/*
* 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.vfs2.util;
import java.lang.ref.WeakReference;
import org.apache.commons.vfs2.FileChangeEvent;
import org.apache.commons.vfs2.FileListener;
import org.apache.commons.vfs2.FileName;
import org.apache.commons.vfs2.FileObject;
import org.apache.commons.vfs2.FileSystem;
/**
* Wrap a listener with a WeakReference.
*
* @author <a href="http://commons.apache.org/vfs/team-list.html">Commons VFS team</a>
* @since 2.0
*/
public class WeakRefFileListener implements FileListener
{
private final FileSystem fs;
private final FileName name;
private final WeakReference<FileListener> listener;
protected WeakRefFileListener(final FileObject file, final FileListener listener)
{
this.fs = file.getFileSystem();
this.name = file.getName();
this.listener = new WeakReference<FileListener>(listener);
}
/**
* This will install the <code>listener</code> at the given <code>file</code>.
* @param file The FileObject to listen on.
* @param listener The FileListener
*/
public static void installListener(final FileObject file, final FileListener listener)
{
WeakRefFileListener weakListener = new WeakRefFileListener(file, listener);
file.getFileSystem().addListener(file, new WeakRefFileListener(file, weakListener));
}
/**
* returns the wrapped listener. If it is gone, the WeakRefFileListener wrapper will
* remove itself from the list of listeners.
* @return The FileListener.
* @throws Exception if an error occurs.
*/
protected FileListener getListener() throws Exception
{
FileListener listener = this.listener.get();
if (listener == null)
{
FileObject file = fs.resolveFile(name);
file.getFileSystem().removeListener(file, this);
}
return listener;
}
/**
* Called when a file is created.
* @param event The FileChangeEvent.
* @throws Exception if an error occurs.
*/
public void fileCreated(final FileChangeEvent event) throws Exception
{
FileListener listener = getListener();
if (listener == null)
{
return;
}
listener.fileCreated(event);
}
/**
* Called when a file is deleted.
* @param event The FileChangeEvent.
* @throws Exception if an error occurs.
*/
public void fileDeleted(final FileChangeEvent event) throws Exception
{
FileListener listener = getListener();
if (listener == null)
{
return;
}
listener.fileDeleted(event);
}
/**
* Called when a file is changed.
* <p/>
* This will only happen if you monitor the file using {@link org.apache.commons.vfs2.FileMonitor}.
* @param event The FileChangeEvent.
* @throws Exception if an error occurs.
*/
public void fileChanged(FileChangeEvent event) throws Exception
{
FileListener listener = getListener();
if (listener == null)
{
return;
}
listener.fileChanged(event);
}
}