FileExtensionConfigurationBuilderProvider.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 org.apache.commons.configuration2.builder.BuilderParameters;
import org.apache.commons.configuration2.builder.FileBasedBuilderParametersImpl;
import org.apache.commons.configuration2.ex.ConfigurationException;

/**
 * <p>
 * A specialized implementation of {@link ConfigurationBuilderProvider} which determines the name of the result
 * configuration class based on the extension of the file to load.
 * </p>
 * <p>
 * This class works analogously to its base class {@link BaseConfigurationBuilderProvider}; especially, the resulting
 * builder is created based on reflection. It extends the super class's functionality by a specific mechanism for
 * determining the resulting configuration class: At construction time two configuration class names and a file
 * extension are passed in. If a file name is provided in the builder's initialization parameters and this file name has
 * the specified extension, then the first configuration class name is used; otherwise the default configuration class
 * name is selected.
 * </p>
 * <p>
 * There are some tags for {@code CombinedConfigurationProvider} which can produce different results depending on the
 * configuration files they have to load. This class can be used to implement this feature in a generic way.
 * </p>
 *
 * @since 2.0
 */
public class FileExtensionConfigurationBuilderProvider extends BaseConfigurationBuilderProvider {
    /** Constant for the file extension separator. */
    private static final char EXT_SEPARATOR = '.';

    /**
     * Extracts the extension from the given file name. The name can be <strong>null</strong>.
     *
     * @param fileName the file name
     * @return the extension (<strong>null</strong> if there is none)
     */
    private static String extractExtension(final String fileName) {
        if (fileName == null) {
            return null;
        }

        final int pos = fileName.lastIndexOf(EXT_SEPARATOR);
        return pos < 0 ? null : fileName.substring(pos + 1);
    }

    /**
     * Tries to obtain the current file name from the given list of parameter objects.
     *
     * @param params the parameter objects
     * @return the file name or <strong>null</strong> if unspecified
     */
    private static String fetchCurrentFileName(final Collection<BuilderParameters> params) {
        for (final BuilderParameters p : params) {
            if (p instanceof FileBasedBuilderParametersImpl) {
                final FileBasedBuilderParametersImpl fp = (FileBasedBuilderParametersImpl) p;
                return fp.getFileHandler().getFileName();
            }
        }
        return null;
    }

    /** The matching configuration class. */
    private final String matchingConfigurationClass;

    /** The file extension. */
    private final String extension;

    /**
     * Creates a new instance of {@code FileExtensionConfigurationBuilderProvider}.
     *
     * @param bldrCls the name of the builder class
     * @param reloadBldrCls the name of a builder class to be used if reloading support is required (<strong>null</strong> if
     *        reloading is not supported)
     * @param matchingConfigCls the name of the configuration class to be used if the provided file extension matches (must
     *        not be <strong>null</strong>)
     * @param defConfigClass the name of the configuration class to be used if the provided file extension does not match
     *        (must not be <strong>null</strong>)
     * @param ext the file extension to select the configuration class (must not be <strong>null</strong>)
     * @param paramCls a collection with the names of parameters classes; an instance of a parameters object with basic
     *        properties is created automatically and does not need to be contained in this list; the collection can be
     *        <strong>null</strong> if no additional parameter objects are needed
     * @throws IllegalArgumentException if a required parameter is missing
     */
    public FileExtensionConfigurationBuilderProvider(final String bldrCls, final String reloadBldrCls, final String matchingConfigCls,
        final String defConfigClass, final String ext, final Collection<String> paramCls) {
        super(bldrCls, reloadBldrCls, defConfigClass, paramCls);
        if (matchingConfigCls == null) {
            throw new IllegalArgumentException("Matching configuration class must not be null!");
        }
        if (ext == null) {
            throw new IllegalArgumentException("File extension must not be null!");
        }

        matchingConfigurationClass = matchingConfigCls;
        extension = ext;
    }

    /**
     * {@inheritDoc} This implementation tries to find a {@link FileBasedBuilderParametersImpl} object in the parameter
     * objects. If one is found, the extension of the file name is obtained and compared against the stored file extension.
     * In case of a match, the matching configuration class is selected, otherwise the default one.
     */
    @Override
    protected String determineConfigurationClass(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
        throws ConfigurationException {
        final String currentExt = extractExtension(fetchCurrentFileName(params));
        return getExtension().equalsIgnoreCase(currentExt) ? getMatchingConfigurationClass() : getConfigurationClass();
    }

    /**
     * Gets the file extension of this provider.
     *
     * @return the file extension to match
     */
    public String getExtension() {
        return extension;
    }

    /**
     * Gets the name of the matching configuration class. This class is used if the file extension matches the extension
     * of this provider.
     *
     * @return the matching configuration class
     */
    public String getMatchingConfigurationClass() {
        return matchingConfigurationClass;
    }
}