org.apache.commons.io

Class FileCleaningTracker

public class FileCleaningTracker extends 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 $

Author: Noel Bergman Martin Cooper

Nested Class Summary
classFileCleaningTracker.Reaper
The reaper thread.
static classFileCleaningTracker.Tracker
Inner class which acts as the reference for a file pending deletion.
Field Summary
booleanexitWhenFinished
Whether to terminate the thread when the tracking is complete.
ReferenceQueueq
Queue of Tracker instances being watched.
Threadreaper
The thread that will clean up registered files.
Collectiontrackers
Collection of Tracker instances in existence.
Method Summary
voidaddTracker(String path, Object marker, FileDeleteStrategy deleteStrategy)
Adds a tracker to the list of trackers.
voidexitWhenFinished()
Call this method to cause the file cleaner thread to terminate when there are no more objects being tracked for deletion.
intgetTrackCount()
Retrieve the number of files currently being tracked, and therefore awaiting deletion.
voidtrack(File file, Object marker)
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.
voidtrack(File file, Object marker, FileDeleteStrategy deleteStrategy)
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.
voidtrack(String path, Object marker)
Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.
voidtrack(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 Detail

exitWhenFinished

volatile boolean exitWhenFinished
Whether to terminate the thread when the tracking is complete.

q

ReferenceQueue q
Queue of Tracker instances being watched.

reaper

Thread reaper
The thread that will clean up registered files.

trackers

final Collection trackers
Collection of Tracker instances in existence.

Method Detail

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)
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: NullPointerException if the file is 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

Throws: NullPointerException if the file is null

track

public void track(String path, Object marker)
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: NullPointerException if the path is 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

Throws: NullPointerException if the path is null

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