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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 static org.jboss.web.FileUploadMessages.MESSAGES;
 
 import java.io.File;
Keeps track of files awaiting deletion, and deletes them when an associated marker object is reclaimed by the garbage collector.

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.

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 exitWhenFinished, typically in javax.servlet.ServletContextListener.contextDestroyed(javax.servlet.ServletContextEvent) or similar.

Author(s):
Noel Bergman
Martin Cooper
Version:
$Id: FileCleaner.java 490987 2006-12-29 12:11:48Z scolebourne $
 
 public class FileCleaningTracker {
    
Queue of Tracker instances being watched.
 
     ReferenceQueue /* Tracker */ q = new ReferenceQueue();
    
Collection of Tracker instances in existence.
 
     final Collection<Trackertrackers = new Vector<Tracker>();  // synchronized
     
Whether to terminate the thread when the tracking is complete.
 
     volatile boolean exitWhenFinished = false;
    
The thread that will clean up registered files.
 
     Thread reaper;
 
     //-----------------------------------------------------------------------
     
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected. The normal deletion strategy will be used.

Parameters:
file the file to be tracked, not null
marker the marker object used to track the file, not null
Throws:
java.lang.NullPointerException if the file is null
 
     public void track(File fileObject marker) {
         track(filemarker, (FileDeleteStrategynull);
     }

    
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected. The speified deletion strategy is used.

Parameters:
file the file to be tracked, not null
marker the marker object used to track the file, not null
deleteStrategy the strategy to delete the file, null means normal
Throws:
java.lang.NullPointerException if the file is null
 
     public void track(File fileObject markerFileDeleteStrategy deleteStrategy) {
         if (file == null) {
             throw .nullFile();
         }
         addTracker(file.getPath(), markerdeleteStrategy);
     }

    
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected. The normal deletion strategy will be used.

Parameters:
path the full path to the file to be tracked, not null
marker the marker object used to track the file, not null
Throws:
java.lang.NullPointerException if the path is null
    public void track(String pathObject marker) {
        track(pathmarker, (FileDeleteStrategynull);
    }

    
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected. The speified deletion strategy is used.

Parameters:
path the full path to the file to be tracked, not null
marker the marker object used to track the file, not null
deleteStrategy the strategy to delete the file, null means normal
Throws:
java.lang.NullPointerException if the path is null
    public void track(String pathObject markerFileDeleteStrategy deleteStrategy) {
        if (path == null) {
            throw .nullPath();
        }
        addTracker(pathmarkerdeleteStrategy);
    }

    
Adds a tracker to the list of trackers.

Parameters:
path the full path to the file to be tracked, not null
marker the marker object used to track the file, not null
deleteStrategy the strategy to delete the file, null means normal
    private synchronized void addTracker(String pathObject markerFileDeleteStrategy deleteStrategy) {
        // synchronized block protects reaper
        if () {
            throw .cannotAddTrackersOnceFinished();
        }
        if ( == null) {
             = new Reaper();
            .start();
        }
        .add(new Tracker(pathdeleteStrategymarker));
    }
    //-----------------------------------------------------------------------
    
Retrieve the number of files currently being tracked, and therefore awaiting deletion.

Returns:
the number of files being tracked
    public int getTrackCount() {
        return .size();
    }

    
Call this method to cause the file cleaner thread to terminate when there are no more objects being tracked for deletion.

In a simple environment, you don't need this method as the file cleaner thread will simply exit when the JVM exits. In a more complex environment, with multiple class loaders (such as an application server), you should be aware that the file cleaner thread will continue running even if the class loader it was started from terminates. This can consitute a memory leak.

For example, suppose that you have developed a web application, which contains the commons-io jar file in your WEB-INF/lib directory. In other words, the FileCleaner class is loaded through the class loader of your web application. If the web application is terminated, but the servlet container is still running, then the file cleaner thread will still exist, posing a memory leak.

This method allows the thread to be terminated. Simply call this method in the resource cleanup code, such as javax.servlet.ServletContextListener.contextDestroyed(javax.servlet.ServletContextEvent). One called, no new objects can be tracked by the file cleaner.

    public synchronized void exitWhenFinished() {
        // synchronized block protects reaper
         = true;
        if ( != null) {
            synchronized () {
                .interrupt();
            }
        }
    }
    //-----------------------------------------------------------------------
    
The reaper thread.
    private final class Reaper extends Thread {
        
Construct a new Reaper
        Reaper() {
            super("File Reaper");
            setPriority(.);
            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 ( == false || .size() > 0) {
                Tracker tracker = null;
                try {
                    // Wait for a tracker to remove.
                    tracker = (Tracker.remove();
                } catch (Exception e) {
                    continue;
                }
                if (tracker != null) {
                    tracker.delete();
                    tracker.clear();
                    .remove(tracker);
                }
            }
        }
    }
    //-----------------------------------------------------------------------
    
Inner class which acts as the reference for a file pending deletion.
    private static final class Tracker extends PhantomReference {

        
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.

Parameters:
path the full path to the file to be tracked, not null
deleteStrategy the strategy to delete the file, null means normal
marker the marker object used to track the file, not null
queue the queue on to which the tracker will be pushed, not null
        Tracker(String pathFileDeleteStrategy deleteStrategyObject markerReferenceQueue queue) {
            super(markerqueue);
            this. = path;
            this. = (deleteStrategy == null ? . : deleteStrategy);
        }

        
Deletes the file associated with this tracker instance.

Returns:
true if the file was deleted successfully; false otherwise.
        public boolean delete() {
            return .deleteQuietly(new File());
        }
    }
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