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Java WatchService stops watching folder if renamed (OSX)

I'm trying to setup a WatchService on an MacOS (High Sierra) and it seems to be working ok except when I rename dir. As an example I rename "test" to "hello" and here's what I get:
ENTRY_CREATE: /Users/david/Desktop/watchme/hello
update: /Users/david/Desktop/watchme/test -> /Users/david/Desktop/watchme/hello
ENTRY_DELETE: /Users/david/Desktop/watchme/test
I would expect to see:
register: /Users/david/Desktop/watchme/hello
But that isn't happening so when I modify anything inside of "hello", the only response I get is:
ENTRY_MODIFY: /Users/david/Desktop/watchme/hello
Nothing about the files or folders inside "hello"
I copied the following code right from Oracle with the exception of hard coding the attrs so I can run it in Idea:
import java.nio.file.*;
import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.LinkOption.*;
import java.nio.file.attribute.*;
import java.io.*;
import java.util.*;
/**
* Example to watch a directory (or tree) for changes to files.
*/
public class WatchDir {
private final WatchService watcher;
private final Map<WatchKey,Path> keys;
private final boolean recursive;
private boolean trace = false;
#SuppressWarnings("unchecked")
private static <T> WatchEvent<T> cast(WatchEvent<?> event) {
return (WatchEvent<T>)event;
}
/**
* Register the given directory with the WatchService
*/
private void register(Path dir) throws IOException {
WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
if (trace) {
Path prev = keys.get(key);
if (prev == null) {
System.out.format("register: %s\n", dir);
} else {
if (!dir.equals(prev)) {
System.out.format("update: %s -> %s\n", prev, dir);
}
}
}
keys.put(key, dir);
}
/**
* Register the given directory, and all its sub-directories, with the
* WatchService.
*/
private void registerAll(final Path start) throws IOException {
// register directory and sub-directories
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
throws IOException
{
register(dir);
return FileVisitResult.CONTINUE;
}
});
}
/**
* Creates a WatchService and registers the given directory
*/
private WatchDir(Path dir, boolean recursive) throws IOException {
this.watcher = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<>();
this.recursive = recursive;
if (recursive) {
System.out.format("Scanning %s ...\n", dir);
registerAll(dir);
System.out.println("Done.");
} else {
register(dir);
}
// enable trace after initial registration
this.trace = true;
}
/**
* Process all events for keys queued to the watcher
*/
private void processEvents() {
for (;;) {
// wait for key to be signalled
WatchKey key;
try {
key = watcher.take();
} catch (InterruptedException x) {
return;
}
Path dir = keys.get(key);
if (dir == null) {
System.err.println("WatchKey not recognized!!");
continue;
}
for (WatchEvent<?> event: key.pollEvents()) {
WatchEvent.Kind kind = event.kind();
// TBD - provide example of how OVERFLOW event is handled
if (kind == OVERFLOW) {
continue;
}
// Context for directory entry event is the file name of entry
WatchEvent<Path> ev = cast(event);
Path name = ev.context();
Path child = dir.resolve(name);
// print out event
System.out.format("%s: %s\n", event.kind().name(), child);
if(child.toString().contains("testdir")) {
System.out.println("This is an update");
}
// if directory is created, and watching recursively, then
// register it and its sub-directories
if (recursive && (kind == ENTRY_CREATE)) {
try {
if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
registerAll(child);
}
} catch (IOException x) {
// ignore to keep sample readbale
}
}
}
// reset key and remove from set if directory no longer accessible
boolean valid = key.reset();
if (!valid) {
keys.remove(key);
// all directories are inaccessible
if (keys.isEmpty()) {
break;
}
}
}
}
private static void usage() {
System.err.println("usage: java WatchDir [-r] dir");
System.exit(-1);
}
#SuppressWarnings("ParameterCanBeLocal")
public static void main(String[] args) throws IOException {
// parse arguments
args = new String[2]; // Added for debug
args[0] = "-r"; // Added for debug
args[1] = "/Users/david/Desktop/watchme"; // Added for debug
if (args.length == 0 || args.length > 2)
usage();
boolean recursive = false;
int dirArg = 0;
if (args[0].equals("-r")) {
if (args.length < 2)
usage();
recursive = true;
dirArg++;
}
// register directory and process its events
Path dir = Paths.get(args[dirArg]);
new WatchDir(dir, recursive).processEvents();
}
}

It's an interesting question. I tried on my own Mac and get the same result.
When we rename test to hello, OS first create hello and then delete test, both of watchme and test will get event. WatchKey of watchme folder gets ENTRY_CREATE and ENTRY_DELETE events.
In this step, though new dir name is hello, but after this code
WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
the key we get is still test's watch key, that's why we see update log in console.
ENTRY_CREATE: /Users/david/Desktop/watchme/hello
update: /Users/david/Desktop/watchme/test -> /Users/david/Desktop/watchme/hello
ENTRY_DELETE: /Users/david/Desktop/watchme/test
WatchKey of test also recieved an event. But this event is an invalid event, the key(Infact this is hello's watchKey now) will be removed from keys map. So the change of hello folder will show nothing in console.
Here is the the interesting thing. Why we get test's watchKey when input dir is hello. When I debug code, stop it at
WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
for a while when receive hello's ENTRY_CREATE event, and I get hello's key not test's key and register log not update log. It seems we can't see the hello folder at once when call dir.register method. I don't know more about what OS do when we rename a folder, hope others' reply.
This is my test code added logs in processEvents, you may try it yourself.
private void processEvents() {
for (; ; ) {
// wait for key to be signalled
WatchKey key;
try {
key = watcher.take();
} catch (InterruptedException x) {
return;
}
Path dir = keys.get(key);
if (dir == null) {
System.err.println("WatchKey not recognized!!");
continue;
} else {
System.out.println("CurrentDir=" + dir.getFileName() + " keySize=" + keys.size() + " valid=" + key.isValid());
}
for (WatchEvent<?> event : key.pollEvents()) {
WatchEvent.Kind kind = event.kind();
// TBD - provide example of how OVERFLOW event is handled
if (kind == OVERFLOW) {
continue;
}
// Context for directory entry event is the file name of entry
WatchEvent<Path> ev = cast(event);
Path name = ev.context();
Path child = dir.resolve(name);
// print out event
System.out.format("%s: %s\n", event.kind().name(), child);
// if directory is created, and watching recursively, then
// register it and its sub-directories
if (recursive && (kind == ENTRY_CREATE)) {
try {
if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
registerAll(child);
}
} catch (IOException x) {
// ignore to keep sample readbale
}
}
}
// reset key and remove from set if directory no longer accessible
boolean valid = key.reset();
if (!valid) {
System.out.println("Remove From keys");
keys.remove(key);
// all directories are inaccessible
if (keys.isEmpty()) {
break;
}
}
}
}

