Source code
Description: source: package: org.apache.commons.configuration2.builder, class: ReloadingFileBasedConfigurationBuilder

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