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/*
* 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.tomcat.util.http.fileupload;
import java.io.File;
import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
/**
* Keeps track of files awaiting deletion, and deletes them when an associated
* marker object is reclaimed by the garbage collector.
* <p>
* This utility creates a background thread to handle file deletion.
* Each file to be deleted is registered with a handler object.
* When the handler object is garbage collected, the file is deleted.
* <p>
* In an environment with multiple class loaders (a servlet container, for
* example), you should consider stopping the background thread if it is no
* longer needed. This is done by invoking the method
* {@link #exitWhenFinished}, typically in
* {@link javax.servlet.ServletContextListener#contextDestroyed} or similar.
*/
public class FileCleaningTracker {
/**
* Queue of <code>Tracker</code> instances being watched.
*/
private final ReferenceQueue<Object> q = new ReferenceQueue<Object>();
/**
* Collection of <code>Tracker</code> instances in existence.
*/
private final Collection<Tracker> trackers = Collections.synchronizedSet(new HashSet<Tracker>()); // synchronized
/**
* Collection of File paths that failed to delete.
*/
private final List<String> deleteFailures = Collections.synchronizedList(new ArrayList<String>());
/**
* Whether to terminate the thread when the tracking is complete.
*/
private volatile boolean exitWhenFinished = false;
/**
* The thread that will clean up registered files.
*/
private Thread reaper;
//-----------------------------------------------------------------------
/**
* Track the specified file, using the provided marker, deleting the file
* when the marker instance is garbage collected.
* The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used.
*
* @param file the file to be tracked, not null
* @param marker the marker object used to track the file, not null
* @throws NullPointerException if the file is null
*/
public void track(File file, Object marker) {
track(file, marker, (FileDeleteStrategy) null);
}
/**
* Track the specified file, using the provided marker, deleting the file
* when the marker instance is garbage collected.
* The speified deletion strategy is used.
*
* @param file the file to be tracked, not null
* @param marker the marker object used to track the file, not null
* @param deleteStrategy the strategy to delete the file, null means normal
* @throws NullPointerException if the file is null
*/
public void track(File file, Object marker, FileDeleteStrategy deleteStrategy) {
if (file == null) {
throw new NullPointerException("The file must not be null");
}
addTracker(file.getPath(), marker, deleteStrategy);
}
/**
* Adds a tracker to the list of trackers.
*
* @param path the full path to the file to be tracked, not null
* @param marker the marker object used to track the file, not null
* @param deleteStrategy the strategy to delete the file, null means normal
*/
private synchronized void addTracker(String path, Object marker, FileDeleteStrategy deleteStrategy) {
// synchronized block protects reaper
if (exitWhenFinished) {
throw new IllegalStateException("No new trackers can be added once exitWhenFinished() is called");
}
if (reaper == null) {
reaper = new Reaper();
reaper.start();
}
trackers.add(new Tracker(path, deleteStrategy, marker, q));
}
//-----------------------------------------------------------------------
/**
* The reaper thread.
*/
private final class Reaper extends Thread {
/** Construct a new Reaper */
Reaper() {
super("File Reaper");
setPriority(Thread.MAX_PRIORITY);
setDaemon(true);
}
/**
* Run the reaper thread that will delete files as their associated
* marker objects are reclaimed by the garbage collector.
*/
@Override
public void run() {
// thread exits when exitWhenFinished is true and there are no more tracked objects
while (exitWhenFinished == false || trackers.size() > 0) {
try {
// Wait for a tracker to remove.
Tracker tracker = (Tracker) q.remove(); // cannot return null
trackers.remove(tracker);
if (!tracker.delete()) {
deleteFailures.add(tracker.getPath());
}
tracker.clear();
} catch (InterruptedException e) {
continue;
}
}
}
}
//-----------------------------------------------------------------------
/**
* Inner class which acts as the reference for a file pending deletion.
*/
private static final class Tracker extends PhantomReference<Object> {
/**
* The full path to the file being tracked.
*/
private final String path;
/**
* The strategy for deleting files.
*/
private final FileDeleteStrategy deleteStrategy;
/**
* Constructs an instance of this class from the supplied parameters.
*
* @param path the full path to the file to be tracked, not null
* @param deleteStrategy the strategy to delete the file, null means normal
* @param marker the marker object used to track the file, not null
* @param queue the queue on to which the tracker will be pushed, not null
*/
Tracker(String path, FileDeleteStrategy deleteStrategy, Object marker, ReferenceQueue<? super Object> queue) {
super(marker, queue);
this.path = path;
this.deleteStrategy = deleteStrategy == null ? FileDeleteStrategy.NORMAL : deleteStrategy;
}
/**
* Return the path.
*
* @return the path
*/
public String getPath() {
return path;
}
/**
* Deletes the file associated with this tracker instance.
*
* @return {@code true} if the file was deleted successfully;
* {@code false} otherwise.
*/
public boolean delete() {
return deleteStrategy.deleteQuietly(new File(path));
}
}
}
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