Watch service acquiring file handle

I am using java watch service in my application to get notified of any file changes.
But the problem is watch service holds the file handle of the parent directory.
For e.g. if my hierarchy is
F
-F1
-F2
When i register watch service on F, F1 and F2. Then if i try to rename or delete the parent folder F, there comes a message of file is opened by another program which is the watch service.
I have found this issue mentioned here http://bugs.java.com/bugdatabase/view_bug.do;jsessionid=76a42b61021a94ffffffffa049f7587fd4149?bug_id=6972833
Also have tried the File_Tree modifier to circumvent this issue but it did not help. Probably i have not used the File_Tree modifier properly.
Below is the sample code which i am testing on. Please check if the usage of FILE_TREE modifier is proper in my code.
/**
* Example to watch a directory (or tree) for changes to files.
* This code is direct copy from https://docs.oracle.com/javase/tutorial/essential/io/examples/WatchDir.java
*/
public class FileWatcher {
private final WatchService watcher;
private final Map<WatchKey,Path> keys;
private final boolean recursive;
private boolean trace = false;
#SuppressWarnings("unchecked")
static <T> WatchEvent<T> cast(WatchEvent<?> event) {
return (WatchEvent<T>)event;
}
/**
* Register the given directory with the WatchService
*/
private void register(Path dir) throws IOException {
WatchKey key = dir.register(watcher, new WatchEvent.Kind[] { ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY, OVERFLOW },com.sun.nio.file.ExtendedWatchEventModifier.FILE_TREE);
if (trace) {
Path prev = keys.get(key);
if (prev == null) {
System.out.format("register: %s\n", dir);
} else {
if (!dir.equals(prev)) {
System.out.format("update: %s -> %s\n", prev, dir);
}
}
}
keys.put(key, dir);
}
/**
* Register the given directory, and all its sub-directories, with the
* WatchService.
*/
private void registerAll(final Path start) throws IOException {
// register directory and sub-directories
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
throws IOException
{
register(dir);
return FileVisitResult.CONTINUE;
}
});
}
/**
* Creates a WatchService and registers the given directory
*/
FileWatcher(Path dir, boolean recursive) throws IOException {
this.watcher = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<WatchKey,Path>();
this.recursive = recursive;
if (recursive) {
System.out.format("Scanning %s ...\n", dir);
registerAll(dir);
System.out.println("Done.");
} else {
register(dir);
}
// enable trace after initial registration
this.trace = true;
}
/**
* Process all events for keys queued to the watcher
*/
void processEvents() {
for (;;) {
// wait for key to be signalled
WatchKey key;
try {
key = watcher.take();
} catch (InterruptedException x) {
return;
}
Path dir = keys.get(key);
if (dir == null) {
System.err.println("WatchKey not recognized!!");
continue;
}
for (WatchEvent<?> event: key.pollEvents()) {
WatchEvent.Kind kind = event.kind();
// TBD - provide example of how OVERFLOW event is handled
if (kind == OVERFLOW) {
continue;
}
// Context for directory entry event is the file name of entry
WatchEvent<Path> ev = cast(event);
Path name = ev.context();
Path child = dir.resolve(name);
// print out event
System.out.format("%s: %s\n", event.kind().name(), child);
// if directory is created, and watching recursively, then
// register it and its sub-directories
if (recursive && kind == ENTRY_CREATE) {
try {
if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
registerAll(child);
}
} catch (IOException x) {
// ignore to keep sample readbale
}
}
}
// reset key and remove from set if directory no longer accessible
boolean valid = key.reset();
if (!valid) {
keys.remove(key);
// all directories are inaccessible
if (keys.isEmpty()) {
break;
}
}
}
}
static void usage() {
System.err.println("usage: java WatchDir [-r] dir");
System.exit(-1);
}
public static void main(String[] args) throws IOException {
// parse arguments
if (args.length == 0 || args.length > 2) {
usage();
}
boolean recursive = false;
int dirArg = 0;
if (args[0].equals("-r")) {
if (args.length < 2) {
usage();
}
recursive = false;
dirArg++;
}
// register directory and process its events
Path dir = Paths.get(args[dirArg]);
new FileWatcher(dir, recursive).processEvents();
}
}

Dug a little bit into the docs and find out a fix for myself.
With the File_Tree modifier a single key is assigned to all the folders/dirs. So we need to work with a single key.
Hence i am trying to reregister with the same root path and then reusing the key on every new creation of an item under the watched directory.
major take aways are
Recursive way of visting every folder in the directory is not required anymore.
Re registering on the same path is required whenever a new folder is created under the root path because only key is required every time
I am not sure on the performance part since everytime i am registering the whole path. probably i will do some performance analysis.
Below is the modified version of my code. Let me know if the code is not clear
package com.sap.mcm;
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.HashMap;
import java.util.Map;
import com.sun.nio.file.ExtendedWatchEventModifier;
/**
* Example to watch a directory (or tree) for changes to files.
* This code is direct copy from https://docs.oracle.com/javase/tutorial/essential/io/examples/WatchDir.java
*/
public class FileWatcher {
private final WatchService watcher;
private final Map<WatchKey,Path> keys;
private final boolean recursive;
private boolean trace = true;
private Path parentDir;
private WatchKey key;
#SuppressWarnings("unchecked")
static <T> WatchEvent<T> cast(WatchEvent<?> event) {
return (WatchEvent<T>)event;
}
/**
* Register the given directory with the WatchService
*/
private void register(Path dir) throws IOException {
try {
parentDir = dir;
key = parentDir.register(watcher, new WatchEvent.Kind[] { ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY, OVERFLOW }, ExtendedWatchEventModifier.FILE_TREE);
} catch (UnsupportedOperationException usoe) {
usoe.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
public void reregister() throws IOException {
// WatchKey key = keys.get(path);
key.cancel();
register(parentDir);
}
/**
* Register the given directory, and all its sub-directories, with the
* WatchService.
*/
private void registerAll(final Path start) throws IOException {
// register directory and sub-directories
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
throws IOException {
register(dir);
return FileVisitResult.CONTINUE;
}
});
}
/**
* Creates a WatchService and registers the given directory
*/
FileWatcher(Path dir, boolean recursive) throws IOException {
this.watcher = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<WatchKey,Path>();
this.recursive = recursive;
if (recursive) {
System.out.format("Scanning %s ...\n", dir);
registerAll(dir);
System.out.println("Done.");
} else {
register(dir);
}
// enable trace after initial registration
this.trace = true;
}
/**
* Process all events for keys queued to the watcher
*/
void processEvents() {
for (;;) {
// wait for key to be signalled
WatchKey key;
try {
key = watcher.take();
} catch (InterruptedException x) {
return;
}
// Path dir = keys.get(key);
// if (dir == null) {
// System.err.println("WatchKey not recognized!!");
// continue;
// }
if (this.key != key) {
return;
}
for (WatchEvent<?> event: key.pollEvents()) {
WatchEvent.Kind kind = event.kind();
// TBD - provide example of how OVERFLOW event is handled
if (kind == OVERFLOW) {
continue;
}
// Context for directory entry event is the file name of entry
WatchEvent<Path> ev = cast(event);
ev.context();
// print out event
System.out.format("%s: %s \n", event.kind().name(), event.context());
// if directory is created, and watching recursively, then
// register it and its sub-directories
if (kind == ENTRY_CREATE) {
try {
// if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
reregister();
// }
} catch (IOException x) {
// ignore to keep sample readbale
}
}
}
// reset key and remove from set if directory no longer accessible
boolean valid = this.key.reset();
if (!valid) {
keys.remove(key);
// all directories are inaccessible
if (keys.isEmpty()) {
break;
}
}
}
}
static void usage() {
System.err.println("usage: java WatchDir [-r] dir");
System.exit(-1);
}
public static void main(String[] args) throws IOException {
// parse arguments
if (args.length == 0 || args.length > 2) {
usage();
}
boolean recursive = false;
int dirArg = 0;
if (args[0].equals("-r")) {
if (args.length < 2) {
usage();
}
recursive = false;
dirArg++;
}
// register directory and process its events
Path dir = Paths.get(args[dirArg]);
new FileWatcher(dir, recursive).processEvents();
}
}

i want to monitor my local disk of my computer to detect any of the file create,rename,delete,modify activity using java

