/*
* 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.watch;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.wicket.util.lang.Generics;
import org.apache.wicket.util.listener.ChangeListenerSet;
import org.apache.wicket.util.listener.IChangeListener;
import org.apache.wicket.util.thread.ICode;
import org.apache.wicket.util.thread.Task;
import org.apache.wicket.util.time.Duration;
import org.apache.wicket.util.time.Time;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Monitors one or more <code>IModifiable</code> objects, calling a {@link IChangeListener
* IChangeListener} when a given object's modification time changes.
*
* @author Jonathan Locke
* @since 1.2.6
*/
public class ModificationWatcher implements IModificationWatcher
{
/** logger */
private static final Logger log = LoggerFactory.getLogger(ModificationWatcher.class);
/** maps <code>IModifiable</code> objects to <code>Entry</code> objects */
private final Map<IModifiable, Entry> modifiableToEntry = Generics.newConcurrentHashMap();
/** the <code>Task</code> to run */
private Task task;
/**
* Container class for holding modifiable entries to watch.
*/
protected static final class Entry
{
// The most recent lastModificationTime polled on the object
public Time lastModifiedTime;
// The set of listeners to call when the modifiable changes
public final ChangeListenerSet listeners = new ChangeListenerSet();
// The modifiable thing
public IModifiable modifiable;
}
/**
* Default constructor for two-phase construction.
*/
public ModificationWatcher()
{
}
/**
* Constructor that accepts a <code>Duration</code> argument representing the poll frequency.
*
* @param pollFrequency
* how often to check on <code>IModifiable</code>s
*/
public ModificationWatcher(final Duration pollFrequency)
{
start(pollFrequency);
}
@Override
public final boolean add(final IModifiable modifiable, final IChangeListener listener)
{
// Look up entry for modifiable
final Entry entry = modifiableToEntry.get(modifiable);
// Found it?
if (entry == null)
{
Time lastModifiedTime = modifiable.lastModifiedTime();
if (lastModifiedTime != null)
{
// Construct new entry
final Entry newEntry = new Entry();
newEntry.modifiable = modifiable;
newEntry.lastModifiedTime = lastModifiedTime;
newEntry.listeners.add(listener);
// Put in map
modifiableToEntry.put(modifiable, newEntry);
}
else
{
// The IModifiable is not returning a valid lastModifiedTime
log.info("Cannot track modifications to resource " + modifiable);
}
return true;
}
else
{
// Add listener to existing entry
return !entry.listeners.add(listener);
}
}
@Override
public IModifiable remove(final IModifiable modifiable)
{
final Entry entry = modifiableToEntry.remove(modifiable);
if (entry != null)
{
return entry.modifiable;
}
return null;
}
@Override
public void start(final Duration pollFrequency)
{
// Construct task with the given polling frequency
task = new Task("ModificationWatcher");
task.run(pollFrequency, new ICode()
{
@Override
public void run(final Logger log)
{
checkModified();
}
});
}
/**
* Checks which IModifiables were modified and notifies their listeners
*/
protected void checkModified()
{
for (Entry entry : modifiableToEntry.values())
{
// If the modifiable has been modified after the last known
// modification time
final Time modifiableLastModified = entry.modifiable.lastModifiedTime();
if ((modifiableLastModified != null) &&
modifiableLastModified.after(entry.lastModifiedTime))
{
// Notify all listeners that the modifiable was modified
entry.listeners.notifyListeners();
// Update timestamp
entry.lastModifiedTime = modifiableLastModified;
}
}
}
@Override
public void destroy()
{
if (task != null)
{
// task.stop();
task.interrupt();
}
}
@Override
public final Set<IModifiable> getEntries()
{
return modifiableToEntry.keySet();
}
}