Package org.apache.commons.io.monitor

Class FileAlterationObserver

java.lang.Object

org.apache.commons.io.monitor.FileAlterationObserver

All Implemented Interfaces:

java.io.Serializable

public class FileAlterationObserver
extends java.lang.Object
implements java.io.Serializable

FileAlterationObserver represents the state of files below a root directory, checking the file system and notifying listeners of create, change or delete events.

To use this implementation:

• Create FileAlterationListener implementation(s) that process the file/directory create, change and delete events
• Register the listener(s) with a FileAlterationObserver for the appropriate directory.
• Either register the observer(s) with a FileAlterationMonitor or run manually.

Basic Usage

Create a FileAlterationObserver for the directory and register the listeners:

      File directory = new File(FileUtils.current(), "src");
      FileAlterationObserver observer = new FileAlterationObserver(directory);
      observer.addListener(...);
      observer.addListener(...);
 

To manually observe a directory, initialize the observer and invoked the checkAndNotify() method as required:

      // initialize
      observer.init();
      ...
      // invoke as required
      observer.checkAndNotify();
      ...
      observer.checkAndNotify();
      ...
      // finished
      observer.finish();
 

Alternatively, register the observer(s) with a FileAlterationMonitor, which creates a new thread, invoking the observer at the specified interval:

      long interval = ...
      FileAlterationMonitor monitor = new FileAlterationMonitor(interval);
      monitor.addObserver(observer);
      monitor.start();
      ...
      monitor.stop();
 

File Filters

This implementation can monitor portions of the file system by using FileFilters to observe only the files and/or directories that are of interest. This makes it more efficient and reduces the noise from unwanted file system events.

Commons IO has a good range of useful, ready-made File Filter implementations for this purpose.

For example, to only observe 1) visible directories and 2) files with a ".java" suffix in a root directory called "src" you could set up a FileAlterationObserver in the following way:

      // Create a FileFilter
      IOFileFilter directories = FileFilterUtils.and(
                                      FileFilterUtils.directoryFileFilter(),
                                      HiddenFileFilter.VISIBLE);
      IOFileFilter files       = FileFilterUtils.and(
                                      FileFilterUtils.fileFileFilter(),
                                      FileFilterUtils.suffixFileFilter(".java"));
      IOFileFilter filter = FileFilterUtils.or(directories, files);

      // Create the File system observer and register File Listeners
      FileAlterationObserver observer = new FileAlterationObserver(new File("src"), filter);
      observer.addListener(...);
      observer.addListener(...);
 

FileEntry

FileEntry represents the state of a file or directory, capturing File attributes at a point in time. Custom implementations of FileEntry can be used to capture additional properties that the basic implementation does not support. The FileEntry.refresh(File) method is used to determine if a file or directory has changed since the last check and stores the current state of the File's properties.

Deprecating Serialization

Serialization is deprecated and will be removed in 3.0.

Since:

2.0

See Also:

FileAlterationListener, FileAlterationMonitor, Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
private java.util.Comparator<java.io.File>	comparator	Compares file names.
private java.io.FileFilter	fileFilter	The file filter or null if none.
private java.util.List<FileAlterationListener>	listeners	List of listeners.
private FileEntry	rootEntry	The root directory to observe.
private static long	serialVersionUID