Now by running below code i am getting "Access Denied Exception". please give any suggestion regarding that.
i just google fr some for some time and i get useful code for the same. i simply put my directory in a path and run a code. But it throws me exception.
This is a sample code that i used
package file_upload_monitor;
import java.nio.file.*;
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
import static java.nio.file.LinkOption.*;
import java.nio.file.attribute.*;
import java.io.*;
import java.util.*;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
public class WatchDir {
private final WatchService watcher;
private final Map<WatchKey,Path> keys;
private final boolean recursive;
private boolean trace = false;
private BlockingQueue<String> fileProcessingQueue;
//******* processedFileQueue **** will be used by other threads to retrive unlocked files.. so I have
// kept as public final
public final BlockingQueue<String> processedFileQueue;
private volatile boolean closeProcessingThread;
private volatile boolean closeWatcherThread;
private void processFiles(){
System.out.println("DirWatchProcessingThread Started");
String fileName;
outerLoop: while(!closeProcessingThread || !fileProcessingQueue.isEmpty()){
try{
fileName = fileProcessingQueue.poll(1000, TimeUnit.MILLISECONDS);
}catch(InterruptedException ie){
fileName = null;
}
if(fileName == null || fileName.equals("")){
continue outerLoop;
}
long startTime = System.currentTimeMillis();
innerLoop: while(true){
FileInputStream fis = null;
File file = new File(fileName);
try{
fis = new FileInputStream(fileName);
break innerLoop;
}catch(FileNotFoundException fnfe){
if(!file.exists() || file.isDirectory()){
System.out.println("File: '"+fileName+"has been deleted in file system or it is not file. Not processing this file.");
continue outerLoop;
}
try{
Thread.sleep(WatchDirParameters.millisToPuaseForFileLock);
}catch(InterruptedException ie){
}
if((System.currentTimeMillis() - startTime) > WatchDirParameters.millisToSwapFileForUnlocking){
if(fileProcessingQueue.offer(fileName)){
continue outerLoop;
}else{
startTime = System.currentTimeMillis();
continue innerLoop;
}
}
}finally{
if(fis != null){
try{
fis.close();
}catch(IOException ioe){
ioe.printStackTrace();
}
}
}
}
System.out.println("Queuing File: "+fileName);
processedLoop:while(true){
try{
if(processedFileQueue.offer(fileName, 1000, TimeUnit.MILLISECONDS)){
break processedLoop;
}
}catch(InterruptedException ie){
//ie.printStackTrace();
}
}
}
closeWatcherThread = true;
closeProcessingThread = true;
System.out.println("DirWatchProcessingThread Exited");
}
/**
* Process all events for keys queued to the watcher
*/
private void processEvents(){
System.out.println("DirWatcherThread started.");
while(!closeWatcherThread) {
// wait for key to be signalled
WatchKey key;
try {
key = watcher.take();
} catch (InterruptedException x) {
// if we are returning from these method, it means we no longer wants to watch directory
// we must close thread which may be waiting for file names in queue
continue;
}catch(ClosedWatchServiceException cwse){
break;
}
Path dir = keys.get(key);
if (dir == null) {
System.err.println("WatchKey not recognized!!");
continue;
}
try{
for (WatchEvent<?> event: key.pollEvents()) {
WatchEvent.Kind kind = event.kind();
if (kind == OVERFLOW) {
continue;
}
// Context for directory entry event is the file name of entry
WatchEvent<Path> ev = cast(event);
Path name = ev.context();
Path child = dir.resolve(name);
if(kind.equals(ENTRY_CREATE)){
// if directory is created, and watching recursively, then
// register it and its sub-directories
if (recursive) {
try {
if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
registerAll(child);
continue;
}
} catch (IOException x) {
// ignore to keep sample readbale
}
}
while(true){
if(fileProcessingQueue.remainingCapacity() < 2){
// if only one last can be inserted then don't queue this we need 1 empty space in queue
// for swaping file names..
// sleep for some time so processing thread may have made some rooms to queue in fileQueue
// this logic will not create any problems as only one this thread is inserting in queue
try{
Thread.sleep(200);
}catch(InterruptedException ie){
}
continue;
}
if(!fileProcessingQueue.offer(child.toString())){
// couldn't queue this element by whatever reason.. we will try to enqueue again by continuing loop
continue;
}else{
// file name has been queued in queue
break;
}
}
}
}
// reset key and remove from set if directory no longer accessible
boolean valid = key.reset();
if (!valid) {
keys.remove(key);
// all directories are inaccessible
if (keys.isEmpty()) {
break;
}
}
}catch(ClosedWatchServiceException cwse){
break;
}
}
closeProcessingThread = true;
closeWatcherThread = true;
System.out.println("DirWatcherThread exited.");
}
public void stopWatching(){
try{
watcher.close();
}catch(IOException ioe){
}
closeProcessingThread = true;
closeWatcherThread = true;
}
public static WatchDir watchDirectory(String dirName, boolean recursive) throws InvalidPathException, IOException, Exception{
try{
Path dir = Paths.get(dirName);
final WatchDir watchDir = new WatchDir(dir, recursive);
watchDir.closeProcessingThread = false;
watchDir.closeWatcherThread = false;
new Thread(new Runnable() {
public void run() {
watchDir.processFiles();
}
}, "DirWatchProcessingThread").start();
new Thread(new Runnable() {
public void run() {
watchDir.processEvents();
}
}, "DirWatcherThread").start();
return watchDir;
}catch(InvalidPathException ipe){
throw ipe;
}catch(IOException ioe){
throw ioe;
}catch(Exception e){
throw e;
}
}
#SuppressWarnings("unchecked")
private static <T> WatchEvent<T> cast(WatchEvent<?> event) {
return (WatchEvent<T>)event;
}
/**
* Register the given directory with the WatchService
*/
private void register(Path dir) throws IOException {
//WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
WatchKey key = dir.register(watcher, ENTRY_CREATE);
if (trace) {
Path prev = keys.get(key);
if (prev == null) {
System.out.format("register: %s\n", dir);
} else {
if (!dir.equals(prev)) {
System.out.format("update: %s -> %s\n", prev, dir);
}
}
}
keys.put(key, dir);
}
/**
* Register the given directory, and all its sub-directories, with the
* WatchService.
*/
private void registerAll(final Path start) throws IOException {
// register directory and sub-directories
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
register(dir);
return FileVisitResult.CONTINUE;
}
});
}
private void retry_registerAll(final Path start) throws IOException {
// register directory and sub-directories
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
// register(dir);
return FileVisitResult.CONTINUE;
}
});
}
/**
* Creates a WatchService and registers the given directory
*/
private WatchDir(Path dir, boolean recursive) throws IOException {
fileProcessingQueue = new ArrayBlockingQueue<String>(WatchDirParameters.fileQueueSize, false);
processedFileQueue = new ArrayBlockingQueue<String>(WatchDirParameters.fileQueueSize, false);
this.watcher = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<WatchKey,Path>();
this.recursive = recursive;
//CreateTxtFile.createFile(dir, 1);
if (recursive) {
System.out.format("Scanning %s ...\n", dir);
try{
***registerAll(dir);*** // i think exception is thrown by this line
}
catch(Exception e1)
{
System.out.println("reg exp"+e1);
}
System.out.println("Done.");
} else {
register(dir);
}
// enable trace after initial registration
this.trace = true;
}
public static void main(String[] args) throws IOException {
boolean recursive = true;
String path = "E:\\";
Path dir = Paths.get(path);
System.out.println(dir);
new WatchDir(dir, recursive).processEvents();
}
}
Exception that m getting in output :
Exception in thread "main" java.nio.file.AccessDeniedException: E:\$RECYCLE.BIN\S-1-5-18
at sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:83)
at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:97)
at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:102)
at sun.nio.fs.WindowsDirectoryStream.<init>(WindowsDirectoryStream.java:86)
at sun.nio.fs.WindowsFileSystemProvider.newDirectoryStream(WindowsFileSystemProvider.java:526)
at java.nio.file.Files.newDirectoryStream(Files.java:411)
at java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:179)
at java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:69)
at java.nio.file.Files.walkFileTree(Files.java:2600)
at java.nio.file.Files.walkFileTree(Files.java:2633)
at file_upload_monitor.WatchDir.retry_registerAll(WatchDir.java:272)
at file_upload_monitor.WatchDir.<init>(WatchDir.java:304)
at file_upload_monitor.WatchDir.main(WatchDir.java:325)

