    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.configuration2.reloading;
    018
    019import java.io.File;
    020import java.net.MalformedURLException;
    021import java.net.URL;
    022
    023import org.apache.commons.configuration2.io.FileHandler;
    024import org.apache.commons.configuration2.io.FileLocatorUtils;
    025
    026/**
    027 * <p>
    028 * A specialized implementation of {@code ReloadingDetector} which monitors a file specified by a {@link FileHandler}.
    029 * </p>
    030 * <p>
    031 * An instance of this class is passed a {@code FileHandler} at construction time. Each time the
    032 * {@code isReloadingRequired()} method is called, it checks whether the {@code FileHandler} points to a valid location.
    033 * If this is the case, the file's last modification time is obtained and compared with the last stored time. If it has
    034 * changed, a reload operation should be performed.
    035 * </p>
    036 * <p>
    037 * Because file I/O may be expensive it is possible to configure a refresh delay as a time in milliseconds. This is the
    038 * minimum interval between two checks. If the {@code isReloadingRequired()} method is called in shorter intervals, it
    039 * does not perform a check, but directly returns <b>false</b>.
    040 * </p>
    041 * <p>
    042 * To initialize an instance either {@code isReloadingRequired()} or {@code reloadingPerformed()} can be called. The
    043 * first call of {@code isReloadingRequired} does not perform a check, but obtains the initial modification date of the
    044 * monitored file. {@code reloadingPerformed()} always obtains the file's modification date and stores it internally.
    045 * </p>
    046 *
    047 * @since 2.0
    048 */
    049public class FileHandlerReloadingDetector implements ReloadingDetector {
    050    /** Constant for the jar URL protocol. */
    051    private static final String JAR_PROTOCOL = "jar";
    052
    053    /** Constant for the default refresh delay. */
    054    private static final int DEFAULT_REFRESH_DELAY_MILLIS = 5000;
    055
    056    /**
    057     * Helper method for transforming a URL into a file object. This method handles file: and jar: URLs.
    058     *
    059     * @param url the URL to be converted
    060     * @return the resulting file or <b>null </b>
    061     */
    062    private static File fileFromURL(final URL url) {
    063        if (JAR_PROTOCOL.equals(url.getProtocol())) {
    064            final String path = url.getPath();
    065            try {
    066                return FileLocatorUtils.fileFromURL(new URL(path.substring(0, path.indexOf('!'))));
    067            } catch (final MalformedURLException mex) {
    068                return null;
    069            }
    070        }
    071        return FileLocatorUtils.fileFromURL(url);
    072    }
    073
    074    /** The associated file handler. */
    075    private final FileHandler fileHandler;
    076
    077    /** The refresh delay. */
    078    private final long refreshDelayMillis;
    079
    080    /** The last time the configuration file was modified. */
    081    private long lastModifiedMillis;
    082
    083    /** The last time the file was checked for changes. */
    084    private long lastCheckedMillis;
    085
    086    /**
    087     * Creates a new instance of {@code FileHandlerReloadingDetector} with an uninitialized {@code FileHandler} object. The
    088     * file to be monitored has to be set later by manipulating the handler object returned by {@code getFileHandler()}.
    089     */
    090    public FileHandlerReloadingDetector() {
    091        this(null);
    092    }
    093
    094    /**
    095     * Creates a new instance of {@code FileHandlerReloadingDetector} and initializes it with the {@code FileHandler} to
    096     * monitor and a default refresh delay.
    097     *
    098     * @param handler the {@code FileHandler} associated with this detector (can be <b>null</b>)
    099     */
    100    public FileHandlerReloadingDetector(final FileHandler handler) {
    101        this(handler, DEFAULT_REFRESH_DELAY_MILLIS);
    102    }
    103
    104    /**
    105     * Creates a new instance of {@code FileHandlerReloadingDetector} and initializes it with the {@code FileHandler} to
    106     * monitor and the refresh delay. The handler is directly used, no copy is created. So it is possible to change the
    107     * location monitored by manipulating the {@code FileHandler} object.
