    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.builder;
    018
    019import java.util.Map;
    020
    021import org.apache.commons.configuration2.FileBasedConfiguration;
    022import org.apache.commons.configuration2.ex.ConfigurationException;
    023import org.apache.commons.configuration2.io.FileHandler;
    024import org.apache.commons.configuration2.reloading.ReloadingController;
    025import org.apache.commons.configuration2.reloading.ReloadingControllerSupport;
    026import org.apache.commons.configuration2.reloading.ReloadingDetector;
    027
    028/**
    029 * <p>
    030 * A specialized {@code ConfigurationBuilder} implementation which can handle
    031 * configurations read from a {@link FileHandler} and supports reloading.
    032 * </p>
    033 * <p>
    034 * This builder class exposes a {@link ReloadingController} object controlling
    035 * reload operations on the file-based configuration produced as result object.
    036 * For the {@code FileHandler} defining the location of the configuration a
    037 * configurable {@link ReloadingDetector} is created and associated with the
    038 * controller. So changes on the source file can be detected. When ever such a
    039 * change occurs, the result object of this builder is reset. This means that
    040 * the next time {@code getConfiguration()} is called a new
    041 * {@code Configuration} object is created which is loaded from the modified
    042 * file.
    043 * </p>
    044 * <p>
    045 * Client code interested in notifications can register a listener at this
    046 * builder to receive reset events. When such an event is received the new
    047 * result object can be requested. This way client applications can be sure to
    048 * work with an up-to-date configuration. It is also possible to register a
    049 * listener directly at the {@code ReloadingController}.
    050 * </p>
    051 * <p>
    052 * This builder does not actively trigger the {@code ReloadingController} to
    053 * perform a reload check. This has to be done by an external component, e.g. a
    054 * timer.
    055 * </p>
    056 *
    057 * @since 2.0
    058 * @param <T> the concrete type of {@code Configuration} objects created by this
    059 *        builder
    060 */
    061public class ReloadingFileBasedConfigurationBuilder<T extends FileBasedConfiguration>
    062        extends FileBasedConfigurationBuilder<T> implements ReloadingControllerSupport
    063{
    064    /** The default factory for creating reloading detector objects. */
    065    private static final ReloadingDetectorFactory DEFAULT_DETECTOR_FACTORY =
    066            new DefaultReloadingDetectorFactory();
    067
    068    /** The reloading controller associated with this object. */
    069    private final ReloadingController reloadingController;
    070
    071    /**
    072     * The reloading detector which does the actual reload check for the current
    073     * result object. A new instance is created whenever a new result object
    074     * (and thus a new current file handler) becomes available. The field must
    075     * be volatile because it is accessed by the reloading controller probably
    076     * from within another thread.
    077     */
    078    private volatile ReloadingDetector resultReloadingDetector;
    079
    080    /**
    081     * Creates a new instance of {@code ReloadingFileBasedConfigurationBuilder}
    082     * which produces result objects of the specified class and sets
    083     * initialization parameters.
    084     *
    085     * @param resCls the result class (must not be <b>null</b>
    086     * @param params a map with initialization parameters
    087     * @throws IllegalArgumentException if the result class is <b>null</b>
    088     */
    089    public ReloadingFileBasedConfigurationBuilder(final Class<? extends T> resCls,
    090            final Map<String, Object> params)
    091    {
    092        super(resCls, params);
    093        reloadingController = createReloadingController();
    094    }
    095
    096    /**
    097     * Creates a new instance of {@code ReloadingFileBasedConfigurationBuilder}
    098     * which produces result objects of the specified class and sets
    099     * initialization parameters and the <em>allowFailOnInit</em> flag.
    100     *
    101     * @param resCls the result class (must not be <b>null</b>
    102     * @param params a map with initialization parameters
    103     * @param allowFailOnInit the <em>allowFailOnInit</em> flag
    104     * @throws IllegalArgumentException if the result class is <b>null</b>
    105     */
    106    public ReloadingFileBasedConfigurationBuilder(final Class<? extends T> resCls,
    107            final Map<String, Object> params, final boolean allowFailOnInit)
    108    {
    109        super(resCls, params, allowFailOnInit);
    110        reloadingController = createReloadingController();
    111    }
    112
    113    /**
    114     * Creates a new instance of {@code ReloadingFileBasedConfigurationBuilder}
    115     * which produces result objects of the specified class.
    116     *
    117     * @param resCls the result class (must not be <b>null</b>
    118     * @throws IllegalArgumentException if the result class is <b>null</b>
    119     */
    120    public ReloadingFileBasedConfigurationBuilder(final Class<? extends T> resCls)
    121    {
    122        super(resCls);
    123        reloadingController = createReloadingController();
    124    }
    125
    126    /**
    127     * Returns the {@code ReloadingController} associated with this builder.
