailEventsCount) {
return detailEvents > limit;
}
}
/**
* Removes all registered error listeners.
*
* @since 1.4
*/
public void clearErrorListeners() {
eventListeners.getRegistrationsForSuperType(ConfigurationErrorEvent.ANY).forEach(eventListeners::removeEventListener);
}
/**
* Removes all registered event listeners.
*/
public void clearEventListeners() {
eventListeners.clear();
}
/**
* Overrides the {@code clone()} method to correctly handle so far registered event listeners. This implementation
* ensures that the clone will have empty event listener lists, i.e. the listeners registered at an
* {@code BaseEventSource} object will not be copied.
*
* @return the cloned object
* @throws CloneNotSupportedException if cloning is not allowed
* @since 1.4
*/
@Override
protected Object clone() throws CloneNotSupportedException {
final BaseEventSource copy = (BaseEventSource) super.clone();
copy.initListeners();
return copy;
}
/**
* Copies all event listener registrations maintained by this object to the specified {@code BaseEventSource} object.
*
* @param source the target source for the copy operation (must not be <b>null</b>)
* @throws IllegalArgumentException if the target source is <b>null</b>
* @since 2.0
*/
public void copyEventListeners(final BaseEventSource source) {
if (source == null) {
throw new IllegalArgumentException("Target event source must not be null!");
}
source.eventListeners.addAll(eventListeners);
}
/**
* Creates a {@code ConfigurationErrorEvent} object based on the passed in parameters. This is called by
* {@code fireError()} if it decides that an event needs to be generated.
*
* @param type the event's type
* @param opType the operation type related to this error
* @param propName the name of the affected property (can be <b>null</b>)
* @param propValue the value of the affected property (can be <b>null</b>)
* @param ex the {@code Throwable} object that caused this error event
* @return the event object
*/
protected ConfigurationErrorEvent createErrorEvent(final EventType<? extends ConfigurationErrorEvent> type, final EventType<?> opType,
final String propName, final Object propValue, final Throwable ex) {
return new ConfigurationErrorEvent(this, type, opType, propName, propValue, ex);
}
/**
* Creates a {@code ConfigurationEvent} object based on the passed in parameters. This method is called by
* {@code fireEvent()} if it decides that an event needs to be generated.
*
* @param type the event's type
* @param propName the name of the affected property (can be <b>null</b>)
* @param propValue the value of the affected property (can be <b>null</b>)
* @param before the before update flag
* @param <T> the type of the event to be created
* @return the newly created event object
*/
protected <T extends ConfigurationEvent> ConfigurationEvent createEvent(final EventType<T> type, final String propName, final Object propValue,
final boolean before) {
return new ConfigurationEvent(this, type, propName, propValue, before);
}
/**
* Creates an error event object and delivers it to all registered error listeners of a matching type.
*
* @param eventType the event's type
* @param operationType the type of the failed operation
* @param propertyName the name of the affected property (can be <b>null</b>)
* @param propertyValue the value of the affected property (can be <b>null</b>)
* @param cause the {@code Throwable} object that caused this error event
* @param <T> the event type
*/
public <T extends ConfigurationErrorEvent> void fireError(final EventType<T> eventType, final EventType<?> operationType, final String propertyName,
final Object propertyValue, final Throwable cause) {
final EventListenerList.EventListenerIterator<T> iterator = eventListeners.getEventListenerIterator(eventType);
if (iterator.hasNext()) {
final ConfigurationErrorEvent event = createErrorEvent(eventType, operationType, propertyName, propertyValue, cause);
while (iterator.hasNext()) {
iterator.invokeNext(event);
}
}
}
/**
* Creates an event object and delivers it to all registered event listeners. The method checks first if sending an
* event is allowed (making use of the {@code detailEvents} property), and if listeners are registered.
*
* @param type the event's type
* @param propName the name of the affected property (can be <b>null</b>)
* @param propValue the value of the affected property (can be <b>null</b>)
* @param before the before update flag
* @param <T> the type of the event to be fired
*/
protected <T extends ConfigurationEvent> void fireEvent(final EventType<T> type, final String propName, final Object propValue, final boolean before) {
if (checkDetailEvents(-1)) {
final EventListenerList.EventListenerIterator<T> it = eventListeners.getEventListenerIterator(type);
if (it.hasNext()) {
final ConfigurationEvent event = createEvent(type, propName, propValue, before);
while (it.hasNext()) {
it.invokeNext(event);
}
}
}
}
/**
* Gets a list with all {@code EventListenerRegistrationData} objects currently contained for this event source. This
* method allows access to all registered event listeners, independent on their type.
*
* @return a list with information about all registered event listeners
*/
public List<EventListenerRegistrationData<?>> getEventListenerRegistrations() {
return eventListeners.getRegistrations();
}
/**
* Gets a collection with all event listeners of the specified event type that are currently registered at this
* object.
*
* @param eventType the event type object
* @param <T> the event type
* @return a collection with the event listeners of the specified event type (this collection is a snapshot of the
* currently registered listeners; it cannot be manipulated)
*/
public <T extends Event> Collection<EventListener<? super T>> getEventListeners(final EventType<T> eventType) {
final List<EventListener<? super T>> result = new LinkedList<>();
eventListeners.getEventListeners(eventType).forEach(result::add);
return Collections.unmodifiableCollection(result);
}
/**
* Initializes the collections for storing registered event listeners.
*/
private void initListeners() {
eventListeners = new EventListenerList();
}
/**
* Returns a flag whether detail events are enabled.
*
* @return a flag if detail events are generated
*/
public boolean isDetailEvents() {
return checkDetailEvents(0);
}
@Override
public <T extends Event> boolean removeEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
return eventListeners.removeEventListener(eventType, listener);
}
/**
* Determines whether detail events should be generated. If enabled, some methods can generate multiple update events.
* Note that this method records the number of calls, i.e. if for instance {@code setDetailEvents(false)} was called
* three times, you will have to invoke the method as often to enable the details.
*
* @param enable a flag if detail events should be enabled or disabled
*/
public void setDetailEvents(final boolean enable) {
synchronized (lockDetailEventsCount) {
if (enable) {
detailEvents++;
} else {
detailEvents--;
}
}
}
}