JAVA文件监控(源码)

package com.filecheck.monitor; import java.io.File; import java.util.HashMap; import java.util.Map; import java.util.Timer; import java.util.TimerTask; public class FileMonitor { private Timer timer; private Map<String, FileMonitorTask> timerEntries; private FileMonitor() { this.timerEntries = new HashMap<String, FileMonitorTask>(); this.timer = new Timer(); } public static FileMonitor getInstance() { //here is a lazy singleton instance. return FileMonitorHolder.instance; } private static class FileMonitorHolder { private static final FileMonitor instance = new FileMonitor(); } public void addFileChangeListener(FileChangeListener listener,String filename, long period) { //remove listener before add a new instance. this.removeFileChangeListener(filename); //create a new instance. FileMonitorTask task = new FileMonitorTask(listener, filename); //put instance into timerQueue. this.timerEntries.put(filename, task); //schedule timer task. this.timer.schedule(task, period, period); } public void removeFileChangeListener(String filename) { //remove timer task from timer entries. FileMonitorTask task = (FileMonitorTask) this.timerEntries.remove(filename); if (task != null) { //cancel monitor task. task.cancel(); } } private static final class FileMonitorTask extends TimerTask { private FileChangeListener listener; private String filename; private File monitoredFile; private long lastModified; public FileMonitorTask(FileChangeListener listener, String filename) { this.listener = listener; this.filename = filename; this.monitoredFile = new File(filename); if (!this.monitoredFile.exists()) { return; } this.lastModified = this.monitoredFile.lastModified(); } public void run() { long latestChange = this.monitoredFile.lastModified(); if (this.lastModified != latestChange) { this.lastModified = latestChange; this.listener.fileChanged(this.filename); } } } }