Constructor Summary

Constructors

Modifier	Constructor	Description
	FileAlterationObserver(java.io.File directory)	Constructs an observer for the specified directory.
	FileAlterationObserver(java.io.File directory, java.io.FileFilter fileFilter)	Constructs an observer for the specified directory and file filter.
	FileAlterationObserver(java.io.File directory, java.io.FileFilter fileFilter, IOCase ioCase)	Constructs an observer for the specified directory, file filter and file comparator.
	FileAlterationObserver(java.lang.String directoryName)	Constructs an observer for the specified directory.
	FileAlterationObserver(java.lang.String directoryName, java.io.FileFilter fileFilter)	Constructs an observer for the specified directory and file filter.
	FileAlterationObserver(java.lang.String directoryName, java.io.FileFilter fileFilter, IOCase ioCase)	Constructs an observer for the specified directory, file filter and file comparator.
private	FileAlterationObserver(FileEntry rootEntry, java.io.FileFilter fileFilter, java.util.Comparator<java.io.File> comparator)	Constructs an observer for the specified directory, file filter and file comparator.
protected	FileAlterationObserver(FileEntry rootEntry, java.io.FileFilter fileFilter, IOCase ioCase)	Constructs an observer for the specified directory, file filter and file comparator.

Method Summary

Modifier and Type	Method	Description
void	addListener(FileAlterationListener listener)	Adds a file system listener.
private void	checkAndFire(FileEntry parentEntry, FileEntry[] previousEntries, java.io.File[] currentEntries)	Compares two file lists for files which have been created, modified or deleted.
void	checkAndNotify()	Checks whether the file and its children have been created, modified or deleted.
private FileEntry	createFileEntry(FileEntry parent, java.io.File file)	Creates a new file entry for the specified file.
void	destroy()	Final processing.
private void	fireOnChange(FileEntry entry, java.io.File file)	Fires directory/file change events to the registered listeners.
private void	fireOnCreate(FileEntry entry)	Fires directory/file created events to the registered listeners.
private void	fireOnDelete(FileEntry entry)	Fires directory/file delete events to the registered listeners.
java.io.File	getDirectory()	Returns the directory being observed.
java.io.FileFilter	getFileFilter()	Returns the fileFilter.
java.lang.Iterable<FileAlterationListener>	getListeners()	Returns the set of registered file system listeners.
void	initialize()	Initializes the observer.
private FileEntry[]	listFileEntries(java.io.File file, FileEntry entry)	Lists the file entries in file.
private java.io.File[]	listFiles(java.io.File directory)	Lists the contents of a directory.
void	removeListener(FileAlterationListener listener)	Removes a file system listener.
private java.io.File[]	sort(java.io.File[] files)
private static java.util.Comparator<java.io.File>	toComparator(IOCase ioCase)
java.lang.String	toString()	Returns a String representation of this observer.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

listeners

private final transient java.util.List<FileAlterationListener> listeners

List of listeners.

rootEntry

private final FileEntry rootEntry

The root directory to observe.

fileFilter

private final transient java.io.FileFilter fileFilter

The file filter or null if none.

comparator

private final java.util.Comparator<java.io.File> comparator

Compares file names.

Constructor Detail

FileAlterationObserver

public FileAlterationObserver(java.io.File directory)

Constructs an observer for the specified directory.

Parameters:

directory - the directory to observe.

FileAlterationObserver

public FileAlterationObserver(java.io.File directory,
                              java.io.FileFilter fileFilter)

Constructs an observer for the specified directory and file filter.

Parameters:

directory - the directory to observe.

fileFilter - The file filter or null if none.

FileAlterationObserver

public FileAlterationObserver(java.io.File directory,
                              java.io.FileFilter fileFilter,
                              IOCase ioCase)

Constructs an observer for the specified directory, file filter and file comparator.

Parameters:

directory - the directory to observe.

fileFilter - The file filter or null if none.

ioCase - what case sensitivity to use comparing file names, null means system sensitive.

FileAlterationObserver

private FileAlterationObserver(FileEntry rootEntry,
                               java.io.FileFilter fileFilter,
                               java.util.Comparator<java.io.File> comparator)

Constructs an observer for the specified directory, file filter and file comparator.

Parameters:

rootEntry - the root directory to observe.

fileFilter - The file filter or null if none.

comparator - how to compare files.

FileAlterationObserver

protected FileAlterationObserver(FileEntry rootEntry,
                                 java.io.FileFilter fileFilter,
                                 IOCase ioCase)

Constructs an observer for the specified directory, file filter and file comparator.