is there any way like when Access Denied Exception will occure we jst skip that path and continue with other path ??
Yes. Check if you have access by calling File.canRead() with something like,
File file = new File(fileName);
try {
if (!file.canRead()) {
continue outerLoop; // <-- can't read the file. continue the loop.
}
} catch (SecurityException se) {
se.printStackTrace();
continue outerLoop; // <-- can't read the file. continue the loop.
}

Watching a Directory for Changes in Java

I want to watch a directory for file changes. And I used WatchService in java.nio. I can successfully listen for file created event. But I can't listen for file modify event. I checked official java tutorial, but still struggling.
Here is the source code.
import static java.nio.file.LinkOption.NOFOLLOW_LINKS;
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;
import java.io.File;
import java.io.IOException;
import java.nio.file.FileSystem;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.WatchEvent;
import java.nio.file.WatchEvent.Kind;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
public class MainWatch {
public static void watchDirectoryPath(Path path) {
// Sanity check - Check if path is a folder
try {
Boolean isFolder = (Boolean) Files.getAttribute(path,
"basic:isDirectory", NOFOLLOW_LINKS);
if (!isFolder) {
throw new IllegalArgumentException("Path: " + path
+ " is not a folder");
}
} catch (IOException ioe) {
// Folder does not exists
ioe.printStackTrace();
}
System.out.println("Watching path: " + path);
// We obtain the file system of the Path
FileSystem fs = path.getFileSystem();
// We create the new WatchService using the new try() block
try (WatchService service = fs.newWatchService()) {
// We register the path to the service
// We watch for creation events
path.register(service, ENTRY_CREATE);
path.register(service, ENTRY_MODIFY);
path.register(service, ENTRY_DELETE);
// Start the infinite polling loop
WatchKey key = null;
while (true) {
key = service.take();
// Dequeueing events
Kind<?> kind = null;
for (WatchEvent<?> watchEvent : key.pollEvents()) {
// Get the type of the event
kind = watchEvent.kind();
if (OVERFLOW == kind) {
continue; // loop
} else if (ENTRY_CREATE == kind) {
// A new Path was created
Path newPath = ((WatchEvent<Path>) watchEvent)
.context();
// Output
System.out.println("New path created: " + newPath);
} else if (ENTRY_MODIFY == kind) {
// modified
Path newPath = ((WatchEvent<Path>) watchEvent)
.context();
// Output
System.out.println("New path modified: " + newPath);
}
}
if (!key.reset()) {
break; // loop
}
}
} catch (IOException ioe) {
ioe.printStackTrace();
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
public static void main(String[] args) throws IOException,
InterruptedException {
// Folder we are going to watch
// Path folder =
// Paths.get(System.getProperty("C:\\Users\\Isuru\\Downloads"));
File dir = new File("C:\\Users\\Isuru\\Downloads");
watchDirectoryPath(dir.toPath());
}
}

Actually you have incorrectly subscribed to events. Only last listener has been registered with ENTRY_DELETE events type.
To register for all kind of events at once you should use:
path.register(service, ENTRY_CREATE, ENTRY_MODIFY, ENTRY_DELETE);

Warning! Shameless self promotion!
I have created a wrapper around Java 1.7's WatchService that allows registering a directory and any number of glob patterns. This class will take care of the filtering and only emit events you are interested in.
DirectoryWatchService watchService = new SimpleDirectoryWatchService(); // May throw
watchService.register( // May throw
new DirectoryWatchService.OnFileChangeListener() {
#Override
public void onFileCreate(String filePath) {
// File created
}
#Override
public void onFileModify(String filePath) {
// File modified
}
#Override
public void onFileDelete(String filePath) {
// File deleted
}
},
<directory>, // Directory to watch
<file-glob-pattern-1>, // E.g. "*.log"
<file-glob-pattern-2>, // E.g. "input-?.txt"
... // As many patterns as you like
);
watchService.start();
Complete code is in this repo.

