    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.Arrays;
    020
    021import org.apache.commons.configuration2.Configuration;
    022import org.apache.commons.configuration2.ConfigurationUtils;
    023import org.apache.commons.configuration2.HierarchicalConfiguration;
    024import org.apache.commons.configuration2.builder.BuilderConfigurationWrapperFactory;
    025import org.apache.commons.configuration2.builder.BuilderConfigurationWrapperFactory.EventSourceSupport;
    026import org.apache.commons.configuration2.builder.ConfigurationBuilder;
    027import org.apache.commons.configuration2.event.Event;
    028import org.apache.commons.configuration2.event.EventListener;
    029import org.apache.commons.configuration2.event.EventType;
    030import org.apache.commons.configuration2.ex.ConfigurationException;
    031import org.apache.commons.configuration2.reloading.ReloadingController;
    032import org.apache.commons.configuration2.reloading.ReloadingControllerSupport;
    033
    034/**
    035 * <p>
    036 * A specialized {@code ConfigurationBuilderProvider} implementation for integrating
    037 * {@link MultiFileConfigurationBuilder} with {@code CombinedConfigurationBuilder}.
    038 * </p>
    039 * <p>
    040 * When using a configuration source managed by {@code MultiFileConfigurationBuilder} it is not sufficient to store the
    041 * configuration once obtained from the builder in the resulting combined configuration. Rather, it has to be ensured
    042 * that each access to this configuration queries the builder anew so that it can evaluate its file pattern and return a
    043 * different configuration if necessary. Therefore, this class returns a specialized wrapper over a
    044 * {@code MultiFileConfigurationBuilder} which returns a configuration wrapping the builder; so accessing the
    045 * configuration's properties actually calls back to the builder. This constellation is compatible with the way
    046 * {@code DynamicCombinedConfiguration} manages its data.
    047 * </p>
    048 *
    049 * @since 2.0
    050 */
    051public class MultiFileConfigurationBuilderProvider extends BaseConfigurationBuilderProvider {
    052    /** Constant for the name of the builder class. */
    053    private static final String BUILDER_CLASS = "org.apache.commons.configuration2.builder.combined.MultiFileConfigurationBuilder";
    054
    055    /** Constant for the name of the reloading builder class. */
    056    private static final String RELOADING_BUILDER_CLASS = "org.apache.commons.configuration2.builder.combined.ReloadingMultiFileConfigurationBuilder";
    057
    058    /** Constant for the name of the parameters class. */
    059    private static final String PARAM_CLASS = "org.apache.commons.configuration2.builder.combined.MultiFileBuilderParametersImpl";
    060
    061    /**
    062     * Creates a new instance of {@code MultiFileConfigurationBuilderProvider} and sets the name of the configuration class
    063     * to be returned by {@code MultiFileConfigurationBuilder}.
    064     *
    065     * @param configCls the name of the managed configuration class
    066     * @param paramCls the name of the class of the parameters object to configure the managed configuration
    067     */
    068    public MultiFileConfigurationBuilderProvider(final String configCls, final String paramCls) {
    069        super(BUILDER_CLASS, RELOADING_BUILDER_CLASS, configCls, Arrays.asList(paramCls, PARAM_CLASS));
    070    }
    071
    072    /**
    073     * {@inheritDoc} This implementation lets the super class create a fully configured builder. Then it returns a special
    074     * wrapper around it.
    075     */
    076    @Override
    077    public ConfigurationBuilder<? extends Configuration> getConfigurationBuilder(final ConfigurationDeclaration decl) throws ConfigurationException {
    078        final ConfigurationBuilder<? extends Configuration> multiBuilder = super.getConfigurationBuilder(decl);
    079        final Configuration wrapConfig = createWrapperConfiguration(multiBuilder);
    080        return createWrapperBuilder(multiBuilder, wrapConfig);
    081    }
    082
    083    /**
    084     * Creates a configuration which wraps the specified builder.
