我没有解释，只是编写了一个框架示例。我没有对它进行很好的测试，但这可能有一定用处。
为了监视（另一个）文件，只需创建一个新的Monitor，并向其传递ScheduledExecutorService。启动和停止监视非常简单。您可以（应该）将同一个执行程序重用于多个监视器。
import java.io.File;import java.io.IOException;import java.util.ArrayList;import java.util.List;import java.util.concurrent.Executors;import java.util.concurrent.ScheduledExecutorService;import java.util.concurrent.TimeUnit;public interface Event{}public interface Listener{ void handle(Event event);}public class Monitor{ private static final int CHECK_EVERY_SEConDS = 10; private static final int RECHECK_AFTER_IF_NOT_EXISTS_SEConDS = 30; private File file; private ScheduledExecutorService executor; private boolean active; private List<Listener> listeners; public Monitor(File file, ScheduledExecutorService executor) { super(); this.file = file; this.executor = executor; listeners = new ArrayList<Listener>(); } public synchronized void start() { if (active) { return; } active = true; executor.execute(new Runnable() { public void run() { synchronized (Monitor.this) { if (!active) { System.out.println("not active"); return; } } if (!file.exists()) { System.out.println("does not exist, rescheduled"); executor.schedule(this, RECHECK_AFTER_IF_NOT_EXISTS_SECONDS, TimeUnit.SECONDS); return; } Event event = doStuff(file); System.out.println("generated " + event); updateListeners(event); System.out.println("updated listeners and rescheduled"); executor.schedule(this, CHECK_EVERY_SECONDS, TimeUnit.SECONDS); } }); } private Event doStuff(final File file) { return new Event() { public String toString() { return "event for " + file; } }; } public synchronized void stop() { active = false; } public void addListener(Listener listener) { synchronized (listeners) { listeners.add(listener); } } public void removeListener(Listener listener) { synchronized (listeners) { listeners.remove(listener); } } private void updateListeners(Event event) { synchronized (listeners) { for (Listener listener : listeners) { listener.handle(event); } } } public static void main(String[] args) throws IOException { ScheduledExecutorService executor = Executors.newScheduledThreadPool(4); File file = new File("test.png"); Monitor monitor = new Monitor(file, executor); monitor.addListener(new Listener() { public void handle(Event event) { System.out.println("handling " + event); } }); monitor.start(); System.out.println("started..."); System.in.read(); monitor.stop(); System.out.println("done"); executor.shutdown(); }}
