Files or no Files - excel

Question

I want my java program to constantly scan for new files in a particular folder.
I am expecting something like:
while(1) {
String csvFile = "D:\\myfiles\\done\\*.*";
br = new BufferedReader(new FileReader(csvFile));
// DO Some thing
}
Is there a good way to do this?

Answer 1

You probably do not want to execute the loop over and over, as this would cause poor performance. You can watch for directory changes instead, which will suspend the working thread while no new files are available (except from the article linked):
WatchKey key;
try {
key = watcher.take(); // blocking call, similar to sleep()
} catch (InterruptedException x) {
return; // this happens if your thread got interrupted
}
// do something with the recived key

Answer 2

You can use File to get all the files.
Check this:
File folder = new File("D:/myfiles/done");
File[] files = folder.listFiles();
for(File f : files){
// Read f in here
}

Answer 3

This FileObserver class looks quite promising:
/**
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright (c) 2007 Sun Microsystems Inc. All Rights Reserved
*
* The contents of this file are subject to the terms
* of the Common Development and Distribution License
* (the License). You may not use this file except in
* compliance with the License.
*
* You can obtain a copy of the License at
* https://opensso.dev.java.net/public/CDDLv1.0.html or
* opensso/legal/CDDLv1.0.txt
* See the License for the specific language governing
* permission and limitations under the License.
*
* When distributing Covered Code, include this CDDL
* Header Notice in each file and include the License file
* at opensso/legal/CDDLv1.0.txt.
* If applicable, add the following below the CDDL Header,
* with the fields enclosed by brackets [] replaced by
* your own identifying information:
* "Portions Copyrighted [year] [name of copyright owner]"
*
* $Id: FileObserver.java,v 1.3 2008/06/25 05:44:08 qcheng Exp $
*
*/
package com.sun.identity.sm.flatfile;
import com.iplanet.am.util.SystemProperties;
import com.sun.identity.shared.Constants;
import com.sun.identity.shared.debug.Debug;
import com.sun.identity.sm.SMSObjectListener;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
class FileObserver extends Thread {
private static Debug debug = Debug.getInstance("amSMSEvent");
private Map snapShot;
private int interval;
private boolean running;
private FlatFileEventManager eventManager;
FileObserver(FlatFileEventManager eventManager) {
setDaemon(true);
getPollingInterval();
this.eventManager = eventManager;
}
private void getPollingInterval() {
String time = SystemProperties.get(
Constants.CACHE_POLLING_TIME_PROPERTY);
interval = Constants.DEFAULT_CACHE_POLLING_TIME;
if (time != null) {
try {
interval = Integer.parseInt(time);
} catch (NumberFormatException nfe) {
debug.error(
"FileObserver.getCachePollingInterval", nfe);
}
}
interval = interval * 60 * 1000;
}
/**
* Returns <code>true</code> if thread is running.
*
* #return <code>true</code> if thread is running.
*/
public boolean isRunning() {
return running;
}
/**
* Stops the thread.
*/
public void stopThread() {
running = false;
}
public void run() {
running = true;
snapShot = getCurrentSnapShot();
try {
while (running) {
/*
* This flag set to false in the begin of the thread.
* when a node is added/delete from the file system, we need
* to toggle this flag which in turn ask the
* SMSEnhancedFlatFileObject to rebuild the directory tree.
*/
boolean needReloadRootNode = false;
sleep(interval);
Map newSnapShot = getCurrentSnapShot();
if (snapShot != null) {
for (Iterator i = newSnapShot.keySet().iterator();
i.hasNext();
) {
String filename = (String)i.next();
if (snapShot.containsKey(filename)) {
long prev =((Long)snapShot.get(filename))
.longValue();
long curr =((Long)newSnapShot.get(filename))
.longValue();
if (prev != curr) {
eventManager.notify(getDN(filename),
SMSObjectListener.MODIFY);
}
} else {
if (!needReloadRootNode) {
eventManager.reloadRootNode();
needReloadRootNode = true;
}
eventManager.notify(getDN(filename),
SMSObjectListener.ADD);
}
}
for (Iterator i = snapShot.keySet().iterator();
i.hasNext();
) {
String filename = (String)i.next();
if (!newSnapShot.containsKey(filename)) {
if (!needReloadRootNode) {
eventManager.reloadRootNode();
needReloadRootNode = true;
}
eventManager.notify(getDN(filename),
SMSObjectListener.DELETE);
}
}
}
snapShot = newSnapShot;
}
} catch (InterruptedException e) {
debug.warning("FileObserver.run", e);
}
}
private String getDN(String filename) {
BufferedReader buff = null;
String dn = null;
try{
buff = new BufferedReader(new FileReader(filename));
String line = buff.readLine();
if ((line != null) && line.startsWith("#")) {
dn = line.substring(1);
}
} catch (IOException e) {
debug.warning("FileObserver.getDN", e);
} finally {
if (buff != null) {
try {
buff.close();
} catch (IOException ex) {
//ignored
}
}
}
return dn;
}
private Map getCurrentSnapShot() {
Map snapshot = null;
String baseDir = SystemProperties.get(
SMSFlatFileObjectBase.SMS_FLATFILE_ROOTDIR_PROPERTY);
File dir = new File(baseDir);
String[] files = dir.list();
// if the war is not configured we may not get any files here.
if (files.length > 0) {
snapshot = new HashMap(files.length *2);
for (int i = 0; i < files.length; i++) {
String filename = baseDir + "/" + files[i];
File f = new File(filename);
if (!f.isDirectory()) {
snapshot.put(filename, new Long(f.lastModified()));
}
}
}
return snapshot;
}
}
If you prefer a library you can also check the Apache commons FileAlterationObserver.

Answer 4

This may be useful.
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 java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
public class DirectoryWatchDemo {
public static void main(String[] args) {
try {
WatchService watcher = FileSystems.getDefault().newWatchService();
Path dir = Paths.get("D:\\Mani_Test\\");
dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
System.out.println("Watch Service registered for dir: " + dir.getFileName());
while (true) {
WatchKey key;
try {
key = watcher.take();
} catch (InterruptedException ex) {
ex.printStackTrace();
return;
}
for (WatchEvent<?> event : key.pollEvents()) {
WatchEvent.Kind<?> kind = event.kind();
WatchEvent<Path> ev = (WatchEvent<Path>) event;
Path fileName = ev.context();
System.out.println(kind.name() + ": " + fileName);
}
boolean valid = key.reset();
if (!valid) {
break;
}
}
} catch (IOException ex) {
System.err.println(ex);
}
}
}

Answer 5

File object can be used for folder also,
Here is the code
String filePath = "D:\\myfiles\\done\\";
File dir = new File(filePath);
if (dir.isDirectory())
{
File[] fileList = dir.listFiles();
if (fileList.length > 0)
{
// Your code here
}
}