I made some classes for this.
public interface FileAvailableListener {
public void fileAvailable(File file) throws IOException;
}
and
public class FileChange {
private long lastModified;
private long size;
private long lastCheck;
public FileChange(File file) {
this.lastModified=file.lastModified();
this.size=file.length();
this.lastCheck = System.currentTimeMillis();
}
public long getLastModified() {
return lastModified;
}
public long getSize() {
return size;
}
public long getLastCheck() {
return lastCheck;
}
public boolean isStable(FileChange other,long stableTime) {
boolean b1 = (getLastModified()==other.getLastModified());
boolean b2 = (getSize()==other.getSize());
boolean b3 = ((other.getLastCheck()-getLastCheck())>stableTime);
return b1 && b2 && b3;
}
}
and
public class DirectoryWatcher {
private Timer timer;
private List<DirectoryMonitorTask> tasks = new ArrayList<DirectoryMonitorTask>();
public DirectoryWatcher() throws URISyntaxException, IOException, InterruptedException {
super();
timer = new Timer(true);
}
public void addDirectoryMonitoringTask(DirectoryMonitorTask task,long period) {
tasks.add(task);
timer.scheduleAtFixedRate(task, 5000, period);
}
public List<DirectoryMonitorTask> getTasks() {
return Collections.unmodifiableList(tasks);
}
public Timer getTimer() {
return timer;
}
}
and
class DirectoryMonitorTask extends TimerTask {
public final static String DIRECTORY_NAME_ARCHIVE="archive";
public final static String DIRECTORY_NAME_ERROR="error";
public final static String LOCK_FILE_EXTENSION=".lock";
public final static String ERROR_FILE_EXTENSION=".error";
public final static String FILE_DATE_FORMAT="yyyyMMddHHmmssSSS";
private String name;
private FileAvailableListener listener;
private Path directory;
private File directoryArchive;
private File directoryError;
private long stableTime;
private FileFilter filter;
private WatchService watchService;
private SimpleDateFormat dateFormatter = new SimpleDateFormat(FILE_DATE_FORMAT);
private Hashtable<File,FileChange> fileMonitor = new Hashtable<File,FileChange>();
public DirectoryMonitorTask(String name,FileAvailableListener listener,Path directory,long stableTime,FileFilter filter) throws IOException {
super();
this.name=name;
this.listener=listener;
this.directory=directory;
this.stableTime=stableTime;
if (stableTime<1) {
stableTime=1000;
}
this.filter=filter;
validateNotNull("Name",name);
validateNotNull("Listener",listener);
validateNotNull("Directory",directory);
validate(directory);
directoryArchive = new File(directory.toFile(),DIRECTORY_NAME_ARCHIVE);
directoryError = new File(directory.toFile(),DIRECTORY_NAME_ERROR);
directoryArchive.mkdir();
directoryError.mkdir();
//
log("Constructed for "+getDirectory().toFile().getAbsolutePath());
initialize();
//
watchService = FileSystems.getDefault().newWatchService();
directory.register(watchService,StandardWatchEventKinds.ENTRY_CREATE,StandardWatchEventKinds.ENTRY_DELETE,StandardWatchEventKinds.ENTRY_MODIFY);
log("Started");
}
private void initialize() {
File[] files = getDirectory().toFile().listFiles();
for (File file : files) {
if (isLockFile(file)) {
file.delete();
} else if (acceptFile(file)) {
fileMonitor.put(file,new FileChange(file));
log("Init file added -"+file.getName());
}
}
}
public SimpleDateFormat getDateFormatter() {
return dateFormatter;
}
public Path getDirectory() {
return directory;
}
public FileAvailableListener getListener() {
return listener;
}
public String getName() {
return name;
}
public WatchService getWatchService() {
return watchService;
}
public long getStableTime() {
return stableTime;
}
public File getDirectoryArchive() {
return directoryArchive;
}
public File getDirectoryError() {
return directoryError;
}
public FileFilter getFilter() {
return filter;
}
public Iterator<File> getMonitoredFiles() {
return fileMonitor.keySet().iterator();
}
#Override
public void run() {
WatchKey key;
try {
key = getWatchService().take();
// Poll all the events queued for the key
for (WatchEvent<?> event : key.pollEvents()) {
#SuppressWarnings("unchecked")
Path filePath = ((WatchEvent<Path>) event).context();
File file = filePath.toFile();
if ((!isLockFile(file)) && (acceptFile(file))) {
switch (event.kind().name()) {
case "ENTRY_CREATE":
//
fileMonitor.put(file,new FileChange(file));
log("File created ["+file.getName()+"]");
break;
//
case "ENTRY_MODIFY":
//
fileMonitor.put(file,new FileChange(file));
log("File modified ["+file.getName()+"]");
break;
//
case "ENTRY_DELETE":
//
log("File deleted ["+file.getName()+"]");
createLockFile(file).delete();
fileMonitor.remove(file);
break;
//
}
}
}
// reset is invoked to put the key back to ready state
key.reset();
} catch (InterruptedException e) {
e.printStackTrace();
}
Iterator<File> it = fileMonitor.keySet().iterator();
while (it.hasNext()) {
File file = it.next();
FileChange fileChange = fileMonitor.get(file);
FileChange fileChangeCurrent = new FileChange(file);
if (fileChange.isStable(fileChangeCurrent, getStableTime())) {
log("File is stable ["+file.getName()+"]");
String filename = getDateFormatter().format(new Date())+"_"+file.getName();
File lockFile = createLockFile(file);
if (!lockFile.exists()) {
log("File do not has lock file ["+file.getName()+"]");
try {
Files.createFile(lockFile.toPath());
log("Processing file ["+file.getName()+"]");
getListener().fileAvailable(file);
file.renameTo(new File(getDirectoryArchive(),filename));
log("Moved to archive file ["+file.getName()+"]");
} catch (IOException e) {
file.renameTo(new File(getDirectoryError(),filename));
createErrorFile(file,e);
log("Moved to error file ["+file.getName()+"]");
} finally {
lockFile.delete();
}
} else {
log("File do has lock file ["+file.getName()+"]");
fileMonitor.remove(file);
}
} else {
log("File is unstable ["+file.getName()+"]");
fileMonitor.put(file,fileChangeCurrent);
}
}
}
public boolean acceptFile(File file) {
if (getFilter()!=null) {
return getFilter().accept(file);
} else {
return true;
}
}
public boolean isLockFile(File file) {
int pos = file.getName().lastIndexOf('.');
String extension="";
if (pos!=-1) {
extension = file.getName().substring(pos).trim().toLowerCase();
}
return(extension.equalsIgnoreCase(LOCK_FILE_EXTENSION));
}
private File createLockFile(File file) {
return new File(file.getParentFile(),file.getName()+LOCK_FILE_EXTENSION);
}
private void createErrorFile(File file,IOException exception) {
File errorFile = new File(file.getParentFile(),file.getName()+ERROR_FILE_EXTENSION);
StringWriter sw = null;
PrintWriter pw = null;
FileWriter fileWriter = null;
try {
//
fileWriter = new FileWriter(errorFile);
if (exception!=null) {
sw = new StringWriter();
pw = new PrintWriter(sw);
exception.printStackTrace(pw);
fileWriter.write(sw.toString());
} else {
fileWriter.write("Exception is null.");
}
//
fileWriter.flush();
//
} catch (IOException e) {
} finally {
if (sw!=null) {
try {
sw.close();
} catch (IOException e1) {
}
}
if (pw!=null) {
pw.close();
}
if (fileWriter!=null) {
try {
fileWriter.close();
} catch (IOException e) {
}
}
}
}
private void validateNotNull(String name,Object obj) {
if (obj==null) {
throw new NullPointerException(name+" is null.");
}
}
private void validate(Path directory) throws IOException {
File file = directory.toFile();
if (!file.exists()) {
throw new IOException("Directory ["+file.getAbsolutePath()+"] do not exists.");
} else if (!file.isDirectory()) {
throw new IOException("Directory ["+file.getAbsolutePath()+"] is not a directory.");
} else if (!file.canRead()) {
throw new IOException("Can not read from directory ["+file.getAbsolutePath()+"].");
} else if (!file.canWrite()) {
throw new IOException("Can not write to directory ["+file.getAbsolutePath()+"] .");
}
}
private void log(String msg) {
//TODO
System.out.println("Task ["+getName()+"] "+msg);
}
}

package p1;
import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import static java.nio.file.LinkOption.NOFOLLOW_LINKS;
import java.nio.file.StandardWatchEventKinds;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.List;
public class WatchForFile {
public void WatchMyFolder(String path )
{
File dir = new File(path);
Path myDir= dir.toPath();
try
{
Boolean isFolder = (Boolean) Files.getAttribute(myDir,"basic:isDirectory", NOFOLLOW_LINKS);
if (!isFolder)
{
throw new IllegalArgumentException("Path: " + myDir + " is not a folder");
}
}
catch (IOException ioe)
{
ioe.printStackTrace();
}
System.out.println("Watching path: " + myDir);
try {
WatchService watcher = myDir.getFileSystem().newWatchService();
myDir.register(watcher, StandardWatchEventKinds.ENTRY_CREATE,StandardWatchEventKinds.ENTRY_DELETE, StandardWatchEventKinds.ENTRY_MODIFY);
WatchKey watckKey = watcher.take();
List<WatchEvent<?>> events = watckKey.pollEvents();
for (WatchEvent event : events) {
if (event.kind() == StandardWatchEventKinds.ENTRY_CREATE) {
System.out.println("Created: " + event.kind().toString());
}
if (event.kind() == StandardWatchEventKinds.ENTRY_DELETE) {
System.out.println("Delete: " + event.context().toString());
}
if (event.kind() == StandardWatchEventKinds.ENTRY_MODIFY) {
System.out.println("Modify: " + event.context().toString());
}
}
}
catch (Exception e)
{
System.out.println("Error: " + e.toString());
}
}
}

