    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.combined;
    018
    019import java.util.Collection;
    020import java.util.LinkedList;
    021import java.util.Map;
    022
    023import org.apache.commons.configuration2.CombinedConfiguration;
    024import org.apache.commons.configuration2.HierarchicalConfiguration;
    025import org.apache.commons.configuration2.XMLConfiguration;
    026import org.apache.commons.configuration2.builder.BuilderParameters;
    027import org.apache.commons.configuration2.builder.ConfigurationBuilder;
    028import org.apache.commons.configuration2.builder.ReloadingFileBasedConfigurationBuilder;
    029import org.apache.commons.configuration2.ex.ConfigurationException;
    030import org.apache.commons.configuration2.reloading.CombinedReloadingController;
    031import org.apache.commons.configuration2.reloading.ReloadingController;
    032import org.apache.commons.configuration2.reloading.ReloadingControllerSupport;
    033
    034/**
    035 * <p>
    036 * An extension of {@code CombinedConfigurationBuilder} which also supports reloading operations.
    037 * </p>
    038 * <p>
    039 * This class differs from its super class in the following aspects:
    040 * </p>
    041 * <ul>
    042 * <li>A {@link ReloadingController} is created which manages all child configuration builders supporting reloading
    043 * operations.</li>
    044 * <li>If no {@code ConfigurationBuilder} is provided for the definition configuration, a builder with reloading support
    045 * is created.</li>
    046 * </ul>
    047 * <p>
    048 * This class can be used exactly as its super class for creating combined configurations from multiple configuration
    049 * sources. In addition, the combined reloading controller managed by an instance can be used to react on changes in one
    050 * of these configuration sources or in the definition configuration.
    051 * </p>
    052 *
    053 * @since 2.0
    054 */
    055public class ReloadingCombinedConfigurationBuilder extends CombinedConfigurationBuilder implements ReloadingControllerSupport {
    056    /**
    057     * Checks whether the passed in builder object supports reloading. If yes, its reloading controller is obtained and
    058     * added to the given list.
    059     *
    060     * @param subControllers the list with sub controllers
    061     * @param builder the builder object to be checked
    062     */
    063    public static void obtainReloadingController(final Collection<ReloadingController> subControllers, final Object builder) {
    064        if (builder instanceof ReloadingControllerSupport) {
    065            subControllers.add(((ReloadingControllerSupport) builder).getReloadingController());
    066        }
    067    }
    068
    069    /** The reloading controller used by this builder. */
    070    private ReloadingController reloadingController;
    071
    072    /**
    073     * Creates a new instance of {@code ReloadingCombinedConfigurationBuilder}. No parameters are set.
    074     */
    075    public ReloadingCombinedConfigurationBuilder() {
    076    }
    077
    078    /**
    079     * Creates a new instance of {@code ReloadingCombinedConfigurationBuilder} and sets the specified initialization
    080     * parameters.
    081     *
    082     * @param params a map with initialization parameters
    083     */
    084    public ReloadingCombinedConfigurationBuilder(final Map<String, Object> params) {
    085        super(params);
    086    }
    087
    088    /**
    089     * Creates a new instance of {@code ReloadingCombinedConfigurationBuilder} and sets the specified initialization
    090     * parameters and the <em>allowFailOnInit</em> flag.
    091     *
    092     * @param params a map with initialization parameters
    093     * @param allowFailOnInit the <em>allowFailOnInit</em> flag
    094     */
    095    public ReloadingCombinedConfigurationBuilder(final Map<String, Object> params, final boolean allowFailOnInit) {
    096        super(params, allowFailOnInit);
    097    }
    098
    099    /**
    100     * {@inheritDoc} This method is overridden to adapt the return type.
    101     */
    102    @Override
    103    public ReloadingCombinedConfigurationBuilder configure(final BuilderParameters... params) {
    104        super.configure(params);
    105        return this;
    106    }
    107
    108    /**
    109     * Creates the {@code ReloadingController} for this builder. This method is called after the result configuration has
    110     * been created and initialized. It is called from a synchronized block. This implementation creates a
    111     * {@link CombinedReloadingController}.
    112     *
    113     * @return the {@code ReloadingController} for this builder
    114     * @throws ConfigurationException if an error occurs
    115     */
    116    protected ReloadingController createReloadingController() throws ConfigurationException {
    117        final Collection<ReloadingController> subControllers = new LinkedList<>();
    118        final ConfigurationBuilder<? extends HierarchicalConfiguration<?>> defBuilder = getDefinitionBuilder();
    119        obtainReloadingController(subControllers, defBuilder);
    120
    121        getChildBuilders().forEach(b -> obtainReloadingController(subControllers, b));
    122
    123        final CombinedReloadingController ctrl = new CombinedReloadingController(subControllers);
    124        ctrl.resetInitialReloadingState();
    125        return ctrl;
    126    }
    127
    128    /**
    129     * {@inheritDoc} This implementation creates a builder for XML configurations with reloading support.
    130     */
    131    @Override
    132    protected ConfigurationBuilder<? extends HierarchicalConfiguration<?>> createXMLDefinitionBuilder(final BuilderParameters builderParams) {
    133        return new ReloadingFileBasedConfigurationBuilder<>(XMLConfiguration.class).configure(builderParams);
    134    }
    135
    136    /**
    137     * {@inheritDoc} This implementation makes sure that the reloading state of the managed reloading controller is reset.
    138     * Note that this has to be done here and not in {@link #initResultInstance(CombinedConfiguration)} because it must be
    139     * outside of a synchronized block; otherwise, a dead-lock situation can occur.
    140     */
    141    @Override
    142    public CombinedConfiguration getConfiguration() throws ConfigurationException {
    143        final CombinedConfiguration result = super.getConfiguration();
    144        reloadingController.resetReloadingState();
    145        return result;
    146    }
    147
    148    /**
    149     * {@inheritDoc} This implementation returns a {@link CombinedReloadingController} which contains sub controllers for
    150     * all child configuration sources with reloading support. If the definition builder supports reloading, its controller
    151     * is contained, too. Note that the combined reloading controller is initialized when the result configuration is
    152     * created (i.e. when calling {@code getConfiguration()} for the first time). So this method does not return a
    153     * meaningful result before.
    154     */
    155    @Override
    156    public synchronized ReloadingController getReloadingController() {
    157        return reloadingController;
    158    }
    159
    160    /**
    161     * {@inheritDoc} This implementation first calls the super method to actually initialize the result configuration. Then
    162     * it creates the {@link CombinedReloadingController} for all child configuration sources with reloading support.
    163     */
    164    @Override
    165    protected void initResultInstance(final CombinedConfiguration result) throws ConfigurationException {
    166        super.initResultInstance(result);
    167        if (reloadingController == null) {
    168            reloadingController = createReloadingController();
    169        }
    170    }
    171}