我正在使用 WatchService 来监视目录中的更改,特别是在目录中创建新文件。以下是我的代码 -
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;
}
}
}
}
当我在“mk”目录中创建文件时,我会收到相关通知。但是当我在这个目录中复制一些文件时,我在打开复制的文件时遇到异常。
我的猜测是 Windows Copier 对话框仍然锁定了该文件,我无法打开该文件。所以基本上我想知道的是如何收到文件已被其他进程关闭的通知。
上面代码的输出是这样的-
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
文件“New Text Document (2).txt
”和“New Text Document (3).txt
”是我创建的,但文件“Config. class
"我已经从其他目录复制了。
请帮我解决这个问题。
最佳答案
我通过实现算法得到了这个工作:观察线程将文件名放在 BlockingQueue 中,其他线程将轮询这个队列,获取文件名,尝试几次打开文件。如果文件被打开,则 Windows Copier 已释放文件锁定,我们可以继续。因此,当其他线程发现文件已解锁时,其他线程会将此文件名放入已处理队列中,我的应用程序将从中检索文件名。还有另一个线程在打开文件检查文件解锁的时候,如果解锁文件运行时间长,我们可以把这个文件名放回BlockingQueue,处理其他文件名,前者可以稍后处理。
解决方案:希望对其他人有帮助:
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;
}
}
参数类:
package dirwatch;
public class WatchDirParameters {
public static final int millisToPuaseForFileLock = 200;
public static final int fileQueueSize = 500;
public static final int millisToSwapFileForUnlocking = 2000;
}
关于java - 目录监视 java 中的更改,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13998379/