    128     * This controller is directly created. However, it becomes active (i.e.
    129     * associated with a meaningful reloading detector) not before a result
    130     * object was created.
    131     *
    132     * @return the {@code ReloadingController}
    133     */
    134    @Override
    135    public ReloadingController getReloadingController()
    136    {
    137        return reloadingController;
    138    }
    139
    140    /**
    141     * {@inheritDoc} This method is overridden here to change the result type.
    142     */
    143    @Override
    144    public ReloadingFileBasedConfigurationBuilder<T> configure(
    145            final BuilderParameters... params)
    146    {
    147        super.configure(params);
    148        return this;
    149    }
    150
    151    /**
    152     * Creates a {@code ReloadingDetector} which monitors the passed in
    153     * {@code FileHandler}. This method is called each time a new result object
    154     * is created with the current {@code FileHandler}. This implementation
    155     * checks whether a {@code ReloadingDetectorFactory} is specified in the
    156     * current parameters. If this is the case, it is invoked. Otherwise, a
    157     * default factory is used to create a {@code FileHandlerReloadingDetector}
    158     * object. Note: This method is called from a synchronized block.
    159     *
    160     * @param handler the current {@code FileHandler}
    161     * @param fbparams the object with parameters related to file-based builders
    162     * @return a {@code ReloadingDetector} for this {@code FileHandler}
    163     * @throws ConfigurationException if an error occurs
    164     */
    165    protected ReloadingDetector createReloadingDetector(final FileHandler handler,
    166            final FileBasedBuilderParametersImpl fbparams)
    167            throws ConfigurationException
    168    {
    169        return fetchDetectorFactory(fbparams).createReloadingDetector(handler,
    170                fbparams);
    171    }
    172
    173    /**
    174     * {@inheritDoc} This implementation also takes care that a new
    175     * {@code ReloadingDetector} for the new current {@code FileHandler} is
    176     * created. Also, the reloading controller's reloading state has to be
    177     * reset; after the creation of a new result object changes in the
    178     * underlying configuration source have to be monitored again.
    179     */
    180    @Override
    181    protected void initFileHandler(final FileHandler handler)
    182            throws ConfigurationException
    183    {
    184        super.initFileHandler(handler);
    185
    186        resultReloadingDetector =
    187                createReloadingDetector(handler,
    188                        FileBasedBuilderParametersImpl.fromParameters(
    189                                getParameters(), true));
    190    }
    191
    192    /**
    193     * Creates the {@code ReloadingController} associated with this object. The
    194     * controller is assigned a specialized reloading detector which delegates
    195     * to the detector for the current result object. (
    196     * {@code FileHandlerReloadingDetector} does not support changing the file
    197     * handler, and {@code ReloadingController} does not support changing the
    198     * reloading detector; therefore, this level of indirection is needed to
    199     * change the monitored file dynamically.)
    200     *
    201     * @return the new {@code ReloadingController}
    202     */
    203    private ReloadingController createReloadingController()
    204    {
    205        final ReloadingDetector ctrlDetector = createReloadingDetectorForController();
    206        final ReloadingController ctrl = new ReloadingController(ctrlDetector);
    207        connectToReloadingController(ctrl);
    208        return ctrl;
    209    }
    210
    211    /**
    212     * Creates a {@code ReloadingDetector} wrapper to be passed to the
    213     * associated {@code ReloadingController}. This detector wrapper simply
    214     * delegates to the current {@code ReloadingDetector} if it is available.
    215     *
    216     * @return the wrapper {@code ReloadingDetector}
    217     */
    218    private ReloadingDetector createReloadingDetectorForController()
    219    {
    220        return new ReloadingDetector()
    221        {
    222            @Override
    223            public void reloadingPerformed()
    224            {
    225                final ReloadingDetector detector = resultReloadingDetector;
    226                if (detector != null)
    227                {
    228                    detector.reloadingPerformed();
    229                }
    230            }
    231
    232            @Override
    233            public boolean isReloadingRequired()
    234            {
    235                final ReloadingDetector detector = resultReloadingDetector;
    236                return detector != null && detector.isReloadingRequired();
    237            }
    238        };
    239    }
    240
    241    /**
    242     * Returns a {@code ReloadingDetectorFactory} either from the passed in
    243     * parameters or a default factory.
    244     *
    245     * @param params the current parameters object
    246     * @return the {@code ReloadingDetectorFactory} to be used
    247     */
    248    private static ReloadingDetectorFactory fetchDetectorFactory(
    249            final FileBasedBuilderParametersImpl params)
    250    {
    251        final ReloadingDetectorFactory factory = params.getReloadingDetectorFactory();
    252        return factory != null ? factory : DEFAULT_DETECTOR_FACTORY;
    253    }
    254}