Parameters:

rootEntry - the root directory to observe.

fileFilter - The file filter or null if none.

ioCase - what case sensitivity to use comparing file names, null means system sensitive.

FileAlterationObserver

public FileAlterationObserver(java.lang.String directoryName)

Constructs an observer for the specified directory.

Parameters:

directoryName - the name of the directory to observe.

FileAlterationObserver

public FileAlterationObserver(java.lang.String directoryName,
                              java.io.FileFilter fileFilter)

Constructs an observer for the specified directory and file filter.

Parameters:

directoryName - the name of the directory to observe.

fileFilter - The file filter or null if none.

FileAlterationObserver

public FileAlterationObserver(java.lang.String directoryName,
                              java.io.FileFilter fileFilter,
                              IOCase ioCase)

Constructs an observer for the specified directory, file filter and file comparator.

Parameters:

directoryName - the name of the directory to observe.

fileFilter - The file filter or null if none.

ioCase - what case sensitivity to use comparing file names, null means system sensitive.

Method Detail

toComparator

private static java.util.Comparator<java.io.File> toComparator(IOCase ioCase)

addListener

public void addListener(FileAlterationListener listener)

Adds a file system listener.

Parameters:

listener - The file system listener.

checkAndFire

private void checkAndFire(FileEntry parentEntry,
                          FileEntry[] previousEntries,
                          java.io.File[] currentEntries)

Compares two file lists for files which have been created, modified or deleted.

Parameters:

parentEntry - The parent entry.

previousEntries - The original list of file entries.

currentEntries - The current list of files entries.

checkAndNotify

public void checkAndNotify()

Checks whether the file and its children have been created, modified or deleted.

createFileEntry

private FileEntry createFileEntry(FileEntry parent,
                                  java.io.File file)

Creates a new file entry for the specified file.

Parameters:

parent - The parent file entry.

file - The file to wrap.

Returns:

A new file entry.

destroy

public void destroy()
             throws java.lang.Exception

Final processing.

Throws:

java.lang.Exception - if an error occurs.

fireOnChange

private void fireOnChange(FileEntry entry,
                          java.io.File file)

Fires directory/file change events to the registered listeners.

Parameters:

entry - The previous file system entry.

file - The current file.

fireOnCreate

private void fireOnCreate(FileEntry entry)

Fires directory/file created events to the registered listeners.

Parameters:

entry - The file entry.

fireOnDelete

private void fireOnDelete(FileEntry entry)

Fires directory/file delete events to the registered listeners.

Parameters:

entry - The file entry.

getDirectory

public java.io.File getDirectory()

Returns the directory being observed.

Returns:

the directory being observed.

getFileFilter

public java.io.FileFilter getFileFilter()

Returns the fileFilter.

Returns:

the fileFilter.

Since:

2.1

getListeners

public java.lang.Iterable<FileAlterationListener> getListeners()

Returns the set of registered file system listeners.

Returns:

The file system listeners

initialize

public void initialize()
                throws java.lang.Exception

Initializes the observer.

Throws:

java.lang.Exception - if an error occurs.

listFileEntries

private FileEntry[] listFileEntries(java.io.File file,
                                    FileEntry entry)

Lists the file entries in file.

Parameters:

file - The directory to list.

entry - the parent entry.

Returns:

The child file entries.

listFiles

private java.io.File[] listFiles(java.io.File directory)

Lists the contents of a directory.

Parameters:

directory - The directory to list.

Returns:

the directory contents or a zero length array if the empty or the file is not a directory

removeListener

public void removeListener(FileAlterationListener listener)

Removes a file system listener.

Parameters:

listener - The file system listener.

sort

private java.io.File[] sort(java.io.File[] files)

toString

public java.lang.String toString()

Returns a String representation of this observer.

Overrides:

toString in class java.lang.Object

Returns:

a String representation of this observer.