    085     *
    086     * @param builder the builder
    087     * @return the wrapping configuration
    088     */
    089    // It is safe to disable any type checks because we manually determine
    090    // the interface class to be passed to BuilderConfigurationWrapperFactory
    091    @SuppressWarnings({"unchecked", "rawtypes"})
    092    private Configuration createWrapperConfiguration(final ConfigurationBuilder builder) {
    093        final Class<?> configClass = ConfigurationUtils.loadClassNoEx(getConfigurationClass());
    094        final Class ifcClass = HierarchicalConfiguration.class.isAssignableFrom(configClass) ? HierarchicalConfiguration.class : Configuration.class;
    095        return (Configuration) BuilderConfigurationWrapperFactory.createBuilderConfigurationWrapper(ifcClass, builder, EventSourceSupport.BUILDER);
    096    }
    097
    098    /**
    099     * Creates the {@code ConfigurationBuilder} to be returned by this provider. This is a very simple implementation which
    100     * always returns the same wrapper configuration instance. The handling of builder listeners is delegated to the wrapped
    101     * {@code MultiFileConfigurationBuilder}. If reloading is support, the builder returned by this method also implements
    102     * the {@link ReloadingControllerSupport} interface.
    103     *
    104     * @param multiBuilder the {@code MultiFileConfigurationBuilder}
    105     * @param wrapConfig the configuration to be returned
    106     * @return the wrapper builder
    107     */
    108    private static ConfigurationBuilder<? extends Configuration> createWrapperBuilder(final ConfigurationBuilder<? extends Configuration> multiBuilder,
    109        final Configuration wrapConfig) {
    110        if (multiBuilder instanceof ReloadingControllerSupport) {
    111            return new ReloadableWrapperBuilder(wrapConfig, multiBuilder);
    112        }
    113        return new WrapperBuilder(wrapConfig, multiBuilder);
    114    }
    115
    116    /**
    117     * A simple wrapper implementation of the {@code ConfigurationBuilder} interface which returns a fix configuration and
    118     * delegates to another builder for event listener management.
    119     */
    120    private static class WrapperBuilder implements ConfigurationBuilder<Configuration> {
    121        /** The configuration managed by this builder. */
    122        private final Configuration configuration;
    123
    124        /** The builder to which this instance delegates. */
    125        private final ConfigurationBuilder<? extends Configuration> builder;
    126
    127        /**
    128         * Creates a new instance of {@code WrapperBuilder}.
    129         *
    130         * @param conf the managed configuration
    131         * @param bldr the underlying builder
    132         */
    133        public WrapperBuilder(final Configuration conf, final ConfigurationBuilder<? extends Configuration> bldr) {
    134            configuration = conf;
    135            builder = bldr;
    136        }
    137
    138        @Override
    139        public Configuration getConfiguration() throws ConfigurationException {
    140            return configuration;
    141        }
    142
    143        @Override
    144        public <T extends Event> void addEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
    145            builder.addEventListener(eventType, listener);
    146        }
    147
    148        @Override
    149        public <T extends Event> boolean removeEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
    150            return builder.removeEventListener(eventType, listener);
    151        }
    152    }
    153
    154    /**
    155     * A wrapper builder implementation which also provides a {@code ReloadingController}. This class assumes that the
    156     * wrapped builder implements {@code ReloadingControllerSupport}. So the reloading controller can be obtained from this
    157     * object.
    158     */
    159    private static class ReloadableWrapperBuilder extends WrapperBuilder implements ReloadingControllerSupport {
    160        /** The object for obtaining the reloading controller. */
    161        private final ReloadingControllerSupport ctrlSupport;
    162
    163        /**
    164         * Creates a new instance of {@code ReloadableWrapperBuilder}.
    165         *
    166         * @param conf the managed configuration
    167         * @param bldr the underlying builder (must implement {@code ReloadingControllerSupport})
    168         */
    169        public ReloadableWrapperBuilder(final Configuration conf, final ConfigurationBuilder<? extends Configuration> bldr) {
    170            super(conf, bldr);
    171            ctrlSupport = (ReloadingControllerSupport) bldr;
    172        }
    173
    174        @Override
    175        public ReloadingController getReloadingController() {
    176            return ctrlSupport.getReloadingController();
    177        }
    178    }
    179}