src/main/java/org/apache/commons/configuration2/builder/combined/ReloadingMultiFileConfigurationBuilder.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.configuration2.builder.combined;

import java.util.Collection;
import java.util.Collections;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;

import org.apache.commons.configuration2.FileBasedConfiguration;
import org.apache.commons.configuration2.builder.FileBasedConfigurationBuilder;
import org.apache.commons.configuration2.builder.ReloadingFileBasedConfigurationBuilder;
import org.apache.commons.configuration2.ex.ConfigurationException;
import org.apache.commons.configuration2.reloading.CombinedReloadingController;
import org.apache.commons.configuration2.reloading.ReloadingController;
import org.apache.commons.configuration2.reloading.ReloadingControllerSupport;

/**
 * <p>
 * A specialized {@code MultiFileConfigurationBuilder} implementation which adds support for reloading.
 * </p>
 * <p>
 * This class - as its super class - allows operating on multiple configuration files whose file names are determined
 * using a file name pattern and a {@code ConfigurationInterpolator} object. It provides the following additional
 * features:
 * </p>
 * <ul>
 * <li>Configuration builder for managed configurations have reloading support. So reloading is possible for all
 * configuration sources loaded by this builder instance.</li>
 * <li>A {@link ReloadingController} is provided which can be used to trigger reload checks on all managed
 * configurations.</li>
 * </ul>
 * <p>
 * Although this builder manages an arbitrary number of child configurations, to clients only a single configuration is
 * visible - the one selected by the evaluation of the file name pattern. Builder reset notifications triggered by the
 * reloading mechanism do not really take this fact into account; they are not limited to the currently selected child
 * configuration, but occur for each of the managed configuration.
 * </p>
 *
 * @since 2.0
 * @param <T> the concrete type of {@code Configuration} objects created by this builder
 */
public class ReloadingMultiFileConfigurationBuilder<T extends FileBasedConfiguration> extends MultiFileConfigurationBuilder<T>
    implements ReloadingControllerSupport {
    /** The reloading controller used by this builder. */
    private final ReloadingController reloadingController = createReloadingController();

    /**
     * Creates a new instance of {@code ReloadingMultiFileConfigurationBuilder} without setting initialization parameters.
     *
     * @param resCls the result configuration class
     * @throws IllegalArgumentException if the result class is <b>null</b>
     */
    public ReloadingMultiFileConfigurationBuilder(final Class<T> resCls) {
        super(resCls);
    }

    /**
     * Creates a new instance of {@code ReloadingMultiFileConfigurationBuilder} and sets initialization parameters.
     *
     * @param resCls the result configuration class
     * @param params a map with initialization parameters
     * @throws IllegalArgumentException if the result class is <b>null</b>
     */
    public ReloadingMultiFileConfigurationBuilder(final Class<T> resCls, final Map<String, Object> params) {
        super(resCls, params);
    }

    /**
     * Creates a new instance of {@code ReloadingMultiFileConfigurationBuilder} and sets initialization parameters and a
     * flag whether initialization failures should be ignored.
     *
     * @param resCls the result configuration class
     * @param params a map with initialization parameters
     * @param allowFailOnInit a flag whether initialization errors should be ignored
     * @throws IllegalArgumentException if the result class is <b>null</b>
     */
    public ReloadingMultiFileConfigurationBuilder(final Class<T> resCls, final Map<String, Object> params, final boolean allowFailOnInit) {
        super(resCls, params, allowFailOnInit);
    }

    /**
     * {@inheritDoc} This implementation returns a file-based configuration builder with reloading support.
     */
    @Override
    protected FileBasedConfigurationBuilder<T> createManagedBuilder(final String fileName, final Map<String, Object> params) throws ConfigurationException {
        return new ReloadingFileBasedConfigurationBuilder<>(getResultClass(), params, isAllowFailOnInit());
    }

    /**
     * Creates the reloading controller used by this builder. This method creates a specialized
     * {@link CombinedReloadingController} which operates on the reloading controllers of the managed builders created so
     * far.
     *
     * @return the newly created {@code ReloadingController}
     */
    private ReloadingController createReloadingController() {
        final Set<ReloadingController> empty = Collections.emptySet();
        return new CombinedReloadingController(empty) {
            @Override
            public Collection<ReloadingController> getSubControllers() {
                return getManagedBuilders().values().stream().map(b -> ((ReloadingControllerSupport) b).getReloadingController()).collect(Collectors.toList());
            }
        };
    }

    /**
     * {@inheritDoc} This implementation returns a special {@code ReloadingController} that delegates to the reloading
     * controllers of the managed builders created so far.
     */
    @Override
    public ReloadingController getReloadingController() {
        return reloadingController;
    }
}