Check this Code...
https://github.com/omkar9999/FileWatcherHandler
This project allows watching files for different file events like create, modify & delete and then act on these events in a generic way.
How to Use?
Create a Path object representing the directory to monitor for file events.
Path path = Paths.get("/home/omkar/test");
Implement the FileHandler interface to perform an action detected by file event registered.
public class FileHandlerTest implements FileHandler {
private static final Logger LOGGER = Logger.getLogger(FileHandlerTest.class.getName());
/*
* This implemented method will delete the file
*
* #see com.io.util.FileHandler#handle(java.io.File,
* java.nio.file.WatchEvent.Kind)
*/
public void handle(File file, Kind<?> fileEvent) {
LOGGER.log(Level.INFO,"Handler is triggered for file {0}",file.getPath());
if(fileEvent == StandardWatchEventKinds.ENTRY_CREATE) {
try {
boolean deleted = Files.deleteIfExists(Paths.get(file.getPath()));
assertTrue(deleted);
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
Create an instance of an Implemented FileHandler
FileHandlerTest fileHandlerTest = new FileHandlerTest();
Create an instance of a FileWatcher by passing path, an instance of an Implemented FileHandler, and types of file events that you want to monitor separated by commas.
FileWatcher fileWatcher = new FileWatcher(path, fileHandlerTest, StandardWatchEventKinds.ENTRY_CREATE);
Now Create and start a new Thread.
Thread watcherThread = new Thread(fileWatcher);
watcherThread.start();
This thread will start polling for your registered file events and will invoke your custom handle method once any of the registered events are detected.

public class FileWatcher implements Runnable {
private static final Logger LOGGER =Logger.getLogger(FileWatcher.class.getName());
private WatchService watcher;
private FileHandler fileHandler;
private List<Kind<?>> watchedEvents;
private Path directoryWatched;
/**
* #param directory
* #Path directory to watch files into
* #param fileHandler
* #FileHandler implemented instance to handle the file event
* #param watchRecursive
* if directory is to be watched recursively
* #param watchedEvents
* Set of file events watched
*
* #throws IOException
*/
public FileWatcher(Path directory, FileHandler fileHandler, boolean watchRecursive,
WatchEvent.Kind<?>... watchedEvents) throws IOException {
super();
this.watcher = FileSystems.getDefault().newWatchService();
this.fileHandler = fileHandler;
this.directoryWatched = directory;
this.watchedEvents = Arrays.asList(watchedEvents);
if (watchRecursive) {
// register all subfolders
Files.walkFileTree(directory, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
LOGGER.log(Level.INFO, "Registering {0} ", dir);
dir.register(watcher, StandardWatchEventKinds.ENTRY_CREATE, StandardWatchEventKinds.ENTRY_DELETE,
StandardWatchEventKinds.ENTRY_MODIFY);
return FileVisitResult.CONTINUE;
}
});
} else {
directory.register(watcher, watchedEvents);
}
}
#SuppressWarnings({ "unchecked" })
public void run() {
LOGGER.log(Level.INFO, "Starting FileWatcher for {0}", directoryWatched.toAbsolutePath());
WatchKey key = null;
while (true) {
try {
key = watcher.take();
if (key != null) {
for (WatchEvent<?> event : key.pollEvents()) {
WatchEvent.Kind<?> kind = event.kind();
WatchEvent<Path> ev = (WatchEvent<Path>) event;
//directory in which file event is detected
Path directory = (Path) key.watchable();
Path fileName = ev.context();
if (watchedEvents.contains(kind)) {
LOGGER.log(Level.INFO, "Invoking handle on {0}", fileName.toAbsolutePath());
fileHandler.handle(directory.resolve(fileName).toFile(), kind);
}
}
key.reset();
}
} catch (InterruptedException ex) {
LOGGER.log(Level.SEVERE, "Polling Thread was interrupted ", ex);
Thread.currentThread().interrupt();
}
}
}
}

Directory watching for changes in java

I am using WatchService to watch change in directory, in particular creation of new file in directory. Below is my code -
package watcher;
import java.nio.file.*;
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
import java.io.*;
public class Watch {
public static void main(String[] args) throws IOException {
Path dir = Paths.get("c:\\mk\\");
WatchService service = FileSystems.getDefault().newWatchService();
WatchKey key = dir.register(service, ENTRY_CREATE);
System.out.println("Watching directory: "+dir.toString());
for(;;){
WatchKey key1;
try {
key1 = service.take();
} catch (InterruptedException x) {
break;
}
for (WatchEvent<?> event: key1.pollEvents()) {
WatchEvent.Kind<?> kind = event.kind();
if (kind == OVERFLOW) {
continue;
}
WatchEvent<Path> ev = (WatchEvent<Path>)event;
Path filename = ev.context();
Path child = dir.resolve(filename);
System.out.println("New file: "+child.toString()+" created.");
try{
FileInputStream in = new FileInputStream(child.toFile());
System.out.println("File opened for reading");
in.close();
System.out.println("File Closed");
}catch(Exception x){
x.printStackTrace();
}
}
boolean valid = key.reset();
if (!valid) {
break;
}
}
}
}
When I create file inside "mk" directory, I am getting notification for that. But when I copy some file in this directory, I am getting exception on opening that copied file.
My guess is Windows Copier dialog has still locked that file and I was unable to open that file. So basically I want to know is how to get notified for file has been closed by other process.
Output of above code is like -
Watching directory: c:\mk
New file: c:\mk\New Text Document (2).txt created.
File opened for reading
File Closed
New file: c:\mk\Config.class created.
java.io.FileNotFoundException: c:\mk\Config.class (The process cannot access the file because it is being used by another process)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(FileInputStream.java:138)
at watcher.Watch.main(Watch.java:36)
New file: c:\mk\New Text Document (3).txt created.
File opened for reading
File Closed
Files "New Text Document (2).txt" and "New Text Document (3).txt" I have created but file "Config.class" I have copied from other directory.
Please help me on this.

