001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.io.monitor;
018
019import java.util.Collection;
020import java.util.Collections;
021import java.util.List;
022import java.util.Optional;
023import java.util.concurrent.CopyOnWriteArrayList;
024import java.util.concurrent.ThreadFactory;
025
026/**
027 * A runnable that spawns a monitoring thread triggering any
028 * registered {@link FileAlterationObserver} at a specified interval.
029 *
030 * @see FileAlterationObserver
031 * @since 2.0
032 */
033public final class FileAlterationMonitor implements Runnable {
034
035    private static final FileAlterationObserver[] EMPTY_ARRAY = {};
036
037    private final long interval;
038    private final List<FileAlterationObserver> observers = new CopyOnWriteArrayList<>();
039    private Thread thread;
040    private ThreadFactory threadFactory;
041    private volatile boolean running;
042
043    /**
044     * Constructs a monitor with a default interval of 10 seconds.
045     */
046    public FileAlterationMonitor() {
047        this(10000);
048    }
049
050    /**
051     * Constructs a monitor with the specified interval.
052     *
053     * @param interval The amount of time in milliseconds to wait between
054     * checks of the file system.
055     */
056    public FileAlterationMonitor(final long interval) {
057        this.interval = interval;
058    }
059
060    /**
061     * Constructs a monitor with the specified interval and collection of observers.
062     *
063     * @param interval The amount of time in milliseconds to wait between
064     * checks of the file system.
065     * @param observers The collection of observers to add to the monitor.
066     * @since 2.9.0
067     */
068    public FileAlterationMonitor(final long interval, final Collection<FileAlterationObserver> observers) {
069        // @formatter:off
070        this(interval,
071            Optional
072                .ofNullable(observers)
073                .orElse(Collections.emptyList())
074                .toArray(EMPTY_ARRAY)
075        );
076        // @formatter:on
077    }
078
079    /**
080     * Constructs a monitor with the specified interval and set of observers.
081     *
082     * @param interval The amount of time in milliseconds to wait between
083     * checks of the file system.
084     * @param observers The set of observers to add to the monitor.
085     */
086    public FileAlterationMonitor(final long interval, final FileAlterationObserver... observers) {
087        this(interval);
088        if (observers != null) {
089            for (final FileAlterationObserver observer : observers) {
090                addObserver(observer);
091            }
092        }
093    }
094
095    /**
096     * Returns the interval.
097     *
098     * @return the interval
099     */
100    public long getInterval() {
101        return interval;
102    }
103
104    /**
105     * Sets the thread factory.
106     *
107     * @param threadFactory the thread factory
108     */
109    public synchronized void setThreadFactory(final ThreadFactory threadFactory) {
110        this.threadFactory = threadFactory;
111    }
112
113    /**
114     * Adds a file system observer to this monitor.
115     *
116     * @param observer The file system observer to add
117     */
118    public void addObserver(final FileAlterationObserver observer) {
119        if (observer != null) {
120            observers.add(observer);
121        }
122    }
123
124    /**
125     * Removes a file system observer from this monitor.
126     *
127     * @param observer The file system observer to remove
128     */
129    public void removeObserver(final FileAlterationObserver observer) {
130        if (observer != null) {
131            while (observers.remove(observer)) {
132                // empty
133            }
134        }
135    }
136
137    /**
138     * Returns the set of {@link FileAlterationObserver} registered with
139     * this monitor.
140     *
141     * @return The set of {@link FileAlterationObserver}
142     */
143    public Iterable<FileAlterationObserver> getObservers() {
144        return observers;
145    }
146
147    /**
148     * Starts monitoring.
149     *
150     * @throws Exception if an error occurs initializing the observer
151     */
152    public synchronized void start() throws Exception {
153        if (running) {
154            throw new IllegalStateException("Monitor is already running");
155        }
156        for (final FileAlterationObserver observer : observers) {
157            observer.initialize();
158        }
159        running = true;
160        if (threadFactory != null) {
161            thread = threadFactory.newThread(this);
162        } else {
163            thread = new Thread(this);
164        }
165        thread.start();
166    }
167
168    /**
169     * Stops monitoring.
170     *
171     * @throws Exception if an error occurs initializing the observer
172     */
173    public synchronized void stop() throws Exception {
174        stop(interval);
175    }
176
177    /**
178     * Stops monitoring.
179     *
180     * @param stopInterval the amount of time in milliseconds to wait for the thread to finish.
181     * A value of zero will wait until the thread is finished (see {@link Thread#join(long)}).
182     * @throws Exception if an error occurs initializing the observer
183     * @since 2.1
184     */
185    public synchronized void stop(final long stopInterval) throws Exception {
186        if (!running) {
187            throw new IllegalStateException("Monitor is not running");
188        }
189        running = false;
190        try {
191            thread.interrupt();
192            thread.join(stopInterval);
193        } catch (final InterruptedException e) {
194            Thread.currentThread().interrupt();
195        }
196        for (final FileAlterationObserver observer : observers) {
197            observer.destroy();
198        }
199    }
200
201    /**
202     * Runs this monitor.
203     */
204    @Override
205    public void run() {
206        while (running) {
207            for (final FileAlterationObserver observer : observers) {
208                observer.checkAndNotify();
209            }
210            if (!running) {
211                break;
212            }
213            try {
214                Thread.sleep(interval);
215            } catch (final InterruptedException ignored) {
216                // ignore
217            }
218        }
219    }
220}