    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.time.Duration;
    020import java.util.Collection;
    021import java.util.Collections;
    022import java.util.List;
    023import java.util.Optional;
    024import java.util.concurrent.CopyOnWriteArrayList;
    025import java.util.concurrent.ThreadFactory;
    026import java.util.stream.Stream;
    027
    028import org.apache.commons.io.ThreadUtils;
    029
    030/**
    031 * A runnable that spawns a monitoring thread triggering any
    032 * registered {@link FileAlterationObserver} at a specified interval.
    033 *
    034 * @see FileAlterationObserver
    035 * @since 2.0
    036 */
    037public final class FileAlterationMonitor implements Runnable {
    038
    039    private static final FileAlterationObserver[] EMPTY_ARRAY = {};
    040
    041    private final long intervalMillis;
    042    private final List<FileAlterationObserver> observers = new CopyOnWriteArrayList<>();
    043    private Thread thread;
    044    private ThreadFactory threadFactory;
    045    private volatile boolean running;
    046
    047    /**
    048     * Constructs a monitor with a default interval of 10 seconds.
    049     */
    050    public FileAlterationMonitor() {
    051        this(10_000);
    052    }
    053
    054    /**
    055     * Constructs a monitor with the specified interval.
    056     *
    057     * @param intervalMillis The amount of time in milliseconds to wait between
    058     * checks of the file system.
    059     */
    060    public FileAlterationMonitor(final long intervalMillis) {
    061        this.intervalMillis = intervalMillis;
    062    }
    063
    064    /**
    065     * Constructs a monitor with the specified interval and collection of observers.
    066     *
    067     * @param interval The amount of time in milliseconds to wait between
    068     * checks of the file system.
    069     * @param observers The collection of observers to add to the monitor.
    070     * @since 2.9.0
    071     */
    072    public FileAlterationMonitor(final long interval, final Collection<FileAlterationObserver> observers) {
    073        // @formatter:off
    074        this(interval,
    075            Optional
    076                .ofNullable(observers)
    077                .orElse(Collections.emptyList())
    078                .toArray(EMPTY_ARRAY)
    079        );
    080        // @formatter:on
    081    }
    082
    083    /**
    084     * Constructs a monitor with the specified interval and set of observers.
    085     *
    086     * @param interval The amount of time in milliseconds to wait between
    087     * checks of the file system.
    088     * @param observers The set of observers to add to the monitor.
    089     */
    090    public FileAlterationMonitor(final long interval, final FileAlterationObserver... observers) {
    091        this(interval);
    092        if (observers != null) {
    093            Stream.of(observers).forEach(this::addObserver);
    094        }
    095    }
    096
    097    /**
    098     * Adds a file system observer to this monitor.
    099     *
    100     * @param observer The file system observer to add
    101     */
    102    public void addObserver(final FileAlterationObserver observer) {
    103        if (observer != null) {
    104            observers.add(observer);
    105        }
    106    }
    107
    108    /**
    109     * Returns the interval.
    110     *
    111     * @return the interval
    112     */
    113    public long getInterval() {
    114        return intervalMillis;
    115    }
    116
    117    /**
    118     * Returns the set of {@link FileAlterationObserver} registered with
    119     * this monitor.
    120     *
    121     * @return The set of {@link FileAlterationObserver}
    122     */
    123    public Iterable<FileAlterationObserver> getObservers() {
    124        return observers;
    125    }
    126
    127    /**
    128     * Removes a file system observer from this monitor.
    129     *
    130     * @param observer The file system observer to remove
    131     */
    132    public void removeObserver(final FileAlterationObserver observer) {
    133        if (observer != null) {
    134            observers.removeIf(observer::equals);
    135        }
    136    }
    137
    138    /**
    139     * Runs this monitor.
    140     */
    141    @Override
    142    public void run() {
    143        while (running) {
    144            observers.forEach(FileAlterationObserver::checkAndNotify);
    145            if (!running) {
    146                break;
    147            }
    148            try {
    149                ThreadUtils.sleep(Duration.ofMillis(intervalMillis));
    150            } catch (final InterruptedException ignored) {
    151                // ignore
    152            }
    153        }
    154    }
    155
    156    /**
    157     * Sets the thread factory.
    158     *
    159     * @param threadFactory the thread factory
    160     */
    161    public synchronized void setThreadFactory(final ThreadFactory threadFactory) {
    162        this.threadFactory = threadFactory;
    163    }
    164
    165    /**
    166     * Starts monitoring.
    167     *
    168     * @throws Exception if an error occurs initializing the observer
    169     */
    170    public synchronized void start() throws Exception {
    171        if (running) {
    172            throw new IllegalStateException("Monitor is already running");
    173        }
    174        for (final FileAlterationObserver observer : observers) {
    175            observer.initialize();
    176        }
    177        running = true;
    178        if (threadFactory != null) {
    179            thread = threadFactory.newThread(this);
    180        } else {
    181            thread = new Thread(this);
    182        }
    183        thread.start();
    184    }
    185
    186    /**
    187     * Stops monitoring.
    188     *
    189     * @throws Exception if an error occurs initializing the observer
    190     */
    191    public synchronized void stop() throws Exception {
    192        stop(intervalMillis);
    193    }
    194
    195    /**
    196     * Stops monitoring.
    197     *
    198     * @param stopInterval the amount of time in milliseconds to wait for the thread to finish.
    199     * A value of zero will wait until the thread is finished (see {@link Thread#join(long)}).
    200     * @throws Exception if an error occurs initializing the observer
    201     * @since 2.1
    202     */
    203    public synchronized void stop(final long stopInterval) throws Exception {
    204        if (!running) {
    205            throw new IllegalStateException("Monitor is not running");
    206        }
    207        running = false;
    208        try {
    209            thread.interrupt();
    210            thread.join(stopInterval);
    211        } catch (final InterruptedException e) {
    212            Thread.currentThread().interrupt();
    213        }
    214        for (final FileAlterationObserver observer : observers) {
    215            observer.destroy();
    216        }
    217    }
    218}