FileChangeWatcher (Apache ZooKeeper - Server 3.9.1 API)

java.lang.Object
- org.apache.zookeeper.common.FileChangeWatcher

```
public final class FileChangeWatcher
extends Object
```
Instances of this class can be used to watch a directory for file changes. When a file is added to, deleted from, or is modified in the given directory, the callback provided by the user will be called from a background thread. Some things to keep in mind:
- The callback should be thread-safe.
- Changes that happen around the time the thread is started may be missed.
- There is a delay between a file changing and the callback firing.
- The watch is not recursive - changes to subdirectories will not trigger a callback.

Nested Class Summary

Nested Classes
Modifier and Type Class Description

static class FileChangeWatcher.State

Constructor Summary

Constructors
Constructor	Description
`FileChangeWatcher(Path dirPath, Consumer<WatchEvent<?>> callback)`	Creates a watcher that watches `dirPath` and invokes `callback` on changes.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`FileChangeWatcher.State`	`getState()`	Returns the current `FileChangeWatcher.State`.
`void`	`start()`	Tells the background thread to start.
`void`	`stop()`	Tells the background thread to stop.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - FileChangeWatcher
```
public FileChangeWatcher(Path dirPath,
                         Consumer<WatchEvent<?>> callback)
                  throws IOException
```
    Creates a watcher that watches dirPath and invokes callback on changes.
    
    Parameters:
    
    dirPath - the directory to watch.
    
    callback - the callback to invoke with events. event.kind() will return the type of event, and event.context() will return the filename relative to dirPath.
    
    Throws:
    
    IOException - if there is an error creating the WatchService.
- Method Detail
  - getState
```
public FileChangeWatcher.State getState()
```
    Returns the current FileChangeWatcher.State.
    
    Returns:
    
    the current state.
  - start
```
public void start()
```
    Tells the background thread to start. Does not wait for it to be running. Calling this method more than once has no effect.
  - stop
```
public void stop()
```
    Tells the background thread to stop. Does not wait for it to exit.