我希望我的 java 程序不断扫描特定文件夹中的新文件。
我期待类似的东西：
while(1) {
String csvFile = "D:\\myfiles\\done\\*.*";
br = new BufferedReader(new FileReader(csvFile));
// DO Some thing
}
有没有好的方法来做到这一点？
问问题
1147 次
5 回答
4
您可能不想一遍又一遍地执行循环，因为这会导致性能下降。您可以改为监视目录更改，这将在没有新文件可用时暂停工作线程（链接的文章除外）：
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
于 2013-09-01T10:58:17.120 回答
2
您可以使用File来获取所有文件。
检查这个：
File folder = new File("D:/myfiles/done");
File[] files = folder.listFiles();
for(File f : files){
// Read f in here
}
于 2013-09-01T10:55:06.777 回答
1
这个FileObserver类看起来很有前途：
/**
* 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;
}
}
如果您更喜欢库，还可以查看 Apache commons FileAlterationObserver。
于 2013-09-01T10:57:06.237 回答
0
这可能很有用。
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);
}
}
}
于 2017-05-17T06:18:35.630 回答
-1
文件对象也可以用于文件夹，这是代码
String filePath = "D:\\myfiles\\done\\";
File dir = new File(filePath);
if (dir.isDirectory())
{
File[] fileList = dir.listFiles();
if (fileList.length > 0)
{
// Your code here
}
}
于 2013-09-01T10:58:02.123 回答