org.apache.commons.io

Class FileCleaningTracker


public class FileCleaningTracker
extends java.lang.Object

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 or similar.

Version:
$Id: FileCleaner.java 490987 2006-12-29 12:11:48Z scolebourne $
Authors:
Noel Bergman
Martin Cooper

Nested Class Summary

private class
FileCleaningTracker.Reaper
The reaper thread.
private static class
FileCleaningTracker.Tracker
Inner class which acts as the reference for a file pending deletion.

Field Summary

(package private) boolean
exitWhenFinished
Whether to terminate the thread when the tracking is complete.
(package private) ReferenceQueue
q
Queue of Tracker instances being watched.
(package private) Thread
reaper
The thread that will clean up registered files.
(package private) Collection
trackers
Collection of Tracker instances in existence.

Method Summary

private void
addTracker(String path, Object marker, FileDeleteStrategy deleteStrategy)
Adds a tracker to the list of trackers.
void
exitWhenFinished()
Call this method to cause the file cleaner thread to terminate when there are no more objects being tracked for deletion.
int
getTrackCount()
Retrieve the number of files currently being tracked, and therefore awaiting deletion.
void
track(File file, Object marker)
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.
void
track(File file, Object marker, FileDeleteStrategy deleteStrategy)
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.
void
track(String path, Object marker)
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.
void
track(String path, Object marker, FileDeleteStrategy deleteStrategy)
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.

Field Details

exitWhenFinished

(package private)  boolean exitWhenFinished
Whether to terminate the thread when the tracking is complete.

q

(package private)  ReferenceQueue q
Queue of Tracker instances being watched.

reaper

(package private)  Thread reaper
The thread that will clean up registered files.

trackers

(package private) final Collection trackers
Collection of Tracker instances in existence.

Method Details

addTracker

private void addTracker(String path,
                        Object marker,
                        FileDeleteStrategy deleteStrategy)
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

exitWhenFinished

public void exitWhenFinished()
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. One called, no new objects can be tracked by the file cleaner.


getTrackCount

public int getTrackCount()
Retrieve the number of files currently being tracked, and therefore awaiting deletion.
Returns:
the number of files being tracked

track

public void track(File file,
                  Object marker)
Parameters:
file - the file to be tracked, not null
marker - the marker object used to track the file, not null

track

public void track(File file,
                  Object marker,
                  FileDeleteStrategy deleteStrategy)
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

track

public void track(String path,
                  Object marker)
Parameters:
path - the full path to the file to be tracked, not null
marker - the marker object used to track the file, not null

track

public void track(String path,
                  Object marker,
                  FileDeleteStrategy deleteStrategy)
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

Copyright (c) 2002-2008 Apache Software Foundation