/*
* 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.wicket.util.listener;
import java.io.Serializable;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import org.apache.wicket.util.collections.ReverseListIterator;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Represents a collection of listeners. Facilitates invocation of events on each listener.
* <p>
* NOTE: Ordering of listeners is not guaranteed and should not be relied upon
* </p>
*
* @author ivaynberg (Igor Vaynberg)
* @author Jonathan Locke
*
* @param <T>
* type of listeners
*/
public abstract class ListenerCollection<T> implements Serializable, Iterable<T>
{
private static final long serialVersionUID = 1L;
private static final Logger logger = LoggerFactory.getLogger(ListenerCollection.class);
/** list of listeners */
private final List<T> listeners = new CopyOnWriteArrayList<>();
/**
* Adds a listener to this set of listeners.
*
* @param listener
* The listener to add
* @return {@code true} if the listener was added
*/
public boolean add(final T listener)
{
if ((listener == null) && !isAllowingNulls())
{
return false;
}
if (!isAllowingDuplicates() && listeners.contains(listener))
{
return false;
}
listeners.add(listener);
return true;
}
/**
* Notifies each listener in this
*
* @param notifier
* notifier used to notify each listener
*/
protected void notify(final INotifier<T> notifier)
{
for (T listener : listeners)
{
notifier.notify(listener);
}
}
/**
* Notifies each listener in this set ignoring exceptions. Exceptions will be logged.
*
* @param notifier
* notifier used to notify each listener
*/
protected void notifyIgnoringExceptions(final INotifier<T> notifier)
{
for (T listener : listeners)
{
try
{
notifier.notify(listener);
}
catch (Exception e)
{
logger.error("Error invoking listener: " + listener, e);
}
}
}
/**
* Notifies each listener in this set in reverse order ignoring exceptions
*
* @param notifier
* notifier used to notify each listener
*/
protected void reversedNotifyIgnoringExceptions(final INotifier<T> notifier)
{
reversedNotify(new INotifier<T>()
{
@Override
public void notify(T listener)
{
try
{
notifier.notify(listener);
}
catch (Exception e)
{
logger.error("Error invoking listener: " + listener, e);
}
}
});
}
/**
* Notifies each listener in this in reversed order
*
* @param notifier
* notifier used to notify each listener
*/
protected void reversedNotify(final INotifier<T> notifier)
{
Iterator<T> it = new ReverseListIterator<>(listeners);
while (it.hasNext())
{
T listener = it.next();
notifier.notify(listener);
}
}
/**
* Removes a listener from this set.
*
* @param listener
* The listener to remove
*/
public void remove(final T listener)
{
listeners.remove(listener);
}
/**
* Whether or not added listeners should be checked for duplicates.
*
* @return {@code true} to ignore duplicates
*/
protected boolean isAllowingDuplicates()
{
return true;
}
/**
* Whether or not to allow {@code null}s in listener collection.
*
* @return {@code} true to allow nulls to be added to the collection
*/
protected boolean isAllowingNulls()
{
return false;
}
/**
* Used to notify a listener. Usually this method simply forwards the {@link #notify(Object)} to
* the proper method on the listener.
*
* @author ivaynberg (Igor Vaynberg)
* @param <T>
*/
protected static interface INotifier<T>
{
void notify(T listener);
}
/**
* Returns an iterator that can iterate the listeners.
*
* @return an iterator that can iterate the listeners.
*/
@Override
public Iterator<T> iterator()
{
return listeners.iterator();
}
}