org.apache.commons.io.monitor
Class FileAlterationObserver

java.lang.Object
  org.apache.commons.io.monitor.FileAlterationObserver

All Implemented Interfaces:

Serializable

public class FileAlterationObserver
extends Object
implements Serializable

FileAlterationObserver represents the state of files below a root directory, checking the filesystem 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(new File("."), "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:

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

Alternatively, register the oberver(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.

Since:

2.0

Version:

$Id: FileAlterationObserver.java 1304052 2012-03-22 20:55:29Z ggregory $

See Also:

FileAlterationListener, FileAlterationMonitor, Serialized Form

Constructor Summary

	FileAlterationObserver(File directory) Construct an observer for the specified directory.
protected	FileAlterationObserver(FileEntry rootEntry, FileFilter fileFilter, IOCase caseSensitivity) Construct an observer for the specified directory, file filter and file comparator.
	FileAlterationObserver(File directory, FileFilter fileFilter) Construct an observer for the specified directory and file filter.
	FileAlterationObserver(File directory, FileFilter fileFilter, IOCase caseSensitivity) Construct an observer for the specified directory, file filter and file comparator.
	FileAlterationObserver(String directoryName) Construct an observer for the specified directory.
	FileAlterationObserver(String directoryName, FileFilter fileFilter) Construct an observer for the specified directory and file filter.
	FileAlterationObserver(String directoryName, FileFilter fileFilter, IOCase caseSensitivity) Construct an observer for the specified directory, file filter and file comparator.

Method Summary

void	addListener(FileAlterationListener listener) Add a file system listener.
void	checkAndNotify() Check whether the file and its chlidren have been created, modified or deleted.
void	destroy() Final processing.
File	getDirectory() Return the directory being observed.
FileFilter	getFileFilter() Return the fileFilter.
Iterable<FileAlterationListener>	getListeners() Returns the set of registered file system listeners.
void	initialize() Initialize the observer.
void	removeListener(FileAlterationListener listener) Remove a file system listener.
String	toString() Provide a String representation of this observer.

Methods inherited from class java.lang.Object

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

Constructor Detail

FileAlterationObserver

public FileAlterationObserver(String directoryName)

Construct an observer for the specified directory.

Parameters:

directoryName - the name of the directory to observe

FileAlterationObserver

public FileAlterationObserver(String directoryName,
                              FileFilter fileFilter)

Construct 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(String directoryName,
                              FileFilter fileFilter,
                              IOCase caseSensitivity)

Construct 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

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

FileAlterationObserver

public FileAlterationObserver(File directory)

Construct an observer for the specified directory.

Parameters:

directory - the directory to observe

FileAlterationObserver

public FileAlterationObserver(File directory,
                              FileFilter fileFilter)

Construct 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(File directory,
                              FileFilter fileFilter,
                              IOCase caseSensitivity)

Construct 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

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

FileAlterationObserver

protected FileAlterationObserver(FileEntry rootEntry,
                                 FileFilter fileFilter,
                                 IOCase caseSensitivity)

Construct 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

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

Method Detail

getDirectory

public File getDirectory()

Return the directory being observed.

Returns:

the directory being observed

getFileFilter

public FileFilter getFileFilter()

Return the fileFilter.

Returns:

the fileFilter

Since:

2.1

addListener

public void addListener(FileAlterationListener listener)

Add a file system listener.

Parameters:

listener - The file system listener

removeListener

public void removeListener(FileAlterationListener listener)

Remove a file system listener.

Parameters:

listener - The file system listener

getListeners

public Iterable<FileAlterationListener> getListeners()

Returns the set of registered file system listeners.

Returns:

The file system listeners

initialize

public void initialize()
                throws Exception

Initialize the observer.

Throws:

Exception - if an error occurs

destroy

public void destroy()
             throws Exception

Final processing.

Throws:

Exception - if an error occurs

checkAndNotify

public void checkAndNotify()

Check whether the file and its chlidren have been created, modified or deleted.

toString

public String toString()

Provide a String representation of this observer.

Overrides:

toString in class Object

Returns:

a String representation of this observer