    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}