Java implementation of directory file monitoring instance code

Versions earlier than Java 7 do not have native support. Let's talk about the solution of JDK 1.7 and earlier:

Event-driven approach, without having to perform directory scans, but related to the platform
Thread round-robin scanning, implemented in java only, perfect cross-platform, but with a large number of listening files, the scanning volume is too large, and the response is not very timely, depending on the scanning interval

JNotify is event-driven, so the processing methods for different platforms are different. Therefore, you need to add jy y. dll/jnotify_64bit.dll in java. library. path. The simplest solution is to directly modify the code. The System. loadLibrary of lines 47 and 51 of jpolicy_win32.java is changed to System. load (dllpath), and the changes on other platforms are also the same. Then, export the dll and so files into a jar package, and the world will be quiet.

The example code is as follows:

The code is as follows:

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Public static void main (String [] args) throws InterruptedException, IOException { String dir = new File (args. length = 0? ".": Args [0]). getCanonicalFile (). getAbsolutePath (); JNotify. addWatch (dir, FILE_ANY, true, new jpolicylistener (){ Public void fileRenamed (int wd, String rootPath, String oldName, String newName ){ System. out. println ("renamed" + rootPath + ":" + oldName + "->" + newName );   }   Public void fileModified (int wd, String rootPath, String name ){ System. out. println ("modified" + rootPath + ":" + name );   }   Public void fileDeleted (int wd, String rootPath, String name ){ System. out. println ("deleted" + rootPath + ":" + name );   }   Public void fileCreated (int wd, String rootPath, String name ){ System. out. println ("created" + rootPath + ":" + name );   } });   System. err. println ("Monitoring" + dir + ", ctrl + c to stop "); While (true) Thread. sleep (10000 ); }

Jpathwath has more code to write. For event description, refer to this. A simple example is as follows:

The code is as follows:

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Public static void main (String [] args ){ WatchService watchService = FileSystems. getDefault (). newWatchService (); Path watchedPath = Paths. get ("E:/temp "); Try { WatchKey key = watchedPath. register (watchService, StandardWatchEventKind. ENTRY_MODIFY ); System. out. println (key. isValid ()); } Catch (UnsupportedOperationException uox ){ System. err. println ("file watching not supported! "); } Catch (IOException iox ){ System. err. println ("I/O errors ");  } For (;;){ // Take () will block until a file has been created/deleted WatchKey signalledKey; Try { SignalledKey = watchService. take (); } Catch (InterruptedException ix ){ Continue; } Catch (ClosedWatchServiceException cwse ){ System. out. println ("watch service closed, terminating ."); Break;   }   List <WatchEvent <?> List = signalledKey. pollEvents ();   SignalledKey. reset (); For (WatchEvent <?> E: list ){ String message = ""; If (e. kind () = StandardWatchEventKind. ENTRY_MODIFY ){ Path context = (Path) e. context (); Message = context. toString () + "modified ";    } System. out. println (message );   }  } }

Note that on Windows, renaming a file produces two events-renaming and modification. You must pay attention to this when processing the event.