I got this working by implementing algorithm: Watcher thread will put file names in BlockingQueue and other thread will poll this queue, takes file names, try few times to open file. If file gets opened, Windows Copier has released file lock and we can proceed. So when other threads finds file has been unlocked, other thread will put this file name in processed queue, from where my application will retrieve file name. Also the other thread while checking for file unlock by opening file, if it runs long time for unlocking file, we can place back this file name in BlockingQueue and process other file names, former can be processed later.
Solution: Hope this may help to other:
package dirwatch;
import java.nio.file.*;
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
import static java.nio.file.LinkOption.*;
import java.nio.file.attribute.*;
import java.io.*;
import java.util.*;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
public class WatchDir {
private final WatchService watcher;
private final Map<WatchKey,Path> keys;
private final boolean recursive;
private boolean trace = false;
private BlockingQueue<String> fileProcessingQueue;
//******* processedFileQueue **** will be used by other threads to retrive unlocked files.. so I have
// kept as public final
public final BlockingQueue<String> processedFileQueue;
private volatile boolean closeProcessingThread;
private volatile boolean closeWatcherThread;
private void processFiles(){
System.out.println("DirWatchProcessingThread Started");
String fileName;
outerLoop: while(!closeProcessingThread || !fileProcessingQueue.isEmpty()){
try{
fileName = fileProcessingQueue.poll(1000, TimeUnit.MILLISECONDS);
}catch(InterruptedException ie){
fileName = null;
}
if(fileName == null || fileName.equals("")){
continue outerLoop;
}
long startTime = System.currentTimeMillis();
innerLoop: while(true){
FileInputStream fis = null;
File file = new File(fileName);
try{
fis = new FileInputStream(fileName);
break innerLoop;
}catch(FileNotFoundException fnfe){
if(!file.exists() || file.isDirectory()){
System.out.println("File: '"+fileName+"has been deleted in file system or it is not file. Not processing this file.");
continue outerLoop;
}
try{
Thread.sleep(WatchDirParameters.millisToPuaseForFileLock);
}catch(InterruptedException ie){
}
if((System.currentTimeMillis() - startTime) > WatchDirParameters.millisToSwapFileForUnlocking){
if(fileProcessingQueue.offer(fileName)){
continue outerLoop;
}else{
startTime = System.currentTimeMillis();
continue innerLoop;
}
}
}finally{
if(fis != null){
try{
fis.close();
}catch(IOException ioe){
ioe.printStackTrace();
}
}
}
}
System.out.println("Queuing File: "+fileName);
processedLoop:while(true){
try{
if(processedFileQueue.offer(fileName, 1000, TimeUnit.MILLISECONDS)){
break processedLoop;
}
}catch(InterruptedException ie){
//ie.printStackTrace();
}
}
}
closeWatcherThread = true;
closeProcessingThread = true;
System.out.println("DirWatchProcessingThread Exited");
}
/**
* Process all events for keys queued to the watcher
*/
private void processEvents(){
System.out.println("DirWatcherThread started.");
while(!closeWatcherThread) {
// wait for key to be signalled
WatchKey key;
try {
key = watcher.take();
} catch (InterruptedException x) {
// if we are returning from these method, it means we no longer wants to watch directory
// we must close thread which may be waiting for file names in queue
continue;
}catch(ClosedWatchServiceException cwse){
break;
}
Path dir = keys.get(key);
if (dir == null) {
System.err.println("WatchKey not recognized!!");
continue;
}
try{
for (WatchEvent<?> event: key.pollEvents()) {
WatchEvent.Kind kind = event.kind();
if (kind == OVERFLOW) {
continue;
}
// Context for directory entry event is the file name of entry
WatchEvent<Path> ev = cast(event);
Path name = ev.context();
Path child = dir.resolve(name);
if(kind.equals(ENTRY_CREATE)){
// if directory is created, and watching recursively, then
// register it and its sub-directories
if (recursive) {
try {
if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
registerAll(child);
continue;
}
} catch (IOException x) {
// ignore to keep sample readbale
}
}
while(true){
if(fileProcessingQueue.remainingCapacity() < 2){
// if only one last can be inserted then don't queue this we need 1 empty space in queue
// for swaping file names..
// sleep for some time so processing thread may have made some rooms to queue in fileQueue
// this logic will not create any problems as only one this thread is inserting in queue
try{
Thread.sleep(200);
}catch(InterruptedException ie){
}
continue;
}
if(!fileProcessingQueue.offer(child.toString())){
// couldn't queue this element by whatever reason.. we will try to enqueue again by continuing loop
continue;
}else{
// file name has been queued in queue
break;
}
}
}
}
// reset key and remove from set if directory no longer accessible
boolean valid = key.reset();
if (!valid) {
keys.remove(key);
// all directories are inaccessible
if (keys.isEmpty()) {
break;
}
}
}catch(ClosedWatchServiceException cwse){
break;
}
}
closeProcessingThread = true;
closeWatcherThread = true;
System.out.println("DirWatcherThread exited.");
}
public void stopWatching(){
try{
watcher.close();
}catch(IOException ioe){
}
closeProcessingThread = true;
closeWatcherThread = true;
}
public static WatchDir watchDirectory(String dirName, boolean recursive) throws InvalidPathException, IOException, Exception{
try{
Path dir = Paths.get(dirName);
final WatchDir watchDir = new WatchDir(dir, recursive);
watchDir.closeProcessingThread = false;
watchDir.closeWatcherThread = false;
new Thread(new Runnable() {
public void run() {
watchDir.processFiles();
}
}, "DirWatchProcessingThread").start();
new Thread(new Runnable() {
public void run() {
watchDir.processEvents();
}
}, "DirWatcherThread").start();
return watchDir;
}catch(InvalidPathException ipe){
throw ipe;
}catch(IOException ioe){
throw ioe;
}catch(Exception e){
throw e;
}
}
#SuppressWarnings("unchecked")
private static <T> WatchEvent<T> cast(WatchEvent<?> event) {
return (WatchEvent<T>)event;
}
/**
* Register the given directory with the WatchService
*/
private void register(Path dir) throws IOException {
//WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
WatchKey key = dir.register(watcher, ENTRY_CREATE);
if (trace) {
Path prev = keys.get(key);
if (prev == null) {
System.out.format("register: %s\n", dir);
} else {
if (!dir.equals(prev)) {
System.out.format("update: %s -> %s\n", prev, dir);
}
}
}
keys.put(key, dir);
}
/**
* Register the given directory, and all its sub-directories, with the
* WatchService.
*/
private void registerAll(final Path start) throws IOException {
// register directory and sub-directories
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
register(dir);
return FileVisitResult.CONTINUE;
}
});
}
/**
* Creates a WatchService and registers the given directory
*/
private WatchDir(Path dir, boolean recursive) throws IOException {
fileProcessingQueue = new ArrayBlockingQueue<String>(WatchDirParameters.fileQueueSize, false);
processedFileQueue = new ArrayBlockingQueue<String>(WatchDirParameters.fileQueueSize, false);
this.watcher = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<WatchKey,Path>();
this.recursive = recursive;
//CreateTxtFile.createFile(dir, 1);
if (recursive) {
System.out.format("Scanning %s ...\n", dir);
registerAll(dir);
System.out.println("Done.");
} else {
register(dir);
}
// enable trace after initial registration
this.trace = true;
}
}
Parameter Class:
package dirwatch;
public class WatchDirParameters {
public static final int millisToPuaseForFileLock = 200;
public static final int fileQueueSize = 500;
public static final int millisToSwapFileForUnlocking = 2000;
}