    108     *
    109     * @param handler the {@code FileHandler} associated with this detector (can be <b>null</b>)
    110     * @param refreshDelayMillis the refresh delay; a value of 0 means that a check is performed in all cases
    111     */
    112    public FileHandlerReloadingDetector(final FileHandler handler, final long refreshDelayMillis) {
    113        fileHandler = handler != null ? handler : new FileHandler();
    114        this.refreshDelayMillis = refreshDelayMillis;
    115    }
    116
    117    /**
    118     * Gets the monitored {@code File} or <b>null</b> if it does not exist.
    119     *
    120     * @return the monitored {@code File} or <b>null</b>
    121     */
    122    private File getExistingFile() {
    123        File file = getFile();
    124        if (file != null && !file.exists()) {
    125            file = null;
    126        }
    127
    128        return file;
    129    }
    130
    131    /**
    132     * Gets the {@code File} object which is monitored by this object. This method is called every time the file's last
    133     * modification time is needed. If it returns <b>null</b>, no check is performed. This base implementation obtains the
    134     * {@code File} from the associated {@code FileHandler}. It can also deal with URLs to jar files.
    135     *
    136     * @return the {@code File} to be monitored (can be <b>null</b>)
    137     */
    138    protected File getFile() {
    139        final URL url = getFileHandler().getURL();
    140        return url != null ? fileFromURL(url) : getFileHandler().getFile();
    141    }
    142
    143    /**
    144     * Gets the {@code FileHandler} associated with this object. The underlying handler is directly returned, so changing
    145     * its location also changes the file monitored by this detector.
    146     *
    147     * @return the associated {@code FileHandler}
    148     */
    149    public FileHandler getFileHandler() {
    150        return fileHandler;
    151    }
    152
    153    /**
    154     * Gets the date of the last modification of the monitored file. A return value of 0 indicates, that the monitored
    155     * file does not exist.
    156     *
    157     * @return the last modification date in milliseconds.
    158     */
    159    protected long getLastModificationDate() {
    160        final File file = getExistingFile();
    161        return file != null ? file.lastModified() : 0;
    162    }
    163
    164    /**
    165     * Gets the refresh delay. This is a time in milliseconds. The {@code isReloadingRequired()} method first checks
    166     * whether the time since the previous check is more than this value in the past. Otherwise, no check is performed. This
    167     * is a means to limit file I/O caused by this class.
    168     *
    169     * @return the refresh delay used by this object
    170     */
    171    public long getRefreshDelay() {
    172        return refreshDelayMillis;
    173    }
    174
    175    /**
    176     * {@inheritDoc} This implementation checks whether the associated {@link FileHandler} points to a valid file and
    177     * whether the last modification time of this time has changed since the last check. The refresh delay is taken into
    178     * account, too; a check is only performed if at least this time has passed since the last check.
    179     */
    180    @Override
    181    public boolean isReloadingRequired() {
    182        final long nowMillis = System.currentTimeMillis();
    183        if (nowMillis >= lastCheckedMillis + getRefreshDelay()) {
    184            lastCheckedMillis = nowMillis;
    185
    186            final long modifiedMillis = getLastModificationDate();
    187            if (modifiedMillis > 0) {
    188                if (lastModifiedMillis != 0) {
    189                    return modifiedMillis != lastModifiedMillis;
    190                }
    191                // initialization
    192                updateLastModified(modifiedMillis);
    193            }
    194        }
    195
    196        return false;
    197    }
    198
    199    /**
    200     * Tells this implementation that the internally stored state should be refreshed. This method is intended to be called
    201     * after the creation of an instance.
    202     */
    203    public void refresh() {
    204        updateLastModified(getLastModificationDate());
    205    }
    206
    207    /**
    208     * {@inheritDoc} This implementation updates the internally stored last modification date with the current modification
    209     * date of the monitored file. So the next change is detected when this file is changed again.
    210     */
    211    @Override
    212    public void reloadingPerformed() {
    213        updateLastModified(getLastModificationDate());
    214    }
    215
    216    /**
    217     * Updates the last modification date of the monitored file. The need for a reload is detected only if the file's
    218     * modification date is different from this value.
    219     *
    220     * @param timeMillis the new last modification date
    221     */
    222    protected void updateLastModified(final long timeMillis) {
    223        lastModifiedMillis = timeMillis;
    224    }
    225}