    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.ArrayList;
    021import java.util.Collection;
    022import java.util.Collections;
    023import java.util.List;
    024import java.util.Optional;
    025import java.util.concurrent.CopyOnWriteArrayList;
    026import java.util.concurrent.ThreadFactory;
    027import java.util.stream.Stream;
    028
    029import org.apache.commons.io.ThreadUtils;
    030
    031/**
    032 * A runnable that spawns a monitoring thread triggering any
    033 * registered {@link FileAlterationObserver} at a specified interval.
    034 *
    035 * @see FileAlterationObserver
    036 * @since 2.0
    037 */
    038public final class FileAlterationMonitor implements Runnable {
    039
    040    private static final FileAlterationObserver[] EMPTY_ARRAY = {};
    041
    042    private final long intervalMillis;
    043    private final List<FileAlterationObserver> observers = new CopyOnWriteArrayList<>();
    044    private Thread thread;
    045    private ThreadFactory threadFactory;
    046    private volatile boolean running;
    047
    048    /**
    049     * Constructs a monitor with a default interval of 10 seconds.
    050     */
    051    public FileAlterationMonitor() {
    052        this(10_000);
    053    }
    054
    055    /**
    056     * Constructs a monitor with the specified interval.
    057     *
    058     * @param intervalMillis The amount of time in milliseconds to wait between
    059     * checks of the file system.
    060     */
    061    public FileAlterationMonitor(final long intervalMillis) {
    062        this.intervalMillis = intervalMillis;
    063    }
    064
    065    /**
    066     * Constructs a monitor with the specified interval and collection of observers.
    067     *
    068     * @param interval The amount of time in milliseconds to wait between
    069     * checks of the file system.
    070     * @param observers The collection of observers to add to the monitor.
    071     * @since 2.9.0
    072     */
    073    public FileAlterationMonitor(final long interval, final Collection<FileAlterationObserver> observers) {
    074        // @formatter:off
    075        this(interval,
    076            Optional
    077                .ofNullable(observers)
    078                .orElse(Collections.emptyList())
    079                .toArray(EMPTY_ARRAY)
    080        );
    081        // @formatter:on
    082    }
    083
    084    /**
    085     * Constructs a monitor with the specified interval and set of observers.
    086     *
    087     * @param interval The amount of time in milliseconds to wait between
    088     * checks of the file system.
    089     * @param observers The set of observers to add to the monitor.
    090     */
    091    public FileAlterationMonitor(final long interval, final FileAlterationObserver... observers) {
    092        this(interval);
    093        if (observers != null) {
    094            Stream.of(observers).forEach(this::addObserver);
    095        }
    096    }
    097
    098    /**
    099     * Adds a file system observer to this monitor.
    100     *
    101     * @param observer The file system observer to add
    102     */
    103    public void addObserver(final FileAlterationObserver observer) {
    104        if (observer != null) {
    105            observers.add(observer);
    106        }
    107    }
    108
    109    /**
    110     * Returns the interval.
    111     *
    112     * @return the interval
    113     */
    114    public long getInterval() {
    115        return intervalMillis;
    116    }
    117
    118    /**
    119     * Returns the set of {@link FileAlterationObserver} registered with
    120     * this monitor.
    121     *
    122     * @return The set of {@link FileAlterationObserver}
    123     */
    124    public Iterable<FileAlterationObserver> getObservers() {
    125        return new ArrayList<>(observers);
    126    }
    127
    128    /**
    129     * Removes a file system observer from this monitor.
    130     *
    131     * @param observer The file system observer to remove
    132     */
    133    public void removeObserver(final FileAlterationObserver observer) {
    134        if (observer != null) {
    135            observers.removeIf(observer::equals);
    136        }
    137    }
    138
    139    /**
    140     * Runs this monitor.
    141     */
    142    @Override
    143    public void run() {
    144        while (running) {
    145            observers.forEach(FileAlterationObserver::checkAndNotify);
    146            if (!running) {
    147                break;
    148            }
    149            try {
    150                ThreadUtils.sleep(Duration.ofMillis(intervalMillis));
    151            } catch (final InterruptedException ignored) {
    152                // ignore
    153            }
    154        }
    155    }
    156
    157    /**
    158     * Sets the thread factory.
    159     *
    160     * @param threadFactory the thread factory
    161     */
    162    public synchronized void setThreadFactory(final ThreadFactory threadFactory) {
    163        this.threadFactory = threadFactory;
    164    }
    165
    166    /**
    167     * Starts monitoring.
    168     *
    169     * @throws Exception if an error occurs initializing the observer
    170     */
    171    public synchronized void start() throws Exception {
    172        if (running) {
    173            throw new IllegalStateException("Monitor is already running");
    174        }
    175        for (final FileAlterationObserver observer : observers) {
    176            observer.initialize();
    177        }
    178        running = true;
    179        if (threadFactory != null) {
    180            thread = threadFactory.newThread(this);
    181        } else {
    182            thread = new Thread(this);
    183        }
    184        thread.start();
    185    }
    186
    187    /**
    188     * Stops monitoring.
    189     *
    190     * @throws Exception if an error occurs initializing the observer
    191     */
    192    public synchronized void stop() throws Exception {
    193        stop(intervalMillis);
    194    }
    195
    196    /**
    197     * Stops monitoring.
    198     *
    199     * @param stopInterval the amount of time in milliseconds to wait for the thread to finish.
    200     * A value of zero will wait until the thread is finished (see {@link Thread#join(long)}).
    201     * @throws Exception if an error occurs initializing the observer
    202     * @since 2.1
    203     */
    204    public synchronized void stop(final long stopInterval) throws Exception {
    205        if (!running) {
    206            throw new IllegalStateException("Monitor is not running");
    207        }
    208        running = false;
    209        try {
    210            thread.interrupt();
    211            thread.join(stopInterval);
    212        } catch (final InterruptedException e) {
    213            Thread.currentThread().interrupt();
    214        }
    215        for (final FileAlterationObserver observer : observers) {
    216            observer.destroy();
    217        }
    218    }
    219}