FileAlterationObserver (Javadocs [I2P+ 2.11.0+]

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 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.
See Also:

FileAlterationListener, FileAlterationMonitor, Serialized Form

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class FileAlterationObserver.Builder
Builds instances of FileAlterationObserver.

Nested Classes
Modifier and Type	Class and Description
`static class`	`FileAlterationObserver.Builder` Builds instances of `FileAlterationObserver`.

Constructor Summary

Constructors
Modifier	Constructor and Description
`protected`	`FileAlterationObserver(FileEntry rootEntry, FileFilter fileFilter, IOCase ioCase)` Constructs an observer for the specified directory, file filter and file comparator.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`addListener(FileAlterationListener listener)` Adds a file system listener.
`static FileAlterationObserver.Builder`	`builder()` Creates a new builder.
`void`	`checkAndNotify()` Checks whether the file and its children have been created, modified or deleted.
`void`	`destroy()` Final processing.
`(package private) Comparator<File>`	`getComparator()`
`File`	`getDirectory()` Returns the directory being observed.
`FileFilter`	`getFileFilter()` Returns the fileFilter.
`Iterable<FileAlterationListener>`	`getListeners()` Returns the set of registered file system listeners.
`void`	`initialize()` Initializes the observer.
`void`	`removeListener(FileAlterationListener listener)` Removes a file system listener.
`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

- Constructor Detail
  - FileAlterationObserver
```
protected FileAlterationObserver(FileEntry rootEntry,
                                 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.
- Method Detail
  - addListener
```
public void addListener(FileAlterationListener listener)
```
    Adds a file system listener.
    
    Parameters:
    
    listener - The file system listener.
  - builder
```
public static FileAlterationObserver.Builder builder()
```
    Creates a new builder.
    
    Returns:
    
    a new builder.
  - checkAndNotify
```
public void checkAndNotify()
```
    Checks whether the file and its children have been created, modified or deleted.
  - destroy
```
public void destroy()
             throws Exception
```
    Final processing.
    
    Throws:
    
    Exception - if an error occurs.
  - getComparator
```
Comparator<File> getComparator()
```
  - getDirectory
```
public File getDirectory()
```
    Returns the directory being observed.
    
    Returns:
    
    the directory being observed.
  - getFileFilter
```
public FileFilter getFileFilter()
```
    Returns the fileFilter.
    
    Returns:
    
    the fileFilter.
  - getListeners
```
public Iterable<FileAlterationListener> getListeners()
```
    Returns the set of registered file system listeners.
    
    Returns:
    
    The file system listeners
  - initialize
```
public void initialize()
                throws Exception
```
    Initializes the observer.
    
    Throws:
    
    Exception - if an error occurs.
  - removeListener
```
public void removeListener(FileAlterationListener listener)
```
    Removes a file system listener.
    
    Parameters:
    
    listener - The file system listener.
  - toString
```
public String toString()
```
    Returns a String representation of this observer.
    
    Overrides:
    
    toString in class Object
    
    Returns:
    
    a String representation of this observer.

Class FileAlterationObserver

Basic Usage

File Filters

FileEntry

Deprecating Serialization

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

FileAlterationObserver

Method Detail

addListener

builder

checkAndNotify

destroy

getComparator

getDirectory

getFileFilter

getListeners

initialize

removeListener

toString