Made an updated version of the file provided by #UDPLover that is built for use in a high rate of file access environment I converted the to process queue into a HashMap<String, WatchEvent> to carry the watch event over to pass to an abstract method inside of the file blocking checker itself. Also made a print() method that allows anything printed to console by the WatchCore to be enabled or disabled. The file polling for loop from the original example was updated to use the JDK8 function for loop, made all parts threaded/interrupted. This is untested as of yet, will update with fixes when I can test it.
package filewatcher;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintStream;
import java.nio.file.ClosedWatchServiceException;
import java.nio.file.FileSystems;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import static java.nio.file.LinkOption.NOFOLLOW_LINKS;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
*
* #author Nackloose
* http://stackoverflow.com/questions/13998379/directory-watching-for-changes-in-java
*/
public abstract class WatchCore extends Thread {
//make class a thread by default
/**
* After the WatchCore recieves an event for a file and deems it unlocked,
* it will be passed to this function
*
* #param e WatchEvent for the file, after it has been affirmed to be
* unlocked.
*/
public abstract void onEventAndUnlocked(WatchEvent e);
private final WatchService watcher;
private final Map<WatchKey, Path> keys;
private final boolean recursive;
private boolean trace = false;
//converted to HashMap to remove the limitation as I need this in a high rate of file access enviroment.
//as well as to carry the event passed for that folder into the block check itself.
//got rid of the finished queue and made events pass to the abstract void above
private final HashMap<String, WatchEvent> fileProcessingQueue;
//create a varible to keep track of the thread checking the file blocking, so we can start and stop it.
private final WatchBlocker blocker;
public WatchCore(String dir) throws IOException {
//defaultly dont recurse
this(dir, false);
}
public WatchCore(String dir, boolean recursive) throws IOException {
this(Paths.get(dir), recursive);
}
public WatchCore(Path dir) throws IOException {
//defaultly dont recurse
this(dir, false);
}
public WatchCore(Path dir, boolean recursive) throws IOException {
fileProcessingQueue = new HashMap<>();
this.watcher = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<>();
this.recursive = recursive;
//CreateTxtFile.createFile(dir, 1);
if (recursive) {
print("Scanning %s ...", dir);
registerAll(dir);
print("Done.");
} else {
register(dir);
}
// enable trace after initial registration
this.trace = true;
//start the thread to process files to be checked for file blocking
blocker = new WatchBlocker();
}
#SuppressWarnings("unchecked")
private static <T> WatchEvent<T> cast(WatchEvent<?> event) {
return (WatchEvent<T>) event;
}
#Override
public synchronized void start() {
//start up our thread _FIRST_
super.start();
//then start the blocking thread
blocker.start();
}
#Override
public void interrupt() {
//Everything backwards, stop the blocker _FIRST_
blocker.interrupt();
//then stop our thread.
super.interrupt();
}
/**
* Register the given directory with the WatchService
*/
private void register(Path dir) throws IOException {
//WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
WatchKey key = dir.register(watcher, ENTRY_CREATE);
if (trace) {
Path prev = keys.get(key);
if (prev == null) {
print("register: %s\n", dir);
} else {
if (!dir.equals(prev)) {
print("update: %s -> %s\n", prev, dir);
}
}
}
keys.put(key, dir);
}
/**
* Register the given directory, and all its sub-directories, with the
* WatchService.
*/
private void registerAll(final Path start) throws IOException {
// register directory and sub-directories
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
register(dir);
return FileVisitResult.CONTINUE;
}
});
}
/**
* Process all events for keys queued to the watcher
*/
#Override
public void run() {
//this was previous called processEvents()
//pruned any un-nessicary continues, labels, and labels on breaks, a lot of them
//were redundant
print("DirWatcherThread started.");
//as long as we're not interrupted we keep working
while (!interrupted()) {
// wait for key to be signalled
WatchKey key;
try {
key = watcher.take();
} catch (InterruptedException x) {
// if we are returning from these method, it means we no longer wants to watch directory
// we must close thread which may be waiting for file names in queue
continue;
} catch (ClosedWatchServiceException cwse) {
break;
}
Path dir = keys.get(key);
if (dir == null) {
printe("WatchKey not recognized!!");
continue;
}
try {
//converted to functional for loop.
key.pollEvents().stream().filter((event) -> {
WatchEvent.Kind kind = event.kind();
return !(kind == OVERFLOW); //make sure we do the filter
}).forEach((event) -> {
WatchEvent.Kind kind = event.kind();
// Context for directory entry event is the file name of entry
WatchEvent<Path> ev = cast(event);
Path name = ev.context();
Path child = dir.resolve(name);
if (kind.equals(ENTRY_CREATE)) {
// if directory is created, and watching recursively, then
// register it and its sub-directories
if (recursive) {
try {
if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
registerAll(child);
return; //continue;
}
} catch (IOException x) {
// ignore to keep sample readbale
}
}
fileProcessingQueue.put(child.toString(), ev);
}
});
// reset key and remove from set if directory no longer accessible
boolean valid = key.reset();
if (!valid) {
keys.remove(key);
// all directories are inaccessible
if (keys.isEmpty()) {
break;
}
}
} catch (ClosedWatchServiceException cwse) {
break;
}
}
print("DirWatcherThread exited.");
}
/**
*
* #author
* http://stackoverflow.com/questions/13998379/directory-watching-for-changes-in-java
* Nackloose
*/
private class WatchBlocker extends Thread {
#Override
public synchronized void start() {
//get it going
super.start();
}
#Override
public void interrupt() {
//interupt our thread
super.interrupt();
}
#Override
public void run() {
//this was perviously processFiles()
//pruned any un-nessicary continues, labels, and labels on breaks, a lot of them
//were redundant
print("DirWatchProcessingThread Started");
Entry<String, WatchEvent> fileEvent;
outerLoop:
//as long as we're not interrupted we keep working
while (!interrupted()) {
if (fileProcessingQueue.isEmpty()) {
try {
Thread.sleep(WatchCoreParameters.timeToIdle);
} catch (InterruptedException ex) {
Logger.getLogger(WatchCore.class.getName()).log(Level.SEVERE, null, ex);
}
continue;
}
fileEvent = fileProcessingQueue.entrySet().iterator().next();
fileProcessingQueue.remove(fileEvent.getKey());
long startTime = System.currentTimeMillis();
while (true) {
FileInputStream fis = null;
File file = new File(fileEvent.getKey());
try {
fis = new FileInputStream(fileEvent.getKey());
break;
} catch (FileNotFoundException fnfe) {
if (!file.exists() || file.isDirectory()) {
print("File: '" + fileEvent + "has been deleted in file system or it is not file. Not processing this file.");
continue outerLoop;
}
try {
Thread.sleep(WatchCoreParameters.millisToPauseForFileLock);
} catch (InterruptedException ie) {
}
if ((System.currentTimeMillis() - startTime) > WatchCoreParameters.millisToSwapFileForUnlocking) {
fileProcessingQueue.put(fileEvent.getKey(), fileEvent.getValue());
}
} finally {
if (fis != null) {
try {
fis.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}
}
print("Queuing File: " + fileEvent);
//pass the unlocked file event to the abstract method
onEventAndUnlocked(fileEvent.getValue());
}
print("DirWatchProcessingThread Exited");
}
}
/**
*
* #author
* http://stackoverflow.com/questions/13998379/directory-watching-for-changes-in-java
* Nackloose
*/
public static class WatchCoreParameters {
public static int timeToIdle = 2000, millisToPauseForFileLock = 200,
millisToSwapFileForUnlocking = 2000;
public static boolean verbose = false;
}
//<editor-fold defaultstate="collapsed" desc="Printing methods">
private void print(String s) {
//defaultly we're not writing an error
print(s, false);
}
public static final void print(String s, boolean error) {
//check verbosity, exit if none.
if (!WatchCoreParameters.verbose) {
return;
}
//if this is an error, assign System.err to a temp varible
//otherise assign System.out for normal printing
PrintStream out = (!error ? System.out : System.err);
if (s.contains("\n")) { // check to see if theirs a new line
out.print(s); //print accordingly
} else {
out.println(s); //print accordingly
}
}
public static final void printe(String s) {
//shortcut/convenience method for printing an error
print(s, true);
}
public static final void print(String s, Object... formatObj) {
//check verbosity, exit if none.
if (!WatchCoreParameters.verbose) {
return;
}
//format the object into the string, and if no newline is there, add it.
System.out.format(s + (s.contains("\n") ? "" : "\n"), formatObj);
}
//</editor-fold>
}