org.apache.commons.io
Class FileCleaningTracker

java.lang.Object
  extended by org.apache.commons.io.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: FileCleaningTracker.java 1005707 2010-10-08 04:02:57Z niallp $
Author:
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)  java.util.List<java.lang.String> deleteFailures
          Collection of File paths that failed to delete.
(package private)  boolean exitWhenFinished
          Whether to terminate the thread when the tracking is complete.
(package private)  java.lang.ref.ReferenceQueue<java.lang.Object> q
          Queue of Tracker instances being watched.
(package private)  java.lang.Thread reaper
          The thread that will clean up registered files.
(package private)  java.util.Collection<FileCleaningTracker.Tracker> trackers
          Collection of Tracker instances in existence.
 
Constructor Summary
FileCleaningTracker()
           
 
Method Summary
private  void addTracker(java.lang.String path, java.lang.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.
 java.util.List<java.lang.String> getDeleteFailures()
          Return the file paths that failed to delete.
 int getTrackCount()
          Retrieve the number of files currently being tracked, and therefore awaiting deletion.
 void track(java.io.File file, java.lang.Object marker)
          Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.
 void track(java.io.File file, java.lang.Object marker, FileDeleteStrategy deleteStrategy)
          Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.
 void track(java.lang.String path, java.lang.Object marker)
          Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.
 void track(java.lang.String path, java.lang.Object marker, FileDeleteStrategy deleteStrategy)
          Track the specified file, using the provided marker, deleting the file when the marker instance is garbage collected.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

q

java.lang.ref.ReferenceQueue<java.lang.Object> q
Queue of Tracker instances being watched.


trackers

final java.util.Collection<FileCleaningTracker.Tracker> trackers
Collection of Tracker instances in existence.


deleteFailures

final java.util.List<java.lang.String> deleteFailures
Collection of File paths that failed to delete.


exitWhenFinished

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


reaper

java.lang.Thread reaper
The thread that will clean up registered files.

Constructor Detail

FileCleaningTracker

public FileCleaningTracker()
Method Detail

track

public void track(java.io.File file,
                  java.lang.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:
java.lang.NullPointerException - if the file is null

track

public void track(java.io.File file,
                  java.lang.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:
java.lang.NullPointerException - if the file is null

track

public void track(java.lang.String path,
                  java.lang.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:
java.lang.NullPointerException - if the path is null

track

public void track(java.lang.String path,
                  java.lang.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:
java.lang.NullPointerException - if the path is null

addTracker

private void addTracker(java.lang.String path,
                        java.lang.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

getTrackCount

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

Returns:
the number of files being tracked

getDeleteFailures

public java.util.List<java.lang.String> getDeleteFailures()
Return the file paths that failed to delete.

Returns:
the file paths that failed to delete
Since:
Commons IO 2.0

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. Once called, no new objects can be tracked by the file cleaner.



Copyright (c) 2002-2012 Apache Software Foundation